Influence of brønsted-acid and cation-exchange sites on ethene adsorption in ZSM-5

Abstract

Abstract Differential heats of adsorption were measured for ethane and ethene on a siliceous ZSM-5, H-[Al]ZSM-5, H-[Fe]ZSM-5, Li-[Al]ZSM-5, H(Zn)-[Al]ZSM-5, and H(Zn)-[Fe]ZSM-5 at 195 K in order to characterize the nature of interactions between the olefin functional group and both Bronsted sites and exchanged metal cations. On siliceous ZSM-5, the differential heats for ethane and ethene were both 31 ± 1 kJ/mol, independent of coverage. While the additional interaction of ethane with Li and Zn-cation sites was negligible and only about 2 kJ/mol with Bronsted sites, the additional heats of adsorption for ethene were negligible on Li sites, 8 kJ/mol on Bronsted sites, and 14 kJ/mol Zn sites. Results were similar for exchanged [Al]ZSM-5 and [Fe]ZSM-5. Density functional theory calculations with different dispersion-corrected generalized gradient approximation functionals correctly predict the increased interaction of ethene with acid sites but overestimate the strength of interaction of proton and Li with C C double bonds.