Dehydrogenation of dehydrogenatable hydrocarbons

Dehydrogenatable hydrocarbons may be subjected to a dehydrogenation reaction in which the hydrocarbons such as ethylbenzene are contacted with a dehydrogenation catalyst comprising a modified iron compound in the presence of steam. The reaction mixture effluent containing unconverted hydrocarbons, dehydrogenatable hydrocarbon, hydrogen and steam is then contacted with an oxidation catalyst in a second oxidation zone whereby hydrogen is selectively oxidized to the substantial exclusion of oxidation of the hydrocarbon. The selective oxidation catalyst which is employed is prepared in a two-step process in which a compound containing a noble metal of Group VIII of the Periodic Table and a compound containing a metal of Group IVA of the Periodic Table is impregnated on a porous inorganic support such as alumina. The impregnated support is then calcined and subjected to a second step impregnation in which the support is impregnated with a solution of a compound containing lithium. Following this the support is then dried and calcined.

BACKGROUND OF THE INVENTION 
It has been known in the prior art that unsaturated hydrocarbons may be 
obtained from the dehydrogenation of dehydrogenatable hydrocarbons. The 
dehydrogenation may be effected by subjecting the dehydrogenatable 
hydrocarbons to a dehydrogenation process at dehydrogenation conditions in 
the presence of certain catalytic compositions of matter which possess the 
ability to dehydrogenate said compounds with the resultant formation of 
olefinic hydrocarbons. The particular dehydrogenation catalysts which are 
employed are well known in the art and comprise such compounds as nickel 
composited on a solid support such as diatomaceous earth, kieselguhr, 
charcoal and iron composited on the same supports, etc. 
Other dehydrogenation processes have employed, in addition to the 
dehydrogenation catalysts, an oxidation catalyst in the reaction process. 
The presence of the oxidation catalyst is necessitated by the fact that it 
is advantageous to oxidize the hydrogen which is produced by contact with 
an oxygen-containing gas in order to maintain the desired reaction 
temperature. For example, styrene, which is an important chemical compound 
utilized for the preparation of polystyrene, plastics, resins or synthetic 
elastomers such as styrene-butadiene rubber, etc., may be prepared from 
the dehydrogenation of ethylbenzene. The dehydrogenation of ethylbenzene 
into styrene, which is effected by treating ethylbenzene with steam in the 
presence of a modified iron catalyst, is endothermic in nature. The heat 
of reaction is about 30 Kcal per mole of ethylbenzene. Therefore, the 
temperature of the catalyst bed decreases significantly during the 
progress of the reaction in a commercial adiabatic reactor resulting in 
limitation of ethylbenzene conversion to a low level. The limitation of 
conversion arises from the fact that the equilibrium conversion of 
ethylbenzene is lowered and the rate of ethylbenzene dehydrogenation 
decreases as the reaction temperature decreases. The decrease of 
temperature adversely affects not only the conversion level, but also the 
selectivity for styrene, since at equilibrium conditions, only undesirable 
side reactions continue to take place. Therefore, it is necessary to 
maintain the desired temperature level in order to provide a high 
equilibrium conversion level and a high reaction rate. In the conventional 
process, the maintenance of temperature is attained by reheating the 
product stream with the addition of superheated steam between 
dehydrogenation catalyst beds using a multicatalyst bed reactor system. 
However, consumption of the additional superheated steam is considerably 
high and makes the dehydrogenation process costly. Accordingly, 
significant process economic improvements over the conventional 
ethylbenzene dehydrogenation processes can be achieved if the reaction 
temperature is somehow maintained while eliminating or reducing the 
additional superheated stream. One method of providing for the maintenance 
of the reaction temperature is to introduce oxygen into the reaction 
mixture by way of oxygen or an oxygen-containing gas such as air which 
will burn the hydrogen formed during the dehydrogenation reaction, this 
combustion resulting in an exothermic reaction which will provide the 
necessary amount of heat and, in addition, will shift the equilibrium 
toward production of styrene since the hydrogen formed in the 
dehydrogenation is consumed. Consequently, a higher conversion and high 
styrene selectivity are achievable. 
The combustion of hydrogen with the oxygen in the oxygen-containing gas 
requires the presence of an oxidation catalyst. There are some key 
requirements for the oxidation catalyst to be usable for such a purpose. 
The most important catalytic property required is good catalytic stability 
since the oxidation catalyst must survive under very severe reaction 
conditions, namely at about 600.degree. C. to 650.degree. C. in the 
presence of steam. Under such conditions, porous inorganic materials such 
as .alpha.-aluminas, silicas and zeolites cannot maintain their pore 
structures for a long period of time, resulting in the permanent damage of 
catalysts prepared using such materials as supports, e.g., platinum 
supported on a porous high surface area alumina, silica, or zeolite. 
Secondly, the oxidation catalyst must be very active to achieve complete 
conversion of oxygen to avoid poisoning of iron-based dehydrogenation 
catalysts which are sensitively oxidized with oxygen to lose their 
dehydrogenation activities. Thirdly, the oxidation catalyst must be 
selective for oxidation of hydrogen. Otherwise, ethylbenzene and styrene 
are consumed to lower the efficiency of styrene production. 
Various U.S. patents have described types of oxidation catalysts which may 
be employed in this process. For example, U.S. Pat. No. 3,437,703 
describes a catalytic dehydrogenation process which employs, as a 
dehydrogenation catalyst, a composition known in the trade as Shell-105 
which consists of from 87% to 90% ferric oxide, 2% to 3% chromium oxide, 
and from 8% to 10% of potassium oxide. In addition, another 
dehydrogenation catalyst which is employed comprises a mixture of nickel, 
calcium, chromic oxide, graphite with a major portion of a phosphate 
species. In addition to these dehydrogenation catalysts, the reaction also 
employs a catalyst for the oxidation step of the process comprising 
platinum or palladium in elemental from or as a soluble salt. Another U.S. 
patent, namely 3,380,931, also discloses an oxidation catalyst which may 
be used in the oxidative dehydrogenation of compounds such as ethylbenzene 
to form styrene comprising an oxide of bismuth and an oxide of a metal of 
Group VIB of the Periodic Table such as molybdenum oxide, tungsten oxide 
or chromium oxide. In addition, the patent also states that minor amounts 
of arsenic may also be present in the catalytic composite as well as other 
metals or metalloids such as lead, silver, tin, manganese, phosphorus, 
silicon, boron and sulfur. 
U.S. Pat. No. 3,855,330 discloses a method for the production of styrene in 
which ethylbenzene is treated in the vapor state by passage over a 
dehydrogenation catalyst and an oxidation catalyst while introducing 
oxygen into the reaction medium. The dehydrogenation catalysts which are 
employed are those which have been set forth in various prior U.S. patents 
and which may be similar in nature to the dehydrogenation catalysts 
previously discussed. The types of oxidation catalysts which may be 
employed will include platinum or palladium catalysts which are composited 
on alumina or molecular sieves zeolite-type which have been charged with 
ferrous, heavy or noble metals. The patent lists the types of catalysts 
which are employed including copper or various zeolites, platinum on 
alumina, platinum on spinel, platinum and sodium on zeolites, platinum, 
sodium and potassium on zeolites, etc. 
U.S. Pat. No. 3,670,044 discloses a method for dehydrogenating cycloalkane, 
arylalkane and alkanes in the presence of gaseous hydrogen or mixture of 
gaseous hydrogen and gaseous oxygen using a catalyst composition 
comprising a Group VIII metal or a mixture of a Group VIII metal and a 
Group IVA metal deposited on a support comprising a Group II aluminate 
spinel. It is noted that the patentee teaches that added hydrogen is used 
in connection with the oxygen, and that when only oxygen is used, the 
conversion and selectivity are generally low. The addition of hydrogen is 
believed to be a significant disadvantage in the dehydrogenation process 
inasmuch as the equilibrium conversion is lowered. This is in 
contradistinction to the process of the present invention wherein the 
dehydrogenation process, prior to the oxidation step, is not effected in 
the presence of any added hydrogen. As will hereinafter be shown in 
greater detail, the present process results in the selective oxidation of 
hydrogen with a concomitantly lower selectivity to carbon monoxide and 
carbon dioxide. In addition, the patentee teaches the use of one catalyst 
for both dehydrogenation and oxidation which is in contrast to the 
separate dehydrogenation and oxidation catalysts which are used in the 
present process. 
Other U.S. patents which pertain to catalytic compositions of matter 
include U.S. Pat. No. 4,113,656 which describes a process for achieving 
the distribution of metals on a support which requires quite small 
particles of the carrier as a nucleating agent for the catalytic metal 
deposited thereon. In addition, U.S. Pat. No. 4,376,724 discloses the 
dispersion of rhodium on a silica or titania support in which the metal is 
dispersed on the support in what is referred to as an eggshell 
distribution. 
In addition to the aforementioned United States patents other patents 
disclose a method for the dehydrogenation of dehydrogenatable hydrocarbons 
utilizing a two-step process which includes dehydrogenation followed by a 
selective oxidation process. U.S. Pat. No. 4,435,607 discloses an 
oxidation catalyst which may, if so desired, contain a metal of Group IA 
or IIA of the Periodic Table, the present species of these metals 
including potassium, rubidium, cesium, barium, francium, radium, these 
metals if present in the catalyst composite being impregnated on the solid 
support containing a Group VIII metal and Group IVA metal in a third 
impregnation. U.S. Pat. No. 4,418,237 also discloses an oxidative catalyst 
comprising a noble metal of Group VIII of the Periodic Table and a metal 
cation which possesses an ionic radius no less than 1.35 Angstroms, and 
particularly those in Group IA and IiA which fall within this definition. 
U.S. Pat. No. 4,652,687 discloses an oxidation catalyst comprising a Group 
VIII noble metal, a Group IVA metal and a Group IA or IiA metal composited 
on a metal oxide support which possesses a particular configuration. Again 
the impregnation of the metals on the support may be effected in a 
coimpregnation method or stepwise. U.S. Pat. No. 4,717,779 also discloses 
a process for the dehydrogenation of dehydrogenatable hydrocarbons 
utilizing a noble metal of Group VIII and a metal of Group IVA composited 
on a solid inorganic support and, if so desired, may also contain a metal 
selected from Groups IA and IIA of the Periodic Table. 
As will hereinafter be shown in greater detail it has now been discovered 
that by preparing a selective oxidation catalyst by coimpregnating a Group 
VIII noble metal and a Group IVa metal on a solid porous support followed 
by a sequential impregnation of lithium on the previously impregnated and 
calcined support it is possible to obtain a superior catalyst with 
relation to stability and performance as measured by activity and 
selectivity than the properties which are possessed by catalysts which 
have been used in prior processes. 
BRIEF SUMMARY OF THE INVENTION 
This invention relates to a process for the dehydrogenation of 
dehydrogenatable hydrocarbons. More specifically, the invention is 
concerned with a process for the dehydrogenation of a dehydrogenatable 
hydrocarbon in which the hydrocarbon which is to undergo treatment is 
subjected to a dehydrogenation step in the presence of a dehydrogenation 
catalyst. This dehydrogenation step is followed by a selective oxidation 
step in which the product mixture which results from the aforementioned 
dehydrogenation step is treated in the presence of certain catalytic 
compositions of matter which are hereinafter set forth in greater detail 
in such a manner whereby the hydrogen which is present and which has 
resulted from the dehydrogenation step is selectively oxidized with a 
concomitant minimum oxidation of the hydrocarbons. By utilizing the 
particular selective oxidation catalyst, it is possible to obtain the 
desired dehydrogenated hydrocarbons in a relatively high yield as well as 
maintaining the stability and activity of the catalyst to a greater degree 
than has heretofore been experienced. By maintaining the aforementioned 
stability and activity, it is possible to obviate the necessity for 
relatively frequent changes of the catalyst or, in the alternative, 
regenerating the catalyst, thereby adding to the commercial attractiveness 
and economical feasibility of the dehydrogenation process. 
It is therefore an object of this invention to provide a process for the 
dehydrogenation of dehydrogenatable hydrocarbons. 
A further object of this invention is to provide a catalyst for the 
selective oxidation step of the process whereby hydrogen which is formed 
during the dehydrogenation process will be selectively oxidized to the 
substantial exclusion of the oxidation of the hydrocarbons. 
In one aspect an embodiment of this invention resides in a process for the 
dehydrogenation of a dehydrogenatable hydrocarbon with separate and 
intermediate selective oxidation of hydrogen which comprises the steps of: 
(a) contacting said hydrocarbon with a dehydrogenation catalyst comprising 
an alkaline metal-promoted iron compound in a first reaction 
dehydrogenation zone in the presence of steam at dehydrogenation 
conditions to produce a first reaction dehydrogenation zone effluent 
stream comprising a mixture of dehydrogenated hydrocarbons, unconverted 
hydrocarbons, hydrogen and steam; 
(b) removing said first reaction dehydrogenation zone effluent stream from 
said first dehydrogenation zone; 
(c) passing said effluent stream of step (b) to a second reaction oxidation 
zone which is separate and discrete from said first reaction 
dehydrogenation zone; 
(d) contacting said first dehydrogenation zone effluent stream in said 
second reaction oxidation zone with oxygen-containing gas in the presence 
of an oxidation catalyst consisting essentially of a Group VIII noble 
metal, a Group IVA metal, and lithium composited on a solid porous support 
at oxidation conditions to selectively oxidize said hydrogen within said 
first reaction zone effluent stream to the substantial exclusion of 
oxidation of said dehydrogenated and unconverted hydrocarbons, wherein 
said selective oxidation of said hydrogen is exothermic in nature to 
provide additional heat and thereby raise the temperature of said 
dehydrogenated and unconverted hydrocarbons; 
(e) withdrawing a dehydrogenated and unconverted hydrocarbon effluent 
stream from said second reaction oxidation zone having an increased 
temperature with respect to the temperature of said first reaction 
dehydrogenation zone effluent stream; 
(f) passing said second reaction oxidation zone product effluent stream of 
step (e) at dehydrogenation conditions to a third reaction dehydrogenation 
zone containing a dehydrogenation catalyst comprising an alkaline 
metal-promoted iron compound to produce dehydrogenated hydrocarbons; and 
(g) withdrawing and recovering said dehydrogenated hydrocarbons, the 
improvement which comprises utilizing as said selective oxidation catalyst 
a composite which has been prepared by the steps of impregnating a solid 
porous support with a compound containing a Group VIII noble metal and a 
compound containing a Group IVA metal, calcining said impregnated support 
and sequentially impregnating said calcined impregnated support with a 
compound containing lithium. 
A specific embodiment of this invention is found in a process for the 
dehydrogenation of ethylbenzene which comprises contacting said 
ethylbenzene with a hydrogenation catalyst comprising an alkaline metal 
modified iron catalyst with a temperature in the range of from about 
500.degree. C. to about 700.degree. C. and a pressure in the range of from 
about 0.1 to about 10 atmospheres in the presence of steam, thereafter 
contacting the resultant mixture of unconverted ethylbenzene, styrene, 
hydrogen and steam with air at a temperature in the range of from about 
500.degree. to about 700.degree. C. and a pressure in the range of from 
about 0.1 to about 10 atmospheres in the presence of a catalyst which has 
been prepared by impregnating an alumina support with a platinum 
containing compound and a tin containing compound, calcining the resultant 
impregnated support, and thereafter impregnating and recalcining the 
previously calcined support with a lithium containing compound, and 
recovering the desired styrene after the final stage of dehydrogenation. 
Other objects and embodiments will be found in the following detailed 
description of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
As hereinafter set forth the present invention is concerned with a 
dehydrogenation process for the dehydrogenation of dehydrogenatable 
hydrocarbons which involves the use, in one step of the process, of a 
selective oxidation catalyst which will provide an improved stability and 
selectivity as well as increasing the activity, as exemplified by the 
conversion of oxygen as well as eliminating some disadvantages which have 
been present when utilizing prior catalytic compositions of matter in the 
same process. 
In the present process, a dehydrogenatable hydrogen of the type hereinafter 
set forth in greater details is contacted with a dehydrogenation catalyst 
in the presence of steam in a multicatalyst bed system. Inasmuch as the 
dehydrogenation of the hydrocarbon is endothermic in nature, it is 
necessary to provide an additional amount of heat before the product 
enters the next catalyst bed in order to provide a high equilibrium 
conversion as well as a high reaction rate. One method of effecting this 
increase in the desired temperature is to provide an internal catalytic 
combustion of the hydrogen which is produced during the dehydrogenation 
reaction in order to reheat the product to the desired level. By effecting 
a selective oxidation of the hydrogen, it is possible to avoid the use of 
superheated steam or other outside sources of heat. This selective 
oxidation of hydrogen with the resultant composition thereof is effected 
by utilizing a selective oxidation catalyst of the type hereinafter set 
forth in greater detail, the selective oxidation catalyst maintaining its 
stability and activity for a considerable length of time. 
The process of the present invention may be effected by utilizing an 
apparatus in which the dehydrogenation catalyst and the oxidation 
catalyst, both of the type hereinafter set forth in greater detail, are 
loaded in the apparatus in alternate layers. The number of alternate 
layers of dehydrogenation catalyst and selective oxidation catalyst may 
vary according to the size or type of apparatus which is employed, the 
number of alternate layers ranging from three to about nine. As will 
hereinafter be shown, the dehydrogenation catalyst and the oxidation 
catalyst are different in nature. Examples of dehydrogenation catalysts 
which may be employed will comprise an alkaline earth metal-promoted iron 
compound. The term "alkaline metal" as used in the present specification 
and appended claims will refer to metals of Groups IA and IIA of the 
Periodic Table which include lithium, sodium, potassium, rubidium, cesium, 
beryllium, magnesium, calcium, strontium and barium. In addition, the 
promoted iron compound catalyst will, in the preferred embodiment of the 
invention, also include a compound containing a metal of Groups IVB, VB 
and VIB of the Periodic Table. For example, a typical dehydrogenation 
catalyst which may be employed in the process of this invention will 
consist essentially of about 85% by weight of ferric oxide, 12% by weight 
of potassium hydroxide, 2% by weight of chromia and 1% by weight of sodium 
hydroxide. Another typical dehydrogenation catalyst which may be used 
comprises 90% by weight of ferric oxide, 4% by weight of chromia and 6% by 
weight of potassium carbonate. In addition these catalysts, other 
well-known dehydrogenation catalysts which may be utilized will include 
those comprising ferric oxide, potassium oxide, as well as other metal 
oxides and/or sulfides of metals of Groups IA, IIA, IVB, VB and VIB of the 
Periodic Table including those of calcium, lithium, strontium, magnesium, 
beryllium, zirconium, tungsten, molybdenum, hafnium, vanadium, copper, 
chromium and mixtures of two or more oxides such as chromia-alumina, 
chromia-titania, alumina-vanadia and the like. 
The dehydrogenation of a dehydrogenatable hydrocarbon such as, for example, 
ethylbenzene, is effected by contacting the dehydrogenatable hydrocarbon 
and steam, in the absence of any added hydrogen, with the aforesaid 
catalyst at dehydrogenation conditions which are in the range of from 
about 500.degree. to about 700.degree. C. and at a reaction pressure in 
the range of from about 0.1 to about 10 atmospheres; the exact 
dehydrogenation conditions are, however, a function of the particular 
dehydrogenatable hydrocarbon undergoing dehydrogenation. Other reaction 
conditions will include a Liquid Hourly Space Velocity based on the 
hydrocarbon charge of from about 0.1 to about 10 hrs.sup.-1 and steam to 
hydrocarbon weight ratios ranging from about 1:1 to about 40:1. The number 
of dehydrogenation zones of the catalyst beds may vary from 1 to about 5 
in number and typically may comprise three reaction zones; however, the 
number of zones is not critical to the invention. After contacting the 
dehydrogenation catalyst with the steam and hydrocarbon, the resulting 
mixture comprising unconverted hydrocarbon, dehydrogenated hydrocarbon, 
steam and hydrogen which has passed through the catalyst bed is contacted 
in a separate zone with the selective oxidative catalytic composition of 
the type hereinafter set forth in greater detail. In addition, 
oxygen-containing gas is introduced into the reactor, preferably at a 
point adjacent to the oxidation catalyst bed. Examples of 
oxygen-containing gases which may be utilized to effect the selective 
oxidation of the hydrogen which is present will include air, oxygen, air 
or oxygen diluted with other gases such as steam, carbon dioxide and inert 
gases such as nitrogen, argon, helium, etc. The amount of oxygen which is 
introduced to contact the product stream may range from about 0.1:1 to 
about 2:1 moles of oxygen per mole of hydrogen contained in the product 
stream. In this particular reaction zone, the product stream, which 
comprises unreacted dehydrogenatable hydrocarbon, dehydrogenated 
hydrocarbon, hydrogen and steam, undergoes a selective oxidation in 
contact with oxygen and the oxidation catalyst whereby hydrogen is 
selectively oxidized to water with a minimal amount of reaction of oxygen 
with the hydrocarbons, either unconverted hydrocarbon or dehydrogenated 
hydrocarbon. The selective oxidation of hydrogen is important inasmuch as 
the competing reaction to this oxidation reaction comprises the oxidation 
of the unconverted hydrocarbons such as ethylbenzene or the dehydrogenated 
hydrocarbon such as styrene. The combustion of the hydrocarbons with 
oxygen has a two-fold deleterious effect on the overall reaction in that 
(1) the combustion of the hydrocarbons leads to the loss of product and 
(2) the combustion reaction leads to the production of carbon monoxide. 
The production of carbon monoxide in the effluent stream from the 
oxidation zone to a subsequent dehydrogenation zone will detrimentally 
affect the performance of the dehydrogenation catalyst in the second 
dehydrogenation zone, thus further lowering the yield of the desired 
dehydrogenated hydrocarbon. 
After passage through the zone containing the oxidation catalyst, the 
mixture may then be passed through a second dehydrogenation zone 
containing a dehydrogenation catalyst of the type hereinbefore set forth 
for further dehydrogenation, the process being completed through the 
plurality of zones followed by withdrawal of the product stream and 
separation of the unconverted hydrocarbon from the desired dehydrogenated 
product. 
It is contemplated that the dehydrogenation process for the dehydrogenation 
of dehydrogenatable hydrocarbons utilizing the oxidative catalytic 
compositions of matter of the present invention will be applicable to a 
wide variety of dehydrogenatable hydrocarbons. Examples of hydrocarbons 
which are susceptible to a dehydrogenation process utilizing the catalysts 
of the present invention will include lower alkyl-substituted aromatic 
hydrocarbons such as ethylbenzene, diethylbenzene, isopropylbenzene, 
diisopropylbenzene, o-ethyltoluene, m-ethyltoluene, p-ethyltoluene, 
o-isopropyltoluene, m-isopropyltoluene, p-isopropyltoluene, 
ethylnaphthalene, propylnaphthalene, isopropylnaphthalene, 
diethylnaphthalene, etc., paraffins such as ethane, propane, n-butane, 
isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, 
n-decane, and branched chain isomers thereof, cycloparaffins such as 
cyclobutane, cyclopentane, cyclohexane, methylcyclopentane, 
methylcyclohexane, ethylcyclopentane, olefins such as ethylene, propylene, 
1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 2-hexene, 
3-hexene, and branched chain derivatives thereof, etc. 
The selective oxidation step of the process utilizes, as hereinbefore set 
forth, the hydrogen which has been produced in the dehydrogenation step of 
the process to supply heat to the inlet of the next dehydrogenation 
catalyst bed. Inasmuch as temperatures which are utilized in the process 
may be as high as 650.degree. C. in the presence of steam, the operating 
conditions in which the oxidation catalyst must function are severe in 
nature. In order for the oxidation catalyst to remain stable and minimize 
the carbon formation thereon, the catalyst support must be calcined at a 
relatively high temperature in order to decrease the surface area, this 
descrease in surface area contributing to the stability of the catalyst. 
Conventional oxidation catalysts utilizing a porous support such as 
alumina which had been calcined at relatively low temperatures, i.e., 
below about 900.degree. C. or lower, lose surface area at a rapid and form 
excessive carbon on the surface thereof, thus resulting in a deactivation 
of the catalyst. 
The particularly effective oxidation catalyst which may be used in the 
dehydrogenation and subsequent selective process of the present invention 
comprises a noble metal of Group VII of the Periodic Table as exemplified 
by platinum along with a Group IVA metal of the Periodic Table such as tin 
plus lithium composited on a solid porous inorganic oxide support. This 
type of inorganic oxide support is not critical to this invention, 
however, a particularly effective support which contributes to the 
stability and effectiveness of the catalyst comprises an alumina. The 
alumina support will be derived from various types of aluminas such as, 
for example, boehmite, pseudoboehmite, gibbsite, etc., or a precursor of 
an alumina such as an aluminum hydroxyl chloride sol. The calcination of 
the support is effected at a temperature within the range of from about 
600.degree. to about 1500.degree. C. prior to impregnation of the metals 
thereon. If so desired, the calcination of this support may be effected in 
a dry atmosphere, preferably at a temperature in the range of from about 
800.degree. to about 1500.degree. C. or the calcination may be effected in 
a hydrous atmosphere such as that provided by steam, the temperatures 
preferably in the range of from about 600.degree. to about 1300.degree. C. 
The calcination of the support within these temperature ranges will be 
effected over a period of time which may range from about 0.5 to about 30 
hours or more in duration and it is to be understood that the particular 
temperature which is selected for the calcination of the support will 
influence or direct the time frame during which the calcination takes 
place. It has been found that a particularly effective type of alumina 
source which may be in the form of pellets, spheres, powder, slurry, etc. 
and which will provide desired catalyst support. In addition, the alumina 
may be present as alpha-alumina or as a mixture of alpha-alumina and 
theta-alumina. 
As was hereinbefore set forth, the selective oxidation catalysts which are 
employed in the process of this invention will comprise a noble metal of 
Group VIII of the Periodic Table and a metal of Group IVA of the Periodic 
Table composited on a solid inorganic support which, prior to the 
compositing of the metals thereon, has been calcined at a temperature 
within the range herebefore discussed. In addition, if so desired, it is 
also contemplated within the scope of this invention that the catalyst 
will also contain a metal selected from Groups IA and IIA of the Periodic 
Table. Of the noble metals of Group VIII of the Periodic Table, platinum, 
palladium and rhodium comprise the preferred species, said metals being 
present in the final composite in an amount in the range of from about 
0.01% to about 5% by weight. Of the metals of Group IVA of the Periodic 
Table, germanium, tin and lead comprise the preferred species, these 
metals also being present in the final catalyst composite in an amount in 
the range of from about 0.005% to about 5% by weight. 
The catalytic metal portions of the finished catalyst comprising the Group 
VIII noble metal and Group IVA metal are impregnated on the surface of the 
catalyst support in a coimpregnation process. For example, in one method 
of preparation the Group VIII noble metal and Group IVA metal may be 
coimpregnated through the formation of a complex in the impregnation 
solution. The formation of this complex constitutes a significant factor 
inasmuch as the complex formed between the two metals is bulky in nature 
and its adsorption properties are such that it is deposited on the 
exterior surface of the catalyst particle during the impregnation step 
thereby insuring the deposition of a higher average concentration of Group 
VIII metal in the aforesaid exterior surface. In one embodiment of the 
invention the formation of the complex is accomplished by utilizing tin of 
the type hereinbefore set forth in greater detail in a +2 form. 
Alternatively, if tin is in a +4 form or other Group IVA metals are used a 
complex may be effected by utilizing, in the impregnation solution, a 
compound which possesses both a functional group as exemplified by a thio, 
amino, hydroxyl, or phosphorus moiety as well as a polar group such as a 
carboxyl or hydroxyl moiety in the compound. Examples of these compounds 
will include thiomalic acid, thiolactic acid, ethylenediaminetetraacetic 
acid, thioglycolic acid, thiopropionic acid, thiodiacetic acid, 
thiodipropionic acid, etc. It is to be understood that these compounds are 
only representative of the type of complexing compounds which may be 
employed, and that the present invention is not necessarily limited 
thereto. 
Another alternative method of preparing the desired selective oxidation 
catalyst of the present invention is to impregnate the alumina support 
with a Group IVA metal which may be in the form of beads, spheres, 
pellets, etc. with an aqueous solution of the metal of Group IVA of the 
Periodic Table in which a soluble salt such as tin chloride, tin bromide, 
tin sulfate, lead chloride, lead persulfate, germanium chloride, etc. is 
present in the solution in an amount sufficient so that the finished 
catalytic composite will contain the desired amount of the metal. The 
impregnation is allowed to proceed for a predetermined period of time 
following which the composite is recovered, dried and calcined. 
Alternatively, the group IVA metal may be incorporated into the alumina 
during the alumina forming step, by employing a suitable Group IVA 
containing compound. In this case, the Group IVA compound may be added to 
an alumina sol or alumina dough which may be oil-dropped or extruded to 
form the desired alumina composite. The composite is dried and calcined to 
form the final support containing Group IVA metal. Thereafter the Group 
IVA metal containing alumina support is then surface-impregnated with an 
aqueous solution of a noble metal of Group VIII of the Periodic Table and, 
if so desired, a polar compound which assists in the surface-impregnation 
of the Group VIII noble metal in an amount sufficient to provide the 
desired amount of the metals in the finished catalytic composite. For 
example, it is possible to employ a soluble salt of a noble metal of Group 
VIII of the Periodic Table such as chloroplatinic acid, chloropalladic 
acid, rhodium chloride, platinum sulfate, palladium sulfate, etc. After 
allowing the impregnation to proceed for a period of time sufficient to 
permit the deposition of the desired amount of metal on the catalyst 
support, the composite is recovered, dried and calcined at a temperature 
in the range of from about 500.degree. to about 600.degree. C. or more in 
an air or air-steam atmosphere and recovered. 
The second step of the preparation of the catalyst of the present invention 
will comprise impregnation the solid support containing the Group VIII 
noble metal and Group IVA metal with a lithium containing compound. As 
will hereinafter be shown in greater detail the two-step process for 
preparing the selective oxidation catalyst according to the process of 
this invention will result in the obtention of a catalyst which possesses 
greater activity and stability than will be found in those catalysts which 
contain no lithium or which have been prepared by a coimpregnation of 
Group VIII noble metal, group IVA metal and lithium. The catalytic 
activity of the selective oxidation catalyst is obtained by the presence 
of catalyst on the alumina support which serves as the active oxidation 
site. The presence of a Group IVA metal such as tin is necessary in order 
to attenuate the active oxidation sites due to the electron withdrawing 
nature of the Group IVA metal. By incorporating lithium in a second 
impregnation step on the catalyst it has been found that the lithium 
neutralizes or passivates the acidic sites on the alumina which could lead 
to undesirable hydrocarbon side reactions such as coking. The presence or 
formation of coke on the surface of the catalyst is undesirable inasmuch 
as it will lead to a loss of activity and thus necessitate replacement of 
the catalyst at shorter intervals, thus contributing to the possibility of 
rendering the process uneconomical to operate. 
The impregnation of the Group VIII noble metal and Group IVA metal 
containing porous support may be effected in a suitable manner similar in 
nature to the first impregnation step, that is, by utilizing an aqueous 
solution of a soluble lithium containing compound such as lithium 
chloride, lithium nitrate, lithium acetate, lithium bicarbonate, lithium 
borate, lithium dithionate, lithium fluorosulfonate, lithium iodide, 
lithium perchlorate, etc. The porous support is impregnated with a 
solution containing the lithium containing compound in an amount 
sufficient to provide a finished catalyst composite which will contain 
from about 0.05% to about 5% by weight of the catalyst composite. After 
effecting the impregnation with the lithium containing compound the 
catalyst composite is recovered, dried and calcined at a temperature of 
from about 500.degree. to about 650.degree. C. in an air or air-steam 
atmosphere in a manner similar to that hereinbefore set forth and 
recovered. 
Some specific examples of selective oxidation catalytic compositions of 
matter which may be used in the dehydrogenation process and which have 
been prepared according to the process previously described in which the 
noble metals of Group VIII and metals of Group IVA have been impregnated 
on an alumina support, calcined and subsequently impregnated in a second 
step with lithium followed by calcination will include platinum, germanium 
and lithium composited on alumina, palladium, germanium and lithium 
composited on alumina, rhodium, germanium and lithium composited on 
alumina, platinum, tin and lithium composited on alumina, palladium, tin 
and lithium composited on alumina, rhodium, tin and lithium composited on 
alumina, etc. It is to be understood that the above-enumerated catalysts 
are only representative of the selective oxidation composites which may be 
used in the process of this invention, and that said invention is not 
necessarily limited thereto. By utilizing a selective oxidative catalytic 
composition of matter in a process which involves the dehydrogenation of 
dehydrogenatable hydrocarbons, it is possible to obtain a process which, 
in addition to obtaining a desirable and commercially attractive yield of 
dehydrogenation products, also permits the operation of the process in an 
economically viable manner due to the catalytic stability of the catalyst 
under the relatively harsh and stringent operating conditions such as high 
temperature and high concentration of steam at which the process is 
operated. 
By utilizing the catalyst which has been prepared by surface impregnating 
the catalytic metals, it is possible to obtain a catalyst system which 
exhibits the desired characteristics of stability and activity which is in 
contradistinction to oxidation catalysts which have been set forth in the 
prior art, the latter being unable to produce the desired stability which 
is exhibited by the catalyst of the present invention, and therefore 
cannot survive in use for a relatively long period of time. This 
relatively short life of a catalyst discourages the commercial use of such 
catalysts as unattractive due to the necessity of having to replace or 
regenerate the catalyst after a short interval of operating time has 
elapsed. In addition, the catalysts of the present invention also exhibit 
a definite activity for the selective oxidation of hydrogen rather than a 
tendency for the oxidation of the dehydrogenated products or unreacted 
hydrocarbons. 
The catalyst of the present invention will exhibit an excellent stability 
in that it possesses the ability to maintain the maximum temperature of 
the reaction at a position which is near the inlet of the catalyst bed. 
The desired reaction, that is, the selective oxidation of hydrogen, is 
highly exothermic in nature and it is therefore an indication of a good 
catalyst that the maximum temperature is maintained near the inlet of the 
catalyst bed, thus indicating that the conversion of the hydrogen occurs 
at a time shortly after the product stream comprising unconverted 
hydrocarbons, dehydrogenated hydrocarbons, steam and hydrogen enters the 
catalyst bed. In addition, as will hereinafter be demonstrated, the 
catalyst of the present invention also possesses the ability to effect a 
relatively high conversion of oxygen as is evidenced by the absence of 
oxygen in the exit gas which is withdrawn from the reaction zone 
containing the selective oxidation catalyst. 
The following examples are given for purposes of illustrating the selective 
oxidation catalyst of the present invention as well as to a process 
utilizing the selective oxidation catalyst in said process. However, it is 
to be understood that these examples are merely illustrative in nature and 
that the present process is not necessarily limited thereto. 
EXAMPLE I 
A selective oxidation catalyst was prepared according to the methods 
heretofore known in the art by impregnating an alumina extrudate which had 
been previously calcined at a temperature of about 1330.degree. C. with a 
mixture of a chloroplatinic acid solution, a lithium nitrate solution and 
a stannous chloride solution, the strength of the solution being 
sufficient to afford a 0.4 weight percent platinum, a 0.2 weight percent 
lithium and a 0.35 weight percent tin based on the calcined support. 
Following this, deionized water was added along with 3% hydrochloric acid 
to afford an impregnated solution/calcined support base ratio of 0.55/1 
(volume/volume). The extrudate base and impregnating solution were charged 
to a glass jacketed rotary evaporator which was then nitrogen purged and 
the rotary evaporator was cold rolled for a period of 30 minutes. 
Following this, steam was charged to the evaporator jacket and the 
evaporator was hot rolled for a period of 6 hours until the presence of 
moisture was not detected at the mouth of the evaporator. The impregnated 
extrudate was then dried and loaded into a quartz tube where it was 
calcined in a stream of air at a temperature of 520.degree. C. for a 
period of 1 hour. At the end of this time the catalyst was cooled to 
ambient temperature in a flowing air stream and recovered. This catalyst 
was designated as catalyst A. 
EXAMPLE II 
A second catalyst was prepared according to the known method by 
coimpregnating an alumina extrudate utilizing chloroplatinic acid, lithium 
chloride and stannous chloride in an amount sufficient to afford 0.4 
weight percent platinum, 0.2 weight percent lithium, and 0.35 weight 
percent tin based upon the weight of the calcined support. The impregnated 
support was treated in a method identical to that set forth in Example I 
above by cold rolling in a glass jacketed rotary evaporator for a period 
of 30 minutes, thereafter hot rolling the evaporator using steam to afford 
the heat, followed by calcination at a temperature of 520.degree. C. for a 
period of 1 hour. This catalyst was labeled catalyst B. 
EXAMPLE III 
A third selective oxidation catalyst was prepared in a manner similar to 
that hereinbefore set forth by coimpregnating an alumina extrudate with a 
chloroplatinic acid solution and a stannous chloride solution in an amount 
sufficient to afford 0.4 weight percent platinum and 0.35 weight percent 
tin based on the weight of the calcined support. The difference between 
this catalyst which was obtained after cold rolling, hot rolling and 
calcination was that the catalyst composite did not contain any lithium. 
This catalyst was designated as C. 
EXAMPLE IV 
The selective oxidation catalyst composite of the present invention was 
prepared by impregnating an alumina extrudate with a chloroplatinic acid 
solution and a tin chloride solution in an amount sufficient to afford 0.4 
weight percent platinum and 0.35 weight percent tin based on the calcined 
support. The impregnated solution and the calcined support extrudates were 
placed in a glass jacketed rotary evaporator which was cold rolled in the 
presence of nitrogen for a period of 30 minutes. Thereafter steam was 
charged to the evaporator jacket and the evaporator was hot rolled for a 
period of 6 hours until the presence of moisture was not detected at the 
mouth of the evaporator. The impregnated extrudate was then dried and 
calcined in a stream of air at a temperature of 520.degree. C. for a 
period of 1 hour. At the end of this time the catalyst was cooled to 
ambient temperature and recovered. 
Following this the impregnated support was then impregnated in a subsequent 
second impregnation step with a solution of lithium nitrate in an amount 
sufficient to afford 0.2 weight percent lithium based upon the impregnated 
support, the amount of lithium nitrate solution being sufficient to afford 
an impregnated solution/impregnated alumina support ratio of 1/1 
(volume/volume). The catalyst base and solution were then placed in the 
glass jacketed rotary evaporator purged with nitrogen and cold rolled for 
a period of 15 minutes. Thereafter steam was charged to the evaporator 
jacket and the evaporator was hot rolled for a period of 2 hours until no 
moisture was detected at the mouth of the evaporator. The doubly 
impregnated extrudate was then dried and calcined in a quartz tube in a 
stream of air for a period of 2 hours while maintaining the temperature at 
650.degree. C. At the end of this date the catalyst was cooled to ambient 
temperature in a flowing air atmosphere. This catalyst was designated as 
catalyst D. 
EXAMPLE V 
The catalysts which were prepared according to the above example were then 
utilized in a selective oxidation process. The catalysts in an amount of 
14 cc were loaded into 1/2" inner diameter stainless steel reactors having 
a 10" long 1/2" diameter bore for the catalyst loading. The reactors were 
heated to an inlet temperature such that the maximum bed temperature was 
maintained at 600.degree. C. and a feedstock comprising a mixture of 7.3 
mole percent nitrogen, 3.9 mole percent hydrogen, 0.8 mole percent oxygen, 
8.7 mole percent of a mixture of 36% ethylbenzene and 64% styrene plus 
79.2 mole percent of steam was fed to the reactors. The feedstream was 
passed over the oxidation catalyst beds at the aforesaid inlet temperature 
at a reactor outlet pressure of 0.7 atmospheres. The feed was maintained 
at a liquid hourly space velocity of 37 hour.sup.-1 for a period of 24 
hours. 
As an indication of the stability and activity of the catalyst, 
measurements were taken periodically to determine the oxygen conversion 
and styrene combustion selectivity of the catalyst. The results of these 
tests are set forth in Tables 1 and 2 below. 
TABLE 1 
______________________________________ 
Oxygen Conversion of Fresh Catalysts (%) 
CATALYST 
Hours on Stream 
A B C D 
______________________________________ 
3 98.0 97.1 93.5 98.4 
12 96.8 94.7 87.6 98.4 
18 96.3 94.8 85.5 97.5 
24 96.2 94.4 82.7 97.5 
______________________________________ 
TABLE 2 
______________________________________ 
Styrene Combustion Selectivity of Fresh Catalysts (%) 
CATALYST 
Hours on Stream 
A B C D 
______________________________________ 
3 7.5 19.5 11 6.3 
12 6 11.8 7.8 5 
18 6 11 7.8 5 
24 6 10.8 7.9 5 
______________________________________ 
EXAMPLE VI 
In order to further differentiate the superior performance of a catalyst 
prepared according to the process of this invention the catalysts were 
subjected to a hydrothermal ageing process in order to determine a 
simulated aged activity. The catalysts were subjected to 24 hours of 
ageing at a temperature of 800.degree. C. and a pressure at 1 atmosphere 
to accelerate the platinum agglomeration of the catalyst, said ageing 
being in the presence of an atmosphere of air and steam. 
The ageing process simulated a period of about 1 year of use in a 
commercial unit. The catalysts were then subjected to a selective 
oxidation test similar in nature to that set forth in Example V above. 
Periodic examination and testing resulted in the figures set forth in 
Tables 3 and 4 below. 
TABLE 3 
______________________________________ 
Oxygen Conversion of Aged Catalysts (%) 
CATALYST 
Hours on Stream 
A B C D 
______________________________________ 
3 69 74.5 76 81 
12 74.5 72.5 68 77.5 
18 73 71 65 81.5 
24 72 71 62.5 78 
______________________________________ 
TABLE 4 
______________________________________ 
Styrene Combustion Selectivity of Aged Catalysts (%) 
CATALYST 
Hours on Stream 
A B C D 
______________________________________ 
3 22.8 28.5 18 18 
12 18.5 22.8 19 18.5 
18 18 22 20 13.5 
24 17.5 22.5 18 15.5 
______________________________________ 
Again it is to be noted that the catalyst of the present invention which 
was prepared in a two-step impregnation process exhibited greater 
stability and activity than was exhibited by catalysts known in the art. 
EXAMPLE VII 
As another indication of the superiorty of the catalyst of the present 
invention, temperature profile measurements were performed during the 
course of the tests that showed that the catalyst of the present invention 
was a more active catalyst than those previously known. For more active 
catalysts, less heat is required to maintain a desired operating 
temperature of about 600.degree. C.; lower inlet temperatures may be 
employed since bed exotherm is greater. This is evidenced by the following 
table showing the temperature differential (T.sub.max -T.sub.inlet) in 
which the greater .DELTA.T indicates the more active catalyst. 
TABLE 5 
______________________________________ 
Temperature Differential 
CATALYST A B C D 
______________________________________ 
.DELTA.T Fresh 
38 45 50 51 
.DELTA.T Aged 23 33 26 35 
______________________________________