HOMOLOGATION OF PROPENE WITH METHANE USING NICKEL-SUPPORTED CATALYSTS - A SURFACE CHARACTERIZATION STUDY

The homologation of propene with methane was studied using alumina- and silica-supported nickel catalysts. The catalysts were activated under a methane flow previous to the reaction. Experiments carried out in a propene/methane mixture at 350C showed that the Ni/SiO2 system was more active for the homologation reaction (81.4% selectivity to butanes) than its alumina analog (6.2% selectivity to C4 compounds). From control experiments carried out under a nitrogen atmosphere and in a hydrogen-activated catalyst, it was concluded that the methane molecule incorporates into the hydrocarbon chain. The XPS studies showed the presence of carbonaceous species (but not necessarily graphitic) on the catalytic surfaces. The concentration in the silica catalyst was higher than that in its alumina analog, suggesting that, most probably, these species were involved as intermediates in the propene homologation reaction. The silica-based catalyst showed higher metal dispersion than that found in its alumina counterpart. This can be attributed to the formation of NiAlO4 on the catalyst surface, which can also explain the lower activity observed for butane production. On the basis of the experimental evidence, a propene homologation mechanism can be proposed which involves the reaction of methane with the metal to generate CHx species (where x = 0, l, 2, or 3), which in turn react with propene, producing the homologation products (butanes). © 1991.