Enhanced activity, selectivity and stability of a CuO-ZnO-ZrO2 catalyst by adding graphene oxide for CO2 hydrogenation to methanol

Recycling of CO2 into methanol has been introduced as a promising way to tackle both global warming and depletion of fossil fuels problems. However, it is still desirable to develop an efficient catalyst to attain high yield and selectivity of methanol as well as catalyst stability. Here, we report a systematic study on the effect of graphene oxide (GO) in CuO-ZnO-ZrO2 catalysts on the catalytic performance in CO2 hydrogenation to methanol. The GO-supported CuO-ZnO-ZrO2 catalysts prepared with 0.5-2.5 wt% GO achieve a higher space-time yield of methanol compared to the GO-free catalyst due to the increased active sites for CO2 and H-2 adsorption. However, adding GO content higher than 2.5 wt% interrupts the co-precipitation of mixed metal oxides which leads to the formation of isolated metal oxides particles as well as a considerable increase in CuO crystallite size, resulting in a lower space-time yield of methanol compared to the GO-free catalyst. Unlike the methanol yield, the methanol selectivity of all catalysts prepared with GO is higher than that of the GO-free catalyst, giving the highest methanol selectivity of 75.88% at 200 degrees C and 20 bars over the CuO-ZnO-ZrO2 catalyst prepared with the optimum GO content of 1 wt% (CZZ-1GO). This can be attributed to a promotional effect of GO nanosheet serving as a bridge between mixed metal oxides which enhances a hydrogen spillover from the copper surface to the carbon species adsorbed on the isolated metal oxide particles. In addition, the stability in terms of CO yield of the CZZ-1GO exceeds that of the GO-free catalyst.