| The rapid expansion of the world’s population and rapid growth of modern industry, will inevitably lead to greenhouse gas carbon dioxide levels rising, research and development of efficient CO2capture and resource utilization technology have gradually become a global issue and research focus. The organic chemical synthesis via carbon dioxide is a way of utilize carbon-rich effectively. The CO2hydrogenation to methanol could help to reduce CO2emissions, and CH3OH is one of the most basic chemical materials or new energy alternatives. Thus, the study of CH3OH synthesis from CO2and H2has great significance and value for the development of the chemical industry and new energy breakthrough.Firstly, the CuO/ZnO/ZrO2ternary composite catalyst were prepared by oxalic acid gels precipitation method and characterized by XRD, BET, H2-TPR, H2/CO2-TPD techniques in this paper. The effections of Cu/Zn molar ratio to the catalyst material phase composition, surface area and pore volume, absorption and desorption properties of the catalyst surface were analyzed. The effections of Cu/Zn ratio of catalytic performance for methanol synthesis were investigated in a fixed-bed flow reactor and the optimizations of reaction temperature, pressure, space velocity were determined. Finally, the stability of CuO/ZnO/ZrO2catalyst was evaluated.The results showed that different Cu/Zn molar ratio caused the active component dispersion change, resulting in differences between the ease of CuO reduction. The catalyst obtained by oxalic acid gels precipitation method were mesoporous materials with large specific surface area and pore volume, the results facilitated the migration of the reaction and the resultant molecules. The suitable Cu/Zn molar ratios facilitated the catalyst surface adsorption and desorption of activated molecules and reaction intermediates further hydrogenation to CH3OH. The catalyst activity showed a volcano trends with the increase of Cu/Zn molar ratio, and the highest activity of CuO/ZnO/ZrO2catalyst could be obtained as Cu/Zn=4. At a reaction temperature of493K, pressure of3.0MPa, space velocity of4800mL·h-1·gcat-1, CO2conversion and CH3OH selectivity and maximum of methanol yield were16.5%,76.1%and6.17mmo1·h-1·gcat-1. CO2conversion and methanol space-time yield not appeared significant decrease within100h. Secondly, the Cu/ZnO/A12O3/ZrO2quaternary composite catalyst were obtained from hydrotalcite-like precursors and prepared by a co-precipitation method and characterized by XRD, BET, N2O chemisorptions, H2-TPR and XPS techniques in this paper. The effections of Zr additive content to the precursors and catalyst products physical and chemical properties and catalytic activity were investigated, in order to obtain the suitable Zr content. Finally, the stability of the catalyst was evaluated and reaction mechanism of Cu/ZnO/Al2O3/ZrO2catalyst was analyzed.The XRD and SEM results revealed that the presence of hydrotalcite-like structures and Zr content have a significant influence on the yield of the hydrotalcite-like phases. The dispersion of Cu and the exposed Cu surface area exhibited a volcano variation trend with an increase in the Zr content and played a crucial role in the space-time yield (STY) and turnover frequency of methanol formation. But, the introduction of excess Zr additives (x=Zr4+/(Al3++Zr4+)>0.1) could lead to the accumulation of Cu active species and the decrease of specific surface area sharply. While Cu/ZnO/Al2O3catalysts showed poor catalytic activity, Zr-modified catalysts significantly improved the productivity of methanol and CO2conversion. Among all the Cu/ZnO/Al2O3/Zro2catalysts, the catalyst (x=0.1) showed higher catalytic activity and the yield of methanol. At a reaction temperature of513K, pressure of2.0MPa, space velocity of6800mL·h-1·gcat-1, the CO2conversion up to29.1%, the STY of methanol could achieve to11.98mmol·gcat-1·h-1. Simultaneously, a low deactivation rate was confirmed, CO2conversion and methanol space-time yield showed no significant decrease within100h. |
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