Carbon dioxide hydrogenation on cu nanoparticles

The reaction mechanism and active sites for CO₂adsorption 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 CO₂molecules, as evidenced by the two main peaks with maxima near 353 (α peak) and 525 K (βpeak) observed during temperature-programmed desorption experiments. The high-temperature peak (525 K), which corresponds to CO₂in the βstate, indicates that β-state CO₂was the dominant species for the RWGS reaction. The values for the activation energy of CO ₂desorption were 33.4 and 74.4 kJ/mol for α-CO₂and β-CO₂, respectively. The sites for CO₂adsorption were different from those for CO adsorption (defect sites and sites with highly dispersed Cu particles). It is likely that CO₂hydrogenation occurs on a low-index plane. We propose that the mechanism for the RWGS reaction mainly involves formation of formate species.