Silica-Zirconia Mixed Oxides Supported Copper Catalysts In The Liquid-Phase Oxidative Carbonylation Of Methanol

Dimethyl carbonate (DMC) is an environmentally benign chemical, and thedevelopment of clean technology for DMC synthesis has gained markedcommercial and academic interest. In the present study we have investigatedsystematically the preparation methods and catalytic performances ofsilica-zirconia mixed oxides supported Cu catalysts in the synthesis of DMC bymethanol oxidative carbonylation in a slurry reactor. The influences of variouspreparation parameters including Cu precursors, supporters, calcinationtemperatures as well as reaction conditions on the catalytic activities werestudied, both the supporters and catalysts were characterized by means of N₂physisorption, XRD, FT-IR, NH₃-TPD along with TG-DTA. Several significantconclusions have been obtained as follows:1) According to the results of N₂ physisorption, XRD, FT-IR, NH₃-TPD andTG-DTA measurements, it is shown that Zr species have segregated toward thesurface and entered the silica matrix, then led to the formation of Si-O-Zr bonds.Both Bronsted acid sites and Lewis acid sites have been detected on the solidwith Si/Zr=30 but neither has been done on that of Si/Zr=1, which areconsistent with Tanabe's models. The amounts of acid sites of SiO₂-ZrO₂ solidswas increased first then declined with increasing Si/Zr ratios, and the highestacid amounts was obtained in the case of Si/Zr=10 (0.750 mmol·g^-1).2) For sol-gel derived catalysts, the optimum preparation conditions are:CuCl₂%=3mol%, Si/Zr=30, V_TEOS/V_Hac=2, V_H2O/V_TEOS=3 and calcinationtemperature=450℃, over which methanol conversion, selectivity as well as STY to DMC attained 11.33%,79.31% and 1.63g·g^-1·h^-1, respectively.3) The highly dispersed Cu species on the supporter was found to be criticalto the high activity for the oxidative carbonylation of methanol. Appropriatecalcination temperatures(450℃) may lead to better catalytic performances, butcalcining at an excessive temperature(550℃) would give rise to a loss ofcatalytic activity..4) The catalysts prepared by a microwave promting process presenteddesirable catalytic activities in the synthesis of dimethyl carbonate, in the case ofmicrowave irradiation for 5h, the obtained experimental data of STY, C_m and S_mwere 1.35g·g^-1·h^-1, 9.04% and 81.92%, respectively.