Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G35/00—Reforming naphtha
  • C10G35/04—Catalytic reforming
  • C10G35/06—Catalytic reforming characterised by the catalyst used
  • C10G35/085—Catalytic reforming characterised by the catalyst used containing platinum group metals or compounds thereof
  • C10G35/09—Bimetallic catalysts in which at least one of the metals is a platinum group metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/90—Regeneration or reactivation
  • B01J23/96—Regeneration or reactivation of catalysts comprising metals, oxides or hydroxides of the noble metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/90—Regeneration or reactivation

Definitions

• This invention relates to catalysts used in hydrocarbon conversion. More particularly this invention is concerned with catalysts containing Group VHT noble metals (Pt,Ir,Os,Pd,Rh,Ru) having improved regeneration characteristics after poisoned by sulphur of deactivated by coking.
• Group VHT noble metals Pt,Ir,Os,Pd,Rh,Ru
• catalytic reforming is a process for improving the octane rating of gasoline in which it is generally aimed to convert straight chain hydrocarbon molecules to branch chain hydrocarbons (isomerization), to aromatic molecules (dehydrocyclization), and to dehydrogenate naphthenes to aromatics.
• Group VIII noble metals finely dispersed on support materials commonly refractory oxides, are widely used as catalysts for such processes. They are generally considered to function by the metallic component providing dehydrogenation/hydrogenation and the refractory oxide support providing isomerization by virtue of its acidic nature. The metallic component also provides dehydrocyclization and, probably, to a limited extent isomerization.
• the support component of the catalysts is selected by consideration of properties such as porosity, absorbtivity and high temperature stability.
• Refractory inorganic oxides such as titania, magnesia, thoria, zirconia, chromia and, in particular, silica and alumina and mixtures thereof are useful catalyst support materials with alumina or chlorided alumina being preferred for reforming catalysts.
• platinum used as a fine dispersion covering generally less than 10% and frequently less than 1% of the surface area of the support material.
• bimetallic or multimetallic components such as platinum-rhenium (e.g. Derosset, A.J. and Morgan, K.A., U.S. Patent 3,855,385), platinum-tin (e.g. Hayes, J.C., U.S. Patent 3,898,173) and platinum-iridium, (e.g., Sinfelt, J.H., U.S. Patent 3,953,368; Paynter, J.D., U.S. Patent 3,867,280; U.S. Patent, Sinfelt, J.H.
• Regeneration generally involves exposure of the catalyst to an oxygen containing gas at temperatures of 400°C or above, followed by a hydrogen reduction treatment.
• an oxygen containing gas at temperatures of 400°C or above
• a hydrogen reduction treatment With bimetallic or multimetallic catalysts serious problems may be encountered in regeneration.
• treatment in oxygen containing atmospheres at elevated temperatures can result in irreversible structural changes.
• iridium is relatively easily oxidized to IrO 2 which forms as separate, relatively large, crystals.
• reduction iridium forms as large crystals which results in significantly reduced catalytic activity and poorer selectivity towards unwanted products.
• Group VIII noble metal-containing catalysts e.g. reforming catalysts
• sulphur-containing compounds are decomposed and sulphur becomes bound to the noble metal surface.
• the effect is a drastic reduction in activity for the preferred hydrocarbon conversions.
• Some degree of in-situ regeneration may be possible for low levels of sulphur poisoning, but the process is still very difficult and requires conditions so severe that the structure of the noble metal component is usually damaged so that a complex redispersion treatment becomes necessary.
• in-situ regeneration is usually so difficult that the catalyst must be replaced.
• One objective of the present invention is to provide improved hydrocarbon conversion catalysts which when deactivated by coking, can be regenerated by procedures which involve treatment in an oxygen-containing atmosphere at temperatures below about 300°C.
• a second objective of the present invention is to provide improved catalysts which when poisoned with sulphur, can be regenerated by procedures which involve low temperature treatment in an oxygen-containing atmosphere.
• the invention also seeks to provide improved regeneration processes for such catalysts. It has been suggested that the regeneration characteristics of the catalysts deactivated by coking and/or poisoned by sulphur would be improved by the incorporation of materials in the catalyst which promote oxidation reactions.
• materials in the catalyst which promote oxidation reactions There are a significant number of substances which are known to be powerful oxidation catalysts. They include oxides of chromium, vanadium, manganese, cobalt nickel, rare earths, etc. (Germain J.E., Inter-Science Chem. Report 6 (1972) 101) and Group VIII noble metals such as palladium and platinum
• Group VIII noble metals like Pt, Ir, Pd, Rh, Ru and Os and alloys containing at least one of these metals are commonly used as catalysts for reactions involving hydrocarbons, but for economic reasons, the noble metals are used in low concentrations covering perhaps 1% of the surface area of the support material. When present in such small amounts they cannot be relied on, as oxidation catalysts, to significantly assist the "burn-off" reaction that occurs during heating of poisoned or deactivated catalysts in an oxygen-containing atmosphere.
• the active component a suitable material of this kind (hereinafter termed "the active component") was based on consideration of the following factors:
• a method for the regeneration of a catalyst of the noble metal type which has been poisoned by sulphur, deactivated by coking, or both characterised in that the catalyst is supported on a material comprising a conventional refractory inorganic oxide support material together with an active component consisting of one or more oxides selected from the group consisting of Cr 2 O 3 , MnO 2 , rare earth oxides, V 2 O 5 and MoO 3 , and the regeneration is effected by heating the catalyst in an oxygen-containing atmosphere at a temperature in the range 100° to 500°C, followed by a reduction treatment.
• the invention also includes a hydrocarbon conversion catalyst composition
• a hydrocarbon conversion catalyst composition comprising a catalyst of the noble metal type dispersed on a support material, characterized in that the support material comprises a conventional refractory inorganic oxide support material together with an active component consisting of one or more oxides selected from the group consisting of
• the catalyst when poisoned by sulphur, deactivated by coking, or both, can be regenerated by heating the catalyst in an oxygen-containing atmosphere at a temperature in the range 100° to 500°C, followed by a reduction treatment.
• the invention further includes a catalytic hydrocarbon conversion process which utilizes a hydrocarbon conversion catalyst composition comprising a catalyst of the noble metal type dispersed on a support material and in which the catalyst, after poisoning by sulphur, deactivation by coking, or both, is regenerated, characterised in that the catalyst support material comprises, a conventional refractory inorganic oxide support material together with an active component consisting of one or more oxides selected from the group consisting of Cr 2 O 3 , MnO 2 , rare earth oxides, V 2 O 5 and MoO 3 , and that regeneration is effected by heating the catalyst in an oxygen-containing atmosphere at a temperature in the range 100° to 500°C, followed by a reduction treatment.
• a hydrocarbon conversion catalyst composition comprising a catalyst of the noble metal type dispersed on a support material and in which the catalyst, after poisoning by sulphur, deactivation by coking, or both, is regenerated, characterised in that the catalyst support material comprises, a conventional refractory in
• the catalysts of the noble metal type to which this invention applies are the Group VIII noble metal and alloys containing at least one such metal.
• the noble metal comprises platinum or a bimetallic mixture of platinum and another. metal, preferably iridium.
• the conventional support material may comprise one of those materials commonly used for this function (as discussed above) such as refractory inorganic oxides, especially alumina and silica, carbon and silicon carbide, zeolitic materials or mixtures thereof.
• the support must contain or comprise an active component which may be one or more of the following oxides: Cr 2 O 3 , MnO 2 , rare earth oxides such as CeO 2 , V 2 O 5 and MoO 3 .
• the active component is Cr 2 O 3 .
• the active component should preferably be present as the oxide and not as an exchanged ion as the metal cations attached to lattice sites, particularly in zeolites, are believed not to be very effective oxidation catalysts.
• the support material should comprise more than 1% of the active component.
• the selection of a preferred concentration within this range is dependent on the consideration of a number of factors, including the following:-
• characteristics of the support such as porosity and absorptivity.
• a preferred support material in accordance with this invention comprises 5-15% of the active component, preferably Cr 2 O 3 , and 85-95% Al 2 O 3 , or SiO 2 , or mixtures thereof.
• the improved regeneration method involves a "burn-off" reaction during the treatment of the catalyst in an oxygen-containing atmosphere.
• oxygen gas or air diluted with an inert gas is used.
• the "burn-off" reaction is exothermal and, consequently, care must be taken to maintain the regeneration treatment temperature within the desired limits.
• One method of doing this is by control of the oxygen concentration. The concentration required will depend on factors such as the degree of coking, the reactor design and the regeneration treatment temperature and, hence, must be determined by experimentation
• the atmosphere may contain halogen compounds to make up for losses of halogens on the catalyst surface which were added during catalyst preparation to increase acidity.
• the regeneration treatment temperature may be in the range 100° - 500°C and preferably in the range
• the temperature selected will be dependent on many factors, for example, the composition of the catalyst and the propensity for detrimental effects to. occur under severe treatment conditions (relatively high temperature and/or long times) , the degree of deactivation by coking and/or poisoning by sulphur and, the desire to limit the time for regeneration by using as high a temperature as possible.
• the "burn-off" will be a function of both time and temperature.
• the treatment may be at a relatively high temperature for a short time or, at a relatively low temperature for a longer time.
• the optimum temperature for the treatment of particular catalyst in a reasonable time can be determined by experimental methods known to those skilled in the art.
• the regeneration treatment temperature range is preferably 250 - 325°C and most preferably 290 - 310°C.
• the regeneration treatment temperature range is preferably 150 - 300°C and most preferably 190-250°C.
• the conditions under which, and the manner in which, the reduction treatment is carried out forms no part of this invention and any suitable known treatment can be used.
• One possible reduction treatment is heating the catalyst in hydrogen at about 400°C.
• the improved method of regeneration of this invention is made possible by the presence in the catalyst composition of the active component.
• the treatment in the oxygen-containing atmosphere can be carried out in reasonable times at a lower temperature than was hitherto possible. As a consequence, permanent detrimental effects that can occur during such treatments under more severe conditions can be avoided.
• catalysts poisoned by sulphur can be regenerated by the method of this invention to an extent hitherto impossible.
• Alumina-chromia (A) support was prepared by a co-precipitation method. Powdered aluminium isopropoxide (Al(i-C 3 H 7 O) 3 , Merck, laboratory grade) and powdered, chromic nitrate (Cr (NO 3 ) 3 .9H 2 O, Hopkins and Williams, laboratory reagent grade) were added simultaneously with vigorous stirring to a 1 molar sodium hydroxide solution held at 50°C. The volume of sodium hydroxide solution was such that there was 10% in excess of NaOH than required for the precipitation of Al 2 O 3 and Cr 2 O 3 .
• the resulting mixture was held at 50°C and stirred for 12 hours and then the precipitate was filtered from the slurry and washed copiously with distilled water until the washings contained no sodium hydroxide.
• the product was finally dried in air at 100°C for 4 hours, and then heated in air at 400°C for 15 hours.
• the proportion of aluminium isopropoxide and chromic nitrate were such that the final product contained 14 weight percent Cr 2 O 3 .
• X-ray diffraction Cu K ⁇ radiation, Siemens diffractometer
• BET Brunauer-Emmett-Teller
• Alumina-chromia (B) support was prepared by impregnation of ⁇ -alumina (Woelm, W200 grade; specific surface area by BET 200m 2 g -1 ) with 0.1 molar chromic nitrate solution at room temperature. Water was removed from the slurry by evaporation at 100°C with continuous vigorous stirring, followed by heating in air at 400°C for 15 hours. The proportions of ⁇ -alumina and chromic nitrate solutions were such that the final product contained 14 weight percent Cr 2 O 3 .
• Silica-chromia support was prepared by the method of Example 2 except in that silica powder (Degussa Aerosil 200; specific surface area by BET 200m 2 g -1 ) was used instead of ⁇ -alumina. The final product contained 14 weight percent Cr 2 O 3 .
• Example 4 Preparation of a Platinum/Alumina Catalyst
• a platinum catalyst (Pt/ ⁇ -Al 2 O 3 ) was prepared by impregnation of ⁇ -alumina support (Woelm, W200 grade) with an aqueous solution of chloroplatinic acid containing 10 -2 g Pt per cc of solution. Impregnation was by the method of incipient wetness, using 1 cc of solution per g of ⁇ -Al 2 O 3 thus giving a platinum loading of 1 weight percent on a dry weight basis. Following impregnation, the material was dried in air at 100°C with vigorous stirring, and then reduced by heating at 400°C for 15 hours in hydrogen fed at a rate of 100 cc/minute at about atmospheric pressure.
• the Pt/ ⁇ -Al 2 O 3 catalyst of Example 4 was tested for the conversion of n-heptane. This was done using a flow reactor containing 0.25 g of catalyst at a reactor temperature of 400°C and at about 1 atmosphere pressure.
• the feed consisted of hydrogen and n-heptane in the molar ratio of 20/1, and the n-heptane feed rate corresponded to a weight hourly space velocity (WHSV) of 1. After 5 hours, 23.2% of the n-heptane was being converted.
• WHSV weight hourly space velocity
• the Pt/ ⁇ -Al 2 O 3 catalyst was poisoned by sulphur by adding 3 x 10 -3 g thiophene to the n-heptane feed stream under the reaction conditions described in Example 5. After this treatment, the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• the reactor was then fed for 2 hours with a mixture of 1 volume percent oxygen in helium at a rate of 100 cc/minute at a reactor temperature of 300°C under a pressure of about 1 atmosphere. Hydrogen at a rate of 100 cc/minute was then fed into the reactor for 2 hours at a reactor temperature of 400°C under a pressure of about 1 atmosphere.
• a platinum catalyst [Pt/Al 2 O 3 -Cr 2 O 3 (A) ] was prepared by the method of Example 4 except in that the alumina-chromia (A) support (Example 1) was used instead of ⁇ -alumina. The platinum loading was 1 weight percent on a dry-weight basis.
• Example 8 Conversion Characteristics of a Platinum/ Alumina-chromia Catalyst
• the Pt/Al 2 O 3 -Cr 2 O 3 (A) catalyst of Example 7 was tested for the conversion of n-heptane using the procedure given in Example 5. After 5 hours 20.0% of the n-heptane was being converted. Of the converted n-heptane, .36.0% appeared as isomerization products (2-ethylpentane, 3-methylhexane, 2,3-dimethylpentane and 2,2-dimethylpentane), 22.5% appeared as alicyclic products (methylcy ⁇ lohexane and ethylcyclopentane) and 18.3% appeared as aromatic products (toluene and benzene) .
• Example 8 the catalyst was poisoned by sulphur by the addition of 3 x 10 -3 g thiophen to the feed stream in a manner similar to that described in Example 6. After this treatment the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• the reactor was fed with an oxygen-helium mixture for 2 hours and then with hydrogen for 2 hours under the conditions described in Example 6 for a similar treatment.
• the activity of the catalyst for the conversion of n-heptane was then tested in the manner described in Example 5. After 5 hours, 15% of the n-heptane was being converted and the distribution of reaction products was similar to that given in Example 8.
• the catalyst was poisoned by a second treatment with 3 x 10 -3 g, thiophen, regenerated by an oxygen/hydrogen treatment, and then tested for n-heptane conversion as described above. After 5 hours, 10% of the n-heptane was being converted.
• a platinum-iridium catalyst (Pt-Ir/SiO 2 ) was prepared by impregnation of silica powder support (Degussa Aerosil 200) with an aqueous solution of chloroplatinic acid and chloroiridic acid containing
• Impregnation was by the method of incipient wetness, using 8 cc of solution per g of silica powder thus giving dry weight loadings of 0.2 weight percent platinum and 0.2 weight percent iridium. Following impregnation the material was processed in a manner similar to that described in Example 4.
• Example 10 The Pt-Ir/SiO 2 catalyst of Example 10 was tested for the conversion of n-heptane using the procedure given in Example 5. After 5 hours, 10% of the n-heptane was being converted. Of the converted n-heptane, 27.8% appeared as isomerization products (2-ethylpentane, 3-methylhexane, 2 , 3-dimethylpentane and 2,2-dimethylpentane), 28.8% appeared as alicyclic products (methylcyclohexane and ethylcyclopentane), and 23.0% appeared as aromatic products (toluene and benzene) .
• Example 12 The Effect of Sulphur poisoning and
• the catalyst was poisoned by sulphur by the method described in Example 6. After this treatment, the catalyst was poisoned to the extent that less than 1% of the. n-heptane was being converted.
• the reactor was fed with an oxygen/helium mixture for 2 hours and then with hydrogen for 2 hours under the conditions described in Example 6 except that for the oxygen treatment the reactor temperature was 200°C and not 300°C.
• the activity of the catalyst was then tested for n-heptane conversion in the manner described in Example 5. The catalyst was shown to have remained poisoned with less than 1% of the n-heptane being converted after 5 hours.
• a platinum-iridium catalyst (Pt-Ir/SiO 2 -Cr 2 O 3 ) was prepared by the method of Example 10 except in that the silica-chromia support (Example 3) was used instead of silica.
• the dry weight loading was 0.2 percent platinum and 0.2 weight percent iridium.
• the Pt-Ir/SiO 2 -Cr 2 O 3 catalyst of Example 13 was tested for the conversion of n-heptane using the procedure given in Example 5. After 5 hours 16.5% of the n-heptane was being converted. Of the converted n-heptane, 22.5% appeared as isomerization products (2-ethylpentane, 3-methylhexane, 2, 3-dimethylpentane and 2,2-dimethyl-pentane), 21.9% appeared as alicyclic products (methylcyclohexane and ethylcyclopentane), and 17.1% appeared as aromatic products (toluene and benzene).
• Example- 15 The Effect of Sulphur and Regeneration on the Conversion Characteristics of a Platlnum-Iridium/Silica-Chromia Catalyst
• Example 14 the catalyst was poisoned by sulphur by the method described in Example 6. After this treatment, the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• the reactor was fed with an oxygen/helium mixture for 2 hours and then with hydrogen for 2 hours under the conditions described in Example 12 for a similar treatment.
• the activity of the catalyst was then tested for n-heptane conversion in the manner described in Example 5.
• the activity of the catalyst as judged in terms of extent of n-heptane conversion an distribution of reaction products was found to be not significantly different from that of the same catalyst prior to sulphur poisoning.
• Pt-Ir/SiO 2 -Cr 2 O 3 catalyst the oxygen/hydrogen treatment resulted in complete regeneration from the sulphurpoisoned state.
• a platinum-iridium catalyst (Pt-Ir/ ⁇ -Al 2 O 3 ) was prepared by impregnating ⁇ -alumina support (Woelm
• Impregnation was by the method of incipient wetness, using 4 cc of impregnating solution per g of ⁇ -alumina thus giving dry weight loadings of 0.2 weight percent platinum and 0.2 weight percent iridium.
• Example 16 The Pt-Ir/ ⁇ -Al 2 O 3 catalyst of Example 16 was tested for the conversion of n-heptane using the procedure given in Example 5. After 5 hours 31.4% of the n-heptane was being converted. Of the converted n-heptane, 26.9% appeared as isomerization products (2-ethylpentane, 3-methylhexane, 2,3-dimethylpentane and
• Example 17 the catalyst was poisoned by sulphur by the method described in Example 6. After this treatment, the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• Oxygen/hydrogen treatment of this sulphur-poisoned catalyst in the manner described in Example 12 had no significant effect on the extent of n-heptane conversion at 400°C: the catalyst remained poisoned and the extent of n-heptane conversion remained less than 1%.
• Example' 19- The Effect of Coking and Regeneration on the Conversion Characteristics of a Platinum- Iridlum/Alumina Catalyst
• Pt-Ir/ ⁇ -Al 2 O 3 catalyst prepared by the method described in Example 17 was used for the conversion of n-heptane for 30 hours under the conditions described in Example 5.
• the n-heptane feed stream was then discontinued and the reactor fed for 1 hour with a gas mixture of 20 volume percent 1, 3-butadiene in nitrogen at a flow rate of 20 cm min at a reactor temperature of 400°C and about atmospheric pressure.
• the resulting activity of the catalyst for the conversion of n-heptane, tested using the procedure described in Example 5 was found to be very low in that less than 1% of the n-heptane was being converted.
• the reactor containing the deactivated catalyst was then fed with an oxygen/helium mixture and then with hydrogen under the conditions described in Example 12.
• Example 20 Preparation of a Platinum-iridium/ Alumina Chromia Catalyst
• a platinum-iridium catalyst [Pt-Ir/Al 2 O 3 -Cr 2 O 3 (A) ] was prepared by the method of Example 10 except in that the alumina-chromia support (Example 1) was used instead of silica.
• the dry weight loading was 0.2 weight percent platinum and 0.2 weight percent iridium.
• the Pt-Ir/Al 2 O 3 -Cr 2 O 3 (A) catalyst of Example 20 was tested for the conversion of n-heptane using the procedure given in Example 5. After 5 hours 36.0% of the n-heptane was being converted. Of the converted n-heptane, 22.9% appeared as isomerization products ( 2-ethylpentane, 3-methylhexane, 2, 3-dimethylpentane and 2,2-dimethylpentane), 8.1% appeared as alicyclic products (methylcyclohexane and ethylcyclopentane), and
• Example 21 the catalyst was poisoned by sulphur by the method described in Example 6. After this treatment the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• Oxygen/hydrogen treatment of this sulphurpoisoned catalyst in the manner described in Example 12 resulted in the regeneration of catalytic activity.
• the extent of n-heptane conversion and the distribution of reaction products was not significantly different from that described in Example 21.
• Three such sulphur-poisoning/regeneration cycles were carried out without any significant change in the activity of the regenerated catalyst for n-heptane conversion.
• Example 23 The Effect of Coking and Regeneration on the Conversion Characteristics of a Platinum- Irldium/Alumina-Chromia Catalyst
• the Pt-Ir/Al 2 O 3 -Cr 2 O 3 (A) catalyst prepared by the method described in Example 20 was used n-heptane conversion, deactivated and tested according to the method described in Example 19. After this treatment the activity of the catalyst was then very low in that less than 1% of the n-heptane was being converted. After treatment with oxygen/hydrogen as described in Example 1 the activity of the catalyst was tested for n-heptane conversion using the procedure described in Example 5. The activity of the catalyst, as judged from the extent of n-heptane conversion and distribution of reaction products, was not significantly different from that prior to deactivation. Three such deactivation/regeneration cycles were carried out without significant change in the activity of the regenerated catalyst.
• a platinum-iridium catalyst [Pt-Ir/Al 2 O 3 -Cr 2 O 3 (B) ] was prepared by the method of Example 16 except in that alumina-chromia (B) (Example 2) was used instead of alumina. The dry weight loading was 0.2 weight percent platinum and 0.2 weight percent iridium.
• Example 25 Conversion Characteristics of a Platinum- Irldlum/Alumlna-Chromia Catalyst
• the Pt-Ir/Al 2 O 3 -Cr 2 O 3 (B) catalyst of Example 24 was tested for the conversion of n-heptane using the procedure described in Example 5. After 5 hours 27.4% of the n-heptane was being converted. Of the converted n-heptane, 21.5% appeared as isomerization products (2-ethylpentane, 3-methylhexane, 2,3-dimethylpentane and 2,2-dimethylpentane), 15.2% appeared as alicyclic products (methylcyclohexane and ethylcyclopentane), and 19.2% appeared as aromatic products (toluene and benzene).
• Example 25 the catalyst was poisoned by sulphur by the method described in Example 6. After this treatment the catalyst was poisoned to the extent that less than 1% of the n-heptane was being converted.
• Oxygen/hydrogen treatment of this sulphur poisoned catalyst in the manner described in Example 12 almost totally restored the activity of the catalyst for n-heptane conversion.
• Oxygen/hydrogen treatment of this sulphur poisoned catalyst in the manner described in Example 12 almost totally restored the activity of the catalyst for n-heptane conversion.

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