Catalysis by nanoscale gold (Au/MO_x): B. Reaction mechanisms of low temperature CO oxidation reactions

摘要

Here, in Part B of this Series, we take a critical look at the reaction mechanisms of low temperature CO oxidation reactions over nanoscale gold, including adsorption, surface reaction, and desorption of key substrates, viz., CO and O_2. Based on a concerted analysis of reactivity data of Au nanoparticles, physicochemical surface characterization, and theoretical first principles calculations, we conclusively prove that out of the 2 most commonly invoked reaction mechanisms, gold-only vs. gold-assisted, the latter is the only mechanism operative for supported gold particles in the quantum size range of 2-5 nm. The Au-MO_x support perimeter interface is a structural motif that is very rich in small metallic particles, and extremely low-coordinated Au sites (with N ~4-5), and some in presence of atomic bonding with Zn atoms. There is both charge and species transfer at this perimeter interface, which also provides highly active sites for adsorption of CO and O_2.