Density Functional Theory Investigation on the Effect of Alkali Metal Cations on the Catalytic Performance for Cu plus Y Zeolites in Oxidative Carbonylation of Methanol

On the basis of density functional theory, influence of co-cations (M = Li+, Na+, K-4, Rb+) adjacenting active center Cu+ on the electronic properties and catalytic activity of Cu+Y zeolites in oxidative carbonylation of methanol to dimethyl carbonate was investigated. CuMY stable configurations were constructed, CO insertion CH3O species to CH3OCO was used to evaluate the catalytic activity of CuY zeolites, due to the fact that it was the rate-limiting step of oxidative carbonylation of methanol. The calculation results indicate that Li+, Na+, K+ cations can locate site I ' in small cages of Y zeolites surrounding the active center Cu+, the adsorption energy of CH3OH, CO, CH3O and co-adsorbed CO/CH3O on CuMY zeolite increases gradually with increase of cation size, the stability of transition states for CO insert into CH3O reaction comes to decrease, increases the activation barriers and the corresponding catalytic performance declines. Whereas, Rb+ and Cs(+)cations located II * in the supercage as increase in cation size, decreases activation energy for CO insertion reaction, improves the stability of transition states and the catalytic activity of CuY zeolites. The order of catalytic activity of CuMY zeolites is CuLiY-I '>CuCsY-II * >CuNaY-I '>CuRbY-II * >CuKY-I '> CuCuY-I '. The CuLiY-I ' catalyst exhibits the best catalytic performance with a lowest rate-limiting reaction activation barrier of 52.74 kJ/mol.