Fig. 3.

Comparison on the surface species on Cu–ZnO, Cu–ZrO₂, and ZnO–ZrO₂ systems in the designed conditions. a–c In situ DRIFT spectra over a Cu–ZnO, b Cu–ZrO₂, and c ZnO–ZrO₂ materials at 493 K after switching feed gas from CO₂ (CO₂ has been loaded into the camber for 10 min) to H₂ with a flow rate of 40 mL/min under atmosphere pressure. d Peak areas of generated intermediate species during the experiments: areas normalized to the values observed at the end of the transient. Only the ZnO–ZrO₂ sample shows obvious formation of formate species (2972, 2878, 1593, 1386, and 1362 cm⁻¹) from carbonate species when the feed gas was switched from CO₂ to H₂