IMPROVED TRANSITION METAL OXIDE CATALYSTS AND USES THEREOF

Abstract: A supported acid catalyst comprising one or more catalytic components selected from either oxides of tungsten, niobium and mixtures thereof or tungsten or niobium oxides in combination with one or more additional metal oxides selected from tantalum oxide, hafnium oxide, chromium oxide, titanium oxide and zirconium oxide, the support being an inorganic refractory oxide support. In one embodiment the support is one which is not in itself an acid cracking catalyst and in another embodiment the support may be itself a silica-containing acid cracking catalyst, provided that the silica content thereof is less than 50 wt.%. These catalysts are useful for hydrocarbon conversion processes such as cracking and, during catalyst regenera­ tion, one may simultaneously produce a low BTU fuel gas. They exhibit enhanced activity and selectivity and resistance to coke make compared to conventional acid catalysts.

Description: Cracking of petroleum fractions over acid catalysts represent the most widely used means of molecular weight reduction in refining processes. In a cracking process, in the presence of steam4 a potentially effective catalyst in the process is required to have components which retain a high level of acid cracking activity in the presence of steam. Most of the conventional acid catalysts used in catalytic cracking processes are knolm to be unsuited for use in the presence of steam at temperatures greater than about 14000F (7600C). The effects of water are considered to be those of a structural poison and result in a weakening of the acid strength of the acid sites. Stability in high steam environments is desirable however, since one way of removing the coke which is inevitably deposited on the catalyst is to steam gasify the coke on the catalyst. The burning off of the coke necessarily requires the presence of steam. In cracking processes it is generally the object to generate lower molecular weight, but commercially valuable products, from higher molecular weight crude feedstocks. The catalysts used in these acid catalyzed processes, however normally suffer from extreme sensitivity to contaminants in the feedstocks such as sulfur, nitrogen and traces of various metals such as nickel, vanadium, iron, chromium. The catalysts are also susceptible to rapid deactivation by the depositing of coke. U.S. Patent 3,649,707 teaches a multistep, multicatalyst dealkylation using steam. The first reaction zone utilizes a catalyst composite containing as active ingredients a cobalt component, a nickel component or a Group VIB component, preferably composited with a high surface area refractory inorganic oxide type carrier characterized in 2 having a surface area of at least 50 m /gm. These carriers include alumina, silica, silica-alumina, zirconia, thoria, magnesia, titania, bauxite, mordenite, faujasite, etc. The cobalt, nickel or Group VIB component can be in the elemental or preferably the oxide forum. This catalyst is used in a first reaction zone for dealkylating an alkyl aromatic at dealkylation conditions controlled to produce a first reaction zone effluent wherein about 1 to about 20 wt. % preferably about 1 to 10 wt. % of the alkylaromatic passed to said zone is dealkylated. Zone one is run at conditions which include a temperature of about 3000C to about 7000C, a pressure of about atmospheric to about 100 atmospheres, a steam to hydrocarbon mole ratio of about 1:1 to about 30 to 1 or more and a liquid hourly hydrocarbon space velocity of about 0.1 to about 20 hr 1 or more. The reaction practiced in this zone is dealkylation as has been previously stated. Steam dealkylation is a catalyzed reaction wherein water is a consumed reactant. This is to be contrasted with acid cat cracking which is associated with acid sites found on the catalyst and which though preferably practiced in the presence of steam does not consume the steam that is, water is not a reactant. U.S. 2,849,383 teaches catalysts for use in hydrocarbon conversion processes and the processes themselves, wherein the catalyst consists essentially of a siliceous cracking catalyst such as silica-alumina and an oxide of a metal from Group VB or VIB, V, NS, Ta, Cr, Mo, W. The siliceous cracking catalyst is described as a synthetic or natural siliceous composition which contains at least 50% silica (calculated as SiO2). The siliceous material can be silica-alumina, silica-magnesia, silica-zirconia and silicaalumina-zirconia. The metal oxide (from Groups VB or VIB) must be incorporated with the cracking catalyst in a quantity of at least 2.9% by weight. The material can be deposited on the carrier or coprecipitated with the siliceous carrier. It is further stated that an essential step in the preparation of the catalyst composition is the steaming of the composition after calcination for from 1 to 8 hours at temperatures of from 6000 to 8000C in 100% steam. While this reference recites the above process in general, there are examples in the specification only of chromia on silicaalumina. The fact that this steaming is effective only for certain combinations of materials when the support is alumina was not recognized by the art. In hydrocarbon conversion processes such as those wherein petroleum fractions are cracked over acid catalysts, it has been discovered that remarkable improvements in the realms of selectivity and % conversion are obtained by running such conversion processes (e.g. gas oil catalytic cracking, heavy ends cat cracking, etc.) in the presence of catalysts comprising a catalytic metal oxide component, wherein said catalytic metal oxide is either an oxide of tungsten, niobium or a mixture thereof, or a tungsten or niobium oxide in combination with one or more additional metal oxides selected from tantalum oxide, hafnium oxide, chromium oxide, titanium oxide and zirconium oxide. The oxide is preferably an oxide of tungsten, niobium or a mixture thereof, most preferably, an oxide of tungsten or niobium. The oxideis supporte on certain refractory metal oxide supports which are not themselves acid cracking catalyst under normally employed conditions, preferably, alumina, zirconia, boria, thoria, magnesia, zirconium titanate, titanium, chromia, silica, kieselguhr and mixtures thereof, preferably the aluminas, i.e., -alumina, t -alumina, z -alumina said catalyst being steamed at elevated temperatures prior to use. In one embodiment, the support is one which is not in itself an acid cracking catalyst under normally employed conditions. In another embodiment, the support may be itself a silica-containing acid cracking catalyst, provided that the support contains less than 50 wt. % silica calculated as SiO2. These catalysts are prepared by techniques known in the art, e.g. incipient wetness impregnation techniques, etc. Metal oxide precursors, for example, ammonium meta-tungstate, are deposited on the selected refractory oxide support followed by the conversion into the oxide form and calcination. Before use the metal/support combination can be subjected to steaming. For certain transition metal oxide concentrations the steaming treatment significantly improves the catalytic cracking activity. These catalysts demonstrate resistance to deactivation and maintain high conversion and selectivity activities. They also resist poisoning by sulfur and nitrogen and are relatively uneffected by techniques utilized to remove coke deposits. Further, these catalysts may be regenerated in a manner so as to simultaneously gasify coke and produce a low BTU fuel gas from the coke. The catalysts of the present invention are prepared by impregnating the desired high surface area refractory oxide with a solution of a precursor of the desired metal oxide. The solution used in impregnating the refractory oxide support may be aqueous or organic, the only requirement being that an adequate amount of precursor compound for the selected metal oxide is soluble in the so1- vent used in preparing the impregnating solution. Aqueous or alcohol solutions, preferably aqueous or ethanol solutions are normally used for convenience. The following is a non-exhaustive exemplary recitation of metal salts which may be used in preparing the desired compositions. Salts of the transition metals which were employed in the catalyst preparations were those which were soluble in, without reaction with, either aqueous or nonaqueous solutions. For the aqueous preparation salts such as ammonium para-molybdate, ammonium meta-tungstate, chromium trioxide, and ammonium metal-vanadate and perrennic acid were employed. For the nonaqueous preparation salts such as TiCl4, ZrCl4, HfCl4, CrO2Cl2, WCl6, Nb2(OC2H5)10, Ta2(0C2H5)10, W(CO)6. Additional salts which can be used are the soluble bromides, iodides and oxychlorides. Also organo-metallic metal catalyst precursor salts such as the cyclic polyolefin carbonyl complexes, or the like, may be employed, i.e., C8H8M(CO)3, M=Cr, W. Also arene-metal complexes such as ( (C6H6)2Cr may be employed. Pseudohalide salts such as Cr(CNC6H5)5 may also be used. Acetates and acetylacetonate metal salts can also be employed. Soluble sulfide complexes such as C4HIoS2W(CO)4 can also be employed. Amine-substituted complexes such as (pyridine)3 W(CO)3 can also be employed. The refractory oxide support should have a high 2 surface area in the region of about 10 to 500 m /g, pref 2 2 erably 20 to 200 m /g, most preferably over 100 m /g prior to the deposition of the metal oxide salt precursor. These surface areas are as measured by the Brunauer-Emmett-Teller (BET) method. The catalyst may also be prepared by conventional coprecipitation techniques, in which case, the metal salt or salts are comingled in solution with a soluble salt precursor of the support. Simultaneous precipitation may be induced by pH changes, the catalyst filtered, dried and calcined in air to convert the metal precursor salt and support precursor salts into oxides. When using the impregnation technique the impregnating solution is contacted¯ with the refractory oxide support for a time sufficient to deposit the precursor material onto the carrier either by selective adsorption or alternatively, the excess solvent may be evaporated during drying leaving behind the precursor salt. Advantageously, the incipient wetness techniques may be used whereby just enough of a precursor salt solution is added to dampen and fill the pores of the high surface area powder of the aboverecited refractory oxide support material. The composite ths prepared by any of the aboverecited techniques, or any other known in the art is dried at a temperature of from 50 to 3000C to remove the excess solvent and then converted into the oxide form by exposure at temperatures of from 150 to 8000C, preferably 300-7000C in an atmosphere such as 2' Air, He, Ar, Ne and combinations thereof. Reducing atmospheres may also be used but require subsequent calcination to convert the reduced metal component to the oxide form. This exposure is for a time sufficient to convert essentially all of the metal salt precursor into metal oxide. The calcination is useful to decompose the metal salt precursor to the oxide form. Calcination, however, may not be required for certain metal precursor salts which readily convert into metal oxides. These metal oxide/carrier composites can optionally be subjectedto high temperature steaming prior to use for periods of from .1 to 60 hours, preferably 1 to 16 hours, at temperatures ranging from 600 to 12000C, preferably 8000C-12000C and preferably in from 0.1 to 100% steam, the balance of the atmosphere being inert gases ( 2 Air, Ar, Ne, He, N2 and mixtures thereof). These catalysts have been found to be effective in hydrocarbon conversion processes, such as gas oil cat cracking, resid cat cracking, heavy ends cat cracking, acid hydrocracking, etc. wherein the hydrocarbonaceous feed to be converted is contacted with the catalysts under conditions sufficient to effect the desired conversion in the presence of water. Typical hydrocarbonaceous feedstreams which are catalytically converted comprise mixed hydrocarbons boiling within the range of from 400 to 12000C. By way of example, two typical gas oils used as feeds for cat cracking are: TABLE I ERDL CAT CRACKING PILOT PLANT FEEDS INSPECTIONS Feed Symbol ETLGO CM Gravity, API 33.3 28.4 Aniline Point, F 192 171 Br.No., g Br/100 gr * 6.5 Ref. Index, ND&commat;67 C 1.477 1.4735 Pour Point, F * 65 Sulfur, Wt. % 0.20 0.78 Nitrogen, wppm * 447 ASTM D-1160 Distillation 5% &commat; OF 546 502 10% &commat; F 552 538 50% &commat; OF 592 693 90% &commat; 0F 653 888 95% &commat; ; OF 664 928 FBP 678 978 *Not available Typical catalytic conversion process parameters include temperatures ranging from 300 to 9000C, preferably 400 to 6000, pressures ranging from 0 to 10,000 psig, preferably 50-500 psig. Contact time can range from less than 1 sec. to as high as 2000 secs., preferably 1 sec. to 120 secs., at from .1 to 50 Weight Feed/Hr/Weight Catalyst (WHW), preferably 1-4 WHW. Optionally, H20 as steam may be added along with the hydrocarbon feedstream. When this is done, the H2O/hydrocarbon mole ratio ranges from .5:1 to 20:1, preferably 1:1 to 10:1. The catalysts employed have metal oxide loadings of from 0.5 to 25 wt. % metal oxide based on total catalyst. composition, preferably 2-10 wt. %, more preferably 4-6 wt. % metal oxide based on total catalyst composition. When using the mixed oxide systems of tungsten oxide or niobium oxide in combination with one or more of tantalum oxide, chromium oxide, titanium oxide, zirconium oxide and hafnium oxide (which additional oxides are used to supply support surface area maintenance as discussed in greater detail below) the ratio of tungsten or niobium oxide to the additional metal oxide is in the order of 1:1, preferably 3:1, most preferably 9:1. The catalysts described as useful in the aboverecited processes may also advantageously contain traces of various promoter materials selected from the group consisting of barium oxides, calcium oxides, magnesium oxides. These materials in the form of precursor salts can be incorporated into the carrier simultaneously with the metal precursor salt or sequentially (the order of addition being merely a matter of choice) or may be coprecipitated with the metal precursor salts and carrier precursor salts. Alternatively, they may be added subsequent to the formation of the catalyst composite. If used at all these promoters are present at from 0.01 to 4.0 wt. % promotor based on total catalyst composition wherein the amount of promoter metal oxide ranges from .18 to 4.0%, preferably .1% to 5% of the catalytic metal oxide content. Alumina Surface Area Maintenance Numerous transition metal oxides appear to stabilize substantially the surface area and hence the acidity of the MOxAl2O3 (M=Group IVb, Vb, VIb transition metal) system by stabilizing the surface area of the alumina. The transition metal oxides which exert the strongest surface area maintenance effect on alumina are the oxides of chromium, titanium, zirconium, niobium, hafnium and tantalum, preferably Cr203, TiO2, ZrO2, Nub205, HfO2 and Tea2 0 The amount of such oxides present may 5. range from 1-8 wt. % metal oxide based on total catalyst composition, preferably 2-6 wt. % the BET surface areas 2 being on the order of 110 to 135 m /g. Following steaming at 9000C in air for 16 hours, the BET surface area of 3.6 2 wt. % TiO2 on A1203 was 117 m /g; of 5.6 wt. % ZrO2 on 2 2 A1203 was 133 m /g; of Nb205 on Al a was 110 m /g; of 22 5 2 3 Ta205 on Awl 0 was 130 m /g. The Al 0 used had an orig 25 23 2 23 inal BET surface area of 190 m /g. The presence of selected Group IVa, Va and Via metal oxides on the support also dramatically reduces the amount of coke which deposits on the system. This reduced coke make coupled with support surface area maintenance results in a catalyst possessing superior activity and conversion characteristics. When the catalyst is used to hydroconvert heavy hydrocarbon feedstocks such as resids or synthetic feeds derived from Cold Lake crude, tar sands, coal liquids, shale oil, etc. which have large coke makes, the coked catalyst can be reactivated and at the same time a low BTU gas can be produced from the coke by a process comprising the steps of: (a) removing the coked catalyst from the hydrocarbon conversion zone; (b) regenerating the coked catalyst by contacting same with steam, oxygen-containing gas or mixture thereof at elevated temperature to produce a regenerated catalyst and an E2 rich gas, a low BTU gas rich in CO and a combination thereof; and (c) recirculating the regenerated catalyst of step (b) to the hydrocarbon conversion zone of step (a). In the case where partial combustion is employed, small amounts of steam might be added along with the air to absorb a portion of the exothermic heat of reaction. In the case where steam gasification is employed a means for providing the endothermic heat for this gasification must be provided. This can be accomplished by adding oxygen along with the steam or by circulating hot catalyst solids from a third vessel where a portion of the coke on the catalyst is combusted with air. The hot regenerated catalyst can be recirculated to the reactor, the sensible heat released as these solids cool to the reactor site temperature providing the endothermic heat of cracking. In general, the process is identical to current cat cracking processes with the exception of an option to include steam in the reactor as a catalyst promoter and the operation of the regenerator to produce a gas from the coke having a significant heating value (i.e. > 100 BTU/SCF). To regenerate the catalyst, the typical conditions employed in the regenerator comprise a pressure not greater than 150 lbs. psig., preferably not greater than 60 psig., more preferably not greater than about 45 psig. The temperature is maintained at a level in the range of about l400-28000F (760-l5350C), preferably at a temperature greater than about 15000F, more preferably at a temperature in the range of about 1600 to 19000F, most preferably at a temperature in the range of about 1700 to 18000F. The coked catalyst is treated under the above conditions in the regenerator in the presence of steam and an oxygen containing gas to produce a hot gaseous steam containing E2 and CO. The conversion of coke into CO and H2 proceeds by the following scheme: EMI10.1 When coke is oxidized, the initial Product is a mixture of CO and CO2 as shown in equation (1). At temperatures of 1600OF+ in the presence of oxygen CO is rapidly oxidized to CO2 according to equation (2). After oxygen has been exhausted, CO2 reacts with carbon to form CO. At high temperatures, equilibrium favors drawing equation (3) to the right to form CO. Low pressure also favors this reaction. Reaction (3) is slower than reaction (2). Thus, equilibrium would favor very high CO/CO2 ratios at conditions of 1700 F-1750 F+ and pressures of 2.7 atm or lower in the gasifier. Steam will also gasify coke as represented by equation (4). This reaction is slightly endothermic and when steam is substituted for some of the oxygen, the gasification zone temperature drops at a constant quantity of coke gasified. Finally, water reacts with CO to produce CO2 and hydrogen in the water gas shift represented by equation (5). Most of the sulfur in the coke will be converted to H2S with a very small amount of COS being formed. in order to obtain significant conversion of coke to low BTU gas, it is necessary to gasify at temperatures in the range of 1600-18000F. These high temperatures in the presence of the steam normally contained in a regenerator place severe requirements on the stability of cracking catalysts. In order for this type of process to be practical, catalyst systems must demonstrate the ability to withstand these severe conditions. To this end the activity of a variety of WO3/A1203 catalysts and some conventional catalysts before and after steaming treatments at 16000F have been compared. Experimental The process unit used for conducting the following experiments was a typical downflow gas phase reactor (40 cc capacity) capable of operation at temperatures as high as 5500C and pressures as high as 500 psig. Liquid oil feed to the unit is by a dual-barrel Ruska pump. Water is fed to the reactor by a Lapp pump. Gas feeds are controlled by Research Control valves coupled to a Foxboro Flow Controller. The reactor is heated by a fluidized sandbath. Typical operating conditions have been 5100C (9500F) and 30 psig. Liquid weight hourly space velocities have been varied from about 1.4 her 1 to 5.6 her 1 for both oil and water. The oil feed used is an East Texas Light Gas Oil (ETLCO) with the properties given in Tables I and II. The principal objective of the initial experiments has been the determination of the stability of the WO3 system compared to standard systems (zeolites and silicaaluminas) after steaming at 16000F (870 C) for 16 hours. The catalyst steamings were carried out in an ups low 3-zone furnace operated at ambient pressure with a gas feed consisting of 90% steam and 10% inert gas. The water was fed to the system by a Milton-Roy mini-pump at the rate of about 35 cc liq. per hour. The temperature in the central zone was held at about 8700C (1600 F). The WO3/A1203 catalysts used in this study were prepared by incipient wetness techniques using aqueous solutions of ammonium meta-tungstate. The alumina used was reforming grade &gamma;-Al2O3 (BET surface area r\) 180 mê/g) extrudate form. The silica-alumina catalysts were either obtained from Davison Chemical Division; or a silica-alumina catalyst obtained from Exxon Research Development Labs either calcined at 10000F or steamed at 14000F for 16 hrs. The zeolite catalysts studied were either calcined at 1000 F or steamed at 14000F for 16 hrs. The silica-alumina-and zeolites were mixed with about 25% Degussa Alumina (BET surface area 100 mê/g) as a binder and pilled prior to activity measurements. TABLE II G.C. DISTILLATION OF ETLGO FEED Pct. Off 0F C 0 421 216 1 442 228 5 491 255 10 520 271 25 559 293 50 605 318 75 656 347 90 695 368 95 713 378 99 761 405 100 850 454 Figure 1 shows the effect of steaming on the activity of a 10% WO3/A1203 catalyst compared to a conven tional silica-alumina catalyst and to the pure alumina substrate. The activity is defined as the amount of 430 liquid material produced per hour per gram of total catalyst. Note that this represents the activity of the various catalysts to produce a gasoline-type liquid. It is seen from Figure 1 that the WO3 catalyst is markedly different from the conventional silica-alumina catalyst with regard to its stability towards severe steaming. The silica-alumina catalyst loses a substantial fraction of its activity whereas the WO3/Á1203 catalyst loses almost none of its activity. The alumina base used in the preparation of the WO3 catalyst has a low fresh (unsteamed) activity and loses virtually all its activity after steaming. Figure 2 depicts the effect of steaming on the acid site strength and distribution for the WO3/A1203 and SiO2Al2O3 cats. Again it is seen that there is substantial difference between the WO3/Al2O3 catalyst and the silicaalumina catalyst. For the WO3/A1203 catalyst there are still a significant number of very strong (-8.2 on a Hammett Acidity Scale) sites which are the sites believed to be primarily responsible for cat cracking reactions. On the other hand, the silica-alumina catalyst loses all of its strongacia (-8.2)sites. It is clear that steaming has caused a major change in the surface morphology of the silica-alumina catalyst resulting in the complete destruction of surface sites having strong acid character. The WO3/A1203 catalyst is apparently not similarly affected thereby indicating a substantial difference in the nature of the strong acid sites on the two catalysts. During steaming the surface area of the WO3/Al2O3 catalyst drops from about 180 mê/g to about 60 - 70 mê/g. The silica-alumina catalyst 2 zoo 2 drops in surface area from 350 m /g to about 40 m /g. The activity maintenance and the constaney of the number and strength of acid sites on the WO3/A1203 system indicate that the WO3 or WO3-A1203 sites remain unchanged after steaming in spite of the large loss in surface area of the catalyst. The collapse of surface area for silica-alumina apparently results in a complete destruction of the active catalytic sites. In summary, the loss in active sites ( -8.2 Ho Acidity) for the steamed WO3 or A1203 catalyst, Figure 2, shows that although significant surface area decrease occurs that a third of the strong acid sites are preserved. These strong acid sites which are maintained following steaming treatment, despite being reduced in number of sites per gram of catalyst, are clearly capable of giving nearly fresh catalyst activity, Figure 1. This is one of the principal discoveries of the catalysts of the present invention and constitute a major advancement over state of the art catalysts. Figure 3 shows the effect of WO3 concentration on the activity at 1 hour and 5 hours on oil for the WO3/Al2O3 catalyst system before and after steaming at 16000F for 16 hours. It is clear that increasing WO3 concentration increases conversion at one hour on oil for the fresh catalysts. The difference in activity for fresh catalysts at one hour on oil compared to five hours on oil increases with increasing WO3 concentration, eventually becoming quite large for the 25% WO3/A1203 catalyst. After steaming similar effects occur but important differences emerge. At the 2% W03 level steaming actually increases activity. At the 10% and 25% loading levels steaming does not substantially alter activity. The activity maintenance indicates that the WO3 remains completely accessible for catalysis. It should be added that under identical reaction conditions to those used in the above discussed experiments a zeolite catalyst steamed at somewhat less severe conditions than either the WO3/A1203 or silica-alumina catalysts lost sub-stantial activity after steaming. The activity at one hour on oil as defined in Figure 1 dropped from 0.74 to 0.24. This again illustrates the inherent system stability of the WO3/A1203 system relative to conventional catalyst systems. The following are a series of examples directed to the catalytic use of the disclosed metal oxides on supports and are presented so as to demonstrate the general applicability of the instant inventive process with the disclosed catalysts. The reaction investigated gas gas oil cracking to break C-C bonds in the presence of a large excess of steam. The cracking reaction produces a liquid gasoline fraction referred to as the C5 -430 fraction or cut. The amount of this gasoline fraction is referred in the below tables as the conversion. The conversion was measured after a 0.5 and a 1 hr. interval. The competing side reactions which are undesirable are gasification and coking. Both side reactions are important in catalytic-cracking because they directly affect the gasoline yields. All the catalysts in the tables below were evaluated at a relatively high space velocity in order to minimize catalyst deactivation by coking. All reactions were for a 12.5 g catalyst charge with an oil flow rate of 80 cc/hr. In the following examples a series of the disclosed metal oxides supported on alumina are compared for catalytic activity. The activity measurements were obtained in a typical downflow gas phase reactor having a total catalyst capacity Of 40 cc. Liquid oil is fed to the reactor by a dual barrel Ruska pump. Water is fed simultaneously to the oil by a Lapp pump. The reactor is maintained at reaction temperature by immersion in a heated fluidized sandbath. Operating conditions are as follows: Oil Feed: East Texas Light Gas Oil, Boiling Range 450-7000F Catalyst Temp: 5100C Pressure: 30 PSIGO (WHSV) + Oil: 5.6 H2O:Oil Molar Ratio: 10 +Weight hourly space velocity Activities are expressed as the amount of oil feed converted to liquid product boiling below 430 F, i.e. this is referred to as 430 OF product. The activity is thus defined by the following expression: Activity = Conversion to 430 OF Liquid x Flow Rate of Oil x (Cat Weight)-1 Prior to activity measurement, the catalyst was brought to reaction temperature and water added for 1/2 hour prior to addition of oil feed. This is necessary to prevent premature coking of the catalyst surface. The thermal stability of the catalyst described in the current invention were determined by subjecting the various catalysts to a high temperature calcination in moist air. The conditions used to determine stability were air calcination at 9000C with air sparged through a water saturator. The steaming treatment was carried out at am bient pressure. EXAMPLE 1 An alumina of high purity (reforming grade, Englehard Industries) was evaluated or acid cat cracking activity under the conditions described previously after a one-half hour period and a one hour period on oil. The A1203 catalyst had an activity of 0.005 and 0.01 cc, 430 OF. liquidproduced/hour/g catalyst, respectively. The total gas production after one hour was 0.4 liter. The coke on catalyst was 1.6 and 0.7 wt. % for the top and the bottom of the catalyst bed, respectively. This example is for comparison to other catalysts of the instant invention. See Table III A. EXAMPLE 2 A 3.6 wt. % TiO on Al 0 catalyst (containing 2 23 450 76Lm/g of Ti) was prepared using a methanol solution of TiC 14 sufficient to fill the pore volume of the alumina described in Example 1. Following drying of the catalyst under vacuum to remove methanol the catalyst was dried at 1l00C overnight. The catalyst was then calcined at 5000C overnight in a muffle furnace. The cat cracking activity was obtained as described previously. The 3.68 TiO2 on A1203 catalyst had an activity of 0.04 and 0.03 cc 430 OF liquid produced/hour/g catalyst following a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 0.6 1. The coke on catalyst was 0.9 and 0.3 wt. % for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate the minor improvement in the cat cracking activity realized for a TiO2 on A1203 catalyst compared to A1203 of Example 1. See Table III A.. EXAMPLE 3 A 5.6 wt. % ZrO2 on A1203 catalyst (containing 450 2m/g of Zr) was prepared using a methanol solution of ZrCl4 sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 5.6% ZrO2 on A1203 catalyst had an activity of 0.03 cc 430 OF liquid product/ hour/g catalyst for both a one-half hour period and a one hour period on oil. The total gas production after one hour was 0.5 1. The coke on catalyst was 0.9 and 0.3 wt. % for the top and bottom of the catalyst bed, respectively. This example again serves to demonstrate the minor improvement in the cat cracking activity realized for this catalyst compared to A1203 of Example I and very similar activity to the Tio2 on A1203 catalyst of Example 2. See Table III B. EXAMPLE 4 A 9.5 wt. % HfO2 on Al2O3 catalyst (containing 450 m/g of Hf) was prepared using a methanol solution of HfC14 sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 9.5% Hf on A1203 catalyst had an activity of 0.01 and 0.02 cc 430 OF liquid product/hour/g catalyst following a one-half hour and an one hour period on oil, respectively. The total gas produced after one hour was 0.2 1. The coke on catalyst was 0.8 and 0.5 wt. % for the top and the bottom of the catalyst bed, respectively. This example again serves to demonstrate the minor improvement in the cat cracking activity realized for this catalyst compared to Al2O3. See Table III C. EXAMPLE 5 A 4.0 wt. % V205 on Al203 catalyst (containing 450 /g of V) was prepared using a methanol solution of VOCl3 sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was-then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 4.0% V205 on A1203 catalyst had an activity of 0.23 and 0.12 cc 430 OF liquid product/hour/g catalyst for both a one-half and a one hour period on oil. The total gas produced after one hour was 0.7 1. The coke on the catalyst was 2.1 and 1.6 wt. % for the top and bottom of the catalyst bed, respectively. This example serves to demonstrate the major improvement in the cat cracking activity realized for this catalyst compared to the previous catalysts, Examples 1, 2, 3 and 4. This example also demonstrates that the activity realized is not associated with large coke deposits on the catalyst, e.g. 2.1 for this example compared to 1.6 of Example 1, respectively. Also, this example further demonstrates that the high activity of the catalyst of this example is realized with very similar gas production compared to the relatively inactive catalysts of the previous Examples 1, 2, 3 and 4. See Table III A. EXAMPLE 6 A 6.0 wt. ( Nb2O5 on Al2O3 catalyst (containing 450in/g of Nb) was prepared using a hexane solution of Nb(OC2H5)5 sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 6.0% Nub205 on A1203 catalyst had an activity of 0.59 and 0.45 cc 430 OF liquid product/hour/g catalyst for both a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 0.8 1. The coke on the catalyst was 1.5 wt. 8 for both the top and the bottom of the catalyst bed. This example serves to demonstrate the major improvement in the cat cracking activity realized for this catalyst compared to the catalysts of Example 1, 2, 3 and 4. This example does indicate that the high activity obtained for this catalyst is about 2.5 times the activity obtained for V205 on Awl203' Example 5. This example also demonstrates that the activity realized is not associated with large coke deposits on the catalyst, e.g. 1.5 compared to 1.6 for this example compared to Example 1, respectively. Also, this example further demonstrates that the high activity of the catalyst of this examples realized with very similar gas production compared to the relatively inactive catalysts of the previous Examples 1, 2, 3 and 4. See Table III B. EXAMPLE 7 Another portion of the catalyst described in Example 6 was charged to a quartz tube, 1" in diameter, and placed in a tube furnace. The catalyst was steamed at 9000C (16600F) with 20% O2 in He sparged through water for 16 hours. The cat cracking activity was obtained as described previously. The steam treated 6% Nb2O5 on Al 203 catalyst had an activity of 0.47 and 0.24 cc 430 OF liquid product/ hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 1.0 1. The coke on the catalyst was 2.5 and 2.3 wt. % for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate the major improvement in the cat cracking activity realized for this catalyst compared to the previous catalysts, Examples 1, 2, 3 and 4. This example also demonstrates that the activity realized is not associated with large coke deposits on the catalyst, e.g, 2.5 for this example compared to 1.6 for Example 1, respectively. Most importantly this example demonstrates that high cat cracking activity is maintained even after severe steam treatment of the catalyst. Also, this example further demonstrates that the high activity of the catalyst of this example is realized with very similar gas production compared to the relatively inactive catalysts of the previous Examples 1, 2, 3 and 4. This exampe serves to demonstrate one of the most important results for the transition metal oxide acid catalysts of the instant invention, i.e. high temperature steam stability. See Table III B. EXAMPLE 8 A 10.0 wt. % Ta2O5 on Al2O3 catalyst (containing 450 > 4m/g of Ta) was prepared using a heptane solution of Ta(OC2H5)5 sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 10.0% Ta O on A1203 2 5 catalyst had an activity of 0.10 and 0.06 cc 430 OF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 0.4 1. The coke on the catalyst was 1.0 and 1.1 wt. % for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate that the cat cracking activity of a transition metal oxide supported on alumina is quite dependent on the transition metal ion chosen. Both V205 and Nb205, Examples 5 and 6, respectively are more active than the Ta2O5 catalyst of this example despite the fact that the transition metal concentration of all three catalysts was identical, i.e. 450/xm/g catalyst. This example, however, does serve to demonstrate higher cat cracking activity of the catalyst of this example compared to the previous catalysts of Examples 1, 2, 3 and 4. The Group VB metal oxides supported on alumina all exhibit greater cat cracking activity than the analogous Group IVB metal oxides supported on alumina. The most active Group VB oxide being niobium oxide, Example 6. See Table III C. EXAMPLE 9 Because of the good cat cracking maintenance of the Nb2O5 on A1203 catalyst following severe steaming con ditions, Example 7, , another portion of the Ta2O5 alumina catalyst was treated under the conditions described in Example 7. The steam-treated 10% Ta2O5 on Al2O3 catalyst had an activity of 0.04 and 0.005 cc 430 F liquid product/ hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 1.7 1. The coke on the catalyst was 6.1 and 8.4 wt. % for the top and the bottom of the catalyst bed, respectively. This example demonstrates that a Ta205 on Al2 0 3 catalyst is not able to maintain cat cracking activity for high temperature steaming conditions unlike that observed for a Nb2O5 on A1203 catalyst, Example 7. This example also demonstrates a major problem with coke production for this steamed catalyst compared to the catalyst of Example 7. See Table III C. EXAMPLE 10 Because of the wide usage of Cr2O3 on A1203 catalysts in heterogeneous catalysis, two different preparations were investigated. Both an aqueous and a non-aqueous preparation was made for comparison. A 4.5 wt. % Cr203 on A1203 catalyst (containing 450 > m/g of Cr) was prepared using an aqueous solution of chromic acid sufficient to fill the pore volume of the alumina described in Example 1. This catalyst will be referred to as Catalyst A. Another 4.5 wt. % Cr2O3 catalyst was prepared using a methanol solution of CrO2C12 sufficient to fill the pore volume of the alumina described in Example 1. This catalyst -will be referred to as Catalyst B. Catalysts A and B were both treated as described in Example 2. The cat cracking activity was obtained as described previously. Catalyst A had an activity of 0.06 and 0.03 cc of 430 OF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 0.7 1. The coke on the:catalyst was 3.4 and 1.9 wt. % for the top and the bottom of the catalyst bed, respectively. Catalyst B had an activity of 0.01 and 0.05 cc 430 OF liquid/pr'oduct/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 0.7 1. The coke on the catalyst was 2.0 and 1.7 for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate the rather low cat cracking activity for both Catalyst A and B of this example. The superior activity of Catalyst A results in a higher coke make than for Catalyst B. This example further serves to demonstrate that the cat cracking activity of a transition metal oxide supported on alumina is quite dependent on the transition metal ion chosen. See Table III A. EXAMPLE 11 A 6.9% MoO3 on Al203 catalyst (containing 450jctt/g Ta) was prepared using an aqueous solution of ammonium molybdate sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 6.9% MoO on A1203 catalyst had an activity of 0.26 and 0.04 cc 430 bF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 4.2 1. The coke on catalyst was 15.5 and 12.9 wt. % for the top and the bottom of the catalyst bed, respectively. This example has many important points to be made in comparison to the results of the other examples of the instant invention. Firstly, it should especially be noted that the gas make and coke deposits of this catalyst are much higher than for any of the catalysts of the previous examples. Secondly, note the marked decrease in the catalytic activity for the one hour compared to the one-half hour run length. This decrease in activity results in an activity only 14% of that for the shorter sample period. In contrast, the Nb205 on A1203 catalyst for Example 6 maintained 76% of activity of the shorter sample period. Clearly, the MoO'3 on A1203 catalyst would result in a cat cracking catalyst with very poor characteristics: high gas production, large coke production and rapid catalyst deactivation. This example further serves to demonstrate that the cat cracking activity of a transition metal oxide supported on alumina is quite dependent on the transition metal chosen. Note, also, the quite different results of the MoO3 on A1203 catalyst compared to Cr2O3 on A1203 catalysts of Example 10. See Table III B. EXAMPLE 12 A 10% WO3 on Al2O3 catalyst (containing 430 m/g of W) was prepared using an aqueous solution of ammonium tungstate sufficient to fill the pore volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 10% WO3 on A1203 catalyst had an activity of 0.79 and 0.68 cc 430 OF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 2.2 1. The coke on catalyst was 4.3 and 6.0 wt. % for the top and the bottom of the catalyst bed, respectively. This example has many important points to be made in comparison to the results of the other examples of the instant invention. Firstly, it should especially be noted that this is the most active catalyst of all those in the previous examples but with relatively low gas production, e.g. 2.2 for WO3 on A1203 compared to 4.2 for MoO3 on At203, Example 11. Secondly, the catalytic activity remains quite high for the one hour reaction period despite the relative high coke production on the catalyst. This is evidence for WO3 on Al 203 tolerating high coke deposits while maintaining high catalytic activity. High coke tolerance for an acid catalyst would be a much desired feature for a heavy resid cat cracking process. See Table III C. EXAMPLE 13 Another portion of the catalyst of Example 12 was steam treated at 9000C as described in Example 7. The cat cracking activity was obtained as described previously. The steam-treated 10% WO3 on A1203 catalyst had an activity of 0.68 and 0.58 cc 430 OF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced was 2.3 1. The coke on the catalyst was 6.0 and 4.1 wt. % for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate that the WO3 on A1203 catalyst steamed at 9000C is not greatly decreased in activity compared to the unstreamed catalyst of Example 12. This example collaborates the results obtained for the Nb2O5 on A1203 catalyst of Example 7. This example constitutes one of the most important results for the transition metal oxide acid catalysts of the instant invention, i.e. high temperature steam stability. See Table iii C. EXAMPLE 14 A 10.9 wt. % Re2O7 on A12 3 catalyst (containing 450 > 4m/g of Re) was prepared using an aqueous solution of perrhenic acid sufficient to fill the volume of the alumina described in Example 1. The catalyst was then treated as described in Example 2. The cat cracking activity was obtained as described previously. The 10.98 Re207 on A1203 catalyst had an activity of 0.06 and 0.04 cc 430 OF liquid product/hour/g catalyst for a one-half hour and a one hour period on oil, respectively. The total gas produced after one hour was 6.8 1. The coke on catalyst was 23.4 and 21.9 for the top and the bottom of the catalyst bed, respectively. This example has many important points to be made in comparison to the results of the other examples of the instant invention. Firstly, this example emphasizes the completely different cat cracking results in changing in the third row of the periodic table from W to Re. The gas make and coke on catalyst of the Rue 207 on A1203 catalyst would make the catlayst completely unsuitable as a catalyst because the valuable liquid product would be converted to a large degree to gases and coke. Secondly, the cracking activity of this catalyst is quite low in comparison to the WO3 on A1203 catalyst of Example 12. This example further serves to demonstrate that the cat cracking activity of a transition metal oxide supported on alumina is quite dependent on the transition metal chosen. See Table III C. TABLE III A FIRST ROW ELEMENTS OF GROUP IV, V, VIB Conver- Conver- Gas %C on sion at sion at Make Cat Top/ Catalyst 0.5 hr. 1 hr. (1) Bottom 3.6% TiO2 on A1203 0.9 0.7 0.6 1/1.4 4% V205 on A1203 4.9 2.7 0.7 2.1/1.6 4.5% Cr2O3 on Al2O3 (Aq. Prep.) 1.2 Q.6 0.7 3.4/1.9 4.5% Cr2O3 on A12 3 0.2 1.1 0.7 2.0/1.7 (Non-Aq. Prep.) 2 Blank 0.1 0.2 0.4 1.6/0.7 It is clear from the data in the above Table that vanadium oxide is the only first row transition metal oxide with appreciable activity. This activity is still a factor of three lower than for 10% WO3 on A1203, however. TABLE III B SECOND ROW ELEMENTS OF GROUP IV, V AND VIB Conver- Conver- Gas % C on sion at sion at Make Cat Top/ Catalyst 0.5 hr. 1 hr. (1) Bottom 5.6% ZrO2 on Al2O3 0.7 0.7 0.5 6% Nb2O5 on Al2O3 12.9 9.8 0.8 1.5/1.5 6% Nb2O5 on Al2O3 10.3 5.2 1.0 2.5/2.3 (Steamed at 900 C) 6.9% MoO3 on A1203 5.7 0.8 4.2 15.5/12.9 Al2O3 Blank 0.1 0.2 0.4 1.6/0.7 The data in the above table is very significant. The cracking activity of Nub 205 on A1203 is very high, only ca. 25% less than 10% WO3 on A1203. However, the gas make and coke on catalyst are both less than WO3 on Al2O3. Also, the above Nb205 on A1203 catalyst shows good steam stability as found for WO3 on Al2O3. This is a very promising catalyst discovery. Note also the much greater activity of Nb2O5 catalyst compared to the other second row elements. Particularly, note the huge coke production of the MoO3 catalyst. TABLE III C THIRD ROW ELEMENTS OF GROUP IV, V, VI, VIIB Conver- Conver- Gas % C on sion at sion at Make Cat Top/ Catalyst 0.5 hr. 1 hr. (1) Bottom 9.5% HfO2 on Al2O3 0.3 0.4 0.2 0.8/0.5 10% Ta2O5 on Al2O3 2.1 1.4 0.4 1/1.1 10% Ta205 on Al2O3 0.9 0.1 1.7 6.1/8.4 (Steamed) 10% WO3 on A12Q3 17.1 14.9 2.2 4.3/6.0 10% WO3 on A1203 14.8 12.5 2.3 6.0/4.1 (Steamed) 10% WO3 on SiO 1.3 0 0.5 (P.P.G. Beads, Non-Aq. Prep.) 10% WO3 on SiO2 Al2O3 i5.4 10.3 2.2 10.9% Re2O7 on Al O3 1.2 0.8 6.8 23.4/21.9 A12 3 Blank 0.1 0.2 0.4 1.6/0.7 The above data demonstrates that the WO3 on Al2O3 catalyst is far superior to any of the third row metals of Group IV, V, VI and VIIB. Also, the W03 on Al 203 catalyst is steam stable as evidenced by the steam catalyst having 85% of the fresh catalyst activity. EXAMPLE 15 An alumina (&gamma;-Al2O3) extrudate available commercially (Englehard Industries) was evaluated for cat cracking activity under conditions described above. At these conditions after 1 hour on oil, the A1203 catalyst had an activity of 0.01 cc 430 F liquid product/hour/g cat. The total gas production after 1 hour was 0.4 liter. This example is for comparison to other catalysts of the instant invention. EXAMPLE 16 A 2% WO3 on Al203 catalyst was prepared by standard *Weight hourly space velocity impregnation techniques using an aqueous solution of ammonium metatungstate (AMT) onto the alumina extrudate described in Example 15. Following drying at 1100C overnight this catalyst was calcined at 5000C for 16 hours and then evaluated for cat cracking activity under identical conditions to those described previously. At these conditions the activity for 430 OF liquid production is 0.40 cc 430 OF liquid product/ hour/g cat. The gas production after 1 hour was 0.5 liter. This example is for comparison to other catalysts of the current invention. This example also illustrates the much higher activity for cat cracking of 2% WO3 on A1203 catalyst compared to the pure A1203 support described in Example 15. EXAMPLE 17 A portion of the 2% WO3 on A1203 catalyst described in Example 16 was steam treated at 9000C for 16 hours in air sparged through water. After steaming, a portion of the catalyst was evaluated for activity for cat cracking of gas oil under conditions identical to those described previously. At these conditions the activity for 430 OF liquid production is 0.22 cc 430 OF/hr/g/ cat. The gas production after 1 hour was 0.5 liter. This example serves to demonstrate the superior catalytic activity of this high temperature steam catalyst compared to alumina itself, Example 15. This catalyst also demonstrates that about one-half the catalytic activity has been maintained following the above high temperature steam treatment compared to the unsteamed catalyst of Example 16. This example is also of value when compared to other tungsten oxide catalysts of the instant invention. EXAMPLE 18 A 4% WO3 on A1203 catalyst was prepared by standard impregnation techniques using an aqueous solution of ammonium metatungstate onto the alumina extrudate described in Example 15. This catalyst was calcined in air at 5000C for 16 hours and then evaluated for cat cracking activity under conditions identical to those described previously. At these conditions the activity for 430 OF liquid production is 0.40 cc 430 OF liquid/hour/g cat. The total gas make after 1 hour is 0.7 liter. This example is useful for comparison to the steamed catalyst of Example 19. The catalytic activity of this example is quite close to the activity obtained for the catalyst of Example 16 despite the factor of two differences in the tungsten oxide content of this catalyst. EXAMPLE 19 A portion of 4% WO3 on Al2 0 3 catalyst described in Example 18 was subjected to a steaming treatment for 16 hours at-a temperature of 9000C. After this treatment the cat cracking activity for 430 OF liquid production was 0.53 cc 430 OF liquid'/hour/g cat. The total gas production after 1 hour was 0.9 liter. This example demonstrates a unique feacture of the WO3 on A1203 catalysts of the instant invention. The catalytic activity of this high temperature steamed catalyst is increased over the unsteamed catalyst, Example 18. In addition, the activity of this steamed 4% WO3 on Al2O3 catalyst is much greater than the activity of the steamed 2% WO3 on A1203 catalyst of Example 17. This example thereby demonstrates the critical dependence of tungsten oxide content on catalytic activity following severe steaming conditions. EXAMPLE 20 A 6% W03 on Al2O3 catalyst was prepared by impregnation of an aqueous solution of ammonium metatungstate onto the alumina extrudate described in Example 15. This catalyst was then calcined in air for 16 hours at 5000C and then evaluated for cat cracking activity under conditions previously described. At these conditions, the activity for 430 OF liquid production is 0.69 cc 430 liq/ hr/g cat. The total gas make after 1 hour is 1.8 liter. This example demonstrates the superior activity of a 6% WO3 on Al2O3 to either the 4% WO3 on A1203 catalyst, Example 18, or the 2% WO3 on A1203 catalyst, Example 16. This example further demonstrates the critical dependence on tungsten oxide content of catalystic activity. This example is useful for comparison to Example 21. EXAMPLE 21 A portion of the 6% WO3 on A1203 catalyst described in Example 20 was subjected to a steaming treatment for 16 hours at 9000. After this treatment the cat cracking activity for 430 OF liquid production was 1.00 cc 430 OF liquid/hour/g cat. The total gas make after 1 hour on stream was 1.8 liter. This example illustrates the superior activity of the steamed 6% WO3 on A1203 catalyst compared to the unsteamed 6% WO3 on A1203 catalyst described in Example 20. This example demonstrates a unique feature of WO3 on Awl 203 catalysts of the instant invention. The catalytic activity of this high temperature steamed catalyst is increased over that of the unsteamed catalyst of Example 30. In addition, the activity of the steamed catalyst is higher than the steamed and unsteamed 4% WO3/A1203 catalysts of Examples 18 and 19 and also higher than the activities of the steamed and unsteamed 2% 1003/A1203 catalysts of Examples 16 and 17. This demonstrates the critical dependence of WO3 content on catalytic activity following severe steaming treatment. EXAMPLE 22 An 8% WO3/A1203 catalyst was prepared by impreg-. nating an aqueous solution of ammonium metatungstate onto the alumina extrudate described in Example 15. This catalyst was calcined for 16 hours at 5000C and then evaluated for cat cracking activity under conditions identical to those described previously. At these conditions, the activity for 430 F liquid production is 0.73 cc 430 OF liq/ hr/g cat. The total gas make after 1 hour is 2.0 liter. This example is useful for comparison to the steamed catalyst of Example 23. EXAMPLE 23 A portion of the 8% WO3 on A1203 catalyst described in Example 22 was subjected to a steaming treatment for 16 hours at 9000C. After this treatment, the cat cracking activity for 430 OF liquid production was 0.81 cc 430 OF/hr/g cat. The total gas make after 1 hour on stream was 2.0 liter. This example demonstrates a unique feature of the WO3/Al203 catalysts of the current invention. The catalytic activity of this high temperature steamed catalyst is increased over the unsteamed catalyst, Example 22. In addition the activity of this steamed catalyst is more active than the steamed 2% WO3 on Al2O3 and 4% WO3 on A1203 catalysts of Examples 17 and 19, respectively. However, the activity of this steamed catalyst is lower in activity compared to the steamed 6% WO3 on A1203 catalyst of Example 21. This example further demonstrates the critical dependence of tungsten oxide content on catalytic activity following severe steaming treatments, EXAMPLE 24 A 108 WO3/A1203 catalyst was prepared by impregnating an aqueous solution of ammonium metatungstate onto the alumina extrudate described in Example 15. This catalyst was calcined in air at 5000C for 16 hours and evaluated for cat cracking activity under conditions identical to those described previously. At these conditions the activity for 430 OF liquid production of 0.95 cc 430-OF/hr/g cat. The total gas make after 1 hour on stream is 2.2 liter. This example is useful for comparison to Example 25. This example also demonstrates a higher activity compared to other unsteamed WO3/A1203 catalysts of lower WO3 concentrations. EXAMPLE 25 A portion of the 10% WO3/A1203 catalyst described in Example 24 was subjected to a steaming treatment at 9000C for 16 hours. After this treatment, the cat cracking activity for 430 OF liquid production was 0.80 cc 430 F/hr/g cat. The total gas make after 1 hour on stream was 2.3 liter. This example demonstrates the unique feature of good high temperature stability of WO3/A1203 catalysts of the instant invention. EXAMPLE 26 A 25% WO3 on Al2 0 3 catalyst was prepared by impregnating an aqueous solution of ammonium metatungstate onto an alumina extrudate identical to and described in Example 15. This catalyst was calcined in air at 5000C for 16 hours and then evaluated for cat cracking activity under conditions identical to those described previously. At these conditions the activity for 430 DF liquid production is 0.49 cc liquid/hour/g cat. The total gas make after 1 hour on stream is 4.6 liter. This example is useful for comparison to catalysts of the instant invention. This example demonstrates little advantage of increased WO3 content much above the 10% WO3 content described in Example 24. EXAMPLE 27 An amorphous silica-alumina catalyst (13% Al2O3) that had been air calcined at 5400C for 16 hours was evaluated for cat cracking activity under conditions identical to those described above. Under these conditions, the activity for 430 F liquid production was 0.83 cc 430 OF liquid/hour/ g cat. The total gas make after 1 hour on stream was 2.8 liter. This example is useful for comparison to catalysts of the current invention. Fresh SiO2 Al2O3 has activity comparable to 8% WO3 on A1203 (Example 22) and 10% XiO3 on A1203 (Example 24). This example is also useful for comparison to Examples 28 and 29. EXAMPLE 28 A portion of the SiO2A1203 catalyst described in Example 27 was steamed for 16 hours at 7600C. The activity of this catalyst was 0.72 cc 430 OF liquid/hour/g cat. The total gas make after 1 hour was 0.7 liter. This example is useful for comparison to Examples 32 and 33 and to catalysts of the current invention. A steaming treatment at 7600 has only a modest effect on activity compared to the activity of a fresh Sio2 1203 catalyst (Example 27). This cata- lyst is comparable in activity to W03 on A1203 catalysts, both fresh and steamed, described in Examples 20 to 25. EXAMPLE 29 A portion of the SiO2 A1203 catalyst described in Example 27 was steam treated for 16 hours at 9000C. The activity of this catalyst was 0.32 cc 430 OF liquid/hour/g cat; The total gas make after 1 hour on stream was 0.8 liter. This example is useful for comparison to Example 27 and 28 and to catalysts of the instant invention. The SiO2 A1203 catalyst steamed at 9000C has lost substantial activity compared to fresh Si02.A203 catalysts (Example 27) and to SiO2 A1203 catalyst steamed at lower temperature (Example 28). This example also serves to show that commercially available SiO2Al 203 cat cracking catalysts have substantially lower thermal stability in the presence of steam compared to catalysts of the current invention (see examples 19 to 253. EXAMPLE 30 A commercial zeolite cracking catalyst consisting of 8.5% zeolite in an amorphous SiO2-A12o3 matrix was calcined at 5400C for 16 hours under conditions identical to those described above. The catalyst had an activity for 430 liquid production of 1.35 cc 430 /hour/g cat. Total gas make after 1 hour was 3.3 liter. This example is useful for comparison to Examples 31 and 32 and to catalysts of the current invention. This example demonstrates that a typical fresh zeolite cat cracking catalyst has activity somewhat higher than catalysts of the current invention. For example the activity of this catalyst is 1.42 times more active than the 10% WO3 on Al2O3 catalyst described in Example 24. EXAMPLE 31 A portion of the catalyst described in Example 30 was steam treated at 7600C for 16 hours. This catalyst had an activity of 1.42 cc 430 OF/hour/g cat. The total gas make after 1 hour on stream was 2.9 liter. This example is useful for comparison to Examples 30 and 32 and to catalysts of the current invention. A steaming treatment at 7600C has a slight beneficial effect on the activity of this catalyst compared to a fresh calcined catalyst described in Example 30. The activity of this catalyst is somewhat higher than catalysts of the current invention. EXAMPLE 32 A portion of the catalyst described in Example 30 was steam treated at 9000C for 16 hours. This catalyst had an activity of 0.10 cc 430 OF/hr/g cat. Total gas make after 1 hour on stream was 0.9 liter. This example is useful for comparison to Examples 30 and 31 and to catalysts of the current invention. The activity of the zeolite cracking catalyst following a severe steaming treatment at 9000C declines more than on order of magnitude compared to the activity of a fresh zeolite catalyst (Example 30) or a zeolite catalyst steamed at lower temperatures (Example 31). This example also serves to show the much superior thermal stability of the catalyst of the current invention compared to a state of the art commercial cat cracking catalyst. See for example the effect of steaming on the activity of catalysts in Examples 19 to 25. Steam Stability of WO3 on A1203 vs Zeolite or SiO2-A1203 In the previous discussion on the Group IV, V, VI and VIIB metal oxides as cracking catalysts the conditions employed to test the catalysts were reported. Therefore, they will not be repeated here. Below is the data obtained by comparing the W03 on Awl203 catalyst to SiO2Al2O3 as well as a commercial zeolite cat cracking catalyst. Each catalyst was investigated fresh, steamed at 14000F and also at 1600 F. The steam stability at 16000F is a crucial requirement for steam gasification of the carbon deposits on the catalyst which might be a requirement for a resid cat cracking process. TABLE IV Conver- Conver- Gas % C on sion at sion at Make Cat Top/ Catalyst ¯ 0.5 Hr. 1 Hr. (1) Bottom 10% WO on A12O 22.5 13.5 2.1 5.2/5.2 (Fresh) 10% WO3 on Al2O3 (Repeat Preparation Fresh) 17.1 14.9 2.2 4.3/6.0 10% WO3 on Al203 14.8 12.5 2.3 6.0/4.1 (Steamed 9000C) Zeolite Catalyst 20.7 21.1 3.3 3.4/4.2 (Fresh) Zeolite Catalyst 38.8 22.2 2.9 2.1/3.4 (Steamed 7600C14000F) Zeolite Catalyst 4.0 1.6 0.9 1.5/1.4 (Steamed 9000C16600F) Silica-Alumina 11.8 12.9 2.8 4.3/5.2 (14% A1203) Fresh Silica-Alumina 19.2 11.3 0.7 2.5/2.1 (Steamed 7600C14000F) Silica-Alumina 5.8 5.0 0.8 2.1/1.8 (Steamed 9000C16600F) The zeolite and silica-alumina catalysts steamed at 16500F are much less active than the steam stable WO3 on Al2O3 catalyst. Also, the activity of the fresh WO3 on A1203 catalyst compares favorably after a one-hour run period with either fresh zeolite or fresh silica-alumina catalyst. It has also been demonstrated that a marked difference in catalyst activity between the WO3 on A1203 catalyst calcined in steam at 9000C and the same weight loading of tungsten oxide impregnated onto pre-steamed alumina. Consider the table below. All catalysts were at the 4 wt. % WO3 level. TABLE V Conver- Conver- Gas % C on sion at sion at Make Cat Top/ Catalyst 0.5 Hr. 1 Hr. (1) Bottom 4% WO3 (Fresh) 8.9 6.2 0.7 0.9/1.0 Above Cat Steamed 11.3 8.3 0.9 2.4/2.2 at 9000C Steamed A1203 9.7 2.8 0.6 2.0/2.7 followed by identical prep. as for 4% WO catalyst above (Fresh) Note the large dfop in catalyst activity following one hour: reaction period. EXAMPLE 33 The preparation of high surface area g -A1203 (190 m /g) in extrudate form where a carbon char was formed in the pores of the extrudate was achieved by the following procedure. A standard sugar solution was prepared by dissolving 250 g of sucrose in 100 milliliters of distilled water heated to 140n e. A 50 milliliter portion of this saturated solution was contacted with 100 g of y -alumina extrudates of reforming grade purity (Englehard Industries, Inc.) This amount of the sugar solution was just that amount which would fill the pore volume of the extrudates. Therefore, this procedure constitutes a quasi-incipient wetness impregnation. The entire amount of material was then dried at 1200C for 16 hours. Following this overnight drying step the weight of the extrudates plus the weight of sugar in the pores was 135 g. Therefore, a 35% weight increase occurred due to the sugar impregnation step. The above preparation was then divided into two equal portions. Each portion was then treated in a tube furnace for 16 hours under a blanket of flowing helium to "char" the sugar in the pores of the alumina extrudate. Large quantities of water were removed in this heat treatment step. The weight percent carbon found on a sample from each bath treated at 6000C was in good agreement, 7.0 and 7.2 wt. % carbon. These two batches were then combined and used in a series of experiments reported in other Examples. EXAMPLE 34 A few gram portion of the carbonized-alumina of Example 33 was heated in a tube furnace at 11000C in a reducing atmosphere of 15% H in Argon to insure that the 2 carbon would not be removed by oxidation. The objective of this heat treatment was to convert the &gamma; -alumina phase to an&alpha;-alumina phase while maintaining high surface area. The sample was kept at this tmeperature for 16 hours. The sample was then removed from the tube furnace at ambient temperature. To remove the carbon from the pores of the alumina the sample was treated in a tube furnace at 6800C in flowing 20% oxygen in helium at a flow rate of 500 cc/ minute for 16 hours. The X-ray diffraction pattern for a powder sample indicated a mixture of alumina phases to be present for the 11000C heat treatment. Both &gamma; - and CL - A1203 phases were present. This example serves to demonstrate that partial conversion of the y -alumina occurs at 1100 C for a portion of the sample of Example 33 with 7% carbon in the pores of the extrudate. The surface area of 2 this extrudate was 80.3 m /g. EXAMPLE 35 A few grams of the carbonized-alumina of Example 33 was treated as described in Example 34 except that the high temperature treatment was increased to 11500C. Treatment at 11500C resulted in complete conversion of the alumina phase to OC- - alumina based on the X-ray diffrac- tion pattern of this sample. The surface area of this 2 sample was 37.6 m /g. This example serves to demonstrate the sensitivity of the &gamma; -alumina to Y -alumina phase transformation as a function of temperature. The weight % carbon on this & -A1203 sample was only 0.06 wt. % following the calcination step. This low carbon level indicates that a carbon-free OC-phase has been produced by the procedure described in Example 34. EXAMPLE 36 A few grams of the carbonized-alumina of Example 33 was treated as described in Example 34 except that the high temperature heat treatment was increased to 12000C. The X-ray diffraction pattern of this sample was quite similar to that of Example 35. This indicates, of course, that the 11500C treatment temperature was very near to the lower temperature limit which converts the alumina described in Example 1 to the Cc -phase. The surface area of the &alpha;-Al2O3 produced by the above 1200 C calcination treatment was 21.3 m /g. This Example serves to demonstrate the advantages of a minimum temperature of heat treatment in maintaining a high surface area for the Oc -alumina phase produced. The Oc -alumina produced in Example 35 at 11500C has a surface area nearly double that of the material of this Example. This Example points to a very important function of temperature in controlling the final -alumina surface area. It is most important in many catalytic processes known to those skilled in the art to maintain the maximum surface area of the catalyst in as high as state as possible. This Example clearly shows the unexpected importance of small temperature differences in producing a material of maximum surface area. EXAMPLE 37 Instead of using a few grams of the carbonizedalumina, 70 g of the material was heat treated at 11500C as in Example 35. However, instead of a calcination treatment at 7000C to remove the carbon a calcination step at 8920C for 16 hours in 20% O2 in helium at 500 cc/min. was used. As noted in Example 35, X-ray analysis of this sample showed complete conversion of Y -alumina to Oc -alumina. Also, the surface area of this sample was found to be 43.2 2 m /g. This example serves to demonstrate two important points. Firstly, a high surface area < -alumina in extrudate form can be prepared in a completely reproducible fashion as described in Example 35 by a 11500C heat treatment. Secondly, the Qc -alumina produced in this example is stable to a 8920C calcination treatment. Note that the calcination treatment is 2000C higher than for the sample of Example 35 while having a slightly higher surface area. This remarkable stability of the < -alumina phase to desurfacing under extreme temperature conditions is an unexpected finding not recognized in the prior art. Also, it is quite significant that the surface area of this sample is over twice that of the 12000C prepared sample of Example 36. EXAMPLE 38 To 55 g of the &alpha; -alumina in extrudate form of Example 37, 3.16 g of ammonium metatungstate containing 2.89 g W03 in 27.5 cc of water was added. This amount of liquid is just that which fill the pores of the extrudate. The sample was then dried for 16 hours at 1200C and finally calcined overnight at 5000C in a muffle furnace. The final catalyst contained 5 wt. % W03 on the ( -A1203 extrudate. An X-ray analysis of a powdered sample indicated the W03 phase to be in less than 4.0 nm diameter particles as no lines due to a W03 phase were observed In order to determine if the W03 on oC'-Al 203 phase was acidic, a standard Benesi titration with n-butylamine was used. (K. Tanabe, "Solid Acids and Bases", Academic Press, N.Y. 1970, p.14). Theo( -alumina itself, Example 37, was shown to have no strong acid sites (-8.2 and -5.6 on the Ho Hammett activity scale). However, for the 5% W03 oC -alumina there were 37 # 12 m/g of -8.2 strength acid centers. This example serves to demonstrate that introduction of W03 onto alumina produces a solid acid with strong acid sites. This material of this Example was investigated for gas oil catalytic cracking and was shown to have significant catalytic activity (Example 39). EXAMPLE 39 The catalyst of Example 38 was investigated for gas oil cracking activity as described in previous examples. The catalytic activity following a one-half hour period was 0.19 cc 430 OF liquid produced/hour/g catalyst. The total gas production after one hour was 0.6 1. The coke on catalyst was 1.3 and 1.3 wt. % for the top and the bottom of the catalyst bed, respectively. This example serves to demonstrate that W03 on 4 -A1203 is an active cat cracking catalyst. The activity of W03 on Cc -A1203 compared to &gamma; A1203 of Example 1 was a factor of 38 higher. The &alpha; -Al 203 of Example 37 itself would be less active than &gamma; -A1203 as &alpha;-Al2O3 was shown to have no strong acid sites (see discussion Example 38). EXAMPLE 40 To 29.34 g of the < -alumina in extrudate form of Example 6, 0.657g of ammonium meta-tungstate was added as described in Example 38. The above sample was dried and calcined as described in Example 38. The final catalyst contained 2 wst. % W03 on < -A1203. Fifteen grams of the above sample was calcined for 16 hours at 9000C in air sparged through water. The surface area of this sample following this severe steaming treatment was found to be 33.7 m2/g. This example serves to demonstrate the good surface area stability of WO3-supported on the z -alumina of the present invention. Note that the surface area of the z -alumina of Example 37, 43.2 m /g is largely pre- served for a sample containing W03 and following a severe steaming treatment. EXAMPLE 41 This example relates to coke buildup and regeneration of the coked catalyst with simultaneous production of low BTU value fuel gas. In this experiment conventional cat cracking reaction conditions were used in a unit employing a batch fluidized catalyst bed. Typical catalyst contact times were about two minutes. This unit is similar to Micro Activity Testing (MAT) Units used industry-wide for cracking catalyst evaluation. These tests are particularly relevant to the conceptual scheme of this invention. The information obtained is the activity defined as the amount of feed converted to 430 OF product and the selectivity to C5-4300F gasoline, C1-C4 gases, hydrogen, 430-6500F middle distillate, and coke. The catalysts tested were a 10% W03/A1203 catalyst and a 2% BaO/l0%W03/Al203 catalyst. These catalysts were tested with two different feeds and in the presence and absence of water. In Tables I and IIA a comparison of the W03/A1203 catalyst to conventional amorphous silica-alumina and commercial zeolite containing catalyst is made by highlighting the principal selectivity factors. In general the activity of the 10% W03/Al2 0 3 catalyst is comparable to the silica-alumina catalyst. The results presented in Tables VI and VII suggest a variety of process opportunities. If it is desirable to minimize coke two options are suggested by the results in Table II. First it can be seen that operating with steam addition to the reactor substantially lowers coke make. Also, as the data in Table VIIB indicates, extending the residence time of the catalyst in the bed from 2 min. to 20 min. greatly lowers the amount of coke produced on feed. The data indicates that there is first a large buildup of coke on catalyst followed then by a long period of time with little additional coke make but nearly constant feed conversion. The significance of this is two-fold; one is that by operating with residual coke on catalyst, the initial rapid coking and resultant poor selectivity to hydrocarbon products is mitigated. Secondly, the gasifier/ regenerator may be reduced in size as the residence time necessary to gasify a smaller amount of coke would correspondingly be lower. On the other hand, depending on the type of feed used it may be advantageous to maximize the amount of coke converted to low BTU gas or synthesis gas in the gasifier/regenerator. Thus, as the data in Table VII show, coke can be maximized by operating the reactor in a steam free environment. TABLE VI COMPARISON OF WO3/Al2O3 TYPE CATALYSTS TO STANDARD CATALYSTS IN MCC EXPERIMENTS Feed: ETLGO Tcat: 950 F Catalyst WO3/Al2O3 Silica-alumina Zeolite Pretreatment 1400 F STM 1400 F STM 1400 F STM Gas Added during Cycle Steam None None Cycle Length, min 2 2 2 W/hr/W 3.06 1.96 14.6 Conversion, Wt% 55.0 60.0 60.0 Carbon, Wt% 7.3 4.3 0.8 C3, Wt% 10.4 12.9 5.1 Tot. C4, Wt% 10.4 14.0 7.7 C5/430 F, Wt% 26.9 28.7 46.4 C3H6, SCF/B 192 199 125 H2, SCF/B 238 68 16 TABLE VII A. WITH ETLGO (500-700 F.) FEED 2% BaO/ 10% 2%BaO/ Catalyst 10%WO3/Al2O3 10%WO3/Al2O3 WO3/Al/O3 10%WO3/Al2O3 Zeolite Pretreatment Htd. &commat; 1000 F Stmd. &commat; 1400 F Gas Added During Cycle Stm. N2 Stm. N2 Stm. Stm. None W/Hr./W 2.09 2.91 2.76 2.77 3.06 2.83 14.6 Conversion, Wt. % 56.5 70.8 38.3 58.7 55.0 38.8 60 Carbon, Wt. % 15.0 22.4 13.8 16.3 7.3 11.0 0.8 C3- Gas, Wt. % 8.1 12.6 3.1 7.7 10.4 4.1 5.1 Tot. C4, Wt. % 8.1 11.6 3.1 7.6 10.4 4.1 7.7 C5/430 F, Wt. % 25.3 24.3 18.3 27.1 26.9 19.5 46.4 C3H6, SCF/B 146 178 50 116 192 75 125 H2, SCF/B 204 655 76 288 238 73 16 TABLE VII (Contd.) B. HEAVY GAS OIL 10% 2% BaO/ Catalyst WO3/Al2O3 10%WO3/Al2O3 2%BaO/10%WO3/Al2O3 Pretreat Stmd. &commat; 1400 F Gas Added Steam during process period Cycle Length, Min. 2 2 2 16 20 W/Hr./W 3.15 3.05 2.94 2.94 2.94 Conversion, Wt. % 67.7 60.3 56.0 48.6 47.3 Carbon, Wt. % 9.6 12.8 3.9* 3.9* 3.9* C3- Gas Wt. % 13.0 7.5 7.7 9.1 6.8 Tot. C4, Wt. % 12.3 6.9 6.8 4.6 3.0 C5/430 F, Wt. % 32.8 33.1 37.7 31.0 33.6 C3H6, SCF/B 263 159 151 147 101 H2, SCF/B 270 90 141 155 132 *Average for total 20 minute cycle based on carbon analysis as measured on catalyst discharged at end of experiment.

Claims: CLAIMS t. A supported acid catalyst comprising one or more catalytic metal oxide components comprising either an oxide of tungsten, niobium or a mixture thereof or a tungsten or niobium oxide in combination of one or more additional metal oxides selected from tantalum oxide, hafnium oxide, chromium oxide, titanium oxide and zirconium oxide, the support being an inorganic refractory metal oxide base which is either not itself an acid cracking catalyst or is a silica-containing cracking catalyst having a silica content of less than 50 wt. % calculated as SiO2 and said acid catalyst being steamed before use at a temperature ranging from between about 600-12000C in an atmosphere comprising from about 0.1 to 100% steam, the balance being an inert gas when less than 100% steam is used. 2. A catalyst according to claim 1 in which said inorganic refractory metal oxide support which is not itself an acid cracking catalyst is alumina, titania, zirconium, boria, thoria, magnesia, zirconiumtitanate, chromia, silica, kieselguhr or a mixture thereof. 3. A catalyst according to claim 2 in which said inorganic refractory metal oxide support comprises alumina. 4. A catalyst according to any one of the preceding claims in which said catalyst contains one or more promoter materials selected from oxides of barium, calcium, and magnesia. 5. A process of hydrocarbon conversion which comprises contacting the catalyst of any one of the preceding claims in a hydrocarbon conversion zone with a hydrocarbon feed stream at elevated temperature for a time sufficient to effect the desired hydrocarbon conversion. 6. A process according to claim 5 in which said elevated temperature is in the range from about 300-9000C. 7. A process according to either of claims 5 and 6 in which said hydrocarbon conversion comprises catalytic cracking. 8. A process according to any one of claims 5 to 7 which includes: (a) removing coked catalyst from the said hydrocarbon conversion zone; (b) regenerating the coked catalyst by contacting same at an elevated temperature with steam, oxygen-containing gas or a mixture thereof to produce a regenerated catalyst and a hydrogen-rich gas or a low BTU gas rich in carbon dioxide or a combination thereof; and (c) recirculating the regenerated catalyst produced in step (b) back to the hydrocarbon conversion zone of step (a).

Inventors: GRENOBLE, DANE CLARK, JUNG, KIM CHANG, MURRELL, LAWRENCE LEE, WEISSMAN, WALTER
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1980
Main classification: B01J23
IPC codes: B01J23, C10G11