DEHYDROCOUPLING OF TOLUENE

Abstract: Toluene dehydrocoupled products are produced by heat­ ing toluene in the vapor phase with an inorganic metal/oxygen composition which functions as an oxygen carrier and has an empirical formula selected from: (a) PbM 1 / aM 2 / bO x where M¹ is at least one element selected from silver, zinc, gallium, indium, thallium, germanium, phosphorus, arsen­ ic, thorium, the lanthanides, Groups 1a, 2a, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M² is an element selected from bismuth and antimony, and wherein a is 0.01 to 10, b is 0 to 10, and x is a number taken to satisfy the average valences of lead, M¹ and M² in the oxidation states in which they exist in the composition, with the proviso that when M² is bismuth, M¹ cannot be gallium or thallium; and when M² is antimony, M¹ cannot be indium, thallium, germani­ um, phosphorus, or thorium; and (b) BiM 3 / aM 4 / bO x where M³ is at least one element selected from zinc, ger­ manium, thorium, the lanthanides, Groups 1a, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M⁴ is at least one element selected from indium, silver, Group 2a of the Periodic Table of the Elements, and mixtures thereof, and wherein a is 0.01 to 10, b is 0 to 10, and x is a number taken to satisfy the average valences of bismuth, M³, and M⁴ in the oxidation state in which they exist in the composition to yield the toluene dehydrocoupled toluene product. Alternatively, the same inorganic metal/oxygen composition can be employed as a catalyst or as a combination catalyst/oxygen carrier for the dehydrocoupling reaction when oxygen or an oxygencon­ taining gas is heated with the toluene.

Description: DEHYDROCOUPLING OF TOLUENE BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the production of dehydrocoupled toluene products. It is particularly related to the oxidative sythesis of 1,2-diphenylethylene (stilbene) from toluene and to inorganic metal/oxygen compositions effective for oxidatively coupling toluene to produce stilbene. Stilbene, because of its unsaturated character is very reactive and may be employed in various organic sytheses. Derivatives of stilbene are useful in the production of products which may be used in the manufacture of dyes, paints and resins It is also useful in optical brighteners, in pharmaceuticals, and as an organic intermediate Description of the Prior Art Dehydrocoupling of toluene by the reaction with lead oxide to form stilbene has been reported by Behr and Van Dorp, Chem Bern, 6, 753 (1873) and Lorenz, Chem. Ber., 7, 1996 (1874) In this reported work, stilbene is obtained by conveying toluene over lead oxide maintained at or about at a dark red glow The coupling of toluene using elemental sulfur as the coupling agent has been reported by Renard, Bull. -Soc; Chim. France, 3, 958 (1889); 5, 278 (1891) and the types of products produced by such coupling reactions have been discussed by Horton, J Org. Chem., 14, 761 (1949). More recently, UOS. Patent No. 3,476,747 discloses arsenic pentoxide, antimony tetroxide, antimony tetroxide, antimony pentoxide, bismuth trioxide, and manganese arsenate as oxidants for the oxidative dehydrocoupling of toluene to form l,2-bis(aryl)ethyl- enes. Similarly, U.S. Patent No. 3,494,956 discloses lead oxide, cadmium oxide, and thallium oxide as suitable oxidants, and in Example 9 a mixture of toluene and oxygen passed over heated le-ad oxide produced bibenzyl In U.S. Patent No. 3,557,235 the stoichiometric toluene coupling reaction is taught using an oxide of bismuth, lead tel¯lrium, barium, thallium, cadmium, or mixtures thereof which serves as the source of oxygen in the reaction. U.S. Patent No 3,963,793 teaches the use of bismuth trioxide and thallium trioxide or mixtures thereof supported on basic carr-ier materials selected from the oxides of Group 2a elements and having a minimum surface area of 20 mê/g as suitable for toluene coupling to produce bibenzyl. The addition to the supported catalyst of small amounts of silver as a promoter is also disclosed, In U.S. Patent No. 3,965,206 oxides of lead, cadmium, bismuth, and mixtures thereof are taught as suitable oxidants for toluene coupling This patent also teaches the disproportionation of the stilbene with ethylene to produce styrene UOS Q Patent No 3,980,580 discloses an oxygen composition of lead, magnesium, and aluminum as an axidant for toluene coupling Also, U.S. Patent No 4,091,044 discloses oxygen compositions of lead and antimony and optionally with bismuth as oxidants for toluene coupling to form stilbene. SUMMARY OF THE INTENTION This invention is directed to a process far the oxidative dehydrocoupling of toluene and toluene derivatives to stilbene and stilbene derivatives, In another aspect, this invention is directed to inorganic metal/oxygen compositions which are useful as the oxygen source for the oxidative dehydrocoupling of toluene to produce stilbene, or alternatively as catalysts or combination catalysts/oxygen source for the dehydrocoupling reaction when oxygen or an oxygencontaining gas is heated with the tolueneO Accordingly, typical objects of this invention are to provide (1) inorganic metal/oxygen compositions useful as the oxygen source in oxidative dehydrocoupling of toluene and toluene derivatives, (2) inorganic metal/oxygen compositions useful as catalysts in the oxidative dehydrocoupling of toluene and toluene derivatives, (3) inorganic metal/oxygen compositions useful as combination catalysts/oxygen source in the oxidatiye dehydrocoupling of toluene and toluene derivatives, (4) a one-step, vapor phase process for the production of stilbene and stilbene derivatives and bibenzyl and bibenzyl derivatives, and (5) a one-step, vapor phase dehydrocoupling process for converting toluene and toluene derivatives to stilbene and stilbene derivatives characterized by high toluene conversions and high stilbene selectivities These and other objects and advantages of this invention are achieved by the process disclosed herein for dehydrocoupling toluene and toluene deriv natives. Toluene dehydrocoupled products are produced by heating toluene toluene derivatives) in the presence of an inorganic metal/oxygen composition which functions in a catalytic mode, a stoichiometric mode as an oxidant or oxygen carrier, or a combined catalytic/stoichiometric mode for the dehydrocoupling reaction. DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with this invention, toluene and toluene derivatives are dehydrocoupled by a process which comprises contacting the toluene (and toluene derivatives) in the vapor phase at a temperature between about 4500C. and about 650" C. with an inorganic metal/oxygen composition characterized by an empirical formula selected from: : (a) PbMÚaMbêOx where My is at least one element selected from silver, zinc, gallium, indium, thallium, germanium, phosphorus, arsenic, thorium, the lanthanides, Groups la, 2a, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M2 is an element selected from bismnth and and antimony, and wherein a is 0.01 to 10, b is O to 10, and x is a number taken to satisfy the average valences of lead, M1 and M2 in the oxidation states in which they exist in the composition, with 'the proviso that when M2 is bismuth, MI cannot be gallium or thallium; and when M2is antimony, M1 cannot be indium, thallium, germanium, phosphorus, or thorium; and (b) BiMa3Mb4Ox where M3 is at least one element selected from zinc, ger manium, thorium, the lanthanides, Groups la, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M4 is at least one element selected from indium, silver, Group 2a of the Periodic Table of the Elements, and mixtures thereof, and wherein a is 0.01 to 10, b is O to 10, and x is a number taken to satisfy the average valences of bismuth, M3, and M4 in the oxidation state in which they existin the composition to yield the toluene dehydrocoupled toluene product. The inorganic metal/oxygen composition functions in a catalytic mode, a stoichiometric mode as an oxidant or oxygen carrier, or a combined catalytic/stoichiometric mode for the dehydrocoupling of toluene,,, In the catalytic mode of operation, oxygen or an oxygen-containing gas such as air or oxygenenriched air is reacted with toluene in the presence of the inorganic metal/oxygen composition in an amount sufficient for the dehydrocoupling reaction In the stoichiometric mode of operation, the inorganic metal/oxygen composition is the sole source of oxygen. That is, in the latter instance the dehydrocoupling of toluene is conducted in'the substantial absence nf added free oxygen such as would be obtained from air. In the combined catalytic/stoichiometric mode of operation, oxygen or an oxygen-containing gas is added as a reactant in a manner similar to that noted hereinabove for the catalytic mode of operation However, the amount of added oxygen is not sufficient for the dehydrocoupling reaction and the required additional oxygen must be supplied by the inorganic metal/oxygen composition" Of these three modes of operation, the stoichiometric mode is generally preferred in that undesirable side reactions -- oxidative dealkylation, for example, to produce benzene and carbon dioxide -- are substantially reduced. It will, of course, be recognized that in spite of the undesirability of producing benzene during the course of the reaction of the present process, benzene is a valuable article of commerce It is therefore highly desirable to recover the benzene values when substantial production thereof occurs, The recovery and purification of such benzene values may be accomplished by any standard method and means known to the art The term "dehydrocoupling't and related terms are employed herein to mean that the toluene molecules are coupled or dimerized -- with carbon-carbon bond formation occurring between the methyl group carbons -and the coupled molecules have- lost either one or two hydrogen atoms from the methyl group of each toluene molecule When two hydrogen atoms per molecule of toluene are lost, the carbon-carbon bond at the coupling or dimerization site is unsaturated as by dehydrogenation, that is, stilbene is the product On the other hand, bibenzyl, having a saturated carbon-carbon bond at the coupling site, is the product when only one hydrogen atom per molecule of toluene is lost. In general, the production of stilbene as the dehydrocoupled toluene product is preferred over- the production of bibenzyl This stated preference is due to the unsaturated character of stilbene as apposed to the saturated character of bibenzyl And, as is well known in the art, the presence af the unsaturated olefinic carbon-carbon double bond causes the stilbene to exhibit high reactivity, thereby facilitating its direct use as an organic intermediate in numerous organic syntheses The process of this invention is conveniently carried out in an apparatus af the type suitable for carrying out chemical reactions in the vapor phase It can be conducted in a single reactor ar in multiple reactors using- either a fixed bed, a moving bedt or a fluidized bed system to effect contacting of the reactant ar reactants and inorganic metaIZogen compo sition The reactant toluene or taluene derivative will generally be heated and introduced into the reactor as a vapor However, the reactant may be introduced to the reactor as a liquid and then vaporized The oxidative dehydrocoupling reaction is carried out in the vapor phase and under the influence of heat. The temperature range under which the reaction can be carried out ranges from about 4500 CO to about 6500 C and preferably is conducted at from about 500 C. to about 600" C Pressure is not critical in the process of this invention. The reaction may be carried out at subatmospheric, atmospheric, or superatmospheric pressures as desired. It will be generally preferred, however, to conduct the reaction at or near atmospheric pressure. Generally, pressures from about 2.53 x 104 pascals or Pa (0.25 atmosphere or atm) to about 4.05 x 105 Pa (4,0 atm) may be conveniently employed. The reaction time for the contact of the reactant with the inorganic metal/oxygen composition in this invention may be selected from a broad operable range which may vary from about 0,,l to about 60 seconds The reaction time may be defined as the length of time in seconds which the reactant gases measured under reaction conditions are in contact with the inorganic metal/oxygen composition in the reactor. The reaction time may vary depending upon the reaction temperature and the desired toluene conversion level. At higher temperatures and lower toluene conversion levels, shorter contact times are required0 Generally, the contact time will vary from about 0,5 second to about 20 seconds0 Preferably, for optimum conversion and selectivity in the preferred temperature range, a contact time from about 1 second to about 12 seconds is employed In addition to the toluene and/or toluene derivatives, other inert substances such as nitrogen, helium, and the like may be present in the reactor. Such inert materials may be introduced to the process alone or may be combined with the other materials as feed. Water or steam may be added to the reaction zone, preferably being introduced with the feed in order to improve the selectivity to the desired products and particularly to suppress complete oxidation to C02. Steam-to-hydrocarbon ratios in the range from 0.1 to 10 or more are suitable, the upper limit being determined by practical cost considerations , Ratios in the range from 0.5 to 3 are preferred0 The inorganic metal/orygen oomposition suitable for use in this invention contains oxygen in such a manner that it is capable of releasing stoichiometric quantities of oxygen under the oxidative reaction conditions employed0 The oxygen in the composition is associated with the metals present, or as mixtures of oxides and complexes. The inorganic metal/oxygen composition can be characterized by an empirical formula selected from: (a) PbMaÚMbêOx where ML is at least one element selected from silver, zinc, gallium, indium, thallium, germanium, phosphorus, arsenic, thorium, the lanthanides, Groups la, 2a, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and Mê is an element selected from bismuth and antimony, and wherein a is 0.01 to 10, b is o to 10. and x is a number taken ta satisfy the average valences of Lead, M1 and M2 in the oxidation states in which they exist in the composition, with the proviso that when is bismuth, M1 cannot be gal- ilium or thallium; and when is antimony, MI cannot be indium, thallium, germanium, phosphorus, ar thorium; and Ma3Mb4Ox where MD is at least one element selected from zinc, ger manium, thorium, the lanthanides, Groups La, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M4 is at least one element selected from indium, silver, Group 2a of the Periodic Table of the Elements, and mixtures thereof, and wherein a is 0.01 to 10, b is O to 10, and x is a number taken to satisfy the average valences of bismuth, M3, and M4 in the oxidation state in which they exist in the composition to yield the toluene dehydrocoupled toluene product. Preferred compositions for formula (a) and formula (b) are those wherein a is 0.5 to 5, b is 0.5 to 5 and x is a number taken to satisfy the average valences of M1 and M2 in the oxidation states in which they exist in the composition. Of the M1 elements listed for formula (a), silver, zinc, lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, indium, arsenic, the lanthanides and those from Groups 3b, 4b and 8 of the Periodic Table of the Elements, and mixtures thereof, are preferred, with silver, zinc, potassium, zirconium, barium, calcium, strontium, nickel, platinum and cerium, and mixtures thereof, being most preferred. Of the M3 elements listed for formula (b), zinc, the lanthamides and those from Groups 3b, 4b and 8 of the Periodic Table of the Elements, and mixtures thereof are preferred, with zinc, cerium, zirconium, cobalt, nickel and platinum being most preferred. For M4 of formula (b) indium, silver, magnesium, calcium, strontium and barium, and mixtures thereof, are preferred, with silver, calcium, strontium and barium being most preferred. The term "Periodic Table of the Elements" as employed herein refers to the Periodic Table of the Elements published in CRC Handbook of Chemistry and Physics, 59th ed., Weast, Ed., CRC Press, Inc., West Palm Beach, FL, 1978, Inside Front Cover. The inorganic metal/oxygen composition may be employed in this invention alone or in association with a support or carrier. The use of a support may be particularly advantageous where th compnsition is toa soft or attrition-prone to retain its structural integrity during reactor charging and/-or under reaction conditions encountered during the course of the reaction process, Suitable supports for the compositions are, for example, silica, alumina, silica-alumlna, metal aluminates such as magnesium aluminate, calcium aluminate, and the like. As noted hereinafter, the dehydrocoupling reaction may be conducted in the presence or absence of added free oxygen. When oxygen is not added to the system, that s, the reaction is conducted in the stoichiometric mode o;ft operation, the oxygen required for the reaction is provided by the inorganic metal/" oxygen composition which enters into the reaction and is consequently reduced Cor, in actual. practice, par tially reduced) during the- course of the reaction. This necessitates regeneration ar re-oxidation which can be easily. effected by heating the material in air or oxygen at temperatures from about 500 C. to about 650 C. for a period of time ranging from about 5 seconds to about one hour. In a semi-continuous operation, regeneration can be effected by periodic interruption of the reaction for re-oxidation of the reduced composition, that is, periods of reaction are cycled with periods of regeneration, Operation, however, can be on a continuous basis whereby a portion of the inorganic metal/oxygen composition can be continuously or intermittently removed, re-oxidized and the re-oxidized material can thereafter be continuously or intermittently returned te the reaction. The latter method is particularly adapted to operations in which the inorganic metal/oxygen composition is fed in the form of a fluidized bed or a moving bed system When oxygen is employed as a reactant, the reaction may be conducted in either a catalytic mode of operation or a combined catalytic/stoichiometric mode of operation, depending on the amount of oxygen supplied. In the catalytic mode of operation, oxygen is supplied in an amount sufficient for the dehydrocoupling reaction, The actual amount of oxygen supplied may be specified as a function of the amount of the toluene or other suitable hydrocarbon component, On this basis the amount of oxygen supplied is ordinarily selected to provide a hydrocarbon-to-oxygen mole ratio from about 1 to about 8 and preferably from about 2 to about 6, In the combined catalytic/stoichiometric mode of operation, the amount of oxygen supplied as a reactant is not sufficient for the dehydrocoupling reaction, thereby requiring an additional source of oxygen. The required additional oxygen will be supplied by the inorganic metal/oxygen composition, that is, the composition will serve as the additional source of oxygen, As a result, the inorganic metal/oxygen composition enters into the reaction and is consequently reduced during the course of the reaction, This necessitates regeneration or re-oxidation of the reduced composition which can-be easily effected as described hereinabove for the stoichiometric mode of operation0 In either mode of operation employing added oxygen as a reactant, whether catalytic or combined catalytic/stoichiometric, the added free oxygen may be supplied either as oxygen or an oxygen-containing gas such as air or oxygen-enriched air0 The inorganic metal/oxygen compositions can be prepared in several ways The simplest method involves intimately mixing the powdered metal oxides in the dry state and calcining. no the method involves adding the metal oxides to water with tirring, filtering to remove excess water or, alternatively, heating to evaporate the water, drying, and calcining In another method of preparation, the powdered metal oxides can be intimately mixed before forming a paste of them with water and further mixing the paste, The paste can be spread and dried in air, after which it can be calcined in air0 The calcined product can then be crushed and sieved to the desired mesh size In still another method of preparatIon, the powdered metal oxides can be mixed in the dry state together with a material which facil- itates forming the mixture into pellets and then pressed to form pellets which are calcined prior to¯use. A further method of preparation involves intimately mixing the powdered metal oxides in water and spray drying the resulting slurry or solution to produce relatively dust-free and free-flowIng spherical particles which are also calcined prior to use In an alternative method of preparation, suitable inorganic metal/oxygen composition precursor salts such as nitrates, carbonates, and acetates are intimately mixed or dissolved in water or nitric acid and heated to thermally decompose the precursor salts to form the corresponding oxides and/or oxygen com plexus The oxides and/or oxygen complexes can then be treated as described hereinabove prior to use, Temperatures employed for calcination of the inorganic metal/oxygen composition may vary from about 4000 C. to about 12000 C. The higher temperatures from about 900" C. to about 11000 C. result in higher selectivity with some loss in activity. Preferred calcination temperatures, therefore, lie in the range from about 7000 C. to about 10000 C. Calcination times may vary from about 1 hour to about 12 hours or more and preferably from about 2 hours to about 10 hours at the higher temperatures, The surface area of the composition is not critical. In general, however, a surface area less than about 10 mê/g is preferredm with values between about 0.1 m2/g and about 5 m2/g being most preferred. As previously indicated, the process of this invention is preferably carried out in the absence of added free oxygen, that is, in the stoichiometric mode of operation, and utilizes only that oxygen supplied by the inorganic metal/oxygen composition. Also, with few exceptions, at substantially comparable conditions, the lower the toluene conversion level, the higher will be the selectivity to the dehydrocoupled products. That is, under similar conditions, the selectivity to the dehydrocoupled toluene products is in general inversely proportional to the toluene conversion level, However, for practical reasons, the dehydrocoupling reaction will generally be conducted at a toluene conversion level of about 20 to about 55 percent, The dehydrocoupled toluene products, stilbene and bibenzyl, may be recovered and purified by any appropriate method and means known to the art and further elucidation here will be unnecessary duplication of the art, As noted previously, stilbene, of course, is the preferred product, The following specific examples illustrating the best presently-known methods of practicing this invention are described in detail in order to facilitate a clear understanding of the invention. It should be understood, however, that the detailed expositions of the application of the invention, while indicating preferred embodiments, are given by way of illustration only and are not to be construed as limiting the invention since various changes and modifications within the spirit of the invention will be come apparent to those skilled in the art from this detailed description0 EXAMPLF I Procedure A - A series of inorganic metal/oxygen compositions having varied Pb/Mê atomic ratios were prepared by intimately mixing the appropriate amount in grams of lead (tri) oxide (PbO) and at least one M2 oxide (or hydroxide) in water, filtering to remove excess water or, alternatively, heating to evaporate the water. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period0 The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below, The parameters for such compositions, conveniently designated as I-A-, are set forth in Table lo TABLE 1 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 1-A-1 PbaZrbOx PbO ZrO2 (a) PbZrO33Ox 90.0 (0.40) 16.6 (0.13) (b) PbZr0.5Ox 80.0 (0.36) 22.1 (0.18) (c) PbZrOx 70.0 (0.31) 38.7 (0.31) (d) PbZr2Ox 50.0 (0.22) 55.2 (0.45) (e) PbZr3Ox 40.0 (0.18) 66.3 (0.54) 1-A-2 PbaKbOx PbO 85% KOH (a) PbK2Ox 55.0 (0.25) 33.0 (0.50) 1-B-1- PbaXbOx PbO Z2O3 (a) PbY0.33Ox 38.0 (0.17) 6.4 (0.028) (b) PbY0.5Ox 36.0 (0.16) 9.0 C0.040) (c) PbYOx 30.0 (0.13) 15.0 (0.066) (d) PbY6Ox 11.2 (0.050) 33.9 (0.15) (e) PbY10Ox 9.0 (0.040) 45.4 (0.20) 1-B-2- PbaHobOx PbO Ho2O3 (a) PbHcOx 11.8 (0.053) 10.0 (0.026) TABLE 1 (Cont'd) CALCINATION CONDITIONS ATOMIC RATION TEMPERATURE, C./TIME, HOURS SAMPLE NO, MÚ/Mê INITIAL FINAL 1-A-1- Pb/Zr (a) 3 400/2 700/12 (b) 2 400/2 700/12 Cc) t 400/2 700/12 Cd) 0.5 400/2 700/12 [e] 0.33 400/2 700/12 1-A-2- Pb/K Ca 0.5 350/2 700/6 1-B-1- Pb/Y Ca) 3 400/12 700/12 Cb) 1 400/12 700/12 [c] 1 400/12 700/12 [d] 0.17 400/12 700/12 [e] 0.1 400/12 700/12 1-B-2- Pb/Ho Ca) I 450/1 800/8 Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was removed from the oven, cooled, crushed, and mixed with a calcium aluminate cement (Alcoa-CA-25) in an amount corresponding to 25t by weight of the dry weight of the calcined material. The resulting solid mixture was slurried with water to form a thick paste and allowed to air dry. The air-dried paste was calcined in air in an open casserole dish for 2 hours at 4000 C. and then at a final temperature of 7000 C for an additional 2 hours. The supported inorganic metal/oxygen composition was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below, The parameters for such compositions, conveniently designated as 1-B-, are set forth in Table 1. EXAMPLE 2 Procedure A - A series of inorganic metal/oxygen compositions having varied Pb/M2 atomic ratios were prepared by dissolving the appropriate amount in grams of lead CTI) acetate trihydrate [Pb(OCOCH3)2.3 H2O], lead CII) nitrate fPb(N03)2i, or lead (II) oxide (PbO) and at least one M2 nitrate in approximately 100 milliliters of concentrated nitric acid (HNO3) and heating to evaporate and decompose the nitric acid and the salts, The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below. The parameters for such compositions, conveniently designated as 2-A-, are set forth in Table 2, Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was supported on a calcium aluminate cement (Alcoa-CA-25) as described in Example 1, Procedure B hereinabove. The parameters for such compositions, conveniently designated as 2-B-, are set forth in Table 2, TABLE 2 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO: MaÚMbêOx MÚ Mê 2-A-1- PbaCobOx PbO Co(NO3)2.6H2O (a) PbCoOx 44.6 (0.20) 59.0 (0.20) 2-A-2- PbaThbOx Pb(OCOCH3)2.3H2) Th(NO3)4. H2O (a) PbThOx 57.0 (0.15) 82.8 (0.15) 2-B-1- PbaZnbOx Pb(NO3)2 TnO (a) PbZn0.2Ox 143.0 (0.43) 7.0 (0.086) (b) PbZn0.33Ox 135.0 (0.41) 11.0 (0.14) (c) PbZn0.5Ox 130.0 (0.39) 16.0 (0.20) (d) PbZnOx 120.0 (0.36) 29.4 (0.36) (e) PbZn2Ox 100.0 (0.30) 49.0 (0.60) (f) PbZn3Ox 90.0 (0.27) 66.0 (0.81) (g) PbZn5Ox 70.0 (0.21) 86.0 (1.057) TABLE 2 (Cont'd) CALCINATION CONDITION ATOMIC RATIO TEMPERATURE, C/TIME, HOURS SAMPLE NO. MÚ/Mê INITIAL FINAL 2-A-1- Pb/Co (a) 1 450/1 750/8 2-A-2- Pb/Th (a) 1 450/1 750/8 2-B-1- Pb/Zn (a) 5 450/1 800/4 (b) 3 450/1 800/4 (c) 2 450/1 800/4 (d) 1 450/1 800/4 (e) 0.5 450/1 800/4 (f) 0.33 450/1 800/4 (g) 0.2 450/1 800/4 EXAMPLE 3 Procedure A - A solution containing an appropriate amount in grams of lead CII) carbonate (PbCO3) dissolved in 300 milliliters of water and acidified to pH 6 with concentrated nitric acid was mixed with a solution containing an appropriate amount in grams of sodium hydrogen phosphate heptahydrate (NaHPO4 .7 H2O; M2 = phosphorus, P) dissolved in 300 milliliters of water The solutions were stirred at high speed for 2 hours. The precipitate was collected by suction filtration, dried, and calcined in air for an initial period at an initial temperature and then at a final temperature for an additonal period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14730 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below. The parameters for such compositions, conveniently designated as 3-A-, are set forth in Table 3O Procedure B - The procedure described in Procedure A above was employed except that sodium hydrogen arsenate heptahydrate (NaHAsO4 7H20; M2 = arsenic, As) was employed and following the final calcination, the calcined material was supported on a calcium aluminate cement (Alcoa-CA-25) as described in Example 1, Procedure B hereinabove The parameters for such compositions, conveniently designated as 3-B-, are set forth in Table 3O TABLE 3 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 3-A-1- PbaPbOx PbCO3 Na2HPO4.7H2O (a) PbPOx 129.0 (0.48) 129.0 (0.48) 3-B-1- PbaAsbOx PbCO3 NaHAsO4.7H2O (a) PbAsxOx 129.0 (0.48) 150.0 (0.48) CALCINATION CONDITIONS ATOMIC RATION TEMPERATURE, C./TIME, HOURS SAMPLE NO. MÚ/Mê INITIAL FINAL 3-A-1- Pb/P (a) 1 400/2 700/3 3-B-1- Pb/As (a) 1 400/2 700/12 EXAMPLE 4 Procedure A - A series of inorganic metal/oxygen compositions having varied Pb/M2 atomic ratios can be prepared by the following described procedure Dissolve the appropriate amount in grams of lead (II) nitrate rPbCNO3)2] and at least one (water soluble) M2 nitrate in water and heat to evaporate the water and decompose the nitrates. Place the resulting solid in an open casserole dish and calcine in air for an initial period at an initial temperature and then at a final temperature for an additional period (usually 1 hour at 4500 C. and 8000 C. for 10 hours, respectively). Remove the calcined material from the oven, cool, crush in a mortar, and sieve to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below. Following these steps should result in compositions, conveniently designated as 4-A-, having properties beneficial for use in the process of this invention. Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was supported on a calcium aluminate cement (Alcoa CA-25) as described in Example 1, Procedure B hereinabove. The parameters for such compositions, conveniently designated as 4-B-, are set forth in Table 4. TABLE 4 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 4-B-1- PbaAgbOx Pb(NO3)2 AgNO3 (a) PbAg0.1Ox 140.0 (0.42) 7.2 (0.042) (b) PbAg0.125Ox 140.0 (0.42) 9.0 (0.053) (c) PbAg0.17Ox 80.0 (0.42) 6.8 (0.040) (d) PbAg0.25Ox 133.0 (0.40) 17.0 (0.10) (e) PbAg0.5Ox 121.0 (0.37) 31.0 (0.18) CALCINATION CONDITIONS ATOMIC RATIO TEMPERATURE, C/TIME, HOURS SAMPLE NO. MÚ/Mê INITIAL FINAL 4-B-1- Pb/Ag (a) 10 450/1 800/10 (b) 8 450/1 800/10 (c) 6 450/1 800/10 (d) 4 450/1 800/10 Ce) 2 450/1 800/10 EXAMPLE 5 Procedure A - A series of inorganic metal/oxygen compositions containing two or more Mê elements were prepared by intimately mixing the appropriate amount of lead (II) oxide CPbO), lead (II) carbonate (PbCO3), or lead CII) nitrate tPb(NO3)2] with at least two M2 carbonates, nitrates, or oxides Cor, alternatively, mixing an appropriate amount of a suitable lead-containing binary metal/oxygen composition with at least one M2 carbonate, nitrate, or oxide) in water and heating to evaporate the water and/or decompose the carbonates and/or nitrates. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 6 below. The parameters for such compositions, conveniently designated as 5-A-, are set forth in Table 5. Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was supported on a calcium aluminate cement (Alcoa-Ca-25) as described in Example 1, Procedure B hereinabove. The parameters for such compositions, conveniently designated as 5-B-, are set forth in Table 5. TABLE 5 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 5-A-1- (a) PbAg0.17Zr0.33Ox PbO AgNO3 ZrO2 107.1 (0.48) 13.6 (0.080) 19.7 (0.16) 5-A-2-(a) PbK0.67Zr0.33Ox PbO K2CO3 ZrO2 93.7 (0.42) 19.3 (0.14) 17.2 (0.14) 5-A-3-(a) Pby.33Zr0.35Ox PbO Y2O3 ZrO2 90.0 (0.40) 15.0 (0.066) 17.0 (0.14) 5-A-A-(a) PbZn0.4Th0.01Ox PbO Zn(NO3)2.6 H2O Th(NO3)4.4H2O 80.0 (0.36) 43.0 (0.14) 2.0 (0.0036) 5-B-1-(a) PbY0.35Zr0.35Ox PbO Y2O3 ZrO2 90.0 (0.40) 15.8 (0.070) 17.0 (0.14) 5-B-2-(a) PbHo0.17Zr0.35Ox PbO Ho2O3 ZrO2 90.0 (0.40) 13.0 (0.034) 17.0 (0.14) 5-B-3-(a) PbZn0.33Co0.17Ox PbO ZnO Co(NO3)2.6H2O 100.0 (0.45) 12.2 (0.15) 21.8 (0.075) TABLE 5 (Cont'd) CALCINATION CONDITIONS TEMPERATURE, C/TIME HOURS SAMPLE NO. INITIAL FINAL 5-A-1-(a) --- 700/12 5-A-2-(a) 400/2 700/12 5-A-3-(a) 400/2 700/12 5-A-4-(a) 400/1 800/4 5-B-1-(a) 400/2 700/12 5-B-2-(a) 400/2 800/8 5-B-3-(a) 450/1 800/4 EXAMPLE 6 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters (8 inches) in length and 0.95 centimeter C0.375 inch) in internal diameter having a usable capacity of 1I milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof was a gas sampling valve into a gas-liquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reaction period0 The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted The reactor was charged with approximately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Examples 1-5 above. Glass wool plugs were used as supports for the composition The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period Steam and toluene in a 2: :1 mole ratio were fed to the reactor at a pressure af 1.013 x 105 pascal (I atmosphere) at a rate sufficient to provide a reactor residence Ccontact) time of 4 seconds (unless otherwise noted) for the toluene Cassuming a 50% vo-id space in the reactor). After the reaction had proceeded for I minute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 6. TABLE 6 TEMPERATURE, C/ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-A-1-(a) 630 82.7 570 41.6 450 3.2 1-A-1-(b) 630 94.2 570 45.3 540 28.6 1-A-1-(c) 630 86.0 570 47.6 480 8.0 1-A-1-(d) 630 49.3 540 44.5 450 3.3 1-A-1-(e) 630 90.3 570 35.3 480 12.3 l-A-2- Ca) 630 24.9 570 18.0 450 4.8 1-B-1-(a) 630 93.6 540 31.9 450 9.9 1-B-1-(b) 630 96.0 540 57,6 510 19,3 450 12.0 l-B-l-Cc) 630 89.0 540 27.7 450 4.5 l-B-l-(d) 630 72.6 540 17.3 450 3.2 TABLE 6 CCont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 45.7 0.3 33.0 46.0 62.1 3.4 22.0 65.5 15.6 27.7 31.6 43.3 1-A-1-(b) 11.8 0.0 60.4 11.8 52.3 0.1 33.6 52.4 56.2 1.6 2.3 57.8 I-A-I-Cc) 33.0 0.0 43.n 33.0 62.2 0.4 27.0 62.6 50.0 15.3 22.0 65.3 1-A-1-(d) 20.7 1.9 53.8 22.6 61.1 4.0 25.3 65.1 15.1 25.2 41.0 40.3 1-A-1-(e) 13.5 0.0 60.7 13.5 43.0 Q.0 41.1 43.0 48.1 5.3 37.0 53.4 l-A-Z-(a) 65.9 8.5 12.7 74.4 77.2 6.2 0.3 83.5 34.2 35.2 7.6 69.4 1-B-1-(a) 6.7 0.0 67.8 6.7 60.2 0.3 30.0 60.5 30.9 7,2 39.3 38.1 1-B-1-(b) 4.8 0.0 70.4 4.8 55.7 0.0 25.7 55.7 63.0 0.6 25.5 63.6 57.1 1.0 25.9 58.1 1-B-1-(c) 6.2 0.0 72.9 6.2 53.1 0.0 39.0 53.1 31.5 6.3 42.3 37.8 1-B-1-(d) 20.7 0.0 60.6 20.7 61.7 0.1 30.8 61.8 29.6 15.9 32.3 45.5 TABLE 6 (Cont'd) TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-B-1-(e) 630 53.7 540 9.1 450 2.1 1-B-2-(a) 630 72.8 540 46.7 450 6.9 2-A-1-(a) 630 90.6 540 19.0 480 7.1 2-A-2-(a) 600 85.5 540 30.0 450 6.5 2-B-1-(a) 630 92.0 540 20.2 480 3.4 2-B-1-(b) 630 70.0 540 14.5 480 1.9 2-B-1-(c) 630 85.0 540 17.6 480 1.7 2-B-1- (d) 630 82.1 540 12.9 480 1.1 2-B-1-(e) 630 58.0 540 10.6 480 1.5 2-B-1-(f) 630 69.1 540 11.0 480 1.8 2-B-1-(g) 630 68.4 540 15.3 480 3.7 TABLE 6 (Cont'd) SELECTIVITY , % STILBENE + SAMPLE NO: STILBENE BIBENZYL BENZENE BIBENZYL 1-B-1-(e) 3.1 0.0 74.2 3.1 7.3 0.0 45.3 7.3 0.0(?) 15.8 36.3 15.8 1-B-2-(a) 19.3 0.0 56.9 19.3 53.5 1.0 42.3 54.5 50.7 9.2 25.6 59.9 2-A-1-(a) 10.3 0.3 59.8 10.6 56.5 3.5 30.3 60.0 65.0 8.0 12.1 73.0 2-A-2-(a) 2.6 0.0 89.1 2.6 19.6 0.1 70.3 19.7 23.1 3.3 47.4 26.4 2-B-1-(a) 12.0 0.0 81.5 12.0 59.9 0.0 41.4 59.9 57.3 1.1 29.8 58.4 2-B-1-(b) 52.6 0.4 34.9 53.0 80.0 1.0 17.9 81.0 54.6 12.4 23.5 67.0 2-B-1-(c) 22.3 0.0 70.5 22.3 69.1 0.0 28.8 69.1 54.2 2.4 33.0 56.6 2-B-1-(d) 41.4 0.0 26.3 41.4 55.8 21.4 15.7 77.2 10.9 22.3 38.7 33.2 2-B-1-(e) 56.2 0.4 28.5 56.6 70.2 6.1 19.3 76.3 38.3 18.9 28.3 57.2 2-B-1-(f) 49.0 0.0 37.0 49.0 75.5 4.2 19.9 79.7 31.9 12.0 40.2 43.9 2-B-1-(g) 47.4 0.0 39.9 47.4 67.7 3.0 26.7 70.7 45.8 11.4 30.5 57.2 TABLE 6 (Cont'd) TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION O 3-A-1-(a) 570 39.1 3-B-1-(a) 570 35.3 4-B-l-(a) 630 60.0 570 20.0 450 0.7 4-B-1-(b) 630 47.7 570 19.5 450 0.6 4-B-1- (c) 630 51.2 570 17.8 450 2.0 4-B-l-(d) 630 43.6 570 14.1 450 0.5 4-B-1-(e) 630 57.5 570 29.6 450 1.3 5-A-l-(a) 630 71.8 570 29.2 450 1.1 5-A-2-(a) 630 65.9 570 33.5 450 2.4 5-A-3-(a) 630 90.0 570 45.7 450 1.9 5-A-4-(a) 630 91.1 570 27.8 450 0.9 5-B-l-(a) 630 90.0 570 45.7 450 1.9 TABLE 6 (Cont'd) SELECTIVITY , % STILBENE + SAMPLE NO: STILBENE BIBENZYL BENZENE BIBENZYL 3-A-1-(a) 38.5 4.3 39.1 42.8 3-B-1-(a) 64.3 3.1 8.5 67.4 4-B-1-(a) 56.2 3.6 24.4 59.8 72.1 16.0 11.0 88.0 10.8 36.5 38.6 47.3 4-B-1-(b) 53.7 7.3 22.0 61.1 60.6 23.3 10.6 83.9 6.5 32.5 40.9 39.0 4-B-1-(c) 36.3 7.5 26.5 43.8 39.7 34.5 13.3 74.2 9.1 29.4 33.0 38.5 4-B-1-(d) 53.2 9.5 21.2 62.7 50.2 30.8 11.8 81.0 0.0 23.0 45.0 23.2 4-B-1-(e) 52.1 2.7 29.4 54.8 66.5 7.7 18.5 74.2 4.8 12.2 56.7 17.0 5-A-1-(a) 57.6 2.5 20.8 60.1 58.9 16.3 14.5 75.2 3.4 31.7 41.4 35.1 5-A-2-(a) 32.6 0.0 49.7 32.6 78.6 0.0 18.6 78.6 13.5 29.3 11.4 42.9 5-A-3-(a) 14.9 0.0 73.6 14.9 54.5 0.0 36.5 54.5 19.9 8.1 56.0 28.0 5-A-4-(a) 11.0 0.0 81.3 11.0 59.7 0.0 31.1 59.7 19.2 2.4 45.1 21.6 5-B-1-(a) 14.5 0.0 73.6 14.9 54.5 0.0 36.5 54.5 20.1 8.0 56.0 28.1 TABLE 6 (Cont'd) TEMPERATURE, C./ CONTACT TTME SAMPLE NO. SECONDS1 CONVERSION, % 5-B-2-(a) 630 80.5 570 53.7 510 23.8 450 3.5 5-B-3-(a) 630 97.9 540 51.4 450 16.1 TABLE 6 (Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 5-B-2-(a) 33.2 0.0 56.2 33.2 57.8 0.0 33.0 57.8 64.9 2.5 25.8 67.4 27.4 18.7 41.9 46.1 5-B-3-(a) 3.3 0.0 65.9 3.3 47.5 0.1 35.8 47.6 16.2 18.1 35.3 34.3 -A contact time of 4 seconds was employed unless otherwise noted. EXAMPLE 7 Procedure A - A series of inorganic metal/oxygen compositions having varied Pb/M2 atomic ratios were prepared by intimately mixing the appropriate amount in grams of lead (II) oxide (PbO) and at least one M2 oxide (or hydroxide) in water, filtering to remove excess water or, alternatively, heating to evaporate the water, and then drying. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 9 below. The parameters for such compositions, conveniently designated at 1-A-, are set forth in Table 7. Procedure B - A series of inorganic metal/oxygen compositions having varied Pb/M2 atomic ratios and supported on a calcium aluminate cement can be prepared according to the procedure described in Procedure A above except as follows. Hollowing tht final calcination, remove the calcined material from the oven, cool, crush, and mix with a calcium aluminate cement CAlcoa-CA-25) in an amount corresponding to 25% by weight of the calcined material. Slurry the solid mixture with water to form a thick paste and allow to air dry in an open casserole dish for 2 hours at 4000 C. and then at a final temperature af 7003 C. for an additional 2 hours. Remove the supported inorganic metaltoxrgen composition from the oven, cool, crush in a mortar, and sieve to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 3 below. Following these steps should result in compositions, conveniently designated as 1-B--, having properties beneficial for use in the process of this invention TABLE 7 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 1-A-1- PbaSrbOx PbO SrO (a) PbSr0.1Ox 145.0 (0.65) 6.7 (0.065) (b) PbSr0.33Ox 130.0 (0.58) 20.0 (0.19) (c) PbSr0.5Ox 120.0 (0.54) 28.0 (0.27) (d) PbSrOx 60.0 (0.27) 28.0 (0.27) (e) PbSr2Ox 80.0 (0.36) 74.3 (0.72) (f) PbSr3Ox 65.0 (0.29) 91.0 (0.88) 1-A-2- PbaMgbOx PbO MgO (a) PbMgOx 89.3 (0.40) 16.0 (0.40) 1-A-3- PbaBabOx PbO BaO (a) PbBaOx 44.6 (0.20) 30.6 (0.20) 1-A-4- PbyT1bOx PbO Tl2O3 (a) PbT1Ox 33.5 (0.15) 68.4 (0.15) TABLE 7 Cont'd) CALCINATION CONDITIONS ATOMIC RATIO TEMPERATURE, C/TIME HOURS SAMPLE NO: MÚ/Mê INITIAL FINAL 1-A-1- Pb/Sr (a) 10 450/1 800/16 (b) 3 450/1 800/16 (c) 2 (1) 450/1 (2) 800/16 (3) 900/12 (d) 1 450/1 800/16 (e) 0.5 450/1 800/16 (f) 0.33 450/1 800/16 1-A-2- Pb/Mg (a) 1 450/1 750/8 1-A-3- Pb/Ba (a) 1 450/1 750/8 1-A-4- Pb/T1 (a) 0.5 350/1 700/6 EXAMPLE 8 A series of inorganic metla/oxygen compositions containing two more Mê elements were prepared by intimately mixing the appropriate amount of lead (11) oxide (PbO), lead (II) carbonate (PbCO3), or lead (II) nitrate tPb(NO3)2] with at least two M2 carbonates, nitrates, or oxides (or, alternatively, mixing an appropriate amount of a suitable lead-containing binary metal/oxygen composition with at least one M2 carbonate, nitrate, or oxide) in water and heating to evaporate the water and/or decompose the carbonates and/or nitrates. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 3 below* The parameters for such compositions, conveniently designated as 2-A-, are set forth in Table 8. TABLE 8 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 2-A-1-(a) PbMg3Sr0.5Ox PbO MgO SrO 111.6 (0.50) 58.9 (1.47) 25.9 (0.25) CALCINATION CONDITIONS TEMPERATURE, C./TIME, HOURS SAMPLE NO. INITIAL FIMAL 2-A-1-(a) 450/1 850/B EXMIPLE 9 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters (8 inches) in length and 0.95 centimeter (0.375 inch) in internal diameter having a usable capacity of 11 milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof via a gas sampling valve into a gas-liquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reaction period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approximately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Examples 1 and 2 above. Glass wool plugs were used as supports for the composition The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2:1 mole ratio were fed to the reactor at a pressure of 1.013 x 5 pascal (1 atmosphere) at a rate sufficient to provide a reactor residence (contact) time of 4 seconds (unless otherwise noted) for the toluene Cassuming a 50% void space in the reactor) After the reaction had proceeded for 1 minute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 9. TABLE 9 TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-A-1-(a) 630 74.4 570 37.0 450 5.2 1-A-1-(b) 630 78.2 540 33.7 480 5.3 1-A-1-(c) 630 48.7 540 19.9 480 2.0 1-A-1-(d) 630 97.5 570 53.1 510 21.0 450 5.9 1-A-1-(e) 630 73.3 540 44.4 480 9.2 1-A-1-(f) 630 63.8 540 19.0 480 4.7 1-A-2- (a) 630 89.2 540 44.0 450 2.4 1-A-3-(a) 630 91.5 540 52.7 1-A-4-(a) 480 10.7 2-A-1-(a) 630 39.5 575 29.8 500 4.9 TABLE 9 Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 45.2 0.5 36.2 45.7 58.8 2.8 22.8 61.6 15.1 24.7 14.3 39.8 1-A-1-(b) 18.9 2.0 45.4 20.9 39.8 16.3 38.9 56.1 9.1 21.6 18. 3 30. 7 1-A-1-(c) 26.0 6.3 34.9 32.3 31.6 15.5 22.6 47.1 3.3 18.0 15.7 21.3 1-A-1-(d) 2.8 0.3 89.8 3.1 57.0 8.7 33.1 55.7 51.1 20.5 22.3 71.6 31.1 39.9 23.3 71.0 1-A-1-(e) 30.8 5.2 46.0 36.0 45.3 14.3 32.8 59.6 37.2 38.1 20.2 75.3 1-A-1-(f) 15.6 6.5 40.4 23.0 37.0 37.1 14.7 74.1 12.2 64.0 15.8 76.2 1-A-2-Ca) 16.7 0.3 52.7 17.0 56.0 0.8 31.6 56.8 38.5 25.8 17.3 64.3 1-A-3-(a) 16.3 0.4 62.2 16.7 32.3 7.3 50.1 39.6 l-A-4-(a) 17.0 43.4 3.8 60.4 2-A-1- (a) 29.2 25.6 19.0 54.8 32.5 37.2 13.9 69.7 9.8 62.7 7.1 72.5 1A contact time of 4 seconds was employed unless otherwise noted. EXAMPLE 10 Procedure A - A series of inorganic metal/oxygen compositions were prepared by intimately mixing the appropriate amount of leadCII) oxide (PbO), leadCII carbonate CPbCO3), or lead(II) nitrate {PbCNO3)2] with 2 at least one of each of an N carbonate, nitrate, or oxide, and an M3 carbonate, nitrate, or oxide for, alternatively, mixing an appropriate amount of a suitable lead-containing binary metal/oxygen composition with at least one M2 carbonate, nitrate, or oxide or one M3 carbonate, nitrate, or oxide, depending on the element other than lead contained in the binary composition] in water and heating to evaporate the water Cand decompose the carbonates and/or nitrates, when employed). The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for- an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 11 below. The parameters for such compositions, conveniently designated as 1-A-, are set forth in Table 10. Procedure B - A series of inorganic metal/ oxygen compositions supported on a calcium aluminate cement can be prepared according to the procedure described in Procedure A above except as follows. Following the final calcination, remove the calcined material from the oven, cool, crush, and mix with a calcium aluminate cement (Alcoa-CA-25) in an amount corresponding to 25% by weight of the calcined material* Slurry the solid mixture with water to form a thick paste and allow to air dry. Calcine the air-dried paste in air in an open casserole dish for 2 hours at 400" C. and then at a final temperature of 700" C. for an additional 2 hours. Remove the supported inorganic metal/oxygen composition from the oven, cool, crush in a mortar and sieve to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 11 below. Following these steps should result in compositions, conveniently designated as 1-B-, having properties beneficial for use in the process of this invention. TABLE 10 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêMc Ox MÚ Mê M 1-A-1-(a) PbMg0.25Y0.5Ox PbO MgO Y2O3 89.3 (0.40) 4.0 (0.10) 22.6 (0.10) PbO SrO 85% KOH 1-A-2-(a) PbSr0.67K0.67Ox 133.9 (0.60) 41.4 (0.40) 26.4 (0.40) PbZrOx SrO -- 100.0 (0.29) 3.0 (0.029) TABLE 10 (Cont'd) CALCINATION CONDITIONS TEMPERATURE, C./TIME HOURS SAMPLE NO. INITIAL FINAL 1-A-1-(a) 450/1 1000/64 1-A-2-(a) 450/1 850/8 1-A-3-(a) 450/1 800/4 ÚThe lead zirconate binary metal/oxygen composition having a (calculated) gram molecular weight of 346.4 grams, was prepared as follows: Lead(II) oxide (PbO; 70.0 grams, 0.31 mole) amd zirconium (IV) oxide (ZrO2; 38.7 grams, 0.31 mole) were intimately mixed in water and then heated to evaporate the water. The resulting solid was placed in an open casserole dish and calcined in air for 2 hours at 400 C. and then at 700 C for an additional 12 hours. The calcined material was removed from the oven, cooled, crushed in a mortar, and ground to a fine powder. EXAMPLE 11 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters (8 inches) in length and 0.95 centimeter (0.375 inch) in internal diameter having a usable capacity of 11 milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof via a gas sampling va-lve into a gas-liquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reacton period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approx imately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Example 1 above. Glass wool plugs were used as supports for the Composition. The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2;1 mole ratio were fed to the reactor at a pressure of 1.013 x 105 pascal C1 atmosphere) at a rate sufficient to provide a reactor residence Ccontact) time of 4 seconds Cunless otherwise noted) for the toluene Cassuming a 50% void space in the reactor). After the reaction had proceeded for 1 minute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 11. TABLE 11 TEMPERATURE, CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-A-1-(a) 630 68.8 575 33.8 500 15.1 l-A-2- (a) 630 44.6 575 43.5 500 2.5 1-A-3-(a) 630 55.5 575 40.0 500 9.7 TABLE 11 (Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 45.9 0.0 55.2 45.9 65.7 1.1 33.8 66.8 48.2 6.0 49.6 54.2 1-A-2-(a) 23.2 5.3 66.5 28.5 66.0 6.6 21.6 72.6 13.0 39.7 26.1 52.7 1-A-3-(a) 65.2 1.3 31.7 66.5 73.6 1.6 24.7 75.2 35.4 11.4 13.1 46.8 ÚA contact time of 4 seconds was employed unless other wise noted. EXAMPLE 12 Procedure A - A series of inorganic metal/oxygen compositions having varied Bi/M2 atomic ratios were prepared by intimately mixing the appropriate amount in grams of bismuth (III) oxide (Bi2O3) and at least one Mê oxide (or hydroxide) in water, filtering to remove excess water or, alternatively, heating to evaporate the water, and then drying. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation In the toluene conversion reactor described in Example 15below. The parameters for such compositions, conveniently designated as 1-A-, are set forth in Table 12. TABLE 12 STARTING MATERIALS SAMPLE NO. MaÚMbêOx MÚ Mê 1-A-1- BiaZnbOx Bi2O3 ZnO (a) BiZnO11Ox 150.0 (0.32) 5.8 (0.071) (b) BiZn0.17Ox 150.0 (0.32) 8.9 (0.11) (c) BiZn0.25Ox 140.0 (0.30) 12.2 (0.15) (d) BiZn0.5Ox 130.0 (0.28) 22.7 (0.28) (e) BiZnOx 110.0 (0.24) 38.4 (0.47) (f) BiZnOx 90.0 (0.19) 63.0 (0.77) (g) BiZn3Ox 70.0 (0.15) 73.0 (0.90) 1-A-2- BiaKbOx Bi2O3 85% KOH (a) BiK0.013 100.0 (0.21) 0.35 (0.0053) (b) BiK0.21Ox 100.0 (0.21) 5.8 (0.088) (c) BiK0*43Ox 100.0 (0.21) 11.6 (0.18) (d) BiKO 96.8 (0.21) 26.4 (0.40) 1-A-3- BiaNiOx BiO3 NiO (a) BiNi0.2Ox 140.0 (0.30) 9.0 (0.12) (b) BiNi0.33Ox 135.0 (0.29) 14.4 (0.19) (c) BiNi0.5Ox 140.0 (0.30) 22.4 (0.30) (d) BiNiOx 110.0 (0.24) 35.3 (0.47) (e) BiNiOx 90.0 (0.19) 57.7 (0.77) (f) BiNi3Ox 80.0 (0.17) 76.9 (1.03) TABLE 12 <RTI ID=56.1> (Cont'd) CALCINATION CONDITIONS ATOMIC RATIO TEMPERATURE, C.%TIME, HOURS SAMPLE NO. M1/M2 INITIAL FINAL 1-A-1- Bi/Zn (a) 9 (1) 400/2 (3) 800/1 (2) 720/8 (4) 730/1 (b) 6 (1) 400/2 (3) 800/1 (2) 720/8 (4) 730/1 (c) 4 (1) 400/2 (2) 800/1 (3) 730/1 (d) 2 (1) 400/2 (3) 800/1 (2) 700/2 (4) 730/1 (e) 1 (l) 400/2 (3) 800/1 (2) 700/8 (4) 730/1 (f) 0.5 (1) 400/2 (3) 800/1 (2) 700/2 (4) 730/1 (g) 0.33 (1) 400/2 (3) 800/1 (2) -700/8 (4) 730/1 1-A-2- Bi/K (a) 79 ¯¯¯¯¯ 750/8 (b) 4.8 ----- 750/8 (c) 2.3 ----- 850/8 (d) 1 --- 750/8 1-A- 3- Bi/Ni (a) 5 450/2 800/6 (b) 3 450/2 800/6 (c) 2 450/2 800/6 (d) 1 (1) 450/2 (2) 800/6 (3) 1000/12 (e) 0.5 (1) 450/2 (2) 800/6 (3) 1000/12 (f) 0.33 (1) 450/2 (2) 800/6 (3) 1000/12 TABLE 12 (Cont'd) STARTING MATERIALS 1 2 GRAMS (MOLES) SAMPLE NO. a b x M1 M 1-A-4- BiaZrbOx Bi2O3 ZrO2 (a) BiZr0.170x 139.8 (0.30) 12.3 (0.10) (b) BiZr0.33Ox 139.8 (0.30) 24.6 (0.20) (c) BiZrOx 93.2 (0.20) 49.2 (0.40) (d) BiZr2Ox 93.2 (0.20) 98.6 (0.80) (e) BiZr0.17Ox 139.8 (0.30) 12.3 (0.10) 1-A-5- BiaGebOx Bi2O3 GeO2 (a) BiGe0.17Ox 116.6 (0.25) 8.9 (0.085) (b) BiGe0.7Ox 46.6 (0.10) 35.5 (0.34) (c) BiGe3.8Ox 61.7 (0.13) 104.5 (1.00) 1-A-6- BiaCebOx Bi2O3 CeO2 (a) BiCe0.17Ox 139.8 (0.30) 17.2 (0.10) (b) BiCe0.33Ox 139.8 (0.30) 34.4 (0.20) (c) BiCe0.5Ox 116.5 (0.25) 43.0 (0.25) (d) BiCeOx 93.2 (0.20) 68.8 (0.40) (e) BiCe2Ox 46.6 (0.10) 68.8 (0.40) (f) BiCe3Ox 46.6 (0.10) 103.2 (0.60) 1-B-1- BiaLabOx Bi2O3 La2O3 (a) BiLa0.33Ox 140.0 (0.30) 31.4 (0.10) (b) BiLa0.33Ox 120.0 (0.26) 40.4 (0.12) (c) BiLaOx 96.8 (0.21) 65.2 (0.20) (d) BiLa2Ox 70.0 (0.15) 94.2 (0.29) (e) BiLa3Ox 55.0 (0.12) 111.0 (0.34) TABLE 12(Cont'd) CALCINATION CONDITIONS ATOMIC RATIO TEMPERATURE, 0C./TIME, HOURS SAMPLE NO. M1/M2 INITIAL FINAL l-A-4- Bi/Zr (a) 6 450/1 900/8 (b) 3 450/1 900/8 (c) 1 450/1 900/8 (d) 0.5 450/1 900/8 (e) 0.33 450/1 900/8 1-A-5- Bi/Ge (a) 6 450/1 850/8 (b)- 0.6 450/1 850/8 (c) 0/26 450/1 800/10 1-A-6- Bi/Ce (a) 6 450/1 850/8 (b) 3 450/1 850/8 (c) 2 450/1 850/8 (d) 1 450/1 850/8 (e) 0.5 450/1 850/8 (f) 0.33 450/1 850/8 1-B-1- Bi/La (a) 3 --- 1000/S (b) 2 --- 1000/5 (c) 1 --- 1000/5 (d) 0.5 --- 1000/5 (e) 0.35 --- 1000/5 Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was removed from the oven, cooled, crushed, and mixed w-ith a calcium aluminate cement tAlcoa-CA-25) in an amount corresponding to 25% by weight of the dry weight of the calcined material. The resulting solid mixture was slurried with water to form a thick paste and allowed to air dry. The air-dried paste was calcined in air in an open casserole dish for 2 hours at 4000 C. and then at a final temperature of 700" C. for an additional 2 hours. The supported inorganic metal/oxygen composition was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 4 below. The parameters for such compositions, conveniently designated as 1-B-, are set forth in Table 12 EXAMPLE 13 Procedure A - A series of inorganic metal/oxygen compositions having varied Bi/M2 atomic ratios can be prepared by the following described procedure. Dissolve the appropriate amount in grams of bismuth (III) oxide (Bi203) and at least one M2-nitrate in approximately 100 milliliters of concentrated nitric acid (HNO3) and heat to evaporate and decompose the nitric acid and nitrates. Place the resulting solid in an open casserole dish and calcine in air for 8 hours at 8500 C. Remove the calcined material from the oven, cool, crush in a mortar, and sieve to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 4 below. Following these steps should result in compositions, conveniently designated as 2-A-, having properties beneficial for use in the process of this invention. Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was supported on a calcium aluminate cement (Alcoa-CA-25) as described in Example 12, Procedure B hereinabove. The parameters for such compositions, conveniently designated as 2-B-, are set forth in Table 13. EXAMPLE 14 A series of inorganic metal/oxygen compositions containing two or more Mê elements were prepared by intimately mixing the appropriate amount of bismuth (III) oxide (Bi2O3) or bismuth (III) nitrate pentahydrate 2.. {3i(NO3)3.5 H2O] with at least two N nitrates or oxides (or, alternatively, mixing an appropriate amount of a suitable bismuth-containing binary inorganic metal/oxygen composition with at least one M2 nitrate or oxide) in water and heating to evaporate the water and/or decompose the nitrates. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and than at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example Below. The parameters for such compositions, conveniently designated as 3-A-, are set forth in Table 14. EXAMPLE 15 A. Toluene Conversion Reactor - .4 stainless steel tube 20.32 centimeters (8 inches) in length and 0.95 centimeter (0.375 inch) in internal diameter having a usable capacity of 11 milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction TABLE 13 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêOx MÚ Mê 2-B-l- BiaThebOx Bi(NO3)305 H2O Th(NO3)404 H2O (a) BiTh0.33Ox 140.0 (0.29) 53.0 (0.10) (b) BiTh0.5Ox 125.0 (0.26) 71.0 (0.13) (c) BiThOx 90.0 (0.19) 102.0 (0.18) (d) biTh2Ox 57.0 (0.12) 130.0 (0.24) (e) BiTh3Ox 44.0 (0.091) 150.0 (0.27) CALCINATION CONDITIONS ATOMIC RATIO TEMPERATURE, C./TIME, HOURS SAMPLE NO. MÚ/Mê INITIAL FINAL 2-B-1- Bi/Th (a) 3 --- 850/8 (b) 2 --- 850/8 (c) 1 --- 850/8 (d) 0.5 --- 850/8 (e) 0.34 --- 850/8 TABLE 14 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbê Ox MÚ Mê 3-A-1-(a) BiTh0.162n0.47Ox Bi2O3 Th(NO3)4.4 H2O ZnO 89.3 (0.19) 33.1 (0.06) 14.7 (0.18) 3-A-2-(a) BiLaK0.5Ox Bi2O3 La2O3 85% KOH 93.2 (0.20) 65.2 (0.20) 13.2 (0.20) 3-A-3-(a) BiGe0.25Ni0.5Ox Bi2O3 GeO2 NiO 93.2 (0.20) 10.5 (0.10) 14.9 (0.20) 3-A-4-(a) BiZnZrOx Bi2O3 ZnO ZrO2 46.6 (0.10) 16.3 (0.20) 24.6 (0.20) 3-A-5-(a) BiCe0.20ThOx BiThOx GeO2 ---- 85.0 (0.086) 2.9 (0.017) ÚPrepared according to the procedure described in Example 13, Procedure A, using the quantities of materials specified in 2-B-1-(c); based on a (calculated) gram molecular weight of 994.0 grams. TABLE 14 (Cont'd) CALCULATION CONDITIONS TEMPERATURE, C./TIME HOURS SAMPLE NO. INITIAL FINAL 3-A-1-(a) 400/1 800/64 3-A-2-(a) 450/1 800/8 3-A-3-(a) 450/1 800/8 3-A-4-(a) 450/1 800/8 3-A-5-(a) 450/1 800/8 ÚPrepared according to the procedure described in Example13, Procedure A, using the quantities of material specified in 2-B-1-(c); based on a (calculated) gram molecular weight of 994.0 grams. effluent or, alternatively, for direct introduction thereof via a gas sampling valve into a gas-liquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reaction period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approximately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Examples 1-3 above. Glass wool plugs were used as supports for the composition. The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2:1 mole ratio were fed to the 5 reactor at a pressure of 1O013 x 105 pascal C1 atom- sphere) at a rate sufficient to provide a reactor residence (contact) time of 4 seconds (unless otherwise noted) for the toluene Cassuming a 50% void space in the reactor). After the reaction had proceeded for 1 minute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 15. TABLE 15 TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDSÚ CONVERSION % 1-A-1-(a) 630 39.0 540 12.6 510 6.8 1-A-1-(b) 630 53.4 540 16.7 510 10.0 1-A-1-(c) 630 36.4 540 9.4 510 4.0 1-A-1-(d) 630 38.0 540 11.9 510 8.6 1-A-1-(e) 630 46.6 540 14*6 510 7.6 1-A-1-(f) 630 49.0 540 13.3 510 6.6 1-A-1-(g) 630 48.8 540 21.5 510 10.0 1-A-2-(a) 630 47.3 575 26.3 I-A-2- (b) 630 15.92 575 14.9 1-A-2-(c) 575 38.4ê 530 14.4ê 500 1.7ê 1-A-2-(d) 575 46.0 500 8.1ê 500 2.9 1-A-3-(a) 630 94.8 540 38.0 450 4.6 TABLE 15 (Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 31.1 14.5 25.7 45.6 42.5 34.9 12.3 77.4 25.2 37.7 18.7 62.9 l-A-l-(b) 26.4 5.9 36.2 32.3 43.8 20.6 22.0 64.4 37.3 23.6 23.9 60.9 1-A-1-(c) 22.5 15.9 24.6 38.4 34.8 44.0 10.6 78.8 15.9 51.6 15.2 67.5 1-A-1-(d) 30.8 13.2 25.3 44.0 45.0 30.5 13.1 75.5 36.4 33.5 15.8 69.9 1-A-1-(e) 31.3 8.4 29.8 39.7 39.4 22.3 25.3 61.7 24.8 28.8 25.3 44.0 1-A-1-(f) 32.0 9.2 27.8 41.2 45.4 29.6 14.3 75.0 27.1 39.5 18.5 66.6 1-A-1-(g) 31.7 7.6 29.9 39.3 42.3 16.2 25.7 58.5 31.9 24.6 26.4 56.5 1-A-2-(a) 39.4 13.6 22.2 53.0 50.2 31.2 7.6 81.4 1-A-2-(b) 41.3 20.9 28.9 62.2 54.2 29.3 15.4 83.5 1-A-2-(c) 72.7 13.4 9.5 86.1 56.7 6.2 32.7 62.9 7.4 64.1 21.8 71.5 1-A-2-(d) 81.3 4.8 8.7 86.1 41.6 34.3 7.2 75.8 22.8 34.5 16.6 57.3 1-A-2-(c) 4.5 0.4 44.0 5.9 50.0 6.4 21.6 56.4 3.9 1.0 29.4 4.9 TABLE 15 (Cont'd) TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDSÚ CONVERSION, % 1-A-3-(b) 630 40.8 540 11.6 450 0.9 1-A-3- Cc) 630 65.9 540 17.2 450 1.6 1-A-3-(d) 630 15.0 540 6.2 450 003 l-A-3-Ce) 630 18.4 540 7.8 450 0.4 1-A-3-(f) 630 21.3 540 9.2 450 0.4 1-A-4-(a) 600/2 58.8 530/2 16.0 500/2 6.7 1-A-4-(b) 630/2 53.1 530/2 14.6 500/2 5.1 1-A-4-(c) 630/2 47.9 530 10.3 500/2 4.8 1-A-4-(d) 630 75.2 530 20.2 500 8.9 1-A-4-(e) 630 55.3 530 24.1 500 16.4 1-A-5-(a) 630 44.8 530 14.9 500 9.5 TABLE 15 (Cont'd) SELECTIVITY, STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-3-(b) 26.6 12.9 24.2 39.5 41.5 38.5 9.2 80.0 0.0 27.3 32.0 27.3 l-A-3-(c) 23.2 4.7 25.2 27.9 47.5 30.4 10.2 77.9 9*9 43.5 20.1 53.4 1-A-3-(d) 24.1 29.9 19.2 54.0 18.1 49.9 13.7 68.0 0.0 57.9 23.0 57.9 l-A-3-(e) 30.5 29.6 17.2 60.1 26.1 48.2 11.1 74.3 000 52.3 34.3 52.3 1-A-3-(f) 36.1 24.1 17.0 60.2 30.7 39.2 13.9 69.9 0.0 47.1 31.8 47.1 l-A-4-(a) 28.4 2.2 41.7 3006 45.9 13.7 22.6 59.6 29.2 25.7 25.4 45.9 1-A-4- (b) 35.2 6.6 45.0 41.8 64.2 20.5 12.6 84.7 40.7 38.7 17.1 79.4 1-A-4-(c) 47.0 10.5 27.7 57.5 41.3 42.4 12.3 83.7 26.4 52.8 15.2 79.2 1-A-4-(d) 19.5 1.8 45.5 21.3 49.3 20.8 13.7 70.1 27.5 35.6 14.8 63.1 1-A-4-(e) 35.4 6.1 43.6 41.5 58.8 16.8 19.5 75.6 50.0 19.2 24.4 69.2 1-A-5-(a) 18.5 8.8 55.5 27.3 42.1 35.7 16.5 77.8 37.5 42.3 16.2 79.8 TABLE 15 (Cont'd) TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDSÚ CONVERSION, % 1-A-5-(b) 630 5.5 530 3.1 500 2.6 1-A-5-(c) 630 58.0 575 24.0 500 10.4 1-A-6-(a) 630 76.4 530 28.3 500 11.4 1-A-6-(b) 630/2 87.6 530/2 33.4 500/2 13.9 1-A-6-Cc) 600/2 93.7 530 57.9 500 28.7 1-A-6-(d) 575/2 85.0 530/2 52.7 450/2 10.8 1-A-6-(e) 575/2 93.0 500/2 36.4 400/2 2.4 1-A-6-(f) 530/2 75.0 400/2 4.5 1-B-1-(a) 630 80.0 570 39.0 450 2.7 1-B-1-(b) 630 80.0 570 16.0 450 3*0 1-b-1-(c) 630 91.4 570 37.5 450 2.7 TABLE 15 (Cont'd) SELECTIVITY, % STILBENE i SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-5-(b) 7.4 14.8 51.7 22.2 12.8 57.2 24.8 70.0 15.6 58.6 19.5 74.2 1-A-5-(c) 16.0 5.5 58.6 21.5 30.1 9.9 42.8 40.0 23.1 27.5 35.0 50.6 1-A-6-(a) 25.2 2.5 61.3 27.7 64.5 15.8 16.9 80.3 45.1 36.7 15.0 81.8 1-A-6-Cb) 9.0 1.0 80.0 10.0 62.5 5.9 24.5 68.4 37.0 23.9 27.6 60.9 l-A-6-(c) 2.2 0.3 94.8 2.5 42.2 2.0 46.1 44.2 49.7 3.0 38.1 52.7 1-A-6-(d) 4.9 0.3 92.5 5.2 28.7 0.6 63.3 29.3 45.8 10.0 24.2 55.8 1-A-6-(e) 0.6 0.0 90.0 0.6 25.3 0.9 66.8 26.2 51.8 17.5 35.8 69.3 1-A-6-(f) 3.6 0.1 89.0 3.7 39.6 11.9 56.5 51.5 1-B-1-(a) 27.8 0.1 42.0 27.9 48.5 2.2 28.3 50.8 31.0 17.0 31.0 48.0 1-B-1-(b) 10.8 0.0 66.0 10.8 27,7 6.3 58.1 34.0 32.0 8.2 43.0 40.2 1-B-1-(c) 2.8 0.0 83.0 2.8 33.3 0.0 61.0 33.3 32.3 4.0 41.9 36.3 TABLE 15 (Cont'd) TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-B-1-(d) 630 85.0 570 26.5 450 3.3 l-B-l-(e) 630 34,7 570 15.0 450 2.6 2-B-1-(a) 600 99.0 570 88,0 450 12.0 2-B-1-(b) 570 92.0 540 70.0 450 7.0 2-B-1- (c) 570 88.9 450 4.0 2-B-1-(d) 570 75.8 450 2.7 2-B-l-(e) 570 84.5 450 3.2 3-A-1-(a) 600 78.8 570 50.8 450 28.4 3-A-2-(a) 630 90.0 530 21.0 500 17.4 3-A-3-(a) 630 6408 575/2 17.0 600 26.3 TABLE 15 (Cont'd) SELECTIVITY, % STILBENE + S.4DIPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-B-1-(d) 2.7 0.0 90.0 2.7 55.5 0.0 38.0 55.5 51.6 2.3 40.0 48.2 l-B-l-(e) 15.4 1.0 83.6 16.4 28.2 1.3 68.5 29.6 47.5 11.0 19.0 58.5 2-B-1- (a) 0.2 0.0 71.0 0.2 12.6 0.3 51.0 12.9 38.9 1.6 53.0 40.5 2-B-1-(b) 8.7 0.0 54.9 8.7 34.7 0.0 39.3 34.7 68.9 2.6 24.0 71.5 2-B-1-(c) 7.7 0.0 59.0 7.7 70.6 4.3 19.7 74.9 2-B-1-(d) 9.7 0.0 64.0 9.7 52.7 4.0 27.6 56.7 2-B-1-(e) 0.7 0,0 77.0 0.7 40.5 0.0 43.0 40.5 3-A-1-(a) 11.9 0.6 66.2 12.5 49.7 3.1 28.4 52.8 20.1 0.0 48.2 20.1 3-A-2-(a) 8.5 0.0 89.6 8.5 53.7 1.9 42.0 55.6 66.3 0.2 30.3 66.5 3-A-3-(a) 7.1 2.8 80.2 9.9 28.5 16.2 40.8 44.7 50.5 9.5 33.4 60.0 TABLE 15 (Cont'd) TEMPERATURE, C./ SAMPLE NO. CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION % 3-A-4-(a) 630 38.3 575 20.2 530 7.1 500 2.8 3-A-5-(a) 575 92.0 500 34.2 400 3.3 TABLE 15 (Cont'd) SELECTIVITY, % STILBENE i SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 3-A-4-(a) 50.4 20.4 16.0 70.8 50.7 35.0 8.6 85.7 32.8 58.6 5.5 91.4 21.0 69.7 6.8 90.7 3-A-5-(a) 2.4 0.0 92.0 2.4 38.8 0.8 69.4 39.6 72.9 5.7 9.8 78.6 A contact time of 4 seconds was employed unless otherwise noted. êThe catalytic mode of operation was employed, using an air/toluene mole ratio of 2/1 in the absence of added steam. EXAMPLE t6 Procedure A - A series of inorganic metal/oxygen compositions were prepared by intimately mixing the appropriate amount in grams of bismuth (III) oxide (Bi203) or bismuth (III) nitrate pentahydrate with at least one of each of an M2 oxide (or hydroxide) or nitrate and an M3 oxide (or hydroxide) or nitrate [or, alternatively, mixing an appropriate amount in grams of a suitable bismuth-containing binary metal/oxygen composition with at least one M2 oxide (or hydroxide) or nitrate, or an M3 oxide (or hydroxide) or nitrate, depending on the element other than bismuth contained in the binary composition] in water and then heating to evaporate the water (and decompose the nitrates, when employed). The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 17 below. The parameters for such compositions, conveniently designated as I-A-, are set forth in Table 16. Procedure B - A series of inorganic metal/oxygen compositions supported on a calcium aluminate cement can be prepared according to the procedure described in Procedure A above except as follows. Following the final calcination, remove the calcined material from the oven, cool, crush, and mix with a calcium aluminate cement (Alcoa-CA-25) in an amount corresponding to 25% by weight of the calcined material. Slurry the solid mixture with water to form a thick paste and allow to air dry. Calcine the air-dried paste in air in an open casserole dish for 2 hours at 4000 C. and then at a final temperature of 700" C. for an additional 2 hours Remove the supported inorganic metal/oxygen composition from the oven, cool, crush in a mortar, and sieve to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 17 below. Following these steps should result in compositions, conveniently designated as 1-B-, having properties beneficial for use in the process of this invention. TABLE 16 STARTING MATERIALS GRAMS(MOLES) SAMPLE NO. MaÚMbêMc Ox MÚ Mê M 1-A-1-(a) BiCa0.33Zn0.33Ox Bi2O3 CaO ZnO 139.8 (0.30) 11.2 (0.20) 16.3 (0.20) 1-A-2-(a) BiCa0.5KOx Bi2O3 CaO 84% KOH 93.2 (0.20) 11.2 (0.20) 26.4 (0.40) 1-A-3-(a) BiCa0.2Ni0.33Ox Bi2O3 CaO NiO 69.9 (0.15) 3.4 (0.061) 7.8 (0.10) 1-A-4-(a) BiCa0.33Ce0.033Ox Bi2O3 CaO CeO2 139.8 (0.30) 11.2 (0.20) 3.4 (0.020) 1-A-5-(a) BiCa0.33Th0.33Ox Bi2O3 CaO Th(NO3)4 . H2O 139.8 (0.30) 11.2 (0.20) 110.4 (0.20) TABLE 16 (Cont'd) CALCINATION CONDITIONS TEMPERATURE, C./TIME SAMPLE NO. INITIAL FINAL 1-A-1-(a) 450/1 800/8 1-A-2-(a) 450/1 800/8 1-A-3-(a) 450/1 800/8 1-A-4-(a) 450/1 800/8 1-A-5-(a) 450/1 800/8 EXAMPLE 17 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters (8 inches) in length and 0.95 centimeter (0.375 inch) in internal diameter having a usable capacity of 11 milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof via a gas sampling valve into a gasliquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reaction period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approximately 11 milliliters of the inorganic metalloxygem composition prepared as described in Example S above Glass wool plugs were used as supports for the composition. The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2:1 mole ratio were fed to the reactor at a pressure 5 of 1.013 x 1O pascal (l atmosphere) at a rate suffic.- ient to provide a reactor residence (contact) time of 4 seconds (unless otherwise noted) for the toluene (assuming a 50% void space in the reactor). After the reaction had proceeded for 1 mlnute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 17. TABLE 17 TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 1-A-1-(a) 630/2 41.6 575/2 15.3 500/2 3.6 l-A-2-(a) 595/2 7.5 575/2 9.1 475 27.5 l-A-3-(a) 630 78.9 575 62.3 500 15.1 l-A-4-(a) 630/2 97.5 530 43.1 450 6.0 1-A-5-(a) 600 93.0 530 60.7 500/2 20.9 SELECTIVITY, % TABLE 17 (Cont'd) STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 52.6 15.2 18.9 67W8 37.5 39.9 16.0 77.4- 18.5 64.4 11.5 82.9 1-A-2-(a) 43.0 28.2 31.8 71.2 69.3 17.7 15.1 87.0 77.7 4.5 15.6 82.2 I-A-3-(a) 34.9 1.4 47.1 36.3 62.5 1.3 28.3 63.8 72.0 12.2 11.5 84.2 I-A-4-(a) 4.0 0.3 58.0 4.3 62.3 5.4 15.0 67.7 32.9 32.0 7.3 64.9 1-A-5-(a) 2.9 0.0 97.6 2.9 50.0 0.5 47.2 50.5 55.8 4.0 36.6 59.8 1A contact time of 4 seconds was employed unless otherwise noted. EXAMPLE 18 A series of inorganic metal/oxygen compositions were prepared by intimately mixing the appropriate amount in grams of lead CII) oxide CPbO), bismuth CIII) oxide (Bi2O3), and at least one M3 oxide Cor hydroxide) in water, filtering to remove excess water or, alternatively, heating to evaporate the water, and then drying. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 20 below The parameters for such compositions, conve- niently designated as 1-A-, are set forth.in Table 18. TABLE 18 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêMc Ox MÚ Mê M 1-A-1-(a) PbBi0.33Zr0.33Ox PbO Bi2O3 ZrO2 80.0 (0.36) 28.0 (0.060) 15.0 (0.12) 1-A-2-(a) PbBi0.33As0.16Ox PbO Bi2O3 As2O3 100.0 (0.45) 35.0 (0.075) 7.4 (0.037) 1-A-3-(a) PbBi0.33Zn0.33Ox PbO Bi2O3 ZnO 100.0 (0.45) 35.0 (0.075) 12.2 (0.15) 1-A-4-(a) PbBiHo0.25Ox PbO Bi2O3 Ho2O3 60.0 (0.27) 63.0 (0.14) 13.0 (0.034) 1-A-5-(a) PbBi3Y4Ox PbO Bi2O3 Y2O3 17.3 (0.078) 54.5 (0.12) 35.0 (0.16) 1-A-6-(a) PbBiSr2Ox PbO Bi2O3 SrO 67.0 (0.30) 69.9 (0.15) 62.2 (0.60) 1-A-7-(a) PbBiGe.25Ox PbO Bi2O3 GeO2 89.3 (0.40) 93.2 (0.20) 10.5 (0.10) 1-A-8-(a) PbBi3In0.3Ox PbO Bi2O3 In2O3 44.6 (0.20) 139.8 (0.30) 8.3 (0.030) 1-A-9-(a) PbBi3NiOx PbO Bi2O3 NiO 44.6 (0.20) 139.8 (0.30) 14.9 (0.20) TABLE 18 (Cont'd) CALCINATION CONDITIONS SAMPLE NO. INITIAL FINAL 1-A-1-(a) 400/1 700/8 1-A-2-(a) 400/1 800/4 1-A-3-(a) 400/1 750/5 1-A-4-(a) 400/1 800/8 1-A-5-(a) 400/1 700/5 1-A-6-(a) 450/1 800/8 1-A-7-(a) 450/1 800/8 1-A-8-(a) 450/1 800/8 1-A-9-(a) 450/1 800/8 EXAMPLE 19 Procedure A - The appropriate amounts in grams of lead CII) nitrate [Pb(NO3)2], bismuth CIII) nitrate pentahydrate tBi(NO3)3.S H20], and at least one M nitrate were dissolved in approximately 100 milliliters of concentrated nitric acid CHNO3) and heated to evaporate and decompose the nitric acid and nitrates. The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example 20 below. The parameters for one such composition, conveniently designated as 2-A-, are set forth in Table 19. Procedure B - The procedure described in Procedure A above was employed except that following the final calcination, the calcined material was removed from the oven, cooled, crushed, and mixed with a calcium aluminate cement (Alcoa-CA- 25) in an amount corresponding to 25% by weight of the dry weight of the calcined material. The resulting solid mixture was slurried with water to form a thick paste and allowed to air dry. The air-dried paste was calcined in air in an open casserole dish for 2 ours at 400 C, and then at a final temperature of 700o C. for an additional 2 hours. The supported inorganic metalgoxygen compost tion was removed from the oven, cooled, crushed in a mortar, and sieved ta 14/30 mesh particles fcr evaluation in the toluene conversion reactor described in Examp-le 20 below.1-A-1-(a) PbBi The parameters for one such composition, conveniently designated as 2-B, are set forth in Table 19. TABLE 19 SAMPLE NO. MaÚMbêM Ox MÚ 2-A-1-(a) PbBi6Th3Ox Pb(NO3)2 Bi(NO3)3.5 H2O Th(NO3)4.4 H2O 16.6 (0.050) 145.5 (0.30) 82.2 (0.15) 2-B-1-(a) PbBiAg0.15Ox Pb(NO3)2 Bi(NO3)3.5 H2O AgNO3 60.0 (0.19) 88.0 (0.18) 5.0 (0.029) CALCINATION CONDITIONS TEMPERATURE, C./TIME, HOURS SAMPLE NO. INITIAL FINAL 2-A-1-(a) 450/1 800/8 2-B-1-(a) 450/1 800/10 EXAMPLE 20 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters 8 inches) in length and 0.95 centimeter (0.375 inch) in internal diameter having a usable capacity of Il milliliters was employed as a reactor for the toluene conversion reaction. The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof via a gas sampling valve into a gasliquid chromatograph for analysis. The outlet means was also equipped with means for introducing an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes. A radiant furnace was used to maintain a constant temperature during the reaction period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approximately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Examples 18 and 19above, Glass wool plugs were used as supports for the composition. The charged reactor was placed in a radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2:1 mole ratio were fed to the reactor at a pres 5 sure of 1.013 x 105 pascal (1 atmosphere) at a rate sufficient to provide a reactor residence Ccontact) tige of 4 seconds Cunless otherwise notedl for the toluene Cassuming a 5Q% void space in the reactor). After the reaction had proceeded for 1 minute, the reaction effluent diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 20. TABLE 20 TEMPERATURE, CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION % 1-A-1-(a) 630 19.9 540 9.2 450 0.4 1-A-2- Ca) 630 35.7 540 5.6 450 0.7 1-A-3-(a) 630 17.4 570 5.3 450 0.6 1-A-4- Ca) 630 35.8 570 16.1 450 0.6 1-A-5-(a) 630 87.6 570 41.7 450 7.1 1-A-6-(a) 630/2 95.4 575/2 68,1 500/2 3.8 1-A-7-(a) 575/2 13.9 500/2 3.4 l-A-8-Cal 630 27.2 575 23.9 500 4.3 1-A-9- Cal 630/2 40.7 575/2 28.6 500/2 4.5 TABLE 20 (Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STIBLENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 18.0 34.4 14.5 52.4 36.4 41.9 10.3 78.3 0.0 16.0 18.5 16.0 l-A-2-Ca) 39.4 16.5 21.3 55.9 22.4 46.0 15.0 68.4 0.0 17.1 11.4 17.1 l-A-3-ta) 16.6 35.1 12.3 51.7 15.0 58.9 10.1 73.9 0.0 16.1 25.5 16.1 l-A-4-Ca2 22.0 18.5 15.4 40.5 19.6 31.2 4.6 50.8 0.0 15.1 40.1 15.1 1-A-S- Ca) 43.4 0.0 40.9 43.4 65.3 5.4 19.2 70.7 5 2 7.5 4.9 12.7 1-A-6-Ca) 35.6 0.0 30.3 35.6 69.0 9.6 5.3 78.6 20.8 57.4 7.4 78.2 l-A-7-Ca) 31.3 48.1 6,8 79.4 12.6 60.9 2.0 73.5 1-A-8-(a) 30.4 27.2 15.5 57,6 49.7 24.9 9.1 74,6 15.3 55.7 4.3 71.0 1-A-9-(a) 26.1 14.6 17.8 40.7 52.2 21.1 8,6 73.3 21.1 55.3 9.2 76.4 TABLE 20 (Cont'd) TEMPERATURE, C. CONTACT TIME, SAMPLE NO. SECONDS1 CONVERSION, % 2-A-1-(a) 630 97.0 530 48.3 500 31.8 2-B-1-(a) 630 43.1 575 22.8 450 2.1 TABLE 20 (Cont'd) SELECTIVITY, % STILBENE + SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 2-A-1-(a) 7.0 0.0 71.0 7.0 71.7 2.3 11.8 74.0 57.9 8.0 8.0 65.9 2-B-1- Ca) 27.9 14.4 21X1 42.3 38.3 30.3 10.8 68.6 6.3 33.9 7.4 40.2 1A contact time of 4 seconds was employed unless otherwise noted. EXAMPLE 21 Procedure A - A series of inorganic metal/oxygen compositions were prepared by intimately mixing the appropriate amount of lead Ul) oxide (PbO), lead (11) carbonate CPbCO3), or lead (II) nitrate [Pb(N03)2] 2 with at least one of each of an M carbonate, nitrate, or oxide and an Mb carbonate, nitrate, or oxide Cor, alternatively, mixing an appropriate amount of a suitable lead-containing binary metalXoxygen composition with at least one N2 carbonate, nitrate, or oxide or one M3 carbonate, nitrate, or oxide, depending on the element other than lead contained in the binary composition) in water and heating to evaporate the water (and decompose the carbonates and/or nitrates, when employed). The resulting solid was placed in an open casserole dish and calcined in air for an initial period at an initial temperature and then at a final temperature for an additional period. The calcined material was removed from the oven, cooled, crushed in a mortar, and sieved to 14/30 mesh particles for evaluation in the toluene conversion reactor described in Example -22 below. The parameters for such compositions, conveniently designated as 1-A-, are set forth in Table 21. Procedure B -- A series of inorganic metal/oxygen compositions supported on a calcium aluminate cement can be prepared according to the procedure described in Procedure A above except as follows. Following the final calcination, remove the calcined material from the oven, cool, crush, and mix with a calcium aluminate cement CAlcoa-CA-25) in an amount corresponding to 25% by weight of the calcined material. Slurry the solid mixture with water to form a thick paste and allow to air dry. Calcine the airdried paste in air in an open casserole dish for 2 hours at 400" C. and then at a final temperature of 7000 C. for an additional 2 hours. Remove the supported inorganic metaljoxygen composition from the oven, cool, crush in a mortar, and sieve to 14/30 mesh paricles for evaluation in the tcluene conversion reactor described in Example22 below. Following these steps should result in compositions having properites beneficial for use in the process of this invention. TABLE 21 STARTING MATERIALS GRAMS (MOLES) SAMPLE NO. MaÚMbêMc Ox MÚ Mê M 1-A-1-(a) PbSb0.33As0.33Ox PbO Sb2O3 As2O3 133.1 (0.60 29.2 (0.10) 19.8 (0.10) 1-A-2-(a) PbSb0.33Ce0.017Ox PbO Sb2O3 CeO2 67.0 (0.30) 15.4 (0.053) 0.9 (0.0052) 1-A-3-(a) PbSb0.25Co0.25Ox Pb4SbOxÚ ---- CoCO3 116.0 (0.056) ---- 6.7 (0.056) 1-A-4-(a) PbSb0.25Ga0.25Ox PbO Sb2O3 GaO3 95.3 (0.43) 15.6 (0.054) 10.0 (0.053) 1-A-5-(a) PbSb0.48La0.48Ox PbO Sb2O3 La2O3 111.6 (0.50) 36.4 (0.12) 40.7 (0.12) 1-A-6-(a) PbSb0.25Ag0.25Ox PbO Sb2O3 AgNO3 100.0 (0.45) 16.3 (0.056) 19.0 (0.11) 1-A-7-(a) PbSb0.33Sr0.33Ox PbO Sb2O3 SrO 133.1 (0.60) 29.2 (0.10) 20.7 (0.20) 1-A-8-(a) PbSb0.5Zn0.5Ox PbO Sb2O3 ZnO 178.5 (0.80) 58.3 (0.20) 32.5 (0.40) TABLE 21 (Cont'd) CALCIANTION CONDITIONS TEMPERATURE, C./TIME, HOURS SAMPLE NO. INITIAL FINAL 1-A-1-(a) 450/1 800/8 1-A-2-(a) 450/1 800/8 1-A-3-(a) 450/1 800/8 1-A-4-(a) 450/1 830/4 1-A-5-(a) 450/1 830/4 1-A-6-(a) 450/1 800/6 1-A-7-(a) 450/1 800/8 1-A-8-(a) 450/1 800/8 ÚThe lead antimonate binary composition, having a (calculated) gram molecular weight of 2077.0 grams, was prepared as follows: Lead (III) oxide (PbO; 178.4 grams, 0.080 mole) and antimony (III) oxide (Sb2O3; 29.2 grams, 0.10 mole) were intimately mixed in water and then heated to evaporate the water. The resulting solid was placed in an open casserole dish and calcined in air for 2 hours at 400 C. and then at 800 C. for an additional 8 hours. The calcined material was removed from the oven, cooled, crushed in a mortar, and ground to a fine powder. EXADipLE 22 A. Toluene Conversion Reactor - A stainless steel tube 20.32 centimeters (8 inches) in length and 0,95 centimeter (0.375 inch) in internal diameter having a usable capacity of 11 milliliters was employed as a reactor for the toluene conversion reaction, The reactor was arranged vertically and equipped at the upper end with reactant inlet means having calibrated flow controllers and vaporizers, and at the lower end with reaction effluent outlet means for collecting the reaction effluent or, alternatively, for direct introduction thereof via a gas sampling valve into a gas-liquid chromatograph for analysis. The outlet means was also equipped with means for introducting an inert gas diluent -- nitrogen or helium, for example -- into the reaction effluent for analysis purposes, A radiant furnace was nosed to maintain a constant temperature during the reaction period. The temperature was measured with a thermocouple in a temperature well located on the lower outside wall of the reactor. B. Toluene Conversion - The reaction was conducted in the stoichiometric mode of operation unless otherwise noted. The reactor was charged with approximately 11 milliliters of the inorganic metal/oxygen composition prepared as described in Example 21 above. Glass wool plugs were used as supports for the composition. The charged reactor was placed in a. radiant furnace and heated to maintain a constant temperature throughout the reaction period. Steam and toluene in a 2:1 mole ratio were fed to the reactor at a pressure of 1.013 x 105 pascal 1 atmosphere) at a rate sufficient to provide a reactor residence (contact) time of 4 seconds Cunless otherwise noted) for the toluene (assuming a 50% void space in the reactor). After the reaction had proceeded for 1 minute, the reaction effluent, diluted with helium, was analyzed by gas-liquid chromatography. The results are tabulated in Table 22. TABLE 22 TEMPERATURE, C./ CONTACT TIME, SAMPLE NO. SECONDSÚ CONVERSION, % 1-A-1-(a) 630/2 14.7 575/2 12.2 500/2 2.3 1-A-2-(a) 630/2 54.5 575/2 13.5 500/2 5,3 1-A-3-(a) 630 44.4 540 15.6 450 1.6 1-A-4- (a) 630 17.7 540 6,4 450 0.7 1-A-5-(a) 630/2 94.0 575/2 65.8 500/2 29.9 1-A-6-(a) 630 50.9 540 16.2 450 2.1 1-A-7- Ca) 630/2 - 83,4 575/2 47.7 500/2 13.3 1-A-8-(a) 630/2 35.9 575/2 10.3 500/2 5.4 TABLE 22 CCont'd) SELECTIVITY, % STILBENE t SAMPLE NO. STILBENE BIBENZYL BENZENE BIBENZYL 1-A-1-(a) 13.2 31.1 21.7 44.3 17.4 32.9 24.0 50.3 9.1 48.2 24.7 57.3 1-A-2-Ca) 37.4 8.4 22.0 45.8 29.2 34.4 21.2 63.6 24.2 46.4 1 16.8 70.6 1-A-3-(a) 42.0 11.7 24.0 53.7 32.5 27.0 20.7 59.5 3.2 16.1 15.5 19.3 1-A-4-Cal 26.6 24.8 27.6 51.4 30.1 33.0 25.4 63.1 0.0 11.6 55.7 11.6 1-A-5-(a) 17.0 0.2 73.0 17.2 48.1 0.8 46.8 48.9 50.7 2.1 36.9 52.8 1-A-6-(a) 13.2 6.3 35.0 19,5 30.6 29.3 13.2 59,9 8.8 41.2 17.9 50.0 I-A-7-Ca) 9.5 0.0 83.9 9.5 34.9 Q.O 53.8 34.9 52.3 Q.O 38.8 52.3 l-A-8-Cal 36.5 6.8 30.6 43.3 31.6 27.7 20.8 59.3 41.7 29.3 12.9 71.0 1 A contact time of 4 seconds was employed unless other wise noted. Thus, it is apparent that there has been provided, in accordance with the present invention, a process that fully satisfies the objects and advantages set forth hereinabove. While the invention has been described with respect to various specific examples and embodiments thereof, it is understood that the invention is not limited thereto and that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A process for dehydrocoupling toluene which comprises contacting the toluene in the vapor phase at a temperature between about 450 C. and about 650 C. with an inorganic metal/oxygen composition characterized by an empirical formula selected from: (a) Pb M12 a Mb Ox where M1 is at least one element selected from silver, zinc, gallium, indium, thallium, germanium, phosphorus, arsenic, thorium, the lanthanides, Groups la, 2a, 3h, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M2 is an element selected from bismuth and antimony, and wherein a is 0.01 to 10, b is O to 10, and x is a number taken to satisfy the average valences of lead, M1 and M2 in the oxidation states in which they exist in the composition, with the proviso that when M2 is bismuth, M1 cannot be gallium or thallium; and when M2 is antimony, M1 cannot be indium, thallium, germanium, phosphorus, or thorium; and (b) Bi M Mb Ox where M3 is at least one element selected from zinc, germanium, thorium, the lanthanides, Groups La, 3b, 4b, and 8 of the Periodic Table of the Elements and mixtures thereof, and M4 is at least one element selected from indium, silver, Group 2a of the Period Table of the Elements, and mixtures thereof, and wherein a is 0.01 to la, b is O to 10, and x is a number taken to satisfy the average valences of bismuth, M3, and M4 in the oxidation state in which they exist in the composition to yield the toluene dehydrocoupled toluene product. 2. The process of Claim 1 characterized in that MÚ is selected from silver, zinc, Lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, indium, arsenic, the lanthanides and Groups 3b, 4b, and 8 of the Periodic Table of the Elements, and mixture thereof. 3. The process of Claim 2 characterized in that M1 is selected from silver, zinc, potassium, zirconium, barium, calcium, strontium, nickel, platinum and cerium, and mixtures thereof. 4, The process of Claim 1 characterized in that M2 is bismuth. 5. The process of Claim 1 characterized in that M3 is selected from zinc, the lanthanides and Groups 3b, 4b, and 8 of the Periodic Table of the Elements, and mix turves thereof. 6. The process of Claim 5 characterized in that M3 is selected from zinc, cerium, zirconium, cobalt, nickel, and platinum, and mixtures thereof. 7. The process of Claim 1 characterized in that M4 is selected from indium, silver, magnesium, calcium, strontinum and barium, and mixtures thereof. 8. The process of Claim 7 characterized in that M4 is selected from silver, calcium, strontinum and barium, and mixtures thereof. 9. The process of Claim 1 characterized in that steam is introduced with the toluene in an amount sufficient to provide a steam-to-toluene mole ratio between about 0.1 and about 10. 10. The process of Claim 1 characterized in that a and b in the empirical formulas are 0.5 to 5. 11. The process of Claim 1 characterized in that the contacting between the toluene and the inorganic metal/ oxygen composition is effected for a period between about 1 second and about 12 seconds. 12. The process of Claim 1 characterized in that the temperature is between about 500Or. and about 6000C. 13. The process of Claim 1 characterized in that the dehydrocoupling reaction is conducted in a stoichiometric mode of operation in the absence of added free oxygen. 14. The process of Claim 1 characterized in that a reactant selected from the group consisting of oxygen and an oxygen-containing gas is introduced with the toluene. 15. The process of Claim 14 characterized in that the oxygen and oxygen-containing gas is introduced in an amount sufficient to conduct the dehydrocoupling reaction in a catalytic mode of operation. 16. The process of Claim 15 characterized in that the oxygen and axygen-containing gas is introduced in an amount sufficient to provide a toluene-to-oxygen mole ratio between about 1 and 8. 17. The process of Claim 14 characterized in that the oxygen and oxygen-containing gas is introduced in an amount sufficient to conduct the dehydrocoupling reaction in a combined catalytic/stoichiometric mode of operation. 18. The process af Claim 1 characterized in that the inorganic metal/oxygen composition is admixed with a support material. 19. The process of Claim 18 characterized in that the support material is a metal aluminate. 20. The process of Claim 19 characterized in that the metal aluminate is calcium aluminate. 21. The process of Claim 1 characterized in that the dehydrocoupling reaction is conducted at a toluene conversion level of about 20 to about 55 percent. 22, The process of CLaims 1 through 16 characterized in that the dehydrocoupled toluene product is stilbene.

Inventors: SOLODAR, ARTHUR JOHN, TREMONT, SAMUEL JOSEPH, WILLIAMSON, ALEX NATHAN
Applicants: MONSANTO COMPANY
Application year: 1980
Main classification: C07C2
IPC codes: C07C2