Preparation Of Cu/Pd Supported ZnO Catalyst And Its Performance Of CO₂ Hydrogenation To Methanol

In recent years,due to the sharp increase in carbon dioxide emissions,global warming has become a serious problem affecting human survival and social development.While reducing CO₂ emissions,its resource utilization can be converted to methanol.As an important chemical raw material and clean energy,methanol can realize industrial production of methanol synthesis by CO₂ hydrogenation,which not only can alleviate the greenhouse effect but also realize the recycling of CO₂.Since CO₂ is characterized by high stability and difficulty in activation,it is essential to obtain a catalyst having high activity in a methanol synthesis reaction.Copper-based catalysts have the most research because of their good catalytic performance and low price.Firstly,based on the importance of the catalyst structure and ZnO,a CuO/ZnO catalyst prepared by deposition-precipitation with different morphologies?stick,plate and ball-flower?ZnO was obtained.Catalytic activity was evaluated by hydrogenation of CO₂ to methanol.The experimental results show that the morphology of ZnO has a certain influence on the catalytic activity of the catalyst.Among them,the b-CuO/ZnO catalyst showed the highest catalytic activity,and the CO₂ conversion and methanol selectivity were 20.02%and 43.64%,respectively.It is found that the b-CuO/ZnO catalyst has the highest polarity ratio and the strongest interaction between b-ZnO and CuO,which improves the methanol selectivity;the higher D_Cu and small particle size CuO particles in the catalyst lead to the higher CO₂ conversion rate and then increases the catalytic activity.Secondly,based on the previous study on the morphology of ZnO,the spheroidal ZnO with oxygen vacancy was used as the carrier,and the noble metal Pd was added on the CuO/ZnO catalyst with different Cu loading to study the effect of Pd doping on catalytic activity.The experimental results show that the loading of copper affects the particle size of CuO,which affects the dispersion of CuO on the ZnO carrier.As the Cu loading increases,the interaction between Cu and ZnO increases.After doping the noble metal Pd,the CuO particle size is significantly reduced,and more Cu phase with higher dispersion and high activity is obtained.Under the synergistic action of copper and zinc,the catalytic performance of Pd-CuO/ZnO catalyst was higher than that of CuO/ZnO catalysts.The methanol yield of 30%CuO/ZnO catalyst increased from 0.022g/(g_cat·h)to 0.222g/(g_cat·h),because the reason can be due to doping of Pd promotes hydrogen spillover.Finally,in order to further study the effect of Pd on the catalytic activity of CuO/ZnO,Pd-CuO/ZnO catalyst was prepared by impregnation method,and the catalyst was reduced at different reduction temperatures?300°C,400°C,500°C?.The experimental results show that PdZn alloy is formed at the reduction temperature of400°C,and more PdZn alloy is formed at 500°C,which promotes the phenomenon of hydrogen spillover,and hydrogen spillover is beneficial to the formation of methanol.Therefore,the Pd-CuO/ZnO-500 catalyst exhibited the highest methanol selectivity?79.18%?and space time yield(0.298g/(g_cat·h)).