CA1100474A

CA1100474A - Catalyst reduction method

Info

Publication number: CA1100474A
Application number: CA287,473A
Authority: CA
Inventors: Robert J. Houston
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1976-12-13
Filing date: 1977-09-26
Publication date: 1981-05-05
Also published as: JPS5375189A; FR2373329A1; NL7713797A; JPS5621468B2; GB1547731A; AU518149B2; NL188624C; FR2373329B1; AU3127977A; DE2754857A1; BE861065A; NL188624B; DE2754857C2

Abstract

ABSTRACT OF THE DISCLOSURE
CATALYST REDUCTION METHOD
An improved method is disclosed for reducing platinum oxide in a catalyst with hydrogen during activation or regeneration of the catalyst by maintaining the temperature of the catalyst below 700°F whenever the catalyst is contacted with a nonoxidizing atmosphere at any time prior to complete reaction of the platinum oxide with hydrogen to form elemental platinum, so that the platinum oxide is not reacted with hydrocarbon contaminants present in the nonoxidizing atmosphere.

Description

BACKGROUND OE THE INVENTION
The present invention relates to a method for reducing an oxidized platinum ca-talyst used in hydrocarbon conversion processes.
Catalysts containing platinum are well kno~m for a variety of uses.
Conventionally, the metal is dispersed on a porous, refractory support, such as alumina, silica, or the like. An acidic function is often supplied by the support, e.g., a silica-alumina mixture, or by addition of a halogen, such as fluorine or chlorine, -to the catalyst.
Platinum catalysts are used in such hydrocarbon con-version pro-cesses as naphtha reforming, isomerization of C4-C6 paraffins, aromatics alkylation, dealkylation and disproportionation, isomerization of alkylaromat-ics, hydrogenation and dehydrogenation. I-t is well known that a high platinum surface area is an important catalyst property. Various methods have been proposed foY providing high platinum surface areas in initial preparation or regeneration of these catalysts.
In addition to the platinum, the refractory support, and a halogen, if used, platinum catalysts often include one or more promoters. One partic-ularly effective catalyst, which has found use in naphtha reforming, includes platinum, rhenium and halogen on an alumina support. Such a catalyst is de-scribed, for example, in United States Patent 3,415,737.
Platinum catalysts usually become deactivated after a period of cataly-tic use. In hydrocarbon conversion operations, the catalysts -typically become fouled with a refrac-tory carbonaceous ma-terial termed coke. It is knowm to regenerate a deactiva-ted catalyst by burning the coke off it at an elevated temperature. In addition tP burning off coke, various other steps are often employed in regenerating pla-tinum catalysts, such as high temper-a-ture oxidation of the metal, ~alogen treatment, steaming, reduction wi-th hydrogen, etc.
A typical procedure used in -the in-situ regeneration of a platinum catalyst after it has become deactivated by use in a naphtha reforming process may, for example, include: (1) burning -the coke off -the ca-talyst in several stages using increasingly higher temperatures be-tween about 700F and 1100 F or higher, with successively higher molecular oxygen concentra-tions in -the regenerating atmosphere; (2) halogen treatment of the catalys-t at a tem-perature of 700F -to 1100 F to redisperse platinum and to adjust the halogen concentration in the catalyst to a desired level; and (3) treatmen-t of the catalyst with hydrogen a-t a temperature of 700F to 1100F to remove oxygen -from -the catalyst and to reduce the oxidized platinum in -the catalyst to its elemental form. One or more of such steps can also be used for activating 10 fresh platinum catalysts in-situ prior to use in a hydrocarbon conversion system.
The various regeneration steps noted above, as well as fresh cat-alyst activation steps, are normally accomplished at temperatures in the range from 700F to 1100F, usually 800F or higher. There have been, however, some suggestions in the art for accomplishing one or more of the activation or re-generation steps after or during a temperature reduction, or at a temperature below the conventional 700F minimum. For example, United Sta-tes Patent 3,617,523 discloses oxida-tion of a platinum group me-tal catalyst at a temper-ature of 500-700F in a sulfur-contaminated hydroconversion unit to avoid 20 sulfur contamination of the catalyst. United States Patent 2,968,631 dis-closes regeneration of an isomerization catalyst including platinum and nickel on a silica-alumina support by oxidation at 880-1000F, cooling to 800F in nitrogen, and reduction in hydrogen at 800F. United S-ta-tes Patent 3,937,660 discloses regeneration of an iridium-co-ntaining catalyst by oxidation of the catalys-t at 572-1112 F, purging at below 752F, and reduction with hydrogen a-t between 392F and 1022F. United Sta-tes Pa-tent 2,879,232 discloses oxida-tion of a platinum group metal catalys-t at 750-1200F, rapia cooling of the catalyst to below 860F, and reduction of the catalyst with hydrogen. United Sta-tes Patents 2,856,349 and 2~856,350 disclose regeneration of a platinum 30 catalyst by oxidation at a temperature of 900-1050 F, cooling the ca-talyst to . .

r~4 a temperature of 800-9ooF in the presence of oxygen, and then reducing the catalyst with hydrogen.
In a typical regeneration operation, most of the hydrocarbons in the conversion system are removed by purging or burn:ing. However, some traces of hydrocarbons almost invariably remain in relatively inaccessible locations in the hydrocarbon conversion system, even after high temperature oxida-tion of the catalyst bed, purging with inert gas and evacuation of the conversion system.
If a platinum-containing catalyst, in which at least a portion of the platinum is combined with oxygen, is exposed to an inert or reducing at-mosphere (as by an inert gas purge~ system evacuation or hydrogen reduction) at the elevated temperatures (above 700F) normally used for platinum catalyst regeneration, it has been found that -trace hydrocarbons in the conversion sys--tem react with the combined oxygen and pla-tinum, forming a very refractory carbon deposit on -the ca-talyst and reducing the pla-tinum. This, in turn, re-sults in an undesirable loss in the platinum surface area in the catalyst, and generally severely decreases the activity and selectivity of the catalyst.
This reaction and its harmful effect are herein referred to as "hydrocarbon reduction" of the catalyst as distinguished from hydrogen reduction of the catalyst. Likewise, during normal hydrogen reduction of oxidized platinum in a catalyst, using hydrogen at conven-tional hydrogen reduction temperatures above 700 F, any traces of hydrocarbons in the hydrogen gas used for reduc-tion can react with the oxidized platinum before hydrogen reduction has taken place, causing the same loss of surface area, selectivity and activity by hy-drocarbon reduction. For this reason, it has been necessary to employ sub-stantially pure, electrolytically generated hydrogen for hydrogen reduction of platinum-containing cataIysts to avoid deleterious hydrocarbon reduction of the platinum in the catalys-t. Electrolytic hydrogen is quite expensive as compared -to manufactured hydrogen available from normal pe-troleu~ refinery sources such as naphtha reformers or hydrogen plants, sometimes being referred to as "plant" hydrogen. It would be highly desirable to subs-titu-te plant hydrogen for electrolytic hydrogen f`or hydrogen reduction of the catalyst in catalyst activation or regeneration procedures, except that plan-t hydrogen is invariably con-taminated with at least some amount of hydrocarbons. Attempts have been made to remove hydrocarbons from COnVerSiOrl systems by one or more evacuations of the internal gases~ followed by repressuring -the system. It would be desirable to eliminate the necessity for such expensive and diffi-cultly carried-out evacuation procedures in activating and regeneratlng a platinum catalyst. The method of the presen-t invention provides a solution to the foregoing problems.
SUMMARY OF THE INVENTION
In one embodiment the present invention relates to an improvement ~`
in a process for hydrogen -treating a platinum oxide component in a cata]ys-t including the platinum oxide component and a refractory inorganic oxide com-ponent, which comprises: maintaining the catalys-t at a tempera-ture below 700F whenever the catalyst, in the presence of a hydrocarbon, is in con-tact with a gaseous atmosphere including less than 0.1 volume percent molecular oxygen un-til subs-tantially all -the platinum oxide in the catalyst is reacted with hydrogen to form elemental platinum.
In another embodiment, the present invention relates to a method for regenerating a catalyst including a platinum component and a refractory inorganic oxide component in~-situ in a hydrocarbon conversion system af-ter coke has been deposited on the catalyst by use of the catalyst in the system, which comprises the s-teps of: (a~ burning coke off the catalyst and forming platinum oxide in the cataLyst by contacting the catalyst with molecuIar ox-ygen at a temperature above 700F; (b) lowering the tempera-ture of -the result-ing platinum oxide-containing catalyst to below 700 F in the presence of a gaseous atmosphere including at least 0.1 volume percent molecular oxygen;
~c) removing substantially all molecular oxygen from contact with the catalyst at a temperature below 700F; and (d) reacting substantially al~L the platinum oxide with hydrogen to form elemental platinum by contac-ting the catalyst with a hydrogen-containing gas at a temperature below 700F.
In a still fur-ther embodimen-t, the present invention relates -to a method for reducing a catalyst with hydrogen in a hycLrocarbon conversion sys-tem, the catalyst including 0.01-10 weight percent platinum in associa-tion with a refractory support, when oxygen is combined with at least a portion of the platinum, comprising the steps of: ~a) heating the ca-talyst to a temper-ature above 700 F in the presence of a molecular oxygen-containing gas;
(b) lowering the -temperature of the catalyst to below 700F in the presence of a gaseous atmosphere including more than 0.1 volume percent molecular ox-ygen; and (c) maintaining the temperature of the catalyst below 700CF and re-moving combined oxygen from the catalyst by contacting catalyst with molecular hydrogen.
I have found that the possibility of deleterious hydrocarbon reduc-tion of a platinum catalyst can be vir-tually eliminated, regardless of the presence of traces, or even fairly large amoun-ts, of hydrocarbons in the gas-eous atmosphere in contact with the catalyst, by carrying oitt hydrogen reauc tion of the platinum catalyst according to the present invention. By main-taining the temperature of a platinum oxide-containing catalys-t ~elow 700 F
whenever the catalyst is in contact with a nonoxidizing atmosphere, the plat-inum remains in the form of the oxide, and does not undergo -the harmful hy-drocarbon reduction reaction to any substan-tial extent. When an oxidizing atmosphere is present, any hydrocarbons con-tacting the catalyst are oxidized or are burned off -the platinum surface of the catalyst if they become deposit-ed thereon. When the temperature is below 700 F, the catalyst can be safely exposed to hydrocarbons in an inert atmosphere, such as a nitrogen-rich gas, or in a reducing atmosphere, such as hydrogen. Thus, combined oxygen in the catalyst can be removed by reducing the platinum oxide with hydrogen even when the hydrogen utilized is contaminated with hydrocarbons, as long as the tem-perature is below 700 F. This hydrogen reduction may be accomplished without `i :'` .

.

the danger of undesirab]e hydrocarbon reduction of the catalyst, therebyeliminating one of the severe problems in the in-situ activation and regener-ation of platinum catalyst. Hydrocarbon-contaminated plan-t hydrogen (manu-factured hydrogen) may accordingly be used in the in~situ hydrogen reduction of platinum catalyst, as opposed to the pure, electrolytic hydrogen which was necessarily used in conven-tional regeneration and activation operations.
Moreover, the need for several evacua-tions and repressurizations of a conver-sion unlt, in order to remove trace hydrocarbons from the gaseous atmosphere in the unit, is likewise elimina-ted by the practice of the present invention.
The present invention allows platinum ca-talyst to be reduced with hydrogen during regeneration or preliminary activation in-situ in a hydro-carbon-contaminated conversion uni-t, while providing a high platinum surface area in the catalyst and providing a highly active and selec-tive catalyst after activa-tion of fresh ca-talyst or regenera-tion of used catalyst. Other obJects, embodiments and advantages of -the present invention will be apparen-t from the following detailed description of the invention.
DETAILED DESCRIPTIO~ OF THE I~VE~TIO~
The catalysts which can be treated by -this invention are those con-taining platinum. The ca-talyst includes between abou-t 0.01-5 weight percent platinum, preferably be-tween about 0.1-3 weight percent platinum. The pres-en-t method may also be used in an analogous manner, with or without modifica-tion, for hydrogen reduction of catalysts containing Group VIII metals other than platinum, particularly palladium or iridium.
The platinum is disposed on a porous, refractory carrier. The car-rier ma-terial may, for example, be a porous, inorganic oxide having a relat-ively high surface area, e.g., from 50~-500 m /g. Suitable carriers include alumina, silica, naturally occurring or synthetic crystalline or amorphous aluminosilicates, magnesia, silica-magnesia~ zirconia, silica-zi-rconia, mix-tures of any two or more of the above-men-tioned materials and similar mate-ri ~ s. Those skilled in the art will recognize that various refractory .' D4~

inorganic oxide supports are suitable for use and that the preferred type ofrefractory support employed in a given pla-tinum ca-talyst is generally dic-tated or suggested by the type of hydrocarbon conversion process in which the catalyst is -to be used.
A particularly suitable refrac-tory suppor-t for use in catalysts em-ployed in ca-talytic naphtha reforming is alumina. A preferred alumina car-rier may be prepared by treating an alpha-alumina monohydrate with a mono-basic acid, neutralizing the acid with a nitrogen base such as ammonia, shap-ing the resulting mass into a desired par-ticle form, and then drying and calcining. The platinum may be combined with the support in an~ conventionàl manner, such as by aqueous impregnation o* the particles of the carrier with a solution of the metal. Likewise, the me-tal may be combined wi-th the cat alyst by cogellation of the metal from a solution along wi-th a solution of the refractory metal. In the case of alumina, the carrier is preferably ~ol~med in-to particles of relatively small size, for example, by extruda-tion, and the particles are then calcined prior to impregnation of the pla-tim~m.
In addition to the refractory carrier and the platinum, i-t may be desirable to include a halogen in the catalyst. Preferred halogens are chlo-rine and fluorine, especially chlorine. Mixtures of halogens may also be used. The halogen may be present in an amount between 0.1 and lO weight per-cent of the weight of the total ca-talyst, with an amount of halogen between 0.5 and 3 weight percen-t being preferred when the catalyst is used in naphtha reforming. The halogen may be added to -the catalyst in any conventional man-ner, e.g.~ during forma-tion of the refractory carrier, by impregnation of the carrier, or by sublimation of a suitable halogen compound, such as aluminum chloride, onto the catalyst.
q'he catalyst may con-tain other metals. Specific met~ls which are effective promoters for platinum include iridium, zinc, germanium, tin, lead and rhenium. The promoters may be presen-t in an amount be-tween 0.~1 and 5 weight percent of the catalyst, with about 0.1-3 weight percent being the 1~

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pre-ferred range for promoter metals. The promoter me-tals may be added to the carrier in any conventional manner, as by impregnation prior -to the impregna-tion of the platinum, impregnation along with the platinum, or impregnation after the platinum. Promo-ter metals may also be added -to -the ca-talyst, e.g., by cogellation with a solution of a precursor of the re-fractory oxide used in forming the support. A particularly preferred catalyst for use with the present inven-tion is one containing 0.1-1 weight percent pla-tinum, 0.1-1 weight percent rhenium, and 0.1-5 weight percent chloride in associa-tion with an alumina carrier. Preferably, the catalyst is prepared by coimpregnation of the platinum, rheni~un, and chloride onto extruded and calcined particles of the alumina, after which the catalyst is dried and calcined.
The present invention can be used in activa-ting or conditioning ei-ther a fresh catalys-t or a ¢at~lyst which has been previously employed in a hydrocarbon conversion operation and is being regenerated for reuse. The presen-t invention is preferably used during in-si-tu treatmen-t of the catalyst in a hydrocarbon conversion unit, since the potential problem of hydrocarbon reduc-tion of the oxidized platinum in the catalyst is particularly serious during in-situ catalyst activation and regeneration in a commerical conversion system. The present invention is particularly preferred for use in in-situ activation and regeneration of a catalyst employed in a naph-tha reforming system or similar hydrocarbon hydroconversion system in which a hydrocarbon charge stream and hydrogen are mixed, heated to the desired conversion temper-a-ture, and then contacted wi-th catalyst in a series of one or more reactors.
The effluent ~rom the last reactor is cooled, and the hydrogen is then separ-ated from the hydrocarbons and at least partially recycled. Various hydro-conversion systems of this type are well ~nown to those skilled in the art, as are methods for in-situ regeneration of platinum-containing catalys-t in such systems.
The presen-t invention is used prior to and durlng hydroeen reduction of a catalyst when oxygen is combined with at least a portion of -the platinum ~ :?~.
.-- .

4'74 in the catalyst. ~he form of combination of oxygen with the platinum can in-clude either an oxide of all or a subs-tantial portion of -the platinum contain-ed in the catalyst, or else the chemisorption of oxygen on the surface of the platinum, so that the combined oxygen is only associa-ted with the surface atoms of platinum in the catalyst, forming a surface layer of platinum oxide.
The oxygen can also be combined with the platinum both by chemisorption and by substantial non-surface pla-tinum oxide forma-tion. Platinum which has been ox-idized either by substantial subsurface oxide formation or by surface chemi-sorption is subject to the problem of hydrocarbon reduc-tion, so that the present me-thod is effective with platinum after either type of oxidation, or both. Combined oxygen is oxygen bound in the catalyst either as non-surface pla-tinum oxide or by surface chemisorption to form a platinum oxide surface layer.
If the ca-talyst is fresh, the reaction of -the platinu~ w:ith oxygen takes place simply by con-tacting a molecular oxygen-containing gas with the cataIyst at a temperature of 100-1000F for a short period of time. When it :... .
is desired to oxidize the platinum in the catalyst, the concentration of ox-ygen in the gas used should be greater than 0.1 volume percent and preferably greater -than 1 volume percent.
If the catalyst has previously been used for conversion of hydro-carbons, the catalyst typically becomes contaminated with a substantial amount of coke before it is necessary to regenerate it. In such cases, it is desir-able to burn the coke off the catalyst as a first step. This may be accom-plished by contacting the catalyst with an oxygen-containing gas a-t a temper-a-ture of above 700 F, preferably above 800F, until heat evolution from the ca-talyst and/or oxygen consumption during passage of an oxygen-containing gas in contact with the catalyst have dropped to a low level, indicating that practically all coke in the catalyst has been burned. When the coke content .
in the catalyst has dropped to a low level~ e.g., less than 0.1 weight per-cen-t, the coke is sufficiently removed, and platinum in the catalyst is _ g _ ~'''~ I - .

D47~L

simultaneously oxidized. The oxida-tion or coke burnoff treatment used in catalyst regeneration may include tne use of successively higher oxygen con-centrations and successively higher temperatures, although it is preferred not to exceed a maximum tem-perature of about 950-1000F during coke burn-off.
The pressure employed in carrying out the coke burn-off is not cri-tical.
Eigher total pressures, and higher oxygen partial pressures~ result in more rapid coke burn-off and more rapid oxidation of the platinum in the catalys-t.
Thus, the total pressure and oxygen partial pressure may be adjus-ted in order to facilitate more rapid or less rapid coke burn-of-f to insure that maximum desirable temperatures are no-t exceeded.
Optionally, the catalyst may be subjected -to a halogen treatment during regeneration, preferably after completion of coke burn-off and plat-inum oxidation. The halogenation temperatures is from 700F to 1000F. The halogen may, for example, be contacted wi-th the catalyst in the form of an organic chloride vapor which is passed in contact with the catalyst in a gas~
eous atmosphere containing a-t least 0.1 volume percent oxygen, preferably at least 1 volume percent oxygen. Such a halogen treatment may aid in dispers-ing or redispersing platinum on the refractory support, providing an increased surface area for the catalytic metal in the ca-talyst. The halogen treatment may also be performed in the presence o-f nitrogen, steam, etc., if desired, in addition to -the molecular oxygen.
When -the platinum has been regenerated by high temperature oxida-tion, and optionally halogen treatment, a-t a -temperature above 700F, -the tem-perature of the catalyst is lowered to preferably to below 600CF bu-t above 300F, and particularly preferably to between 450F and 550F, while the cat-alyst is kept in the presence of an oxidizing atmosphe~re, retainlng combined oxygen in the catalyst in the platinum oxide. The molecular oxygen concen-tration in the gaseous atmosphere in contact with the oxidized catalys-t is carefully controlled during adjustment of the temperature so that the atmos-phere ~s at least 0.1 ~olume percent molecular ox~ygen, and preferably between ~l 7~

1 and 10 volume percent molecular oxygen, and particularly preferably between2 and 5 volume percent molecular oxygen. By main-taining an oxidizing atmo-sphere, as specified, during adjustment of the temperature of the catalyst to below 700F, but preferably above 300F, platinum in the ca-talyst is main-tained in an oxidized state, and trace hydrocarbons present in the regenera-tion gases contacting the catalyst do not react with the oxidized platinum in an undesirable hydrocarbon reduction reaction. If a small amount of hydro-carbon reacts with any platinum oxide during adjustment of the temperature, the pla-tinum thereby reduced is immediately reoxidized to platinum oxide by contact with oxygen in the oxidizing atmosphere surrounding -the catalyst.
Accordingly, the platinum surface area, achieved during preparation of the fresh catalyst or during regeneration by coke burn-off-platinum oxida-tion, and optional halogen trea-tment, is maintained at a high level. In catalyst regeneration procedures, the pressure of the gaseous atmosphere in con-tact with the catalyst during adJustment of the temperature after oxida-tion and halogenation) of the catalyst is not critical. When the temperature of the catalyst is lowered af-ter coke burn-off and platinum oxidation at an elevated tempera;ture above 700F in an in-situ regeneration operation, then i-t may be convenient to depressurize the conversion sys-tem a-t the same time as -the tem-pera-ture of the catalyst is being lowered. ~he tempera-ture of the ca-talyst thus preferably adjusted to below 700 F, preferably below 600F but above 300F, and particularly preferably be-tween 1~50F and 550F, in -the presence of the oxidizing atmosphere.
When platinum has been oxygen treated a-t a temperature above 700F, after the temperature of the catalyst has been adjusted to within the spec-ified range in an oxidizing atmosphere, the platinum in the catalyst is hydrogen reduced. Combined oxygen present in the catalyst, including either chemisorbed oxygen forming a surface layer of platinum oxide or oxygen in the form of a substantial amoun-t of non-surface platinum oxide, is removed from the platinum in the catalyst by contacting the catalyst with molecular ?47~

hydrogen, forming water vapor and elemental platinum. Before the hydrogen is introduced into the atmosphere in con-tact with the catalyst, the concentra-tion of molecular oxygen in the atmosphere should be lowered, i~ necessary, at least below the level at which explosive combination of hydrogen and ox-ygen would occur. Preferably the oxygen concentration in the gaseous atmo-sphere is lowered to below 0.1 volume percent, i.e., substantially all un~
combined molecular oxygen is removed from contact with the catalyst. Molec-ular oxygen in the atmosphere in contact with the catalyst may be removed from contact with the catalyst by purging the system with an inert gas, such as nitrogen, by evacuation of the system, or by any other conventional pro-cedure. Preferably the catalyst is purged with inert gas, as by passing an inert gas continuously across the catalyst until the amount of ~olecular oxygen present in the inert gas after contac-t with the catalyst is below 0.1 volume percent.
When the amount of molecular oxygen in contact with the ca-talyst is sufficiently low~ the catalyst is con-tacted with a molecular hydrogen-con-taining gas. The hydrogen-containing gas may be pure hydrogen or a mixture of hydrogen with one or more of inert or relatively inert gases, such as nitrogen or steam. According to the invention, the hydrogen used in the re-duction operation need not be electrolytic hydrogen, as found necessary inprior art regeneration operations. Electrolytic hydrogen has previously been used in regeneration because hydrogen from more economical sources i.e., man-ufac-tured hydrogen, is contaminated with hydrocarbons. When hydrocarbon-con-taminated hydrogen has been used for reducing a platinum catalyst, the hydro-carbon contaminants have reacted with oxidized p'atinum in the catalyst, re-sulting in a severe loss of platinum surface area and in lower catalyst activ-ity and selectivity when the catalyst is placed on stream. I have found that, when the temperature of the catalyst is below 700F, preferably below 600F
but above 300 F, and particularly preferably between 1~50F and 550F, the catalyst is not subject to undesirable hydrocarbon reduction in the absence , ~'~ ' ' ' ' -: ' ' . ' ' : '. ' ::: . - .:

of -the molecular oxygen-containing gases. The deleterious effects of hydro-carbon reduction of oxidized platinum in -the ca-talyst are not encountered when the present invention is employed in catalyst activation, even when the catalyst is contacted with fairly substantial concentrations of hydrocarbon contaminants in any nonoxidizing atmosphere used in the system, such as purge gases, reducing gases, or even in vacuums in evacuated catalyst-holding ves-sels. Various steps conventionally taken to remove trace hydrocarbons from conversion systems during conventional regeneration or activation operations to avoid hydrocarbon reduction of the platinum can also be eliminated from the regeneration procedures used when the method of the present invention is employed. Thus, a series of pressurizations and evacuations to remove hydro-carbons need not be carried out when the present method is used during ac-tiv-ation of fresh catalyst or regeneration.
The hydrogen content of the gas used to remove the combined oxygen from the catalyst and to reduce the platinum oxide to elemental platinum may, if desired, be increased from a low initial pressure or partial pressure up to a higher level such as the pressure desired in carrying out the hydroconver-sion process in w~hich the catalyst is used. The chemically combined oxygen in the catalyst may fairly readily be removed from the catalyst by treatment in the specified te~perature range with a gas including at least 2 volume percent hydrogen. In any case, a hydrogen partial pressure of at least 0.3 psi should be used. The required duration of the hydrogen reduction treatment may be measured by determining the water content of the hydrogen-containing gas after it has been contacted with the catalyst. When a $ubstantial amount of water is no~longer evolved from the catalyst by reaction of hydrogen and oxygen, then the combined oxygen has been substantially all removed from the catalyst and~the plat1num ln the ca-talyst has been substantially all reduced to~elem-ental platinum, so that undesirable hydrocarbon reduction of the platinum in the catalyst~will not occur, even at higher temperatures. The hydrogen reduc-tion treatment is performed while the tempera-ture of the cstalyst~i~s maintained ::~ : : :
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below 700F, preferably below 600F but above 300F, and particularly pref-erably between 450F and 550F. Thereafter, the catalys-t is preferably main-tained in contact with a hydrogen-containing atmosphere until the catalyst is to be used in a hydrocarbon conversion operation.

Tests were undertaken -to demonstrate the conditions at which hydro-carbon reduction of platinum oxide in a catalyst took place, and to demonstrate the deleterious effect of hydrocarbon reduction on the platinum surface area of a catalyst. A catalyst containing 0.3 weight percent platinum on an alum-ina carrier was reduced by heating in hydrogen at 1000 F for one hour. Oneportion of the reduced catalyst was oxidized slightly by being exposed to air at room temperature. This por-tion was labeled Catalyst A. Another portion of the catalyst was substantially oxidized by being calcined in air at 900F
and was labeled Catalyst B. Nitrogen was saturated a-t 70F with a reformed Arabian naphtha. The nitrogen used was substantially oxygen-free. The hydrocarbon-saturated nitrogen was contacted with samples of Catalysts A and B at various temperatures, as shown in Table I, each test being undertaken for one hour. In each test, the nitrogen was passed over the sample of the cat- -alyst, with the catalyst and gas being maintained at the temperature shown.
Thereafter, the carbon content and platinum surface area (by CO chemisorp-tion) of each sample were measured and folmd to be as shown in ~able I.

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The results set forth in Table I show -tha-t -the platinum surface area in the catalyst samples decreased subs-tantially as the temperature of naphtha-saturated nitrogen treatment was increased. A-t 800 and 900 F, the pla-tinum surface area was decreased -to a very low level. There was a good correlation be-tween the carbon content of each sample and the loss of plat-inum surface area in each sample. The relative loss of platinum surface area was much larger for the catalyst samples which had been substantially oxid-ized at 900 F than for the samples which had been reduced and simply exposed to room temperature air. It was noted that the loss of platinum surface area was extremely severe considering the extremely small amounts of carbon which were deposited on each of the samples in comparison with the loss of plat-inum surface area normally observed in catalysts after much larger amounts of carbon deposition in normal naphtha reforming with the same catal.yst. Thus, the type of carbon deposition on the catalyst which took place in -the inert n:itrogen atmosphere tests was felt to be particularly dele-terious -to -the ca-t-alyst, and to be at least partially a different -type of carbon inactivation than is observed with coke normally deposited on a catalyst in hydrocarbon hydroconversion operations.

In a preferred embodiment, the me-thod of the present invention was employed during an in-situ regeneration of a catalyst in a commercial naphtha reforming uni-t after the ca-talys-t had become substantially deactivated by usein naphtha reforming in the system. The ca-talys-t contained about 0.3 weight perceNt pla-tinum, about 0.3 weight percent rhenium and about o.8 weight per-cen-t chloride and had an alumina carrier. Prior -to regeneration the catalys-t contai.ned about 10 wt.% coke and had a low platinum surface area (typically

2-5 micromo1s per gram C0 chemisorption) due both to growth of metal par-ticles and to deposition of carbonaceous material. In carrying out the re-generation, the flow of naphtha feed into the unit was discontinued. The platinurn in -the catalyst was oxidi~ed and carbonaceous materials were burned '',Zqk, "
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off the catalyst by use of successively higher concentra-tions of oxygen a-t suecessively higher temperatures above 700 F. Carbon tetraehloride was then injeeted into the circulating gases -to adjust the ehlorlde eoncentration in the catalyst at a temperature above 700F. According to the invention, the tempera-ture of the eireulating oxidizing atmosphere and the catalyst was then adjusted to 500 F. The catalyst was cooled in the presence of an oxidizing atmosphere consisting of 2-3 volume percent molecular oxygen in ni-trogen at a total pressure of 100 psig. After the catalyst temperature had reached 500F, the pressure in the unit was redueed to 50 psig, and the unit was substantial-ly purged of moleeular oxygen by passing nitrogen through the unit. When -the moleeular oxygen eoncentration was less than 0.3 volume percen-t, -the catalyst was redueed by passing hydrogen through t~e unit to remove eombined oxygen from the platinum oxide in the ea-talyst and reduee the platinum to elemental platinum. The hydrogen emplo~ed in the reduetion was inexpensive plan-t hy-drogen obtained ~rom a naphtha reformer. It contained a subs-tantial concen-tration of light hydrocarbons sueh as methane and ethane. The surfaee area of the eatalyst was measured af-ter the hydrogen reduetion treatment and was found to give 13.1 mieromols per gram in a C0 chemisorption test. This indi-eated a very satisfaetory catalyst regeneration in ter~s of restoration o~
the platinum surfaee area o~ the eatalyst. When the eatalyst was returned to on-stream use in naphtha reforming, it was ~ound to be highly aetive and se-leetive, fur-ther indieating that the regener~tion was sueeessful and that hy-droearbon reduction o~ the eatalyst had not taken plaee during the regenera-tion operation.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for hydrogen treatment of a platinum oxide component of a catalyst including said platinum oxide component and a refractory inor-ganic oxide component, the improved method for maintaining the platinum sur-face area in said catalyst which comprises: maintaining said catalyst at a temperature below 700°F whenever said catalyst, in the presence of a hydro-carbon, is in contact with a gaseous atmosphere including less than 0.1 vol-ume percent molecular oxygen until substantially all said platinum oxide in said catalyst is reacted with hydrogen to form elemental platinum.

2. A method according to Claim 1 wherein said catalyst is maintained at a temperature below 600°F and above 300°F.

3. A method according to Claim 1 wherein said platinum oxide is formed by contacting molecular oxygen with said catalyst at a temperature be-tween 700°F and 1000°F.

4. A method according to Claim 1 wherein said catalyst includes 0.1 to 3 weight percent platinum and further includes 0.1 to 3 weight percent rhenium and 0.1 to 10 weight percent halogen.

5. A method according to Claim 4 wherein a gas including a halogen and more than 0.1 weight percent molecular oxygen is contacted wi-th said cat-alyst before said hydrogen treatment.

6. A method according to Claim 1 wherein manufactured hydrogen con-taminated with a hydrocarbon is employed in said hydrogen treatment.

7. A method according to claim 1 wherein said hydrogen treatment is performed in situ in a hydrocarbon conversion system.

8. A method according to claim 7 wherein said catalyst is hydrogen treated after having coke deposited thereon in use in said system and having substantially all said coke burned off by treatment with molecular oxygen at a temperature above 700 F.

9. A method according to claim 1 wherein the temperature of said cata-lyst is maintained between 450 F and 550 F

10. A method for reducing a catalyst with hydrogen in a hydrocarbon conversion system, said catalyst including 0.01 to 10 weight percent platinum in association with a refractory support, when oxygen is combined with at least a portion of said platinum, comprising the steps of:
(a) adjusting the temperature of said catalyst to between 300°F
and 700°F in the presence of a gaseous atmosphere including more than 0.1 volume percent molecular oxygen; and (b) maintaining the temperature of said catalyst between 300°F and 700°F while said catalyst is in the presence of hydrocarbons and removing combined oxygen from said catalyst by contacting said catalyst with molecular hydrogen.

11. A method for regenerating a catalyst including platinum and a refractory inorganic oxide in situ in a hydrocarbon conversion system after coke has been deposited on said catalyst by use of said catalyst in said system, which comprises the steps of:
(a) burning coke off said catalyst and forming platinum oxide in said catalyst by contacting said catalyst with molecular oxygen at a tempera-ture above 700°F;
(b) lowering the temperature of said catalyst to below 700°F in the presence of a gaseous atmosphere including at least 0.1 volume percent mole-cular oxygen;
(c) removing substantially all uncombined molecular oxygen from contact with said catalyst while maintaining said catalyst at a temperature below 700°F while said catalyst is in the presence of hydrocarbons; and (d) reacting substantially all said platinum oxide with hydrogen to form elemental platinum by contacting said catalyst with hydrogen at a temperature below 700 F when said catalyst is in the presence of hydrocarbons.

12. A method according to claim 11 wherein manufactured hydrogen com-taminated with a hydrocarbon is employed in Step (d).

13. A method according to claim 11 wherein uncombined molecular oxygen is removed from contact with said catalyst in Step (c) by purging said cata-lyst with an inert gas.

14. A method according to claim 11 wherein uncombined molecular oxygen is removed from contact with said catalyst in Step (c) by evacuating a vessel containing said catalyst.