Methanol is a viable chemical energy carrier, offering convenient solutions for energy storage, and can also serve as C1 feedstock. With the threat of global warming, great global efforts have been devoted to produce methanol from CO2 via hydrogenation reaction. We recently reported about 90% CO2 conversion and 〉95% methanol selectivity with very good methanol weight time yield (1.0 gMeOH gcat-1 h-1) at stoichiometric feed (CO2:H2 = 1:3) at 442 bar, 280 °C using a Cu/ZnO-based commercial catalyst. While Cu is known to be active for reaction, Cu-ZnO interface is recognized to provide active interfaces for the reaction due to a unique Cu-ZnO synergy. To maximize synergy, it is necessary to obtain catalyst morphology that avoids Cu agglomeration by separating Cu particles with ZnO while keeping high contact areas between Cu and ZnO. For this aim, we developed a unique surfactant-free, non-aqueous synthesis method for simple and rapid core-shell Cu/ZnO materials where Cu2O core (after pretreatment Cu2O is reduced to Cu) is coated with ZnO nanoparticles. The materials exhibited a uniform morphology at a desired ratio of Cu and ZnO. These materials were tested in CO2 hydrogenation at stoichiometric CO2 and H2 ratio. Figure 1a shows the micrographs of 30 wt% Cu/ZnO with uniform thin coating of ZnO over Cu2O core. The material at the Cu wt% showed the highest catalytic performance (Figure 1b) with 53%CO2 conversion, 84% methanol selectivity at 320 °C, 331 bar at 4000 h-1 GHSV. Furthermore operando XRD study was performed at 200 bar to elucidate phase evolution and its impact on catalytic activity. Crystallization of Cu, ZnO were found responsible for catalyst deactivation. Surprisingly study revealed ZnO transformation into crystalline ZnCO3 under operando conditions, whereas Cu did not undergo significant crystalline phase change. The dynamic nature of Zn structure was suggested and relations between its phase transformation and catalytic activity are discussed.

Cu/ZnO core-shell catalysts for methanol synthesis from CO2: Structure-Activity relationship

253rd National Meeting (2017)

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