| CO2 exists widely in atmosphere and water, in which the amount of carbon is 10 times more than that of petroleum, coal and natural gas. Conversion of CO2 to useful chemicals is widely investigated by many workers from the view of point of finding technologies for suppressing the green house effect caused by CO2 emission. Catalysts containing Cu are known to be efficient for production of methanol from CO2 and H2. The methanol synthesis from CO2/H2 is considered as a promising process. Because of thermodynamic limitation, the yield of methanol is not high enough for one-pass operation. The utilization of industrial Cu/ZnO/Al2O3 catalysts, which exhibited a high activity for methanol synthesis from syngas, was not successful in CO2 hydrogenation. It is interesting to develop new catalysts with high activity.A system of metallic oxides with copper and manganese was chosen, because these mixed oxides are well known as excellent catalysts in oxidation of carbon monoxide since 1920. The copper/manganese oxide system has mainly been studied as unsupported catalyst. Kotowski, Huang reported that CuO/ZnO or Cu/SiO2 promoted by Mn2+ enhanced the turnover of CO. So it is interesting to investigate the activity over the hydrogenation of carbon dioxide.The catalytic activity of Cu-based catalyst depends on the properties of its supports. It is generally accepted that metals supported on reducible oxides, e.g. TiO2 or Nb2O5, have a high activity in comparison to the conventional supports, e.g. Al2O3 or SiO2. This promoting effect of the reducible supports has been attributed to the creation of new active sites at metal-support interface which originates from the migration of support suboxide species onto metal surface. Arakawa et al have reported that the methanol synthesis from CO2 hydrogenation over Cu/TiO2 shown high turnover frequency because the rate of hydrogenation of formate hydrogenation was enhanced by the synergetic effect between Cu and TiO2.
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