Acid Site Density as a Kinetic Descriptor of Catalytic Reactions over Zeolites

Abstract

A mathematical framework for the quantitative description of site density dependence of catalytic data (activity and selectivity) was developed considering that changes in the electrostatic contribution to the Gibbs energy of an elementary reaction on the acid sites in zeolites depend on the proximity of these sites. For the two-step sequence with the most abundant surface intermediate, an expression for turnover frequency explicitly containing the acid site density was derived. The treatment was extended to linear sequences of elementary reaction and analysis of the acid site density on selectivity in parallel and consecutive reactions, allowing to quantitatively relate the ratio between products for such reactions. Experimental data on Prins condensation of isopulegol with acetone and transformations of syngas over mesoporous H-ZSM-5 supported cobalt nanoparticles to a mixture of iso- and normal hydrocarbons were used as a show case.