Experimental evidence for the pore continuum in hybrid catalysts used in the selective deep catalytic cracking of n-hexane and petroleum naphthas

The hybrid catalyst investigated in this work comprises an acidified silica-rich ZSM-5 zeolite, the microporous H-silicalite, and a mesoporous cocatalyst, being an amorphous silica-alumina doped with molybdenum and cerium oxides. When compared to a mechanical mixture of extrudates made of H-silicalite and silica-alumina based cocatalyst, respectively, the hybrid catalyst gives faster adsorption of nitrogen and desorption of preadsorbed nitrogen. On the other hand, a much higher conversion of n-hexane (cracking) was obtained with the hybrid catalyst while the product selectivities are almost the same for all the cases. Such behavior is ascribed to the kinetic effect of the pore continuum being formed in the hybrid catalyst pore system, which has as a consequence to speed up the diffusion of reactant molecules and that of reaction products from the zeolite micropores. By changing the support for the cocatalyst, which is now a mesoporous silica, we observe the same pore continuum effect, i.e. the resulting hybrid catalyst experiences a very significant activity enhancement. (c) 2005 Elsevier Inc. All rights reserved.