Effect of environment around the active center Cu~+ species on the catalytic activity of CuY zeolites in dimethyl carbonate synthesis: A theoretical study

摘要

A density functional theory method has been used to investigate the effect of environment around the active center Cu~+ species on the catalytic activity in the oxidative carbonyiation of methanol to dimethyl carbonate over CuY zeolites. Based on the configuration of Cu~+ located in the supercage, Cu~+ or Cs~+ species at the sites adjacent to the active center Cu~+ species in the supercage are considered as the surrounding environment. The results indicate that the presence of Cu~+ in the supercage adjacent to the active center improves the adsorption energy of co-adsorbed CO and elongates the Cu-OCH3 bond in co-adsorbed CO/CH3O system, stabilizes the transition state for the reaction of CO insertion, and ultimately makes the active center Cu~+ species exhibit better catalytic activity. Whereas, Cu~+ species at adjacent site in the smallcage plays an opposite role. More importantly, introducing Cs species into the supercage of CuY zeolite significantly improves the adsorption energy of co-adsorbed CO and the stability of transition state configuration for CO insertion reaction, thus, leads to the best catalytic performance among four types of catalysts, which is consistent with the previous experimental results.