Study On Surface Modification Of Cu-ZnO-ZrO 2 Catalyst For Hydrogenation Of CO

CO2 was a highly oxidized compound, owning stable thermodynamic property and low activity.To utilize CO2, it was necessary to overcome the thermodynamic energy barrier, so it was key and difficult to research and develop the catalyst. The preparation conditions and basic additives could change the surface properties of the catalysts and then influence the activity of the catalysts.In this paper, with the co-precipitation method, the effects of pH value, precipitation temperature, aging time and CaO promoter on the performance and structure of Cu-ZnO-ZrO2 catalyst for the synthesis of methanol from the hydrogenation of CO2 were explored:pH value affected the composition of precursor phase. When pH was 8, in addition to aurichalcite,the malachite also appeared in the precursor. With the increase of the pH, aurichalcite increased, malachite gradually disappeared; the particle size of CuO and ZnO decreased first and then increased; weak activity and strong activity transformed moderate activity on surface acidity and alkaline of the catalyst; the specific surface area of copper, the dispersions of copper, the conversion of CO2, the selectivity of methanol, the yield of methanol all increased first and then decreased. Catalyst activity was influenced by both aurichalcite and malachite.Precipitation temperature affected the composition of precursor phase.when precipitation temperature changed, the content of aurichalcite and malachite was different.With the increase of precipitation temperature, the specific surface area of Copper, the dispersion of copper, the conversion of CO2, the selectivity of methanol and the yield of methanol all increased first and then decreased; the surface alkaline of catalyst enhanced first and then weakened; the acid center would be transformed. When precipitation temperature was too high, the pore structure of catalyst was destructed and the specific surface area of Copper and the dispersion of Copper decreased. With the increase of aging time, the specific surface area of Copper, the dispersion of Copper, the conversion of CO2, the selectivity of methanol and the yield of methanol all increased first and then decreased; the surface basicity of the catalyst increased; weak acid sites transformed moderately strong acid sites and strong acid sites; the amount of acidic sites reduced. When aging time was too long, Cu particles grew up, and the surface basicity of catalyst became stronger.CaO, an alkaline earth metal oxide, active, owning good adsorption effect on acid CO2, could adjust the surface acidity of catalyst. After adding CaO, more aurichalcite phase appeared in the catalyst precursor; the amout of high temperature carbonate in the catalyst increased; the thermal stability of catalyst improved;CuO particles became smaller, the dispersion of Copper increased and Copper more easily moved into the ZnO lattice to form a solid solution; the synergy effect between Copper and Zinc was reinforced and the activity of the catalysts was improved; Lewis acidity and surface basicity of the catalyst were enhanced; the specific surface area of the catalyst was improved. The activity of catalyst was influenced by the surface acidity, the surface area of copper, the synergistic effect of Cu-Zn and the dispersion of copper.Excessive CaO occupied the pore of catalyst and covered the surface active sites, so that Lewis acid and surface alkaline of the catalyst became too strong.