Study On The Performance Of Supported Copper - Based Catalysts For CO ₂ Hydrogenation

A series of high surface areas and different mental oxide content and different Zn/Cu ratios of Cu-Zn-Zr/SBA-15 mesoporous catalysts CZZx/SBA-15(X=0.3,0.4, 0.5,0.6) and CZyZ/SBA-15(Y=0.3、0.5、0.8、1.0) were directly synthesized by impregnation method. The catalysts were characterized by N2 adsorption-desorption(BET), X-ray diffraction(XRD), transmission electron microscopy(TEM), H2 temperature-programmed reduction(H2-TPR), CO2 temperature-programmed desorption(CO2-TPD) and N2O titration technique(N2O-RFC). The catalytic activities of these catalysts were determined on the hydrogenation of CO2 to methanol in a fixed-bed reactor.The results showed that CZZX/SBA-15 and CZyZ/SBA-15 catalysts possessed a highly ordered mesoporous structure, in which different grain size CuO、ZnO、ZrO2 species dispersed on the surface of SBA-15. A approximate linear relationship between the methanol synthesis activity and the total Cu° surface area SCu(m2/g) was observed. CZZ0.4/SBA-15 catalyst showed the largest methanol selectivity SCH3OH = 54.32%, which increased by 24.85% as compared with CZZ catalyst. However, the methanol synthesis selectivity and yield decreased with the increasing of metal oxide content, which strongly suggested that the surface structure of the CZZX/SBA-15 catalysts played an important role in CO2 hydrogenation to methanol. With the increase of Zn/Cu ratios, the CO2 hydrogenation to methanol catalytic activitys of CZyZ/SBA-15 catalysts were "volcanic" changes, but CO2 conversion rate trends were not obvious, the result indicated that the catalyst the active sites Cu°directly affect methanol synthesis. Besides the interaction ZnO and active sites Cu°in the catalysts promoted CO2 hydrogenation to methanol, combined with known the catalytic activities, when the Zn/Cu ratio was close to 0.5, the active sites were located at the Cu°-ZnO interface suggested that its were optimum catalytic activity.A small scale test plant with a methanol production capacity of 10 kg/day has been designed and constructed in order to examine the performance of CZA+CZAZ Cu-based multicomponent double catalysts under nearly practical reaction conditions. The production rate of methanol over the multicomponent double catalysts was around 132.9g-CH3OH/(L-1h-1) under the reaction conditions of T=240℃, P=4MPa and SV=6000h-1.