| In recent years, the natural cycle of carbon dioxide has been disturbed due to massive exploitation of oil, gas and coal fields, increase in world population, decrease in forest area and land desertification, resulting in the accumulation of carbon dioxide. The greenhouse effect caused by carbon dioxide has caused widespread public concern. Therefore, using and fixing of carbon dioxide has become an important subject with its great strategic significance for human. Catalytic hydrogenation of carbon dioxide is an important way of effectively using carbon dioxide. In this paper, methanol and higher alcohols were synthesized by hydrogenation of carbon dioxide using modified Cu/Zn/Fe/ZrO2as catalyst, which is important for the resource utilization of carbon dioxide.A series of Cu/Zn/Fe/ZrO2catalysts used in the hydrogenation of carbon dioxide to synthesize higher alcohols were prepared by modifying Cu/Zn/ZrO2with different contents of Fe. Methods such as X-ray powder diffraction (XRD), N2adsorption and desorption, H2temperature programmed reduction(H2-TPR) and CO2temperature programmed desorption(CO2-TPD) were used to study the crystal structure, specific surface area, aperture parameters and carbon dioxide adsorption capacity of the catalysts and the redox properties of active components in the catalysts and the catalytic activity in the hydrogenation of CO2to synthetize higher alcohols were evaluated. The results showed that Copper, Zine, Iorn and Zirconium had the strongest synergistic effect and the catalyst also displayed high catalytic activity when the content of Fe accounted for6%of the catalyst, and the CO2conversion rate and the space and time conversion rate were24.15%and0.24g/ml·h, respectively. Results of XRD, BET, H2-TPR and CO2-TPD indicated that the catalytic activity was higher when the XRD diffraction peak was more dispersive and broad and the reduction temperature was lower, and the CO2adsorptive capacity was stronger.To further improve the catalytic activities of the catalyst Cu/Zn/Fe/ZrO2used in the hydrogenation of carbon dioxide to synthesize higher alcohols, rare earth oxide (La2O3, CeO2), transition metal oxides (MnO2) and alkali metal oxide (K2O) were doped into the catalyst Cu/Zn/Fe/ZrO2to study their effects on the hydrogenation of carbon dioxide to synthesize higher alcohols. When the content of doped La2O3accounted for2%of the catalyst, the catalyst showed the best catalytic activity, and the conversion rate of CO2and time-space yield of ROH were26.17%and0.26g/ml·h, respectively. When the content of doped CeO2accounted for4%of the catalyst, the catalyst showed the best catalytic activity, and the conversion rate of CO2and time-space yield of ROH were23.14%and0.27g/ml·h, respectively. In conclusion, adding a proper amount of rare earth oxide to modify the catalyst Cu/Zn/Fe/ZrO2can improve the activity of the catalyst in synthesizing higher alcohols and change the selectivity of the catalyst and hence improve the time-space yield of alcohols and their distribution.Catalytic activity of Cu/Zn/Fe/ZrO2was changed to some extent by the doped transition metal oxides MnO2. Along with MnO2added in, the XRD diffraction peaks of the catalyst became more dispersive and broad and the reduction peaks of the catalyst moved to high temperature area, and the reduction of catalysts became very difficult. When the content of doped MnO2accounted for2%of the catalyst, the catalyst showed good catalytic activity, and the conversion rate of CO2and time-space yield of ROH were29.07%and0.26g/ml·h, respectively.The number of desorption peaks of CO2increased when doping alkali metal oxide into the catalyst. This indicates that when increasing the amount of K2O doped into the catalyst, the activity centers of the catalyst increased in number, which is benefit to the improvement of the catalytic activities. When the content of doped K2O accounted for5%of the catalyst, the conversion rate of CO2was only20.49%, but the time-space yield of ROH reached0.32g/m·h. |
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