Insights into the interfacial structure of Cu/ZrO2 catalysts for methanol synthesis from CO2 hydrogenation: Effects of Cu-supported nano-ZrO2 inverse interface

Abstract

The performance of Cu-based catalysts in the low temperature CO2 conversion to methanol highly correlates with interfacial structure. In this paper, the interfacial structure of Cu/ZrO2 catalysts is tuned by changing the molar ratio and precipitation sequence of Cu and Zr precursors in the oxalate precipitation method. Structural characterizations demonstrate that the interface structure gradually transforms from the conventional ZrO2-supported nano-Cu interface to the Cu-supported nano-ZrO2 inverse interface with the ascending Cu/Zr ratio. The space–time yield (STY) of methanol over 90 molCu% Cu/ZrO2 inverse catalyst is 518 gCH3OH/kgcat/h, which far exceeds that of the optimized 40 molCu% Cu/ZrO2 catalyst (351 gCH3OH/kgcat/h). The inverse catalyst also exhibits the best methanol selectivity and lowest apparent activation energy. The correlation of the exposed Cu surface area, Cu particle size, and CO2 adsorption capacity with STYmethanol reveal that there is an optimal coverage of fine ZrO2 particles and the Cu supported nano-ZrO2 inverse configuration is a more suitable structure for methanol synthesis from CO2. High-pressure in situ DRIFTS experiment shows that the adsorbed formate and methoxy intermediates over 90 molCu% Cu/ZrO2 inverse catalyst are more reactive for further hydrogenation. In addition, the inverse configuration is more favorable for the methanol desorption from surface. The enhanced hydrogenation ability and relatively weak oxygenates adsorption of Cu-supported nano-ZrO2 interface is probably the main reasons for the improved catalytic performances of inverse catalysts.