Active sites on Cu/SiO_2 prepared using the atomic layer epitaxy technique for a low-temperature water-gas shift reaction

摘要

The atomic layer epitaxy (ALE) technique has been used to prepare uniform copper nanoparticles dispersed on a silica support (ALE-Cu/SiO_2 with 2.85 ± 0.32 nm), which are highly active in the water-gas shift reaction. Infrared spectra of CO adsorption are employed to study the active sites on ALE-Cu/SiO_2 surface, suggesting that two major active sites are found on the copper surface, namely defect sites and highly dispersed Cu particles and/or isolated Cu atoms sites. We report here that the defect sites on these small Cu particles or isolated Cu atoms provide high activity for the water gas shift reaction. The high efficiency of the water gas shift reaction on the ALE-Cu/SiO_2 catalyst may be ascribed to its strong activity in promoting H_2O dissociation. Nanoscale Cu particles may be involved in strong interactions with the SiO_2 support, leading to a partially electropositive state as a result of interactions with oxygen atoms at the surface of the support, even if the copper is reduced.