ZrO2 Morphology-Dependent Cu–ZrO2 Interfacial Catalysis in CO2 Hydrogenation to Methanol Reaction

Abstract

In this study, we utilize monoclinic ZrO₂ with different morphologies, including nanoparticulate ZrO₂, rod-like ZrO₂, and star-like ZrO₂, to investigate the ZrO₂ morphology effect on Cu–ZrO₂ interfacial catalysis in the CO₂ hydrogenation to methanol reaction. ZrO₂ morphology strongly affects the structures, adsorption behaviors, and catalytic performance of Cu/ZrO₂ catalysts. Various Cu/ZrO₂ catalysts show very different catalytic selectivities, although their catalytic activities are rather poor. Bridged (bri-HCOO*) and monodentate (m-HCOO*) formate species form on Cu/ZrO₂ catalysts during the CO₂ hydrogenation to methanol reaction. Elementary surface reaction kinetics analysis using temporal in situ DRIFTS in combination with online mass spectrometry reveals elementary reaction activation energies of 61.3 ± 5 kJ/mol for bri-HCOO* hydrogenation mainly to methanol and 85.0 ± 14 kJ/mol for m-HCOO* hydrogenation mainly to CO. Meanwhile, the apparent activation energy for CH₃OH and CO formations from the CO₂ hydrogenation reaction catalyzed by Cu/nanoparticulate ZrO₂ is 65.7 ± 4 and 118.6 ± 14 kJ/mol, respectively. These results suggest that bri-HCOO* should be the formate intermediate for methanol production by CO₂ hydrogenation, and its hydrogenation reaction should be the rate-limiting step. Our findings clearly differentiate the reaction pathways of bri-HCOO* and m-HCOO* intermediates on Cu/ZrO₂ during the CO₂ hydrogenation to methanol reaction and demonstrate catalyst structural engineering in combination with elementary surface reaction kinetics analysis as a powerful strategy for fundamental studies of complex heterogeneous catalytic reactions.