Structural changes on RuCu/KL bimetallic catalysts as evidenced by n-hexane reforming

The reaction of n-hexane was studied over two series of bimetallic RuCu/KL and the results were related to the surface characteristics of the catalysts. The catalysts containing 2 wt% of ruthenium and copper between 0 and 1.5%, were prepared following two different procedures: series (s) by successive wetness impregnation of KL-zeolite support with tri-ruthenium dodecacarbonyl and copper nitrate acetone solutions; series (c) by coimpregnation of the zeolite support with tri-ruthenium 2,4-pentanedionate and copper nitrate acetone solutions. The catalytic activity measurements were performed in a fixed bed flow reactor at 650 K and atmospheric pressure. For series (s) both metal dispersion and activity decrease as the copper content increases, while the TOF is not modified. For series (c) dispersion, activity and TOF decrease with the increasing of copper content. All the catalysts essentially exhibit hydrogenolysis activity with a low selectivity towards benzene that, nevertheless, increases with the copper loading more appreciably for series (c) than for series (s). The catalytic results suggest that copper and ruthenium form bimetallic particles in both series. For series (s) a covering effect of the ruthenium particles by copper without significant Ru-Cu interaction, is deduced. For series (c) important changes in the catalytic properties by effect of the copper are observed, which indicate the formation of a surface alloyed phase. In addition, copper seems to increase the fraction of active sites outside the KL-zeolite, which are more easily poisoned by coke deposition than those located inside the KL channels. (C) 2007 Elsevier B.V. All rights reserved.