The Thermo-Catalytic Cracking of Hydrocarbons: Effect of Polymethylbenzenes Added to the n-Hexane Feed on the Reactivity of ZSM-5 Zeolite Containing Hybrid Catalyst

摘要

Hybrid catalyst containing an acidic ZSM-5 zeolite and a Ni bearing co-catalyst, when compared to its reference ZSM-5 catalyst, showed significant differences in terms of conversion and product yields in the thermo-catalytic cracking (TCC) of feeds comprising n-hexane and some 1,2,4-trimethylbenzene (TMB). Almost no difference was observed with the n-hexane feed containing bulkier pentamethylbenzene (PMB). The obtained results were interpreted using two physico-chemical properties of these aromatics and the catalysts used, i.e. (1) the accessibility of the zeolite internal surface to these molecules and (2) the compliance of these catalytic data with the hydrocarbon pool mechanism when hydrogen spillover species HSO phenomena were involved. TMB, when adsorbed by the ZSM-5 micropores, might induce some partial pore blocking, whereas PMB was completely excluded from the internal surface of the zeolite particles. At larger concentrations of TMB, the hydrogen spillover species showed some significant retarding effect on the coke formation while with a n-hexane feed containing PMB, this effect was much less visible because the adsorbed PMB was structurally much closer to the coke-precursor ion than the TMB, or because the less methylated benzene could undergo conversion in accordance with a newly hypothesized mechanism. Finally, the (HSO) species could affect the reaction intermediates only when the latter were formed on the external surface of the zeolite.