A PROCESS FOR REACTIVATING IRIDIUM-CONTAINING CATALYSTS

Abstract: The invention concerns a process for reactivating an agglomerated catalyst containing metallic iridium compris­ ing the steps of: (a) pretreating the catalyst by contact with a substantial­ ly elemental oxygen-free atmosphere comprising a halide-­ providing compound at an elevated temperature to provide a catalyst comprising about 1.3 weight percent, halide based on the coke-free dry, catalyst; and (b) redispersing the metallic iridium from step (a) by contact at an elevated temperature with an atmosphere comprising a redspersing gas selected from elemental halogen, elemental oxygen, a mixture of hydrogen halide and elemental oxygen and mixtures thereof. Further embodiments are described including a prefer­ red one wherein the redispersing gas is a mixture of hydrogen halide and elemental oxygen.

Description: This invention relates to a process for reactivating an agglomerated iridium-containing catalyst involving the sequential steps of reducing agglomerated iridium oxides if present on the catalyst surface to the free metal, pretreating the catalyst surface with a halide-providing compound, preferably hydrogen chloride in the absence of elemental oxygen, and redispersing the iridium metal by contacting with an atmosphere containing a redispersing gas selected from elemental halogen, elemental oxygen, a mixture of hydrogen halide and oxygen, or mixture thereof. Preferably, an oxygen source is also used in the redispersion step. It has been found that iridium-containing catalysts containing agglomerated metallic and/or iridium oxides can be efficiently redispersed and reactivated by the use of a halide pretreatment prior to a redispersion step, both steps following decoking and reduction of the iridium oxides, if present. The halide pretreatment step is conducted with two limitations, (1) that about 1.3 weight percent or greater halide and, preferably 1.4 to 2.5 weight percent halide, taken as the coke-free, dry catalyst, and most preferably saturated with halide under the conditions used, is present on the catalyst surface after the pretreatment and maintained at or above this level up to and during the subsequent redispersion step with elemental halogen or a mixture of hydrogen halide and elemental oxygen, and (2) that during the halide pretreatment step, no elemental oxygen is present in the feedstream or is generated in situ. If this halide level is not maintained during subsequent redispersion and if elemental oxygen is present during the pretrNeatment, then substantially lower redispersion values will be obtained with concomitant decrease in catalyst metal surface area and activity. The present process is applicable to a wide variety of iridium-containing catalysts and particularly to reforming catalysts employing platinum-iridium on alumina, which are completely or partially decoked. Generally, halide-producing compounds are used in the pretreatment step including organic halides and hydrogen halides with gaseous hydrogen chloride being the preferred hydrogen halide-generating compound used in the pretreatment and chloride levels of about 1.3 weight percent of catalyst and above, on the catalyst surface are necessary to ensure effective redispersion. The halide weight percent is expressed on the basis of dry, coke-free catalyst. The pretreatment step is generally conducted in the temperature range of about 250 to 6000C, and the halide weight percentage can be monitored, for example, by X-ray fluorescence versus known standards. Generally, with the exception of very severely coked and agglomerated iridium-containing catalyst, the subject process is capable of producing substantially decoked, highly redispersed, iridium-containing catalyst in a one-cycle treatment. In accordance with this invention there is provided a process for reactivating an agglomerated catalyst containing metallic iridium which comprises the steps of: (a) pretreating the catalyst by contact with a substantially elemental oxygen-free atmosphere comprising a halide-providing compound at an elevated temperature to provide a catalyst comprising about 1.3 weight percent or greater halide based on the coke-free dry, catalyst; and (b) redispersing the metallic iridium from step (a) by contact at an elevated temperature with an atmosphere comprising a redispersing gas selected from - - elemental halogen, elemental oxygen, a mixture of hydrogen halide and elemental oxygen, and mixtures thereof. A preferred embodiment is wherein said redispersing gas in step (b) is a mixture of hydrogen halide and elemental oxygen. Further provided is an embodiment using a halogen redispersion step in step (b) comprising elemental halogen at elevated temperature, at a halogen mass flow rate of less than about one gram of elemental halogen per 100 grams of catalyst per hour. Also provided is an embodiment of the present process for reactivating agglomerated catalysts containing metallic iridium value comprising the steps of: (a) pretreating said catalyst be contact with a substantially elemental oxygen-free atmosphere comprising a halide-generating compound at an elevated temperature to provide about 1.6 weight percent and above, halide to the catalyst, taken as the coke-free, dry catalyst; and (b) redispersing the metallic iridium from step (a) by contact at an elevated temperature with an atmosphere of elemental oxygen. A further embodiment of the subject process for reactivating coked iridium-containing catalysts comprising the sequential steps prior to step (b) of: (1) partially decoking said catalyst in an oxygen-containing atmosphere at a temperature below about 4300C for a sufficient time so that the remaining catalyst coke level is less than 1 weight percent and the iridium agglomeration on said catalyst is less than about 50 percent; (2) reducing said catalyst from step (1) by contact with a reducing atmosphere at elevated temperature for a sufficient time to substantially convert said iridium value to metallic iridium; ; (a) pretreating said catalyst from step (2) by contact with an elemental oxygen-free atmosphere comprising a halide-providing compound at elevated temperature for a sufficient time to provide the catalyst with about 1.3 weight percent or above halide taken as the coke-free, dry catalyst; and (b) redispersing the metallic iridium catalyst from step (a) by contact with an atmosphere comprising elemental halogen and water at a temperature of about 4800C or above for a time sufficient to substantially complete decoking and substantially redisperse metallic iridium. A still further embodiment provided is a process for reactivating partially or completely decoked agglomerated iridium-containing catalysts, said catalysts being in series, said process further comprising the step prior to step (b) of: (1) reducing a first said catalyst by contact with a reducing atmosphere at elevated temperature for a sufficient time to substantially convert iridium value to metallic iridium; and in step (a) pretreating said catalyst from step (1) by contact with an elemental oxygen-free atmosphere comprising a halide-providing compound at elevated temperature for a sufficient time to provide the cata lyst with about 1.3 weight percent b r above halide, taken as the coke-free, dry material; and in step (b) redispersing the iridium metal from step (a) by contact with an atmosphere comprising elemental halogen and water vapor at a temperature of about 4800C or above, for a time sufficient to substantially complete decoking and to substantially redisperse metallic iridium; and still further comprising in step (c) contacting a second said catalyst, in series, with the effluent halogen/water vapor atmosphere from step (b) to partially decoke said second catalyst. A particularly preferred embodiment is the process for reactivating partially or completely decoked agglomerated platinum-iridium on alumina catalyst containing platinum and iridium oxides further comprising the step prior to step (a) of: (1) contacting said agglomerated catalyst with a hydrogen atmosphere at a temperature in the range of about 300 to 5400C and a pressure of about 0.1 to 2.0 MPa for a sufficient time to substantially convert said oxides of platinum and iridium to the respective metals; and in step (a) pretreating the catalyst from step (1) by contact with an elemental oxygen-free atmosphere comprising hydrogen chloride at a temperature in the range of about 300 to 5400C and a pressure of about 0.1 to 2.0 MPa to saturate the catalyst with chloride; and in step (b) redispersing the metallic platinum and iridium from step (a) by contact with an atmosphere comprising hydrogen chloride and elemental oxygen in an oxygen/hydrogen chloride volume ratio of about 4:1 to 20:1, at a temperature in the range of about 500 to 5400C for a sufficient time to effect about a 75 to 100 percent redispersion of both metallic platinum and iridium. Another further einbodiment of the process is where the agglomerated catalyst further initially contains iridium oxide which is contacted with a reducing atmosphere at elevated temperature to substantially convert said iridium oxide to metallic iridium prior to step (a). The novel process of the present invention includes a halide pretreatment step, prior to a redispersion step, which enhances the potential of the process for mono-cycle reactivation/redispersion and eliminates the need as practised in the prior art, for rigorous, extended multi-cycle hydrogen/halogen treatment to achieve high redispersion values. It has been observed that treating a catalyst, which is low in halide content with halogen in a redispersion step without the halide pretreatment, results in the generation of water and oxygen. The generated oxygen moves through the catalyst bed ahead of the halogen "wave". Minimal or only partial redispersion is obtained. However, halide pretreatment prior to halogen redispersion, results in an increase in catalyst halide without the generation of oxygen even though water is being produced. A subsequent halogen treatment of the catalyst, for example, results in excellent redispersion. Furthermore, exposing the halide pretreated catalyst to oxygen during the halogen redispersion step also leads to excellent redispersion. It appears that successful redispersion in the process can be achieved-by the elimination of oxygen exposure of the reduced catalyst when the catalyst halide level is low. Thus, processes which provide the means of upgrading the catalyst halide level, without the release of oxygen before the halogen redispersion step or bring about the elimination of oxygen during the halogen redispersion step, will result in successful redispersion. Catalysts which can be treated by the subject process include generally, iridium-containing catalysts, with and without co-catalysts, preferably being supported. Other metallic co-catalysts, which can be present with iridium, which are applicable in the process include metals such, for example, as platinum, rhodium, rhenium, palladium mixtures thereof and the like. The metals can be present in bimetallic, trimetallic combinations and higher combinations, as alloys or physical mixtures on the same support particles or where the metals are individually present on separate support particles. Preferred metal combinations in the catalyst for treatment by the subject process are platinum-iridium, and platinumiridium-rhenium. Tow or more catalysts in series can be treated by the sub3ect process. The catalyst can also contain non-metallic promoters, for example sulphur or selenium or their compounds, to moderate hydrocracking activity in the reforming process. The metals can be supported on a suitable support, which is conventional, with the proviso that the support is stable during the pretreatment process and does not undergo any deleterious reactions. Representative examples include silica, zeolites, alumina, silica-alumina, zirconia, alumina-zirconia, mixtures thereof, and the like. In general, the active metallic components, if supported, are present in an amount of preferably up to about 10 weight percent of the supported catalysts. A preferred catalyst which can be reactivated in the process is agglomerated platinum-iridium, preferably supported on alumina. By the term, "agglomerated catalysts", as used herein, is meant a supported or unsupported catalyst containing metallic iridium singly, or in combination with other metals described herein, in the agglomerated state, sufficient to reduce the catalytic activity of the metal catalyst. The agglomerated metal, e.g., metallic iridium, can be present due to the result of oxygen burn-off of coke deposits producing agglomerated iridium oxide which then must be reduced to metallic iridium by hydrogen gas. Also, hydrogen stripping at high temperature, preferably about 450 to 600 C, will result in partial removal of coke deposits and leave the agglomerated iridium in an metallic state. The metallic iridium in the agglomerated catalyst will undergo effective redispersion by the process described herein. Where the catalyst additionally. contains iridium oxide, a hydrogen reducing step is necessary to convert the iridium oxide to metallic iridium prior to redispersion. The agglomerated metallic iridium-containing catalysts operable in the process can be completely or partially decoked as described above by separate oxygen or hydrogen treat steps or not decoked at all, but simply removed from an on-stream process, e.g., reforming in the presence of hydrogen gas at elevated temperature and subjected to the described process herein. Agglomerated, coked catalysts are usually industrially decoked by an oxygen burn-off of carbon deposits. Generally, a typical used catalyst from industrial operation may contain up to about 6 weight % of carbon deposits and may be agglomerated after the decoking step up to about a 100% extent as evidenced by X-ray diffraction. Generally, depending on the conditions used in the coke burn, carbon deposits remaining may be present in about 0.05 to 1.0 weight percent of the catalyst, taken as the dry catalyst. In general, the agglomerates may be greater than about 50 and up to about 100 8 and greater in crystallite size. Decoking of the catalyst may be conducted under a variety of conditions, but is generally conducted by heating in an atmosphere containing 0.01 to 10 volume % 2 at a temperature of about 400 to 5500C, to remove surface and embedded carbon deposits, and particularly "active" carbon deposits which can react with halogen during the redispersion step to form halogenated species which are not readily removed from the catalyst surface. Generally, about 60-100 weight percent of carbon depos its can be removed in the decoking step. For example, USP 3,904,510 describes a typical procedure employed in decoking. As an optional first step of the subject process, a low temperature partial decoking of the catalyst can be conducted by heating the spent catalyst in an atmosphere containing less than 1.0 volume percent oxygen and preferably less than 0.5 volume percent, at a temperature of below -about 4300C preferably in the range of about 375 to 4300C to remove surface and embedded carbon deposits and particularly "active" carbon deposits which can react with halogen during the redispersion step to form halogenated species which are not readily removed from the catalyst surface. Generally, about 0.3 to 0.8 weight percent of carbon deposits are present after:the decoking step and metal iridium agglomeration is present in about 50 numerical percent or less. The subject process is applicable to a wide range of agglomerated catalysts containing varying amounts of remaining carbon deposits, different degrees of agglomeration, varying particle size ranges and varying impurities. A second optional step in the present process is wherein said partially or completely decoked agglomerated catalyst is treated with a reducing atmosphere, generally comprising hydrogen gas to reduce primarily metal oxides and oxide layers which may be present on agglomerated metallic iridium particles, formed during decoking, and as a further aid in removing residual active carbon deposits from the decoking step. If no metallic oxides are present, then the reduction step, as described herein, is not mandatory. However, if metallic oxides are present, the reduction step must be conducted in order to achieve high values of redisper sion. Other reducing or inert gases may also be present including nitrogen, helium and the like. The reducing step is generally conducted by contacting the catalyst at an elevated temperature generally in the range of about 250 to 6000C, preferably about 300 to 5400C in a reducing atmosphere comprising above about one volume % hydrogen gas or above, for a time to substantially reduce metal oxides present to the free metal as evidenced by the absence of metal oxide lines and the appearance of iridium metal lines in the X-ray diffraction pattern. Larger and smaller volume percentages of hydrogen can also be effectively used. X-ray diffraction patterns taken on fresh iridium-containing catalysts show no lines corresponding to any metal component, which indicates that the metal components are present in very small particle sizes, less than about 50 i. X-ray diffraction patterns as taken on the same catalysts used in reforming, from which coke has been burned in numerous cycles of use, generally show distinct metal lines which indicate highly agglomerated metal particles, of about 10 to 100 weight percent agglomeration of crystallites of about 100 i and greater. Thus, X-ray diffraction is a useful and convenient technique for measuring the extent of agglomeration, reduction and redispersion of the catalyst in the subject process. Preferred conditions in the reducing step are the use of hydrogen as the reducing gas in a reducing atmosphere comprising essentially hydrogen, at a volume concentration of 0.05 to 5 volume percent and a pressure of about 0.1 to 2.0 MPa, and an inert gas carrier such as nitrogen or helium, particularly preferred at a temperature of about 300 to 5400C for a time sufficient to achieve a substantial reduction of the iridium oxide and other metal oxide to the free metals. By the term "substantially reduce" is meant a reduction in the numerical amount of iridium oxides present by about 75-100% and preferably about 90-100%. Generally, time requirements for the reduction will be in the range from about one to several hours depending on the process conditions. Shorter and longer times are also applicable. Following the reduction step, if performed, the partially or completely decoked-reduced catalyst is then subjected to halide pretreatment with a halideproviding compound. By the term "halide-providing compound" is meant a compound containing ionically or covalently bound halogen which, under the process conditions, can release the halogen in halide form, preferably as hydrogen chloride, to the catalyst surface. Representative examples include haloorgano compounds and preferably hydrogen halides. Haloorgano compounds include chlorocarbons such as carbon tetrachloride, methylene chloride, chloroform, methyl chloride, 1,2dichloroethane, hexachloroethane, mixtures thereof, and the like. When using haloorgano compounds, hydrogen, in a large excess over the stoichiometric amount, must also be used to convert the haloorgano compound to a hydrogen halide. The hydrogen halides can be hydrogen fluoride, hydrogen chloride, hydrogen bromide or hydrogen iodide. Preferably hydrogen chloride is the halide-generating compound used in the process. The atmosphere contacting the catalyst in this step can contain other inert gases, e.g., nitrogen and the like, and also including water vapor for more uniform distribution of halide on the catalyst surface prior to the halogenation treatment, and also preferably hydrogen gas or reducing gas in an amount of about 1-2 volume percent, to ensure that the reduced catalyst remains in the reduced state during hydrogen halide pretreatment. It is essential that the atmosphere be substantially elemental oxygen-free during the halide pretreatment. Within this context, the halide feedstream should also preferably be elemental halogen-free since it is believed that elemental halogen reacts with surface hydroxyl groups to generate elemental oxygen. However, if chlorine is an impurity in the pretreating step gaseous mixture, then a small amount of hydrogen gas should be added to insure the absence of elemental oxygen. The temperature of the halide pretreatment is generally conducted in the range of about 250 to 6000C and preferably about 300 to 5400C, and the halide providing compound, at the above-identified temperature, is contacted with the catalyst in a gaseous stream until about 1.3 weight percent halide or - above, is provided to the catalyst, as detected, for example, by X-ray fluorescence. Preferably, the catalyst is pretreated to a range of about 1.4 to 2.5 weight percent halide, or higher, and most preferably up to saturation by halide of the. catalyst surface under the process conditions. As described hereinabove, the weight percentage of halide provided to the catalyst is taken as about 1.3 weight percent .. or above, said catalyst taken on a dry and coke-free basis. Where the catalyst has been extensively used in commercial processes having a lower surface area and catalytic activity as a result of this continued use, a minimum weight percentage of about one percent halide is reasonably believed to be effective in promoting high redispersion values in the subject process. For example, fresh catalysts having BET surface areas of 180 m2/9 or higher will require 1.3 weight percent halide or above. Used catalysts having surface areas of about 100-180 m2/g will generally require a minimum of 1-1.3 weight percent halide prior to redispersion. However, an exact minimum value can't be stated for a commercial spent catalyst due to large variances in surface area, coke deposits, impurities and poisons present, and the like. One skilled in the art, however, will be able to utilize this disclosure successfully for efficient redispersion. It is important that the halide content be maintained up to the halogen redispersion treatment. If a "purge" of hydrogen, nitrogen, water, mixtures thereof, or other materials is used subsequent to the halide pretreatment, then such purge or contacting step should not reduce the halide level to below about 1.3 weight percent. If this happens, then the halide pretreatment should again be conducted to ensure about 1.3 weight percent halide being present. This is particularly true in cases where multicycle treatment may be necessary in which the weight percent of halide present on the catalyst must be replenished again to about 1.3 weight percent or above, prior to each halogen redispersion treatment. In the case where the redispersion step is to be carried out with elemental oxygen, the catalyst is contacted with the halide-containing gaseous stream until about 1.6 weight percent or above halide is provided to the catalyst, as detected, fpr example, by X-ray fluorescence. Preferably, the catalyst is pretreated to a range of about 1.7 to 2.5 weight percent halide, or higher, and most preferably up to saturation by halide of the catalyst surface under the process conditions. The halide pretreatment is conducted for sufficient time to achieve a halide loading as described above. In practice, a fast flowing stream of preferably hydrogen chloride is contacted with the catalyst up to and slightly beyond breakthrough. By the term "breakthrough" is meant the first visible detection by an analytical method such as, for example, the color change of an acid-base indicator, e.g., phenolphthalein. Halide pretreatment is conducted to. breakthrough to achieve desired halide loading of the catalyst and also to ensure a uniform distribution of halide over the entire length of the catalyst bed to prevent "halide gradients" which can lead to non-uniform redispersion. In general, water vapor present in the halide feedstream will tend to lower the halide loading slightly below that compared to a dry halide application, by approximately about 0.4 weight percent, but generally results in a more uniform halide distribution. Thus, saturation by dry HCL of a-coke-free, dry catalyst will result in up to about a 2.8 weight percent halide loading, whereas saturation with a wet stream of HCL will result in up to about 2.4 weight percent, or even slightly lower, halide loading. Time required for the halide pretreatment will, of course, be dependent on many factors including flowrate, hydrogen halide gaseous concentrations, amount of catalyst, and can be desirably adjusted, for example, to run for about 1 to 3 hours per catalyst regeneration in general. Concentration of hydrogen halide can be from 0.05 to about 5 volume percent, or higher, in the feedstream, which can be at a total pressure of about 0.1 to 2 MPa. Higher and lower values of both variables can also be used effectively. Following the halide pretreatment step, the catalyst is then subjected to a redispersion step by contacting the catalyst with an atmosphere comprising a redispersing gas selected from elemental halogen, elemental oxygen, a mixture of hydrogen halide and elemental oxygen, or mixture thereof. Although it is not mandatory, it is highly preferable to employ an oxygen source, such as water vapor or elemental oxygen to enhance the redispersion step. In the halogen redispersion step, elemental halogen gases that are applicable are fluorine, chlorine, bromine and iodine, with chlorine being a preferred embodiment. The halogen redispersion is generally carried out at a temperature of about 450 to 6000C and preferably about 500 to 5400C. At this temperature, the gaseous halogen atmosphere, industrially, is generally run at a flow rate over the surface of the catalyst of about 1.1 to 4.4 grams halogen or higher/100 grams catalyst/hour, said catalyst taken on the same basis as described in the hydrogen halide pretreatment, to achieve rapid halogen contact with the catalyst surface. Also, in a further embodiment, the halogen gaseous atmosphere is-passed at a reduced mass flow rate, over the surface of the catalyst at a mass flow rate of about 1 grams or less, halogen per 100 grams catalyst per hour, in the range of about 0.05 to 1.0 gram halogen per 100 grams catalyst per hour and preferably about 0.3 grams halogen per 100 grams catalyst per hour, and particularly preferred about 0.1 gram halogen per 100 grams catalyst per hour, said catalyst taken as dry and coke-free. By carrying out a reduced halogen mass flow rate of the subject process, the effluent chlorine gas is generally decreased about ten-fold, and preferably about one hundred-fold or more, resulting in a significant decrease in corrosion of downstream equipment and a decrease in halogen scrubbing equipment. In a preferred embodiment, following the halide pretreatment step, the catalyst can alternatively be subjected to a hydrogen halide/oxygen redispersion step by contacting the catalyst with a mixture of hydrogen halide and oxygen. Hydrogen halide gases applicable are hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide with hydrogen chloride being a preferred embodiment. The redispersion step is generally carried out at the same temperature used for the halogen redispersion step being of about 450 to 6000C and preferably about 500 to 5400C. The hydrogen halide/oxygen atmosphere in the redispersion generally contains oxygen/hydrogen halide in a volume ratio of about 1:5 to 100:1, preferably about 2:1 to 60:1, and most preferably about 4:1 to 20:1. The elemental oxygen also acts to remove residual carbon deposits from the decoking step. However, the presence of oxygen is necessary in the metal redispersion process. The concentration of hydrogen halide in the feedstream can be from about 0.05 to 5 volume percent, or higher, which can be at a total pressure of about 0.1 to 2.0 MPa. Higher and lower values of both variables can also be used effectively. In a further embodiment, following the halide pretreatment step, the partially or completely decoked and reduced catalyst can alternatively be subjected to the redispersion process by contacting the catalyst with a gaseous stream consisting essentially of elemental oxygen. This redispersion step is carried out at the same temperature as for halogen redispersion of about 450 to 6000C and preferably about 500 to 5400C, At this temperature, the oxygen atmosphere is usually run at a slow flow rate over the surface of the catalyst at about a space velocity of up to about 11 v/v/hr., which will not reduce the catalyst halide level below about 1.6 weight percent of said catalyst. A preferred space velocity is in the range of about 2 to 8 v/v/hr. and, particularly preferred about 2 to 6 v/v/hr. The oxygen redispersion can also be accomplished under static conditions wherein the oxygen gas is contacted with the catalyst in a closed catalyst container. Oxygen redispersion under static conditions, i.e. in a closed container, can be conducted by pressuredepressure cycles. After the halide pretreatment, the reactor is pressurized with diluted oxygen up to about 3.0 MPa and preferably about 1 to 2 MPa in the closed container. The pressure is then slowly decreased in about one-half hour, or longer, down to about one atmosphere and then pressurised back to 1 to 2 MPa. This cycle may be repeated several times. The oxygen atmosphere may also contain inert gases as carrier gases but preferably is dry with no substantial amount of water vapor being present. r The concentration of elemental oxygen in the gaseous redispersion feedstream is from 0.05 to 100 volume percent, preferably 0.2 to 50 volume percent and most preferred being 4 to 21 volume percent. A particularly preferred gaseous stream for use in the redispersion is air. In the embodiment employing a low temperature decoking step, following the halide pretreatment step, the partially decoked, reduced catalyst is then subjected to a halogen redispersion step by contacting the catalyst with a stream comprising a mixture of elemental halogen gas and water at elevated temperature. Elemental halogen gases applicable are fluorine, chlorine, bromine and iodine, with chlorine being a preferred embodiment. The halogen/water redispersion step is generally carried out at a temperature of about 480 to 6000C and preferably about 500 to 5400C. The elemental halogen and water are present in the redispersion feed stream in a halogen/water volume ratio of about 0.2 to 5 and preferably 0.5 to 2 at elevated temperature, the water vapor is generally present mainly as steam. The halogen/water atmosphere may also contain inert gases such as nitrogen or helium as carrier gases. In another embodiment, it has been found that iridium-containing catalysts, in series, can be efficiently and effectively redispersed and reactivated by the use of a reduction step followed by a halide pretreatment prior to an elemental halogen redispersion step. The redispersion step is conducted with a mixture of elemental halogen and water vapor, as described hereinabove, in order to complete the decoking of the catalyst surface. The effluent chlorine/watertis then delivered to a second spent catalyst, in series, to initiate a second redispersion cycle. The effluent halogen/water stream at elevated temperature from the first catalyst reactor is directed into a subsequent reactor chamber containing a second catalyst, in series, as described herein. A sufficient amount of chlorine/water effluent is contacted with the second catalyst to provide about 1.3 weight percent or higher chloride to the catalyst prior to the coke burn. This acts as an aid in inhibiting metal agglomeration during the oxygen-atmosphere coke-burn, and functions as a means of reducing the amount of hydrogen chloride needed in the pretreatment step. It also serves as a means for partially decoking the catalyst surface prior to the coke burn. The temperature of the second catalyst during contacting with the halogen/water treatment is about 480 to 5400C. The gaseous redispersing atmosphere may also contain inert gases such as nitrogen or helium as carrier gases carbon dioxide from combustion processes. Water vapor as an oxygen source and for corrosion inhibition can also be present and if present is in an amount of about 0.05 to 2 volume percent. As described above the gaseous halogen redispersion atmosphere can also contain elemental oxygen as a redispersion aid and if present, is present in an amount of about 0.05 to 25 volume percent. Preferably, elemental oxygen is present in a concentration of about 0.2 to 21 volume percent. Preferred is wherein elemental halogen and elemental oxygen are present in a volume ratio of about 0.05 to 10, respectively, and a particularly preferred range is 0.2 to 5 v/v. The presence of elemental oxygen also serves as an aid in removing small quantities of carbon deposits which may remain after the initial decoking step. Redispersion is generally conducted until halide or oxygen breakthrough occurs, as evidenced or detected, for example, by a starch-iodide indicator or by an oxygen analyzer. Generally, this requires about 0.5 to 2 hours of treatment for used catalyst, which depends upon flowrate, halogen or oxygen concentration in the feedstream, and amount of catalyst. Generally, however, slightly longer times of halogen treatment are required for substantially complete redispersion as evidenced by the absence of crystalline metal or metal oxide lines in the X-ray diffraction patterns. Preferably a time of about 30 to 90 minutes past breakthrough, i.e., substantially past breakthrough, is necessary for substantially complete redispersion. Operation past breakthrough of the redispersing gaseous atmosphere is preferred to avoid redispersion gradients along the catalyst bed of redispersed iridium metal. Where gradients are present, usually redispersion levels of iridium metal are high at the front part (entrance) of the reactor but decrease towards the tail (exit) of the reactor. By carrying out the process described herein substantially complete redispersions of iridium-containing catalysts have been achieved, as described in the following Examples, and particularly those of platinumiridium on alumina used in hydrocarbon reforming operations. In the latter case, 75 to 100 percent redispersion of both the platinum and iridium agglomerated metals have been achieved in the process. The number of cycles necessary should preferably be one. However, in certain cases such as where minimum halogen treatment past breakthrough times are desired, multi-cycle treatment may prove necessary with concomitant need for additional pretreatment steps, as described hereinabove. By the term "substantially complete redispersion" as used herein, is meant redispersion values, as determined by X-ray diffraction, of greater than about 55 numerical percent and preferably about 75 to 100 numerical percent of the iridium on the catalyst surface, also including other metals where present. Apparatus useful for carrying out the subject process will be conventional in the art and whether operating on a laboratory scale, pilot plant or full commercial plant scale, the apparatus will be obvious to one skilled in the art. In practice, following successful redispersion of iridium on the catalyst surface, a reduction of halide to about 1.0 weight percent is carried out prior to the actual reforming process since excess halide, at this stage, leads to cracking of the liquid hydrocarbon fraction to undesirably smaller hydrocarbon fragments. This reduction can be accomplished by a wet hydrogen stream, for example, which also serves to convert all of the metal species present after redispersion to the metallic state prior to use in a reforming process. The following examples are illustrative of the present invention. EXAMPLE 1 Into a quartz, tubular, horizontal reactor was charged about 60 grams of a coke-free platinum-iridium on alumina catalyst, wherein 87% of the iridium was agglomerated (BET surface area of 200 m2/g). It contained 0.3 wt. % iridium and 0.3 wt. % platinum, based on the total weight of the catalyst. The catalyst was divided into three approximately equal sections with quartz wool plugs as spacers between the sections. The catalyst in section 1 was at the entry of the reactor and the catalyst in section 3 was at the reactor exit. The chloride level on this catalyst was 0.67 wt. %, as determined by x-ray fluorescence. The catalyst was treated with a gaseous mixture of 20% hydrogen in helium at one atmosphere for 2 hours at 5240C, whereby substantially all of the iridium oxide was reduced to metallic iridium, as evidenced by the absence of the X-ray diffraction line at 28.05 degrees (29)- ascribed to IrO2. The hydrogen was purged from the catalyst bed with helium. The catalyst was then treated with a gaseous mixture of 1 volume percent hydrogen chloride and 1.4 volume percent water in helium at a temperature of about 5240C, until the exit HC1 gas concentration was equal to that of the inlet. The e catalyst was then treated with a gaseous mixture of 1 vol. % chlorine and 1.4 vol. % water in helium carrier gas at 524oC. The purpose for the presence of water was to minimize ferrous metal corrosion in the apparatus. The chlorine and water mixture treatment was discontinued after about 20 minutes when the chlorine concentration in the exit gas reached a steady state concentration. A dynamic gas chromatograph technique was developed to analyze the gas phase composition at the exit of the reactor as the redispersion process proceeded. It was observed that elemental oxygen was not observed in the exit gas until shortly before the detection of chlorine. By contrast, in a related run where HC1 pretreatment was not conducted prior to the chlorine redispersion (as in Example lA), before chlorine was detected in the exit gas, oxygen appeared shortly after the introduction of chlorine. The results for Example 1 are listed below in Table I under abbreviated columns for "8 Iridium Agglomeration", "% IrO2 Agglomeration", "% Total Agglomeration" and "8 Redispersion", respectively, TBHB in the Table is the abbreviation for "Time Beyond Halogen Breakthrough". The symbol "I" represents "initial value" and the terms S-1, S-2 and S-3 represent values obtained after treatment for the catalyst in the first, second and third sections of the catalyst bed. The first section represents the entry section, and the third, the exit region. The agglomerated catalyst described above was treated substantially the same in a related run except that before the. introduction of gaseous chlorine into the catalyst bed to effect redispersion, the catalyst was not contacted with a gaseous mixture of hydrogen chloride and water in helium. In the chlorine redispersion step, the chlorine and water mixture treatment was discontinued after about 55 minutes when the chlorine concentration in the exit gas reached a steady state concentration. The results are given in the Table as Example IA. As is seen from comparing the data of Examples 1 and 1A, about 4 times higher metal redispersion was obtained -in the reactivation process consisting of hydrogen reduction coupled with hydrogen chloride treatment before chlorine redispersion, as compared with the absence of hydrogen chloride pretreatment. The agglomerated catalyst described above was treated by substantially the same procedure as described in Example 1, including the reduction step, the HC1 pretreatment step, and the elemental halogen redispersion step, except that after the hydrogen reduction and before HC1 pretreatment step, a gaseous mixture of 0.5 vol. % oxygen and 1.4 vol. % water was introduced to the catalyst bed for a duration of one hour. During the chlorine redispersion treatment, chlorine flow was continued for 30 minutes past breakthrough (TBHB). The results are given in Table I as Example 1B. As is seen, exposure of the low chloride content (0.67 wt. %) catalyst to oxygen produces the same dertimental effect on catalyst reactivation as oxygen generated in situ indicated in Example 1A. Utilizing substantially the same procedure of Example 1A, 60 grams of a 100% agglomerated fresh coke-free, platinum-iridium catalyst were subjected to the described reduction step and the halogen redispersion step with the exception that the feedstream in the halogen redispersion step contained 1 vol. % oxygen as well as 1.37 vol. % chlorine. Total halogen treatment time was 120 minutes. Results are given in Table I as Example 1C. The data illustrate that oxygen present with chlorine in the redispersion step has no beneficial effect on the efficiency of redispersion in the absence of an HC1 pretreatment step. EXAMPLE 2 The catalyst of Example 1 was given a twocycle redispersion treatment in which the first cycle was a duplicate of the procedure described in Example 1. The catalyst was left in the reactor while the second cycle was initiated and a second hydrogen reduction was carried out for one hour. After the reduction step, the reactor was purged with a gaseous mixture of 1.4 vol. % water in helium for 15 minutes. However, no HC1 pretreatment was conducted prior to chlorine redispersion. Then the reduced catalyst was treated with a gaseous mixture of 1.0 vol. % chlorine and 1.4 vol. % water in helium until the outlet concentration of chlorine attained a steady state concentration. The results are given in Table I. During the second hydrogen reduction, 0.41 wt. % of chloride was stripped from the catalyst as determined by gas phase analysis. Catalyst chloride level after the second hydrogen reduction could be estimated by subtracting lost chloride, 0.41 wt. %, from the values listed in Table I. However, the chloride concentration of the catalyst in the reactor was above the minimum level of 1.3 wt. % as indicated in the Table which resulted in high overall percent redispersion. Analysis of the exit gas during the second chlorine treatment showed that oxygen at about 0.35 vol. %, was present in the exit gas, shortly after chlorine introduction. However, the duration of this high level oxygen exposure was relatively short, being about 15 minutes. It is reasonably believed that the high degree of the redispersion obtained after two cycles is the result of the protecting effect of high chloride concentration achieved in the first cycle which eliminates the adverse effect of elemental oxygen generated in situ during the second cycle. EXAMPLE 3 The catalyst of Example 1 was treated substantially by the same procedure described in Example 1 except that in both the hydrogen chloride atnd chlorine treatment steps, the treatment times were extended for a period of about 45 minutes past breakthrough in a single-cycle treatment. The results are given below in Table I. In a comparison of the data with that from Example 1, it is seen that longer treatment times past halogen breakthrough provide even greater iridium redispersion. EXAMPLE 4 An alumina catalyst containing 0.3 wt. % iridium and 0.3 wt. % platinum, based on the total weight of the catalyst (BET surface area of 165 m2/g), had been used in a reformer in the production of Cg+ gasoline. Several weight percent of coke deposit was found on the catalyst after the catalyst had been on stream for several months. The catalyst was regenerated stepwise in the reactor with dilute oxygen at a flame front temperature up to 4960C. The coke-depleted catalyst suffered metal agglomeration and X-ray diffraction measurements taken after hydrogen reduction showed 68% of the total iridium as crystallites greater than 502. There was about 0.1 wt. % of carbon left on the catalyst. Sixty grams of this catalyst was charged into the reactor and the reactivation procedure used was substantially the same as the single-cycle process described in Example 3. The results are given in Table I below. This Example illustrates that the subject process is equally applicable to redispersing commercially spent catalysts with comparable efficiency. EXAMPLE 5 The procedure of Example 1 was substantially rerun except that during the halogen redispersion step, elemental oxygen was also present in about 2 vol. % in addition to 1.36 vol. % chlorine. Total halogen treatment time was 25 minutes. Results are given below in Table I. This Example illustrates that addition of oxygen to the halogen redispersion step which followed the HCL pretreatment results in even greater improvement in the redispersion, as compared to Example 1, in which no oxygen was added during the chlorine treatment. In a related run, the same procedure described in Example 5 was utilized except that after the HC1 pretreatment, a second wet hydrogen treatment was conducted for one hour with a stream containing 20 volume percent hydrogen and 1.4 vol. % water, followed by a wet helium purge prior to the chlorine redispersion. The weight percent chloride in the catalyst was measured by X-ray fluorescence prior to redispersion. The results are indicated below in Table I as Example 5A. As is seen, where the weight percent chloride on the catalyst surface was only 1.2% following halide pretreatment, only 38% redispersion was obtained following halogen treatment. TABLE I %Ir Agglom. %IrO2 Agglom. % Total Agglom. %Redis. Example TI(a) S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 TBHB 1(b) 87 37 36 36 0 0 0 37 36 36 58 59 59 10 min. 1A(c) 87 74 73 67 0 0 9 74 73 76 15 16 13 10 min. 1B 87 42 48 45 21 23 21 63 71 66 27 18 24 30 min. 1C 100 59 54 64 5 11 16 64 65 80 36 35 20 78 min. 2(d) 87 9 0 21 0 0 0 9 0 21 90 100 76 -3(e) 87 9 11 -- 0 0 -- 9 11 -- 90 87 -- 45 min. 4 68 -- 13 17 -- 0 0 -- 13 17 -- 81 75 43 min. 5 100 28 16 6 0 0 0 28 16 6 72 84 94 20 min. 5A(g) 100 62 26 17 0 0 0 62 26 17 38 74 83 23 min. (a) Total initial iridium agglomeration. (b) Weight percent chloride on catalyst: initial, 0,67; S-1, 1.88; S-2, 2.0; S-3, 2.12. (c) Weight percent chloride on catalyst: initial, 0,67. (d) Weight percent chloride on catalyst: initial, 0,67; S-1, 1.47, S-2, 1.59; S-3, 1.71 (after second H2 reduction). (e) Values of Section 3 were not reported due to a lower observed temperature during the run. (f) Values of Section 1 were not reported due to a lower observed temperature during the run. (g) Weight percent choride on catalyst prior to halogen redispersion: initial, 0,67; S-1, 1.20; S-2, 1.45; S-3, 1.52. EXAMPLE 6 Into the quartz, tubular, horizontal reactor described in Example 1 was charged about 60 grams of a coke-free, platinum-iridium catalyst in which the iridium was 100% agglomerated. It contained 0.3 weight. percent iridium and 0.3 weight percent platinum based on the total weight of the catalyst (BET surface area 200 m2/g). The catalyst was divided into three approximately equal sections with a quartz wool plug as a spacer between the sections. The catalyst in Section 1 was at the entry of the reactor and the catalyst in Section 3 was at the reactor exit. The chloride level on this catalyst was determined to be 0.67 weight percent. The catalyst was-treated with a gaseous mixture of 20 percent hydrogen in helium at one atmosphere for 2 hours at 5240C. At the end of the hydrogen treatment, a gaseous mixture of 1 volume percent hydrogen chloride and 1.4 volume percent water in helium was allowed to contact the catalyst up to a point at which the concentration of hydrogen chloride in the exit gas equaled that in the inlet. At this point, the HC1 flow was terminated. Chlorine was then added to the gaseous stream at about 0.9 volume percent at a mass flow rate of about 0.36 grams of chlorine per 100 grams of catalyst per hour. The chlorine and water injections were discontinued at a point in time at which the chlorine concentration in the exit gas reached a steady state concentration. One primary reasdn of the water addition is to suppress ferrous metal corrosion. The results are given in Table II. Table II lists results under "% Ir Agglomeration", "% Redispersion and "C12 Mass Flow Rate". The . symbol "I" represents the total initial value of iridium agglomeration, and the terms S-1, S-2, and S-3 represent values obtained after treatment for the catalyst in the first, second and third sections of the catalyst bed. The first section represents the entry section and the third, the exit section. In a related run, the catalyst was treated exactly as Example 6 except that the mass flow rate of chlorine was 1.45 grams per 100 grams of catalyst per hour. The results are given in Table II as Example 6A. As is seen by comparing Examples 6 and 6A, lowering the mass flow rate of chlorine from 1.45 to 0.36 increases the percent of metal redispersion, even though the amount of chlorine used in Example 6 was less than that used in the corresponding Example 6A. Chlorine concentration at the exit gas was reduced from 7440 ppm to 6540 ppm. Furthermore, exposure of downstream equipment to chlorine was minimized in Example 6 since the amount of chlorine treatment beyond C12 detection had been reduced to 0.18 grams per 100 grams of catalyst. Further reduction in chlorine concentration at the reactor outlet can be achieved at even lower mass flow rate of chlorine by reducing the inlet concentration of chlorine, as is illustrated by Example 7. EXAMPLE 7 A run was made wherein the reactor described in Example 6, was charged with about 60 grams of the agglomerated coke-free platinum-iridium catalyst described in Example 6. The catalyst was treated with a gaseous mixture of 20 percent hydrogen in helium at one atmosphere for 2 hours at 524oC. At the end of hydrogen treatment, a gaseous mixture of 0.52 volume percent hydrogen chloride and 0.72 volume percent water in helium was allowed to contact the catalyst up to a point at which the concentration of hydrogen chloride in the exit gas equaled that in the inlet. After stopping the hydrogen chloride flow, chlorine was added to the helium stream at about 0.25 volume percent, at a mass flow rate of 0.073 grams per 100 grams of catalyst per hour. The gas mixture also contained 4.8 volume percent oxygen and 0.50 volume percent water. This treatment was continued for 3 hours. The results are given in Table II. In a related run, the procedure of Example 7 was employed except that during the HC1 treatment, the HC1 concentration was 1.13 volume percent and H20 was 1.4 volume percent. Also in the redispersion step, the oxygen concentration was 2.1 volume percent and C12 was 1.36 volume percent. A chlorine mass flow rate of 1.98 grams per 100 grams catalyst per hour was employed and the results are listed in Table II as Example 7A. As is seen from comparing Examples 7 and 7A, complete metal redispersion was obtained at less than one-half the amount of chlorine used in Example 7A. It appears that by lowering the chlorine mass flow rate, a closer balance between the redispersion rate and utilization of chlorine is realized. EXAMPLE 8 A run was conducted in a verticle reactor consisting of 1 1/2 inch diameter and 42 inch long stainless steel pipe. Into this reactor was charged about 640 grams of the agglomerated coke-free platinum iridium catalyst described in Example 6. The catalyst was treated with hydrogen at 65 psig for 2 hours at 5210C. At the end of hydrogen treatment, a gaseous mixture containing 2000 ppm hydrogen chloride in nitrogen was allowed to contact the catalyst up to a point at which the concentration of hydrogen chloride in the exit gas was about 90 percent that of the inlet. After stopping the hydrogen chloride flow, chlorine was added to the nitrogen stream at 500 ppm at a mass flow rate of 0.073 grams per 100 grams of catalyst per hour. The gaseous mixture also contained 1.3 volume percent oxygen. This treatment was continued for about three and a quarter hours. The results are given in Table II below. Complete metal redispersion was obtained at this low mass flow rate of chlorine. In addition, the low chlorine concentration at the reactor outlet minimized chlorine scrubbing requirement. TABLE II %Ir Agglom. %Redis. Example I S-1 S-2 S-3 S-1 S-2 S-3 Cl2 Mass Flow Rate 6(a) 100 6 17 30 94 83 70 0.36 6A(b) 100 30 42 49 70 58 51 0.45 7(c) 100 0 0 0 100 100 100 0.073 7A(d) 100 28 16 6 84 84 94 1.98 8(e) 100 0 0 0 100 100 100 0.073 (a) Amount of Cl2 treatment to detection (g./100g.cat.): 0.30; Amount of Cl2 treatment beyond detection (g./100g. cat.): 0.18; Concentration of Cl2 [gas at exit (ppm)]: 6540. (b) Amount of Cl2 treatment to detection (g./100g.cat.): 0.29; Amount of Cl2 treatment beyond detection (g./100g. cat.): 0.24; Concentration of Cl2 [gas at exit (ppm)]: 7440. (c) Amount of Cl2 treatment to detection (g./100g.cat.): 0.068; Amount of Cl2 treatment beyond detection (g./100g. cat.): 0.15; Concentration of Cl2 [gas at exit (ppm)]: 900. (d) Amount of Cl2 treatment to detection (g./100g.cat.): 0.17; Amount of Cl2 treatment beyond detection (g./100g. cat.): 0.66; Concentration of Cl2 [gas at exit (ppm)]: 9000. (e) Amount of Cl2 treatment to detection (g./100g.cat.): 0.02; Amount of Cl2 treatment beyond detection (g./100g. cat.): 0.22; Concentration of Cl2 [gas at exit (ppm)]: 300. EXAMPLE 9 Into the quartz tubular, horizontal reactor described in Example 1, was charged about 60 grams of a coke-free platinum-iridium on alumina catalyst, wherein 100% of the iridium was agglomerated. It contained 0.3 weight percent iridium and 0.3 weight percent platinum, based on the total weight of the catalyst (BET surface area of 200 m2/9. The catalyst was divided into three approximately equal sections with quartz wool plugs as spacers between the sections. The catalyst in Section 1 (S-l in the Table) was at the entry of the reactor and the catalyst in Section 3 (S-3 in the Table) was at the reactor exit. The chloride level on this catalyst was 0.67 weight percent, as determined by X-ray fluorescence. The catalyst was treated with a gaseous mixture of 20 percent hydrogen and 1.4 percent water in helium at one atmosphere for 2 hours at 5240C, whereby substantially all of the iridium oxide was reduced to metallic iridium, as evidenced by the absence of the X-ray diffraction line at 28.05 degrees (20) ascribed to IrO2. The hydrogen was purged from the catalyst bed with helium. The catalyst was then treated with a gaseous mixture of 1.1 volume percent hydrogen chloride and 1.4 volume percent water in helium at 500 cc/min. After about 83 minutes, rhydrogen chloride was detected at the reactor outlet. 'Hydrogen chloride treatment was continued until concentration of hydrogen chloride at the reactor outlet was about 90 percent of that at the reactor inlet. This required about 15 minutes. At this point, 2.4 volume percent of oxygen was added to the gaseous mixture and the HC1/O2 treatment continued for 200 minutes. The catalyst was then rereduced with 20 volume percent hydrogen and 1.4 volume percent water in helium for 75 minutes. The results are shown below in Table III. The results for Example 9 are listed below in Table III under abbreviated columns for "% Iridium Agglomeration", "% IrO2 Agglomeration", "% Total Agglomeration" and "t Redispersion", respectively, TBHB in Table III is the abbreviation for "Time Beyond Halogen Breakthrough1r. The symbol "I" represents "initial value" and the terms S-i, 5-2 and S-3 represent values obtained after treatment for the catalyst in the first, second and third sections of the catalyst bed. The first section represents the entry section, and the third, the exit region. In a related run, the catalyst described above was treated substantially the same as Example 9 except that no oxygen was added to the HC1 stream after its concentration reached 90% at the outlet. The results are shown below in Table III as Example 9A. As is seen from contrasting Examples 9 and 9A, near complete iridium redispersion was obtained when the present invention was practised whereas treating the agglomerated catalyst with HC1 in the absence of oxygen resulted in essentially no metal redispersion. EXAMPLE 10 The catalyst of Example 9 was treated substantially the same as in Example 9 except that in the HC1 + 02 treatment, the gas flow rate was lowered from 500 to 110 cc/min and this treatment was continued for 329 minutes. The results are shown in Table III. In a related run, the catalyst of Example 9 was treated in a 'similar manner as in Example 10 except that there was no hydrogen chloride pretreatment before the HCl/O2 redispersion. During the HCl/O2 treatment, the oxygen level was 2.8 volume percent and no water was added to the HC1/02 gaseous feedstream. The HC1 + 2 treatment was continued for 280 minutes. The results are shown in Table III as Example 10A. As is seen from contrasting Examples 10 and 10A, omission of the hydrogen chloride treat before the HC1 + 2 treatment greatly reduced the extent of metal redispersion and, in particular, it resulted in the formation of iridium oxide agglomerates. The HC1 pretreatment raised the catalyst chloride level from 0.67 to 1.8 weight percent. EXAMPLE 11 The catalyst of Example 9 was treated in a similar manner as in Example 10 except that the treatment gases contained no water and in the HC1 + 02, treatment the concentration of oxygen was 27 volume percent. This treatment was continued for 45 minutes. At the end of this treatment, the inlet and outlet of the reactor were blocked off and the catalyst was soaked in the gas mixture for 3 hours. The e results are shown in Table III. Example 11 indicates that high oxygen concentration in the HC1 + 2 treat step was equally effective in metal redispersion. Furthermore, soaking the catalyst in the gaseous mixture appears to improve the redispersion of the catalyst situated near the reactor entrance. EXAMPLE 12 An alumina catalyst containing 0.3 weight percent iridium and 0.3 weight percent platinum, based on the total weight of the catalyst, had been used in a commercial reformer in the production of C5+ gasoline. Several weight percent of coke deposit was found on the catalyst. The catalyst was regenerated in the reactor with dilute oxygen up to a flame front temperature of 4800C, resulting in an iridium agglomeration of 47 percent and the carbon content of the regenerated catalyst was 0.18 weight percent. Sixty grams of this catalyst were charged into the reactor and the reactivation procedure used was substantially the same as Example 9 except that in the HC1 + 2 treatment, the concentration of HC1 and oxygen were 1.2 and 20.6 volume percent, respectively. The results are shown in Table III. Another portion of the same catalyst was regenerated in the reactor with dilute oxygen at a flame front temperature of 4000C. The carbon content of the regenerated catalyst was 0.62 weight percent. Sixty grams of this catalyst were charged into the reactor and the reactivation procedure used was exactly as in Example 12 except that the HC1 + 2 treatment was 153 minutes. The results are shown in Table III as Example 12A. Examples 12 and 12A show that the present invention works well with coked catalyst. High degrees of metal redispersion were obtained when the present invention was practiced with coked catalyst, wherein the; coke was removed by oxygen in the gas phase during redispersion under the high reaction temperature. EXAMPLE 13 The catalyst of Example 12 was further decoked at 5380C in air for 16 hours. After this treatment, the carbon content of the catalyst decreased to 0.1 weight percent. The coke-depleted catalyst suffered further metal agglomeration and X-ray diffraction showed essentially all the iridium was agglomerated. Sixty grams of this catalyst were charged into the reactor and were treated in a similar manner as in Example 12, except that no water was present in the treat gases and in the HC1 + 02 treatment, oxygen concentration was increased from 2 to 25 volume percent in four steps, which were: 2 volume percent for 15 minutes, 5.3 volume percent for 15 minutes, 13.0 volume percent for 19 minutes and 25 volume percent for 60 minutes. The results are shown in Table III. As is seen from contrasting Examples 9 and 13, a higher degree of metal dispersion was obtained when no water was added to the treating gas and the oxygen concentration was increased in several steps. This stepwise increase in oxygen concentration is very advantageous when the present invention is used to redisperse catalysts containing substantial amounts of coke deposit. The limited oxygen concentration in the initial coke burn removes most of the coke and, at the same time, avoids uncontrolled temperature exotherms. TABLE III (a) %Ir Agglom. %IrO2 Agglom. %Total Agglom. %Redis. Example Ti(b) S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 9 100 28 14 0 0 0 0 28 14 0 72 86 100 9A 100 95 92 101 0 0 0 95 92 101 5 8 0 10 100 5 0 0 0 0 0 5 0 0 95 100 100 10 A 100 32 38 62 7 10 15 39 48 77 61 52 23 11 100 0 0 0 0 0 0 0 0 0 100 100 100 12 (c) 47 11 15 9 0 0 0 11 15 9 76 68 81 12A(d) 49 17 9 0 0 0 0 17 9 0 65 82 100 13 100 9 0 0 0 0 0 9 0 0 91 100 100 (a) S-1, S-2, S-3 are the entrance, middle and sections, respectively, after redispersion treatment. (b) Total initial iridium agglomeration. (c) % Carbon on catalyst: initial, 0.18, S-1, 0.06, S-2, 0.07, S-3, 0.07. (d) % Carbon on catalyst: initial, 0.62; S-1, 0.08; S-2, 0.08; S-3, 0.08. EXAMPLE 14 A catalyst containing 0.3 weight percent iridium and 0.3 weight percent platinum, based on the total weight of the catalyst (BET surface area of 158 m2/g) had been used in a reformer in the production of C5+ gasoline. Several weight percent of coke deposit was found on the catalyst after the catalyst had been on stream for several months. The catalyst was regenerated stepwise in the reactor with dilute oxygen up to a flame front temperature of 4960C. The coke depleted catalyst suffered metal agglomeration and X-ray diffraction showed 80 percent of the total iridium as crystallites greater than 50 55. There was about 0.11 weight percent of carbon left on the catalyst. Sixty grams of this catalyst was charged into a quartz, tubular, horizontal reactor. The catalyst was divided into three approximately equal sections with a quartz wool plug as a spacer between the sections. The catalyst in Section 1 was at the entry of the reactor and the catalyst in Section 3 was at the reactor exit. The chloride level on this catalyst was determined to be 0.78 weight percent by X-ray fluorescence. The catalyst was treated with a gaseous mixture of 20 percent hydrogen and 1.4 volume percent water in helium at one atmosphere for 2 hours at 5240C. The hydrogen was purged from the catalyst bed with helium. The catalyst" was then treated with a gas mixture of 1.13 volume percent hydrogen chloride and 1.4 volume percent water in helium at 500 cc/min. After about 59 minutes, hydrogen chloride was detected at the reactor outlet. Hydrogen chloride treatment was continued for another 34 minutes. At this point, the hydrogen chloride concentration in the exit gas approached to that of hydrogen chloride in the inlet gas. Air at 4 cc/min. was introduced into the reactor and the flowstreams of hydrogen chloride, helium and water vapor were discontinued. The air treatment was continued for 3 1/4 hours. The results are shown in Table IV. In a related run, Example 14 was repeated substantially as described except that during the air treatment, the flow rate of air was increased to 100 cc/min. from 4 cc/min. The air treatment was continued for 5-1/2 hours. The e results are given in Table IV as Example l4A. Chlorine was observed at the reactor outlet during the air treatment even though no chlorine was supplied to the reactor in both Examples 14 and 14A. In Example 14A, the concentration of chlorine was 0,15 volume percent after it was air treated 16 minutes. Chlorine concentration decreased to 0.02 volume percent in 1 1/2 hours. By contrast, chlorine concentration in Example 14 increased from 0.15 volume percent to 0.41 volume percent at the end of the air treatment. High air flow rate in Example 14A continuously removed chlorine from the reactor, and in turn, lowered the chloride level of the catalyst, whereas the low air flow rate in Example 14 minimized the purging of the reactive gases and conserved the catalyst chloride level. The catalyst chloride levels in Example 14A were lower than those of Example 14 by more than 0.2 weight percent. In a further related run, Example 14 was repeated substantially as described except that the HC1 treatment was discontinued after 30 minutes of treatment and before HC1 was detected at the reactor outlet. The air treatment was continued for 7 hours. The results are shown in Table IV as Example 14B. This example indicates that the chloride level on the catalyst before the low flow oxygen treatment step is critical. The chloride levels after oxygen treatment do reflect the chloride levels of the catalyst at the end of the HC1 treatment since during the low flow oxygen treatment, no significant concentrations of chlorine was detected at the reactor outlet. As is indicated in the data, moderate metal redispersion was obtained when the catalyst chloride level was 1.2 weight percent and essentially no overall metal redispersion was realised when the catalyst chloride level was below 1 weight percent. EXAMPLE 15 Example 14 was -repeated substantially as described except that no water vapor was added in the hydrogen reduction step and the hydrogen chloride treat step. In the oxygen treat step, 10 percent oxygen in helium was used instead of air. The oxygen treatment was continued for 6.7 hours. The results are shown in Table IV. As is seen from comparing Example 15 with Example 14, complete metal redispersion was obtained when water was omitted in the treating gases and correspondingly, this resulted in an increase in catalyst chloride content of the treated catalyst. EXAMPLE 16 The catalyst of Example 14 was treated substantially the same as in Example 15, except that during the oxygen treatment, 8 cc/min. gas flow rate was employed and the oxygen treatment time was about 2.3 hours. The results are shown in Table IV. It appears that though the oxygen flow rate was double, it still was sufficiently low that no significant loss of catalyst chloride occurred during the oxygen treatment and therefore excellent metal redispersion was realized. EXAMPLE 17 A run was made using a fresh coke-free alumina catalyst containing 0.3 weight percent platinum and 0.3 weight percent iridium, based on the total weight of the catalyst -(BET surface area of 200 m2/g). The iridium component in this freshly prepared catalyst was completely agglomerated to large iridium particles by air calcined at 5400C for 16 hours. Sixty grams of this catalyst were loaded into a reactor as described in Example 14. The catalyst was treated substantially the same as in Example 14 except that the air treatment was continued for 1.25 hours. The results are shown in Table IV. As is seen from the data, the present invention is highly effective in redispersing metal agglomerates present on fresh, coke-free and used catalysts from a reformer. However, the chloride level of the fresh, coke-free catalyst is higher than the latter by about 0.4 weight percent after the redispersion treatment. The lower chloride level on the used catalyst is mainly due to a reduction in the alumina surface area as a result of numerous cycles of on oil and coke burn regeneration. EXAMPLE 18 The catalyst of Example 17 was treated substantially the same exactly as in Example 17, except that after the HC1 treatment, a ten-minute dry helium purge was employed before the slow flow air treatment. The air treat step was continued for 4 hours. The results are shown in Table IV. This example indicates that even a short purging between the hydrogen chloride and the slow air flow treatment steps leads to a loss of catalyst chloride and a reduction in metal redispersion. EXAMPLE 19 The catalyst of Example 17 was treated substantially the same as in Example 17 except that 2.6 volume percent water was employed in the hydrogen and hydrogen chloride treatment steps. The gaseous flow rate in the hydrogen chloride treatment was 660 cc/min. containing HC1 in about 0.3 volume percent. The slow flow air treatment was continued about 2 hours. The results are shown in Table IV below. TABLE IV %Ir Agglom. %IrO2 Agglom. %Total Agglom. %Redis. Example Ti(a) S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 S-1 S-2 S-3 14(b) 80 8 8 0 0 0 0 8 8 0 90 90 100 14A(c) 80 44 37 28 34 35 30 78 72 58 3 10 28 14B(d) 80 17 18 46 5 26 41 22 44 87 73 45 -9 (n) 15(e) 80 0 0 0 0 0 0 0 0 0 100 100 100 16(f) 80 0 0 7 0 0 0 0 0 7 100 100 91 17(g) 100 0 0 < 5 0 0 0 0 0 < 5 100 100 > 95 18(h) 100 14 11 0 12 9 0 26 20 0 74 80 100 19(i) 100 13 14 22 57 69 49 70 83 71 30 27 29 20(j) 100 0 0 5 0 0 0 0 0 5 100 100 95 21(k) 100 0 0 0 0 0 0 0 0 0 100 100 100 22(l) 100 75 37 79 0 0 0 75 37 79 25 63 21 23(m) 47 16 13 13 0 0 0 16 13 13 66 72 72 (a) Total initial iridium agglomeration. (b) % Cl : initial, 0.78; S-1, 1.44; S-2, 1.44; S-3, 1.45. (c) % Cl : initial, 0.78; S-1, 1.16; S-2, 1.20; S-3, 1.23. (d) % Cl : initial, 0.78; S-1, 1.28; S-2, 1.22; S-3, 1.97. (e) % Cl : initial, 0.78; S-1, 1.63; S-2, 1.57; S-3, 1.59. (f) % Cl : initial, 0.78; S-1, 1.73; S-2, 1.69; S-3, 1.70. (g) % Cl : initial, 0.67; S-1, 1.85; S-2, 1.87; S-3, 1.86. (h) % Cl : initial, 0.67; S-1, 1.73; S-2, 1.75; S-3, 1.74. (i) % Cl : initial, 0.67; S-1, 1.51; S-2, 1.46; S-3, 1.44. (j) % Cl : initial, 0.67; S-1, 1.80; S-2, 1.77; S-3, 1.73. (k) % Cl : initial, 0.67; S-1, 1.77; S-2, 1.81; S-3, 1.82. (l) % Cl : initial, 0.67; S-1, 1.53; S-2, 1.60; S-3, 1.57. (m) % Cl : initial, 0.79; S-1, 1.46; S-2, 1.49; S-3, 1.52. % C : initial, 0.18; S-1, 1.09; S-2, 1.10; S-3, 0.07. n) Indicates some agglomeration occured during the redisperation step. As is seen from contrasting Examples 17 and 19, an increase in H20/HC1 ratio from 1.24 to 8.67 greatly reduces metal redispersion and lowers the chloride level of the catalyst by about 0.4 weight percent. EXAMPLE 20 The catalyst of Example 17 was treated substantially the same manner as in Example 17 except that about 0.3 to 0.4 volume percent water was employed in the hydrogen and the hydrogen chloride treatment steps. The gas flow rate in the hydrogen chloride treat was 773 cc/min. and HC1 was present in 0.32 volume percent. The slow flow air treatment was continued for about 3 hours. The results are shown in Table IV. As is seen from contrasting Examples 19 and 20, by lowering the concentration of water to match that of hydrogen chloride, i.e., maintaining the H20/HC1 ratio at 1.25, excellent metal redispersion is obtained despite the low concentration of HC1. Additionally, the chloride level of the catalyst increases by about 0.3 weight percent. EXAMPLE 21 The catalyst of Example 17 was treated substantially the same as in Example 17 except that in the slow flow air treatment, pure oxygen was used. The oxygen treatment was continued for 2.75 hours. The results are shown in Table IV. This example indicates oxygen concentration as high as 100 percent can be employed in the slow flow oxygen treatment step. EXAMPLE 22 Six hundred and forty grams of the catalyst of Example 17 was charged into a high pressure reactor. The catalyst was treated with a gas mixture containing 0.3 volume percent water and about 50 percent hydrogen in nitrogen at 5210C for about 2 hours. The reactor pressure was 65 psig. At the end of the hydrogen treatment, hydrogen concentration was reduced to 1.5 volume percent and 0.2 volume percent of HC1 was added. This treatment was continued until the concentration of HC1 at reactor outlet was about 90 percent of the inlet HC1 concentration. Then hydrogen was shut off 15 minutes before the end of the HC1 treatment. This reduced the hydrogen concentration in the reactor close to zero before the introduction of air. The reactor exit was blocked off and it'was pressurized with dry air up to 205 psig. The catalyst was allowed to soak in the gas mixture for 3 hours. The results are shown in Table IV. In this example, the amount of oxygen per gram of catalyst introduced into the reactor was equivalent to that in Example 17. However, much lower metal redispersion was obtained when the air treatment was conducted under static conditions. This may be due fto the build-up of water vapor in the reactor. Addi tionally, the catalyst chloride level in this example is lower than that of Example 17 by 0.3 weight percent. A possible method to avoid buildup of water vapor is by oxygen pressure-depressure cycles. After the HC1 pretreatment, the reactor may be pressurized with diluted oxygen (plus inert carrier) to a desired pressure, e.g. 100 psig. Then the pressure is slowly decreased to atmospheric pressure and then repressurized to about 100 psig (about 0.7 MPa) . Repeating this cycle several times allows the oxygen to contact the catalyst to effect redispersion without a significant buildup of water vapor. EXAMPLE 23 An alumina catalyst containing 0.3 weight percent iridium and 0.3 weight percent platinum, based on the total weight of the catalyst, had been used in a reformer in the production of Cg+ gasoline. Several weight percent of coke deposit was found on the catalyst. The catalyst was regenerated in the reactor with dilute oxygen up to a flame front temperature of 48000. Carbon content of the regenerated catalyst was 0.18 weight percent. Sixty grams'of this catalyst was charged into the reactor and the reactivation procedure used was substantially the same as Example 14 except that the HC1 concentration was 1.23 volume percent in the HC1 treatment and the slow flow air treatment was 8.2 hours. The results are shown in Table IV. This Example indicates that the present invention can be applied to carbon-containing catalysts. Metal redispersion as well as coke burn-off can be effected during the oxygen redispersion step. EXAMPLE 24 The quartz, tubular horizontal reactor described in Example 1 was charged with about 60 grams of a coke-free platinum-iridium catalyst, wherein the iridium was 100 percent agglomerated, (produced by agglomeration at 5400C) . It contained 0.3 weight percent iridium and 0.3 weight percent platinum based on the total weight of the catalyst (BET surface area of 200 m2/g). The catalyst was divided into three approximately equal sections with a quartz wool plug as a spacer between the sections. The catalyst in Section 1 was at the entry of the reactor and the catalyst in Section 3 was at the reactor exit. The chloride level on this catalyst was determined to be 0.67 weight percent. The catalyst was treated with a gas mixture of 20 percent hydrogen in helium at one atmosphere for 2 hours at 5240C. At the end of hydrogen treatment, a gaseous mixture of 1 volume percent hydrogen chloride and 1.4 volume percent water in helium was allowed to contact the catalyst up to a point at which the concentration of hydrogen chloride in the exit gas was 90 percent that in the inlet. At this point, chlorine was added to the gas stream at about 1 volume percent and at a mass flow rate of 0.36 gram per 100 gram of catalyst per hour, and water concentration was lowered to 1.1 volume percent. Chlorine was detected at the reactor exit at a chlorine treat equaled to 0.31 gram of chlorine per 100 gram of catalyst. Chlorine injection was extended beyond the point of detection until 0.49 grams of chlorine per 100 grams of catalyst had been introduced into the reactor. The results are given in Table V. EXAMPLE 25 An alumina catalyst containing 0.3 weight percent iridium and 0.3 weight percent platinum based on the total weight of the catalyst (BET surface area of 170 m2/g) had been used in a commercial reformer in the production of C5+ gasoline. Several weight percent of coke deposit was found on the catalyst. The catalyst was regenerated in the reactor with dilute oxygen at a low flame front temperature of 4000C. The metal agglomeration was below 50%. Carbon content of the regenerated catalyst was 0.62 weight percent. Sixty grams of this catalyst was charged into the reactor and the reactivation procedure used was substantially the same as in Example 24 except that in the chlorine treatment, no chlorine was detected up to a chlorine treatment of 3.24 gram per 100 gram of catalyst. The results are shown in Table V. This example indicates that coke deposit is quantitatively removed in the absence of added oxygen. Complete metal redispersion was obtained when coke deposit was reduced to below 0.1 weight percent. It appears that in the presence of water, chlorine oxidizes carbon to carbon oxides. EXAMPLE 26 The catalyst of Example 24 was treated in a similar manner as Example 1 except that no water was present in the treat gases and the mass flow rate of the chlorine treat was 2 grams per 100 grams of catalyst per hour. The results are shown in Table V below. As is seen from the data, coke deposits were not quantitatively removed by the dry chlorine treat since the carbon contents in the three sections were quite uniform. For this particular catalyst, about 0.3 weight percent of coke deposit was the maximum amount that could be removed by dry chlorine treat since more than 2.5 times longer chlorine exposure of catalyst in Section 1, as compared to that in Section 3, did not significantly increase the carbon removal of the former. TABLE V % Ir Agglom. %Redis. %Cl %C Example Ti(a) S-1 S-2 S-3 S-1 S-2 S-3 I S-1 S-2 S-3 I S-1 S-2 S-3 24 (b) 100 6 17 30 94 83 70 0.67 1.90 1.90 1.02 - - - 25 (c) 49 0 19 46 100 61 6 0.78 1.70 2.10 2.40 0.62 0.09 0.12 0.46 26 (d) 49 6 7 34 88 86 31 0.78 3.3 3.3 3.3 0.62 0.31 0.32 0.36 (a) Total initial iridium agglomeration. (b) Chlorine mass flow rate (g/100 g cat./hr.): 0.36; Amount of Cl2 used until detection (g/100 g cat.): 0.31; Amount Cl2 used beyond detection; 0.49. (c) Mass flow rate (g/100 g cat./hr.); 0.36; Amount of Cl2 used at end of redispersion (g/100 g cat.), 3.24; no chlorine was detected at reactor exit at end of run. (d) Mass flow rate (g/100 g cat./hr.): 2.0; Amount of Cl2 used until Cl2 detection (g/100 g cat.): 3.1; Amount Cl2 at the end of the redispersion (g/100 g cat.): 5.1. EXAMPLE 27 A quartz, tubular, horizontal reactor was charged with about 60 grams of an agglomerated, cokefree platinum-iridium catalyst wherein 100 percent of the iridium was agglomerated. It contained 0.3 weight percent iridium and 0.3 weight percent platinum based on the total weight of the catalyst. The catalyst was divided into three approximately equal sections with a quartz wool plug as a spacer between the sections. The catalyst in Section 1 was at the entry of the reactor and the catalyst in Section 3 was at the reactor exit. The chloride level on this catalyst was determined to be 0.67 weight percent. The catalyst was treated with a gas mixture of 20 percent hydrogen in helium at one atmosphere for 2 hours at 5240C. At the end of hydrogen treat, a gaseous mixture of 1 volume percent hydrogen chloride and 1.4 volume percent water in helium was allowed to contact the catalyst up to a point at which the concentration of hydrogen chloride in the exit gas equaled that in the inlet. At this point, chlorine was added to the gas stream at 0.83 volume percent and at a mass flow rate of 0.29 grams per 100 grams of catalyst per hour. Chlorine was detected at the reactor exit at a chlorine treat equaled to 0.27 grams chlorine per 100 grams of catalyst. Chlorine injection was extended beyond the point of detection until 0.74 grams chlorine per 106 grams of catalyst had been introduced into the reactor. The results are given in Table VI. Excellent metal redispersion is obtained when the chlorine treat is continued beyond the point of chlorine detection. The amount of chlorine injected beyond the point of detection was 0.47 grams per 100 grams of catalyst. The downstream equipment would be contacted with this amount of chlorine if there was no provision for its removal. EXAMPLE 28 The catalyst described in Example 27 was mixed with carbon black powder to give a carbon content of 0.37 weight percent based on anhydrous catalyst. The catalyst was treated exactly as in Example 27 except that the mass flow rate of chlorine was 0.36 grams per 100 grams of catalyst per hour. No chlorine was detected at the reactor exit after the catalyst had been in contact with 2.35 grams halogen per 100 grams of catalyst. The results are given in Table VI below. The data indicated that when the catalyst contained 0.37 weight percent coke deposits, the chlorine front traveled from the catalyst bed entrance to about 40 percent of the total bed length at a chlorine treat equaled to 2.35 grams chlorine per 100 grams catalyst. Coke deposits on this portion of the catalyst were nearly quantitatively removed. Therefore, if catalyst in Example 28 was downstream of catalyst in Example 27, i.e., the two reactors were in series and the carbon-containing catalyst was at the back reactor, no chlorine would be detected in the exit gas of the back reactor and, in fact, it can easily be calculated that less than 10 percent of the carbon-containing catalyst is needed to react with the 0.47 grams chlorine per 100 grams catalyst emerging from the exit of the front reactor. EXAMPLE 29 An alumina catalyst containing 0.3 weight percent iridium and 0.3 weight percent platinum, based on the total weight of the catalyst, was used in a reformer in the production of Cg+ gasoline. Several weight percent of coke deposit was found on the catalyst. The catalyst was regenerated in the reactor with dilute oxygen at a flame front temperature of about 4000C. The resulting iridium agglomeration was 49 percent and the carbon content in the regenerated catalyst was 0.62 weight percent. Sixty grams of this catalyst was charged into the reactor and the reactivation procedure used was substantially the same as in Example 28 except that no water was present in the treating gases and the mass flow rate of the chlorine treatment was 2 grams per 100 grams catalyst per hour. The results are given below in Table VI. This example indicates that coke deposits were not quantitatively removed by the dry chlorine treatment since the carbon deposits in the three sections were quite uniform. Indeed, for this particular catalyst, about 0.3 weight percent of coke deposits was the maximum amount that could be removed by the dry chlorine treatment since the more than 2.5 times longer chlorine exposure of catalyst in Section (1) , as compared to Section (3) , did not significantly increase the carbon removal of the former. TABLE VI % Ir Agglom. %Redis. %Cl %C Example Ti(a) S-1 S-2 S-3 S-1 S-2 S-3 I S-1 S-2 S-3 I S-1 S-2 S-3 27 (b) 100 0 0 10 100 100 90 0.67 1.79 1.90 1.90 - - - 28 (c) 100 0 100 100 100 0 0 0.67 2.0 2.7 2.6 0.37 0.05 0.36 0.37 29 (d) 49 6 7 34 88 86 31 0.78 3.3 3.3 3.3 0.62 0.31 0.32 0.36 (a) Total initial iridium agglomeration. (b) Chlorine mass flow rate (g/100 g cat./hr.): 0.29; Amount of Cl2 used until detection (g/100 g cat.): 0.27; Amount Cl2 used beyond detection; 0.47. (c) Chlorine mass flow rate (g/100 g cat./hr.); 0.36; no chlorine was detected at reactor exit at end of run; Amount of Cl2 used at end of run (g/100 g cat.), 2.35. (d) Chlorine mass flow rate (g/100 g cat./hr.): 2.0; Amount of Cl2 used until detection (g/100 g cat.): 3.1; Amount Cl2 used beyond detection: 2.0.

Claims: CLnlMS: 1. A process for reactivating a catalyst comprising metallic iridium in an agglomerated state wherein a coked catalyst comprising metallic iridium is at least partially decoked in an oxygen-containing atmosphere at an elevated temperature and thereafter contacted with a reducing atmosphere at elevated temperature for a sufficient time to substantially convert the iridium value to metallic iridium which comprises (a) pretreating the at least partially decoked catalyst by contact with a substantially elemental oxygen-free atmosphere comprising a halide-providing compound at an elevated temperature to provide a catalyst comprising about 1.3 weight percent or greater of halide based on the coke-free dry catalyst; and (b) contacting the pretreated catalyst of step (a) at an elevated temperature with an atmosphere comprising a redispersing gas selected from elemental halogen, elemental oxygen, a mixture of hydrogen halide and elemental oxygen,and mixtures thereof and thereby redispersing the agglomerated metallic iridium. 2. A process according to claim 1 wherein said redispersing gas is an elemental halogen in combination with an oxygen source. 3 A. process according to claim 2 wherein said oxygen source is water or elemental oxygen. 4. A process according to anyone of claims 1-3 wherein - said elemental halogen in step (b) is chlorine. 5. A process according to any one of claims 1-3 wherein said redispersing gas in step (b) is a mixture of hydrogen chloride and elemental oxygen. 6. A process according to any one of claims 1-5 wherein - . . after the pretreatment of step (b) the catalyst comprises about 1.4 to 2.5 weight percent of said halide based on the coke-free dry catalyst. 7. A process according to any one of claims 1-5 wherein - after the pretreatment of step (a) said catalyst is saturated with said halide. 8. A process according to any one of claims 1-5 wherein said halide-providing compound of step (a) is hydrogen chloride. 9 A process accordi-ng to any one of claims 1-5 and claim 7 wherein - step (a) is carried out to provide said catalyst with about 1.6 weight percent Qr greater of halide based on the coke-free dry catalyst and the contacting in step (b) is carried out with elemental oxygen. 10. A process according to any one of claims 1-4 wherein said contacting in step (b) with elemental halogen is carried out at a halogen mass flow rate of less than about one gram of elemental halogen per 100 grams of catalyst per hour. + 11. A process according to any one of claims 1-10 wherein ¯ the temperature in step (a) is in the range from about 250 to 6000C. 12. A process according to any one of claims 1-11 wherein said elevated temperature in step (b) is in the range from about 450 to 6000C. 13. A process according to any one of claims 1-4 and 10-12 wherein said at least partial decoking of said coked catalyst is carried out at a temperature below about 4300C for a sufficient time so that the remaining catalyst coke level is less than 1 weight percent and the iridium agglomeration on said catalyst is less than about 50 percent and said step (b) is carried out with a redispersing gas comprising elemental halogen and water vapor at a temperature of about 4800C or above for a time sufficient to substantially complete decoking and substantially redisperse said metallic iridium. 14. A process according to any one of claims 1-4 and 10-13 wherein said catalyst is present in a series of two. catalysts and wherein the redispersing gas in step (b) of the treatment of the first catalyst in the series comprises elemental halogen and water vapor and thereafter contacting said second catalyst of the series with the effluent halogen-water atmosphere from step (b) of the first catalyst to partially decoke said second catalyst. 15. A process according to any one of claims 1-14 whereia the catalyst comprises platinum and iridium supported on alumina.

Inventors: CARTER, JAMES LESLIE, FUNG, SHUN CHONG, KMAK, WALTER STEVEN, RICE, RICHARD WAYNE, WEISSMAN, WALTER
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1983
Main classification: B01J23
IPC codes: B01J23