Hydrogen regeneration of monofunctional dehydrogenation and aromatization catalysts

The process is a hydrogen regeneration of spent Group VIII metal modified non-acidic microporous crystalline materials employed as catalysts in dehydrogenation and dehydrocyclization.

FIELD OF THE INVENTION 
Non-acidic microporous crystalline materials in combination with platinum 
group metals, as catalysts, have been found to exhibit high 
dehydrogenation and dehydrocyclization selectivity under dehydrogenation 
and dehydrocyclization conditions of paraffins for production of the 
unsaturated analog of the paraffin. Those catalysts are substantially 
monofunctional. 
The present invention is directed to hydrogen regeneration of aged 
catalysts. Accordingly, an object of the invention is to substantially 
recover process activity of dehydrogenation and/or dehydrocyclization of 
the first cycle, prior to regeneration, in cycle(s) subsequent to 
regeneration. 
Various dehydrogenation products are commercially significant. Isobutylene 
is one such desirable product which is used as a reactant for the 
production of alkylate, an oligomer of petroleum refinery C.sub.3 -C.sub.4 
off gases, which includes high octane gasoline components, and for the 
production of methyl-t-butyl ether, when isobutylene is reacted with 
methanol. 
An object of the invention is to provide a 
dehydrogenation/dehydrocyclization catalyst exhibiting high selectivity in 
cyclical processes. 
Accordingly, an object of the process is to produce unsaturated products 
with high selectivity. 
Another object of the invention is to produce isobutylene product with high 
selectivity. 
BACKGROUND OF THE INVENTION 
The term "crystalline" used to refer to these materials relates to the 
ordered definite crystalline structure of the material which is unique and 
thus identifiable by a characteristic X-ray diffraction pattern. 
The term "microporous" as it refers to such material relates to pores, or 
channels, with diameters of less than 20 Angstroms. Examples of these 
microporous crystalline materials include crystalline silicates, 
crystalline alumino-silicates (zeolites), crystalline ALPOs, crystalline 
SAPO and related compositions and intercalated pillared materials derived 
from clays, layered silicates and titanates. The crystalline silicate, 
alumino silicate (zeolites), ALPOs and SAPOs, have pores of uniform size 
and channel systems which are uniquely determined by unit structure of the 
material. The uniform pore size and/or channel systems allow such a 
material to selectively absorb molecules of certain dimensions and shapes. 
In the art, microporous material having pores, or channels, of less than 
20 Angstroms, can be divided into small, medium and large pore by the 
diameters of those pores, or channels. The pores of the small pore 
material have an average diameter of less than 5 Angstroms; medium size 
pores range from an average diameter of about 5 to about 7 Angstroms, and 
large pore silicates indicates a diameter of greater than about 7. The 
word "average" is used to refer to diameter to embrace those species in 
which the pore is elliptical. Alternatively, the demarcation between 
small, medium, and large pore materials can be based on the following 
sorption properties (measured at room temperature for crystallites having 
a minimum dimension of 0.1 micron): 
1. Small pore: n-C.sub.6 /i-C.sub.6 sorption ratio greater than 
approximately 10. 
2. Medium pore: n-C.sub.6 /i-C.sub.6 is less than 10 and n-C.sub.6 
/Mesitylene sorption ratio greater than approximately 5. 
3. Large pore: n-C.sub.6 /Mesitylene sorption ratio less than approximately 
5. 
In the art, zeolites are a subclass of crystalline microporous silicates. 
Zeolites can contain aluminum as well as silicon. In some zeolites, the 
upper limit of the silicon/aluminum atomic ratio is unbounded. ZSM-5 is 
one such example wherein the silicon/aluminum atomic ratio is at least 2.5 
and up to infinity. By way of illustration, U.S. Pat. No. 3,941,871, 
reissued as RE 29,948, discloses a porous crystalline silicate made from a 
reaction mixture containing no deliberately added aluminum and exhibiting 
the X-ray diffraction pattern characteristic of ZSM-5 zeolites; in certain 
examples tin is deliberately added to the silicate synthesis mixture. 
Zeolites can be acidic or non-acidic, depending on the framework aluminum 
content and on the amount of compensating cations, such as Na.sup.+, 
K.sup.+, etc. ALPOs described in U.S. Pat. No. 4,310,440, which is 
incorporated by reference herein, are neutral. SAPOs described for example 
in U.S. Pat. No. 4,440,871, which is incorporated by reference herein, can 
be acidic or non-acidic depending on the ratio of framework Al:P therein 
and the compensating cation, such as Na.sup.+, K.sup.+ (other than proton 
species and other than proton forming species such as NH.sup.+.sub.4). 
SUMMARY OF THE INVENTION 
The process of the invention comprises regenerating a monofunctional 
dehydrogenation/dehydrocyclization catalyst in hydrogen. The process of 
the invention comprises aging that non-acidic catalyst in a 
dehydrogenation and/or dehydrocyclization process, regenerating the aged 
catalyst under conditions of elevated temperature in the absence of 
oxygen, and employing the regenerated catalyst in a subsequent cycle of 
the dehydrogenation and/or dehydrocyclization process. Oxygen (air) 
regeneration requires high exotherms, which frequently lead to platinum 
metal migration and agglomeration. Such metal migration and agglomeration 
can necessitate subsequent metal redispersion via expensive rejuvenation 
techniques. 
It is noted that mild air treatment of these catalysts at 300.degree. to 
350.degree. C. for their regeneration restores catalyst activity but with 
a significant increase in catalyst aging rates following air treatment. 
Regeneration, in the absence of oxygen, is particularly effective for 
monofunctional metal catalysts. In the presence of high pressure hydrogen, 
metal sites of the monofunctional catalysts appear to catalyze coke 
removal by hydrogenation. By comparison, dual functional catalysts, such 
as those containing platinum on an acidic microporous crystalline material 
generally require air regeneration. 
The non-acidic catalyst comprises a platinum group metal, the non-acidic 
microporous crystalline material, and is monofunctional because of the 
non-acidic nature; optionally, the non-acidic catalyst comprises a 
platinum group metal, the non-acidic microporous crystalline material 
combined with titanium or catalytically inert titania, wherein the amount 
of titanium and/or catalytically inert titania is effective to decrease 
the ageing of the non-acidic microporous crystalline material, under said 
conditions of paraffin dehydrogenation and paraffin dehydrocyclization. 
In a preferred embodiment, the composition comprises a microporous 
crystalline material containing a modifier (such as tin, lead, thallium or 
indium). It has been discovered that these modifier containing microporous 
crystalline materials in non-acidic form combined with a dehydrogenation 
metal exhibit high selectivity for dehydrogenation and/or 
dehydrocyclization of paraffins, while exhibiting decreased selectivity 
for cracking.

DETAILED DESCRIPTION OF THE INVENTION 
The non-acidic catalyst comprises a hydrogenation/dehydrogenation metal, 
and a non-acidic microporous crystalline material. Optionally, that 
monofunctional catalyst may be combined with titanium or catalytically 
inert titania, wherein the amount of titanium and/or catalytically inert 
titania is effective to decrease the aging of the non-acidic microporous 
crystalline material, under dehydrogenation and/or dehydrocyclization 
conditions, described below. As catalysts these non-acidic forms of 
compositions exhibit extremely high selectivity for paraffin 
dehydrogenation and/or dehydrocyclization reactions, under conditions 
effective for paraffin dehydrogenation and/or aromatization. 
The amount of hydrogenation/dehydrogenation metal in the catalyst can range 
from 0.01 to 30 weight percent and preferably 0.1 to 10 weight percent of 
the crystalline material. In a preferred embodiment, platinum is the 
hydrogenation/dehydrogenation metal. However, the 
hydrogenation/dehydrogenation metal can be any Group VIII metal including 
those of the platinum group, chromium and vanadium. 
The microporous crystalline materials, if acidic as a result of synthesis, 
can be rendered non-acidic by base exchange to remove acidic functions 
contained therein. For example, if the microporous crystalline material 
contains framework aluminum, in the as-synthesized form, the microporous 
crystalline material can be base exchanged. In this embodiment, base 
exchange is effected after hydrogenation/dehydrogenation metal 
incorporation. Base exchange can be with an ionic Group IA metal. The 
base-exchange can be accomplished by slurring the material in an aqueous 
solution of suitable Group IA compound such as sodium hydroxide, potassium 
chloride, cesium hydroxide and the like. The base exchange can be 
accomplished under selected conditions of reagent concentration, pH, 
contact time, and the like, so as to eliminate substantially the 
base-exchangeable acidic content. Such a base-exchanged 
hydrogenation/dehydrogenation metal containing zeolite is essentially 
"non-acidic". 
In a preferred embodiment the microporous crystalline material is 
non-acidic, in the sense that it contains substantially no framework 
aluminum, in the as-synthesized form. In a preferred embodiment, the 
microporous crystalline material, also contains a modifier selected from 
the group consisting of tin, lead, thallium or indium. The modifier 
content of the crystalline microporous materials can range from 0.01 to 20 
weight percent. Practically, the modifier content will range from 0.1 to 
10 weight percent. These modifier containing microporous crystalline 
materials are described in U.S. Pat. Nos. 4,886,926; 4,931,416; and 
4,868,145, each of which is incorporated by reference herein. 
The crystalline microporous modifier containing materials of the invention 
are characterized by Si/Al ratios of at least 2. However, the 
silica:alumina ratio of the zeolite can be up to 1000, or greater. In a 
preferred embodiment the aluminum content of these materials is less than 
0.1 weight percent and more preferably less than 0.02 weight percent. 
The crystalline microporous modifier-containing or modifier-free material 
of the invention can contain other elements including boron, iron, 
chromium, gallium, iridium, ruthenium and rhenium. The content of these 
other elements in the crystalline microporous silicates can range from 0 
to 1? weight percent. 
The modifier containing crystalline materials, described herein, are 
crystalline in the sense that they are identifiable as isostructural with 
zeolites by X-ray powder diffraction pattern. 
The crystalline microporous containing material has an X-ray diffraction 
pattern which corresponds to a zeolite, SAPO, ALPO, etc. 
In a preferred embodiment the pore size of the microporous crystalline 
containing silicates ranges from about 5 to about 8 Angstroms. Preferably, 
the silicates exhibit X-ray diffraction patterns of zeolites which are 
characterized by Constraint Index of 1 to 12. 
The method by which Constraint Index is determined is described fully in 
U.S. Pat. No. 4,016,218, incorporated herein by reference for details of 
the method. Constraint Index (CI) values for some typical zeolites 
including some which are suitable as catalysts in the process of this 
invention are: 
______________________________________ 
CI (at test temperature) 
______________________________________ 
ZSM-4 0.5 (316.degree. C.) 
ZSM-5 6-8.3 (371.degree. C.-316.degree. C.) 
ZSM-11 5-8.7 (371.degree. C.-316.degree. C. 
ZSM-12 2.3 (316.degree. C.) 
ZSM-20 0.5 (371.degree. C.) 
ZSM-22 7.3 (427.degree. C.) 
ZSM-23 9.1 (427.degree. C.) 
ZSM-34 50 (371.degree. C.) 
ZSM-35 4.5 (454.degree. C.) 
ZSM-48 3.5 (538.degree. C.) 
ZSM-50 2.1 (427.degree. C.) 
MCM-22 1.5 (454.degree. C.) 
TMA Offretite 3.7 (316.degree. C.) 
TEA Mordenite 0.4 (316.degree. C.) 
Clinoptilolite 3.4 (510.degree. C.) 
Mordenite 0.5 (316.degree. C.) 
REY 0.4 (316.degree. C.) 
Amorphous Silica-alumina 
0.6 (538.degree. C.) 
Dealuminized Y 0.5 (510.degree. C.) 
Erionite 38 (316.degree. C.) 
Zeolite Beta 0.6-2.0 (316.degree. C.-399.degree. C.) 
______________________________________ 
The above-described Constraint Index is an important and even critical 
definition of those zeolites which are useful in the process of the 
present invention. The very nature of this parameter and the 
above-referenced procedure by which it is determined, however, admits of 
the possibility that a given zeolite can be tested under somewhat 
different conditions and thereby exhibit different Constraint Indices. 
Constraint Index appears to vary somewhat with the severity of the 
conversion operation and the presence or absence of binder material. 
Similarly, other variables such as crystal size of the zeolite, the 
presence of occluded contaminants, etc., may affect the observed 
Constraint Index value. It will therefore be appreciated that it may be 
possible to select test conditions, e.g. temperature, as to establish more 
than one value for the Constraint Index of a particular zeolite. This 
explains the range of Constraint Indices for some zeolites, such as ZSM-5, 
ZSM-11 and Beta. 
It is to be realized that the above CI values typically characterize the 
specified zeolites but that such are the cumulative result of several 
variables useful in the determination and calculation thereof. Thus, for a 
given zeolite exhibiting a CI value within the range of 5 or less, 
depending on the temperature employed during the test method within the 
range of 290.degree. C. to about 538.degree. C., with accompanying 
conversion between 10% and 60%, the CI may vary within the indicated range 
of 5 or less. Accordingly, it will be understood to those skilled in the 
art that the CI as utilized herein, while affording a highly useful means 
for characterizing the zeolites of interest, is approximately taking into 
consideration the manner of its determination including the possibility in 
some instances of compounding variable extremes. However, in all 
instances, at a temperature within the above-specified range of 
290.degree. C. to about 538.degree. C., the CI will have a value for any 
given zeolite of interest herein of not greater than about 5 and 
preferably not greater than about 3. 
In a preferred embodiment the microporous crystalline material containing 
tin exhibits the structure of ZSM-5, by X-ray diffraction pattern. The 
X-ray diffraction pattern of ZSM-5 has been described in U.S. Pat. No. 
3,702,886 and RE 29,948 each of which is incorporated by reference herein. 
The compositions comprising hydrogenation/dehydrogenation metal combined 
with the crystalline tin containing silicates do not exhibit any 
appreciable acid activity. These catalysts would meet the criteria of 
non-acidic catalysts described by Davis and Venuto, J. CATAL. Vol. 15, 
p.363 (1969 . Thus, a non-equilibrium mixture of xylenes are formed from 
either n-octane or each individual methylheptane isomer, with the octane 
yielding more o-xylene and 2-methyl-heptane yielding mostly m-xylene, at 
conversions between 10 and 60%. 
When, as in embodiments herein, the crystalline tin dehydrogenation metal 
containing material exhibits an X-ray diffraction pattern of a zeolite, at 
least some of the dehydrogenation metal may be intrazeolitic, that is, 
some of that metal is within the pore structure of the crystal, although 
some of that metal can be on the surface of the crystal. A test for 
determining whether, for example, Pt is intrazeolitic or extrazeolitic in 
the case of ZSM-5 is reported by R. M. Dessau, J. CATAL. Vol. 89, p. 520 
(1984). The test is based on the selective hydrogenation of olefins. 
In accordance with the invention, the compositions of the invention may, 
optionally, contain titanium or catalytically inert titania. Such 
compositions exhibit high selectivity for dehydrogenation. The titanium, 
expressed as TiO.sub.2, or catalytically inert titania can be present in 
amounts ranging from 10 to 99 weight percent of the catalyst composition. 
The catalytically inert titanium source may be admixed directly with the 
microporous crystalline material prior to noble metal incorporation or the 
catalytically inert titanium source may be admixed with the microporous 
crystalline material after noble metal incorporation. 
Compositions of the invention used in catalysis decrease the hydrogen 
content of the reactant to produce a product having the same number of 
carbon atoms as the number of carbon atoms in the reactant. By comparison, 
acidic counterparts of those compositions catalyzed also cracking of 
paraffins, as a major competing side reaction; and, accordingly, the 
latter compositions exhibit decreased selectivity for the aromatization of 
paraffins but increased selectivity for C.sub.1 -C.sub.5 paraffin 
production. 
In a preferred embodiment, the non-acidic crystalline microporous silicates 
of the invention are treated with Pt(NH.sub.3).sub.4 Cl.sub.2 in aqueous 
solution which has a pH of at least about 7 to incorporate the necessary 
platinum for catalyst composition formulation. 
The non-acidic, crystalline, microporous, dehydrogenation metal containing 
materials of the invention can be combined with a matrix or binder 
material to render them attrition resistant and more resistant to the 
severity of the conditions to which they will be exposed during use in 
hydrocarbon conversion applications. The combined compositions can contain 
1 to 99 weight percent of the materials of the invention based on the 
combined weight of the matrix (binder) and material of the invention. When 
used in dehydrogenation and/or dehydrocyclization, the material of the 
invention will preferably be combined with non-acidic matrix or binder 
materials. A preferred matrix or binder material would be silica, when the 
materials of the invention are used in dehydrogenation/hydrogenation or 
dehydrocyclization. Inactive materials suitably serve as diluents to 
control the amount of conversion in a given process so that products can 
be obtained economically and orderly without employing other means for 
controlling the rate of reaction. These materials may be incorporated into 
naturally occurring clays, e.g. bentonite and kaolin, to improve the crush 
strength of the catalyst under commercial operating conditions. Said 
materials, i.e. clays, oxides, etc., function as binders for the catalyst. 
It may be desirable to provide a catalyst having good crush strength 
because in commercial use it is desirable to prevent the catalyst from 
breaking down into powder-like materials. These clay binders have been 
employed normally only for the purpose of improving the crush strength of 
the overall catalyst. 
Naturally occurring clays which can be composited with the new crystal 
include the montmorillonite and kaolin families which include the 
subbentonites, and the kaolins commonly known as Dixie, McNamee, Georgia 
and Florida clays or others in which the main mineral constituent is 
halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays can be 
used in the raw state as originally mined or initially subjected to 
calcination, acid treatment or chemical modification. Binders useful for 
compositing with the present crystal also include inorganic oxides, 
notably alumina. 
In addition to the foregoing materials, the crystalline material can be 
composited with a porous matrix material such as silica-alumina, 
silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, 
silica-titania we well as ternary compositions such as 
silica-alumina-thoria, silica-alumina-zirconia silica-alumina-magnesia and 
silica-magnesia-zirconia. The relative proportions of finely divided 
crystalline material and inorganic oxide gel matrix vary widely, with the 
crystal content ranging from about 1 to about 90 percent by weight and 
more usually, particularly when the composite is prepared in the form of 
beads, in the range of about 2 to about 80 weight percent of the 
composite. 
The compositions of the invention exhibit high selectivity for 
dehydrogenation and/or dehydrocyclization which is evidenced by the 
examples. 
Catalytic Dehydrogenation and Dehydrocyclization 
In accordance with the invention catalytic dehydrogenation comprises 
contacting an aliphatic, with the catalyst composition of the invention to 
produce the corresponding unsaturated analog together with H.sub.2. 
In dehydrogenation the feedstocks comprise at least one unsubstituted or 
substituted straight or branched chain aliphatic compound in which the 
aliphatic moiety has two to five carbon atoms. In accordance with the 
invention, dehydrogenation of the aliphatic moiety occurs to yield the 
unsaturated analog. When the aliphatic moiety is substituted, the 
substituents can be aryls substituted or unsubstituted. The class of 
reactants includes alkanes of 2 to 5 carbon atoms, such as ethane, 
propane, butane, isobutane, pentane and 2-methylbutane. Dehydrogenation of 
those respective alkane reactants will yield ethylene, propylene, butene, 
isobutene, pentene and isopentene. 
The class of reactants includes olefins of 2 to 5 carbon atoms such as 
ethylene, butene, isobutene, pentene, and isopentene. Dehydrogenation of 
ethylene will produce acetylene; dehydrogenation of butene will produce 
butadiene and dehydrogenation of isopentene will produce isoprene. 
The class of reactants employed in the dehydrogenation of the invention 
includes aromatic substituted aliphatics, aryl substituted aliphatics. 
Preferably, the aliphatic group of the aryl substituted aliphatic contains 
less than four carbon atoms and more preferably more than 1 carbon atom. 
The aryl substituted aliphatic reactants embrace unsubstituted 
arylaliphatics and alkyl substituted aryl aliphatics and; similarly, each 
of the alkyls of said alkyl substituted alkylaryls contains preferably 
less than 4 carbon atoms. By way of illustration reactants such as ethyl 
benzene, diethylbenzene, ethyl toluene, and cumene are representative of 
these compounds. On dehydrogenation in accordance with the invention, 
ethyl benzene will produce styrene; ethyl toluene will produce 
methylstyrene; cumene, isopropenylbenzene; and diethylbenzene, 
divinylbenzene. 
In accordance with the invention, catalytic dehydrogenation conditions 
include pressures varying from subatmospheric, to atmospheric to greater 
than atmospheric. Preferred pressures range from 0.1 atmospheres to 
atmospheric. However, pressures up to 500 psig can be employed. The 
dehydrogenation is conducted at elevated temperatures ranging from 
400.degree. C. to 700.degree. C. and most preferably from 300.degree. C. 
to 600.degree. C. Reactor inlet H.sub.2 /feed ratios are 5 or less; even 
at reactor inlet ratios of zero (0), there will be a hydrogen partial 
pressure in the reactor because hydrogen is a bi-product of 
dehydrogenation. The liquid hourly space velocity is 0.1 to 50, preferably 
0.5 to 10. 
Dehydrogenation may be conducted in the presence or absence of purposefully 
added hydrogen and in the presence of diluents inert to conditions of the 
catalytic dehydrogenation such as nitrogen and methane. In particular, 
dehydrogenation can be advantageously conducted at low hydrogen pressure. 
Dehydrocyclization in accordance with the invention comprises contacting an 
aliphatic of at least six (6) carbon atoms with the catalytic composition 
comprising a dehydrogenation/hydrogenation metal which can be any Group 
VIII metal, preferably platinum. 
In accordance with the invention, catalytic dehydrocyclization conditions 
include pressures varying from subatmospheric, to atmospheric to greater 
than atmospheric. Preferred pressures range from 0.1 atmospheres to 
atmospheric. However, pressures up to 500 psig can be employed. The 
dehydrocyclization is conducted at elevated temperatures ranging from 
400.degree. C. to 700.degree. C. and most preferably from 300.degree. C. 
to 600.degree. C. Reactor inlet H.sub.2 /feed ratios are 5 or less; even 
at reactor inlet ratios of zero (0), there will be a hydrogen partial 
pressure in the reactor because hydrogen is a bi-product of 
dehydrogenation and dehydrocyclization. The liquid hourly space velocity 
is 0.1 to 50, preferably 0.5 to 10. 
The feedstock charge(s) to the new process can be those which are 
feedstocks for reforming, such as straightrun, thermal, or hydrocracker 
naphtha. Preferably, for high increases in the aromatic content and high 
octane numbers of the reformate, the charge to the reformer is a naphtha 
rich in C.sub.6 and C.sub.7 paraffins; these are generally difficult to 
reform selectively using conventional catalysts (such as chlorided 
Pt-alumina). Naphthas can be obtained by separating the charge into two 
fractions: a light naphtha and a heavy naphtha. Conventionally such 
separation is by distillation. The boiling range of the light naphtha is 
from about 80.degree. F. to about 250.degree. F. and the boiling range of 
the heavy naphtha will be from 250.degree. F. up to about 450.degree. F. 
The naphtha will be rich in C.sub.6 -C.sub.10 paraffins, and specifically 
C.sub.6 and C.sub.7 paraffins. In accordance with one embodiment when the 
light naphtha is reformed in accordance with the invention, the heavy 
naphtha will be processed by conventional reforming. The naphtha fractions 
may be hydrotreated prior to reforming; but hydrotreating is not 
necessarily required when using the catalyst in accordance with the 
invention. Initial hydrotreating of a hydrocarbon feed serves to convert 
sulfur, nitrogen and oxygen derivatives of hydrocarbon to hydrogen 
sulfide, ammonia, and water while depositing metal contaminant from 
hydrodecomposition of any organo-metal compounds. Where desired, 
interstage processing of the effluent from the hydrotreating zone may be 
effected. Such interstage processing may be undertaken, for example, to 
provide additional hydrogen, to add or remove heat or to withdraw a 
portion of the hydrotreated stream for treatment which need not be 
reformed. Hydrotreating of the heavy naphtha fraction may be essential, 
prior to reforming in a conventional reforming process. Suitably, the 
temperature in the hydrotreating catalyst bed will be within the 
approximate range of 550.degree. F. to 850.degree. F. The feed is 
conducted through the bed at an overall spaoe velocity between about 0.1 
and about 10 and preferably between 0.2 and about 2, with hydrogen 
initially present in the hydrotreating zone in an amount between about 
1000 and 10,000 standard cubic feet per barrel of feed, corresponding to a 
ratio of between about 2.4 and about 24 moles of hydrogen per mole of 
hydrocarbon. The catalyst may be any of the known hydrotreating catalysts. 
These include Group VIB metals such as molybdenum, chromium and tungsten 
and Group VIII metals include nickel, cobalt, palladium and platinum. 
These metal components are deposited, in the form of metals or metal 
oxides, on the indicated supports in amounts generally between about 0.1 
and about 20 weight percent. One particularly useful hydrotreating 
catalyst is a commercial catalyst known as Chevron ICR 106 which is a 
nickel-tungsten-alumina-silica-titania catalyst. 
When dehydrogenation, dehydrocyclization or reforming is undertaken over 
the catalyst in accordance with the invention, the temperature can range 
broadly from 800.degree. F. to 1100.degree. F., generally being greater 
than about 900.degree. F., preferably being 900.degree. F. (482.degree. 
C.) to 1050.degree. F.; the pressure will be from about 0 psig to 500 
psig, preferably from 0 psig to 250 psig; inlet H.sub.2 /hydrocarbon can 
be 5 or less, even zero (0) (because of hydrogen production during 
reforming, there will be a hydrogen partial pressure in the unit); while 
the LHSV (liquid hourly space velocity) can be 0.1 to 20, preferably 0.1 
to 10. 
Regeneration of the aged non-acidic microporous crystalline materials in 
combination with platinum group metals, in the absence of oxygen provides 
a catalyst, which exhibits high dehydrogenation and dehydrocyclization 
selectivity under dehydrogenation and dehydrocyclization conditions of 
paraffins in second and subsequent cycles of dehydrogenation and/or 
dehydrocyclization. Regeneration is undertaken at elevated temperatures 
and pressures, in a hydrogen atmosphere. Regeneration is undertaken when 
due to aging the yield and/or selectivity of olefin and/or aromatic 
product falls off under the dehydrogenation and/or dehydrocyclization 
conditions. Regeneration in accordance with the invention involves passing 
hydrogen over the aged catalyst, to maintain a hydrogen atmosphere, at 
elevated pressure over a programmed temperature increase. The pressure may 
be maintained from at least about 20 psig to 600 psig. The aged catalyst 
is subjected to elevated temperature from above ambient to a temperature 
up to 600.degree. C., preferably from 100.degree. C. to 600.degree. C., 
and most preferably from 300.degree. to 600.degree. C. The time duration 
can range from 0.5 to 24 hours or more. 
EXAMPLES 
Example A 
In the following experiments, isobutane dehydrogenation reactions were 
conducted using 0.75 g of 14/30 mesh catalyst in a stainless steel reactor 
at atmospheric pressure, in the absence of added hydrogen. The external 
furnace temperature was 554.degree. C. 535.degree. C. for the silica-bound 
catalyst); weight hourly space velocities were 4.8 and 8.7. Reactor 
effluents were monitored by on-line gas chromatography. 
A non-acidic Pt/Sn-ZSM-5 catalyst, containing 0.43% Pt, 1.03 % Sn, 0.67% 
Na, and only 56 ppm Al, was used to dehydrogenate isobutane to isobutene. 
The reaction was conducted at 554.degree. C. (oven temperature), 4.8 WHSV, 
in the absence of added hydrogen, and at atmospheric pressure. An 
isobutene yield of about 47% was obtained initially; however, the yield 
dropped gradually over a period of several days to below 35%. 
After eight days on stream, the catalyst was regenerated in flowing 
hydrogen at 400 psig by heating at 1.degree. C./minute to 540.degree. C., 
where it was held for 6 hours. The reaction was then resumed, and an 
isobutene yield of 47% was regained. 
Catalyst aging was again observed, with the yield dropping to 37% after 5 
days. 
The catalyst was hydrogen-regenerated a second time at 450.degree. C. and 
again full activity was restored. The isobutene yield ranged from 48% to 
33% after 4.5 days on stream. 
The catalyst was then subjected to a third regeneration, which again 
restored full catalyst activity. Dehydrogenation selectivity was as good 
or better than that observed over the fresh catalyst. The effect of these 
hydrogen regenerations is shown graphically in FIG. 1 below: 
The aging rates of the regenerated catalysts appeared to be greater than 
that of the fresh catalyst, with the triply regenerated catalyst aging at 
about twice the rate of the fresh catalyst. 
Example B 
A second set of hydrogen reactivations were performed on a more stable 
0.65% Pt/1.0% Sn-ZSM-5 catalyst (one that was air treated at 350.degree. 
C. rather than at 500.degree. C.). Hydrogen regeneration at 400 psig was 
now done at 450.degree. C. As this catalyst was more active, isobutane 
dehydrogenation was studied at 8.7 WHSV. The effect of three hydrogen 
regenerations is shown graphically in FIG. 2 below: 
Example C 
Isobutane dehydrogenation was also investigated over an iridium-impregnated 
35% silica-bound Pt/Sn-ZSM-5 catalyst. The reaction was conducted at 
535.degree. C. and 4.8 WHSV in the absence of added hydrogen. Fairly 
stable operation was observed under these conditions, with the yield of 
isobutene declining gradually from 39% to 33% over a period of 7 weeks. 
The aging rate corresponded to an isobutene yield loss of 0.11% per day. 
After seven weeks, this catalyst was regenerated in 400 psig hydrogen at 
450.degree. C. for 16 hours, and then restreamed. Full activity was 
restored; however, the aging rate appeared to double for the first two 
weeks on stream. Surprisingly, however, the aging rate decreased 
dramatically after that, with no discernible aging occurring over a period 
of four weeks. At 45 days on stream, the hydrogen-regenerated catalyst 
produced comparable isobutane yields to that obtained over the fresh 
catalyst.