Effect of extra-framework silicon on the catalytic activity of Cuβ zeolite catalyst, for synthesis of diethyl carbonate by oxidative carbonylation of ethanol

Effect of extra-framework silicon of Cu beta catalysts was investigated by oxidative carbonylation of ethanol in the gas-phase reaction. Zeolite beta crystals with varying Si/Al ratio were obtained after different content aqueous NH3 center dot H2O solution treatment. CO catalyst with low Si/Al ratio has shown better catalytic activity for oxidative carbonylation of ethanol to diethyl carbonate (DEC). From X-ray powder diffraction (XRD). XPS, and ICP analysis, it can be concluded that the treatment of NH3 center dot H2O for beta zeolite facilitated selective extraction of extra-framework silicon, which produce enough room for the active center Cu+. The reaction of forming active sites for Cu beta without extra-framework silicon was studied on a molecular level using density functional theory (DFT) and transition-state theory. The reactive energy barrier of the reaction over H beta without extra-framework silicon was lower than that with extra-framework silicon, mainly because the stereo-hindrance of SiO2 in the support has great effect on CuCl activation. And the presence of extra-framework silicon of the support blocked the attack of Cu+ to O atom. Hence, Cu beta catalyst without extra-framework silicon has better catalytic activity. (C) 2011 Elsevier B.V. All rights reserved.