Study Of CuO-ZnO Catalyst For CO₂ Hydrogenation To Methanol

The greenhouse effect caused by the increase in carbon dioxide (CO2) concentration in the atmosphere has affected the survival and offspring of hunman greatly. The decrement of CO2 emission and the effective utilization of CO2 have been an urgent problem recently. Methanol is an important feedstocks for the organic chemical industry, as well as a potential alternative to fossil fuel. Therefore, CO2 hydrogenation to methanol is of great significance in the field of environmental protection and energy.In this article, the CuO-ZnO catalysts were prepared by different method. The effects of ZnO with different morphology, the ratio of copper to zinc and the addition of Mn on the physicochemical properties of CuO-ZnO and catalytic properties for CO2 hydrogenation to methanol were studied. The results obtained are as follows.1. The influence of ZnO with different morphology on the CuO-ZnO catalystsThree different morphologies (plate, rod, filament) for ZnO crystal were synthesized by hydrothermal method, and the CuO-ZnO catalysts were synthesized by a method of physical mixing. The results indicate that ZnO enhances the dispersion of CuO, and the dispersion ability of catalysts increase in the order of CZ-plate< CZ-rod< CZ-filament. ZnO with different morphology exhibits different lattice plane superiority, and the I(002)/I(100)of ZnO decreases in the order of plate> filament> rod. The different lattice plane leads to different interaction between Cu and ZnO. There is a strong interaction between Cu and ZnO-plate, which is unfavorable for the reduction of CuO. The CuO-ZnO catalysts prepared with different ZnO exhibit different surface basicity, and the rod ZnO possesses the weakest surface basicity. The CO2 conversion is related to the SCu, as well as the reduction of CuO. The CO2 conversion increases in the order of CZ-plate< CZ-rod< CZ-filament. The methanol selectivity is related to the catalysts surface basicity, the higher basicity can enhance methanol selectivity.2 The influence of the ratio of copper to zinc on CuO-ZnO catalystsCuO-ZnO catalysts with different ratio of copper to zinc were prepared by hydrothermal synthesis. With increasing the Cu content, the Cu surface area takes on a volcano varation trend, and similar variation was observed for the reduction of CuO. There is a small change for the strength of the basic sites, but the amount of basic site decreases. A maximum of CO2 conversion was obtained on the sample CZ-2. The CO2 conversion depends on the SCu.3 The influence of Mn on the CuO-ZnO catalystsMnO2-CuO/ZnO catalysts with different Mn/Cu mole ratio were prepared by ultrasound-assisted impregnation. An appropreate amount of Mn can promote CuO dispersion and leads to the easier reduction of CuO. The surface basicity of catalysts is related to the amount of Mn. However, the excessive Mn will cover the catalyst surface and lead to less active site. As the Mn/Cu mole ratio is 0.6, the highest CO2 conversion and methanol yield are obtained.