______________________________________component , wt . % broad range preferred range______________________________________pt 0 . 1 - 2 0 . 3 - 1 . 0cl 0 . 1 - 3 . 0 0 . 5 - 2 . 0cs ( 1 ) ( 2 ) support balance______________________________________ ( 1 ) sufficient to provide a cs / cl atomic ratio of about 0 . 005 - 0 . 2 . ( range , 0 . 0019 - 2 . 25 wt . %) ( 2 ) sufficient to provide a cs / cl atomic ratio of about 0 . 010 - 0 . 15 . ( range 0 . 0038 - 1 . 69 wt . %) the support material is preferably alumina xerogel , but may comprise mixtures of alumina with minor proportions of silica , zirconia , titania or the like . conventional catalyst preparation techniques are employed , usually involving at least two separate impregnations of calcined 1 / 32 - 1 / 8 inch diameter alumina extrudates with aqueous solutions of the metal salts and additional chloride if required . the cesium is separately impregnated , preferably in the form of a solution of cesium nitrate , cesium chloride , cesium carbonate , etc . a preferred procedure consists in first impregnating the support with an aqueous solution of h 2 ptcl 6 and hcl if required to give the desired cl content in the finished catalyst , drying at about 100 °- 250 ° f ., and then impregnating with an aqueous solution of csno 3 , followed by final drying and calcination at about 800 °- 1200 ° f . however , suitable catalysts have been prepared by first impregnating with cesium , drying and then either simultaneously or sequentially impregnating with pt and any other desired components . preferred catalysts of this invention also comprise small proportions , about 0 . 02 - 0 . 5 wt . %, preferably about 0 . 05 - 0 . 25 wt . %, of iridium and / or rhodium . these metals contribute thermal stability to the catalyst , which is particularly desirable in the case of high severity operations carried out at average bed temperatures above about 925 ° f . they may be incorporated into the catalyst by conventional methods , as e . g . impregnation with aqueous solutions of h 2 ircl 6 and / or h 2 rhcl 6 , either sequentially or simultaneously with impregnation of the pt component . in addition to , or in lieu of iridium and rhodium , similar proportions of other metals known to enhance stability and / or selectivity of pt -- al 2 o 3 reforming catalysts may be incorporated , e . g . rhenium , manganese , gallium , indium , germanium , tin , zinc , nickel , cobalt , iron , etc . the finished catalysts are particularly useful for the severe reforming of naphthas boiling between about 125 °- 420 ° f ., preferably about 150 °- 375 ° f . preferably the naphtha feed should comprise a substantial proportion , i . e . at least about 30 weight - percent of c 6 - c 12 paraffin hydrocarbons , such as are normally found in straight - run naphthas . suitable reforming - dehydrocyclization conditions for such feeds fall within the following ranges : ______________________________________reforming - dehydrocyclization conditions broad range preferred range______________________________________temp ., ° f . ( av . bed ) 850 - 1150 900 - 1050h . sub . 2 pressure , psi 25 - 500 50 - 250lhsv , v / v / hr 0 . 5 - 5 1 - 3h . sub . 2 / oil , scf / b 100 - 6000 1000 - 4000______________________________________ the selection of optimum conditions from the above ranges will of course depend upon a great variety of factors related to feed and catalyst composition , market economy and the like . those skilled in the art will readily understand that severe process combinations will increase the yield of c 6 - c 8 aromatics while decreasing c 5 + yields , and vice versa . under the foregoing conditions , adequate catalyst activity is usually maintained for periods of 3 - 10 days , whereupon the catalyst is oxidatively regenerated and rejuvenated by oxychlorination as described for example in u . s . pat . nos . 3 , 981 , 823 and 4 , 044 , 955 . presently available data indicates that at least about 50 of such reforming - regeneration - oxychlorination cycles are feasible before replacement of the catalyst becomes necessary as a result of unfavorable product distribution ratios . for the dehydrocyclization of pure or mixed c 7 - c 12 paraffins the same general process conditions and preferences described above are utilized . however , for the dehydrocyclization of n - hexane , temperatures in the range of about 950 °- 1100 ° f . are preferred . a base catalyst was first prepared by impregnating 1 / 16 inch diameter extrudates of gamma alumina with an aqueous solution containing dissolved therein sufficient h 2 ptcl 6 , h 2 ircl 6 , and hcl to give final pt , ir and cl contents of 0 . 6 %, 0 . 10 % and 1 . 2 % by weight , respectively . the extrudates were drained , dried at about 250 ° f ., and divided into several lots which were then separately impregnated with aqueous solutions of cesium nitrate of varying concentration , calculated to give four final catalysts of the following compositions : table 1______________________________________catalyst a b c d______________________________________pt , wt . % 0 . 6 0 . 6 0 . 6 0 . 6ir , wt . % 0 . 1 0 . 1 0 . 1 0 . 1cl , wt . % 1 . 2 1 . 2 1 . 2 1 . 2cs , wt . % 0 . 12 0 . 35 0 . 41 3 . 4cs / cl atomic ratio 0 . 0265 0 . 077 0 . 091 0 . 75______________________________________ after calcination for 1 hour at 1050 ° f ., each of the foregoing catalysts , as well as a sample of the base catalyst containing no cs , were activity tested for the reforming - dehydrocyclization of a blend of a straight run naphtha and a catalytically cracked naphtha , the blend having the following characteristics : ______________________________________ feed characteristics______________________________________gravity , ° api 59 . 0boiling range , ° f . 155 - 362octane no . ( res . calculated ) 64 . 5sulfur 0 . 88 ppmnitrogen 0 . 7 ppm______________________________________ ______________________________________ hydrocarbon components , wt . % ______________________________________paraffinic , total 55 . 8n - hexane 7 . 14c . sub . 7 15 . 31c . sub . 8 10 . 54c . sub . 9 7 . 10c . sub . 10 3 . 67naphthenic , total 20 . 11cyclohexane 1 . 03cyclo c . sub . 7 6 . 51cyclo c . sub . 8 4 . 19cyclo c . sub . 9 2 . 66cyclo c . sub . 10 2 . 01aromatic , total 24 . 01benzene 1 . 43toluene 5 . 15c . sub . 8 9 . 48c . sub . 9 5 . 78c . sub . 10 1 . 65______________________________________ each catalyst was tested at 925 °, 950 °, and 975 ° f ., and in all runs at 2 . 0 lhsv , 225 psig , and 5000 scf h 2 / barrel . the c 1 - c 3 and c 5 yields , and yields of benzene synthesized ( over and above benzene present in the feed ) were as follows : table 2______________________________________ temp ., ° f . yields , wt .% of feed 925 950 975______________________________________base catalyst - 0 % csc . sub . 1 - c . sub . 3 9 . 7 12 . 8 18 . 1c . sub . 5 + 82 . 3 78 . 2 71 . 8benzene 3 . 58 4 . 65 6 . 06catalyst a - 0 . 12 % csc . sub . 1 - c . sub . 3 8 . 6 10 . 3 11 . 9c . sub . 5 + 84 . 1 81 . 6 78 . 2benzene 3 . 59 4 . 37 5 . 94catalyst b - 0 . 35 % csc . sub . 1 - c . sub . 3 7 . 0 8 . 9 13 . 4c . sub . 5 + 86 . 8 84 . 3 78 . 4benzene 3 . 05 3 . 68 5 . 30catalyst c - 0 . 41 % csc . sub . 1 - c . sub . 3 5 . 6 8 . 1 12 . 5c . sub . 5 + 89 . 8 85 . 6 80 . 6benzene 2 . 69 3 . 26 4 . 01catalyst d - 3 . 4 % csc . sub . 1 - c . sub . 3 2 . 5 3 . 5 5 . 1c . sub . 5 + 95 . 7 94 . 5 92 . 4benzene 1 . 0 1 . 08 1 . 23______________________________________ the foregoing results are plotted on the attached drawing and it will be seen that consistently higher benzene yields are obtained at any given c 5 + yield as a result of adding 0 . 12 % to 0 . 41 % of cs to the base catalyst . catalyst c , containing 0 . 41 % cs , gave a slightly unfavorable result at 975 ° f ., but is advantageous at below that temperature . in all probability it would also be advantageous at above 975 ° f . for other feedstocks and / or operating conditions . the results for catalyst d clearly show that 3 . 4 % cs is highly detrimental to dehydrocyclization activity . while it is somewhat difficult to accurately assess relative hydrocracking selectivity in the reforming of the low end point feed employed in the foregoing examples , a clear indication of desirable selectivity is found by comparing the ratios of dry gas produced vs . pentanes produced at 975 ° f . : table 3______________________________________ product mol - ratio , catalyst c . sub . 1 - c . sub . 3 / c . sub . 5______________________________________base catalyst , 0 % cs 6 . 44a - 0 . 12 % cs 4 . 41b - 0 . 35 % cs 5 . 07c - 0 . 41 % cs 6 . 13d - 3 . 4 % cs 6 . 65______________________________________ it will be seen that in all cases except catalyst d , the addition of cs gave reduced dry gas make per mole of pentanes produced . another catalyst of this invention was prepared by first impregnating alumina extrudates with a solution of cesium nitrate , drying , impregnating with a solution of iridium chloride , drying again , impregnating with a solution of platinum chloride , and finally drying and calcining . the resulting catalyst contained 0 . 59 wt . % pt , 0 . 1 wt . % ir , 0 . 17 wt . % cs and 0 . 8 wt . % cl . a feedstock consisting essentially of n - hexane was subjected to dehydrocyclization over this catalyst at 2 . 0 lhsv , 100 psig and 5000 scf / b of hydrogen . the results at various temperatures were as follows : table 4______________________________________ product , wt . % of feedtemp ., ° f . benzene c . sub . 5 + ______________________________________ 900 6 . 9 82 . 5 950 11 . 4 75 . 01000 23 . 9 58 . 31050 19 . 5 44 . 3______________________________________ data obtained from similar runs utilizing a pt -- ir -- al 2 o 3 -- cl catalyst free of cs , but ( by an inadvertence in its preparation ) containing only about 0 . 3 wt . % pt , clearly indicate that much improved selectivity was achieved by the addition of cs , but the relative activities are probably not comparable due to the differences in pt content . results substantially similar to those presented in the foregoing examples are obtained when equivalent atomic proportions of rh are substituted for the ir component of the catalysts . the principal function of the ir and / or rh component is to increase stability of the catalysts . the following claims and their obvious equivalents are believed to define the true scope of the invention .