Enhanced stability of Fe-modified CuO-ZnO-ZrO_(2)-Al_(2)O_(3)/HZSM-5 bifunctional catalysts for dimethyl ether synthesis from CO_(2)hydrogenation

摘要

A series of iron(Fe)modified CuO-ZnO-ZrO_(2)-Al_(2)O_(3)(CZZA)catalysts,with various Fe loadings,were prepared using a co-precipitation method.A bifunctional catalyst,consisting of Fe-modified CZZA and HZSM-5,was studied for dimethyl ether(DME)synthesis via CO_(2)hydrogenation.The effects of Fe loading,reaction temperature,reaction pressure,space velocity,and concentrations of precursor for the synthesis of the Fe-modified CZZA catalyst on the catalytic activity of DME synthesis were investigated.Long-term stability tests showed that Fe modification of the CZZA catalyst improved the catalyst stability for DME synthesis via CO_(2)hydrogenation.The activity loss,in terms of DME yield,was significantly reduced from 4.2%to 1.4%in a 100 h run of reaction,when the Fe loading amount was 0.5(molar ratio of Fe to Cu).An analysis of hydrogen temperature programmed reduction revealed that the introduction of Fe improved the reducibility of the catalysts,due to assisted adsorption of H2 on iron oxide.The good stability of Femodified CZZA catalysts in the DME formation was most likely attributed to oxygen spillover that was introduced by the addition of iron oxide.This could have inhibited the oxidation of the Cu surface and enhanced the thermal stability of copper during long-term reactions.