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 Cuβ catalysts was investigated by oxidative carbonylation of ethanol in the gas-phase reaction. Zeolite β crystals with varying Si/Al ratio were obtained after different content aqueous NH3·H2O solution treatment. Cuβ 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·H2O for β zeolite facilitated selective extraction of extra-framework silicon, which produce enough room for the active center Cu+. The reaction of forming active sites for Cuβ 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 Hβ 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, Cuβ catalyst without extra-framework silicon has better catalytic activity.

• Effect of extra-framework silicon of Cuβ catalysts. • The treatment of NH3·H2O for β zeolite facilitated selective extraction of extra-framework silicon. • Extraction of extra-framework silicon will reduce the reactive energy barrier.