Carbon Dioxide Hydrogenation on Cu Nanoparticles

The reaction mechanism and active sites for CO 2 adsorption during the reverse water-gas shift (RWGS) reaction on silica-supported Cu nanoparticles were investigated. The Cu nanoparticles prepared by an atomic layer epitaxy technique were shown to strongly bind CO 2 molecules, as evidenced by the two main peaks with maxima near 353 (α peak) and 525 K (β peak) observed during temperature-programmed desorption experiments. The high-temperature peak (525 K), which corresponds to CO 2 in the β state, indicates that β-state CO 2 was the dominant species for the RWGS reaction. The values for the activation energy of CO 2 desorption were 33.4 and 74.4 kJ/mol for α-CO 2 and β-CO 2, respectively. The sites for CO 2 adsorption were different from those for CO adsorption (defect sites and sites with highly dispersed Cu particles). It is likely that CO 2 hydrogenation occurs on a low-index plane. We propose that the mechanism for the RWGS reaction mainly involves formation of formate species.