A Theoretical Investigation of Dimethyl Carbonate Synthesis on Cu−Y Zeolite

Abstract

A theoretical analysis of the mechanism of dimethyl carbonate (DMC) synthesis via oxidative carbonylation of methanol on Cu-exchanged Y zeolite, Cu−Y, was explored using density functional theory. These calculations show that methanol adsorbs in the presence of oxygen to form coadsorbed methoxide and hydroxide species and dimethoxide species on extraframework Cu+ cations. DMC can form by CO addition to the former species to produce monomethyl carbonate species, which then react with additional methanol or by CO addition to dimethoxide species to form DMC directly. The turnover frequency for DMC synthesis is estimated to be 1.2 × 10-5 s-1 for the reaction conditions used in the experimental work of Zhang and Bell (J. Catal., in press). This value compares very closely with that observed, 5 × 10-5 s-1. The calculated value of the apparent activation energy is 15.0 kcal/mol, in good agreement with that measured experimentally, 14.8 kcal/mol. The effects of methanol and oxygen on the adsorption of CO have als...