Formation of Cu nanoparticles in SBA-15 functionalized with carboxylic acid groups and their application in the water-gas shift reaction

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 [Cu^δ+⋯O^δ-⋯Cu ^δ+]_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.