The reaction of H 2 O dissociation on Cu nanoparticles prepared by an atomic layer epitaxy (ALE) technique is discussed in this article. The activation energy of H 2 O dissociation, desorption energy of H 2 O, active sites for H 2 O adsorption, and structural changes of the Cu surface were studied using temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), in situ IR spectroscopy, and X-ray absorption spectroscopy (XAS). The reduced Cu nanoparticles of the ALE-Cu/SiO 2 catalyst possess a slightly positive charge (Cu δ+ ) due to the effect of the nanosized particles. The very low activation energy of H 2 O dissociation (23 kJ/mol) and the exothermic dissociation heat were obtained from a series of H 2 -TPR experiments on Cu nanoparticles. It is suggested that the Cu nanoparticles might be partially oxidized to Cu 2 O, while some oxygen atoms are proposed to be located on the surface of the Cu particles over the course of water adsorption.

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 (R 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 R-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.

SBA-15 functionalized with carboxylic acid groups has been used to synthesize Cu nanoparticles 2–6 nm in average size with 7.6–25.2 wt % Cu. In this study, the formation mechanism and characterization of Cu nanoparticles at various Cu concentrations are described. For samples with 7.6 and 11.9 wt % Cu, linear [Cuδ+···Oδ−···Cuδ+] n chains generated through calcination are possibly located inside the SBA-15 channels. When the concentration of Cu is increased to 18.3 wt %, the Cu2(OH)3NO3 species becomes the dominant intermediate before bulky CuO is formed. It is found that the average 2-nm Cu particles provided a significantly higher turnover rate for water–gas shift (WGS) reaction than did higher Cu contents on SBA-15. We propose that the highly dispersed Cu particles or isolated Cu atoms on Cu/SBA-15 catalysts can serve as major active sites for the WGS reaction. The 7.6 and 11.9 wt % Cu/SBA-15 catalysts provide abundant sites on highly dispersed Cu particles or isolated Cu atoms, which lead to a highly efficient WGS reaction.