Bimetallic Au-Pd Alloy Catalysts for N2O Decomposition: Effects of Surface Structures on Catalytic Activity

Highly dispersed and well-homogenized Au-Pd alloy nanoparticles with average particle sizes of similar to 2 nm and tunable Au/Pd ratios were prepared by an adsorption- reduction method on the amine-functionalized SBA-15 support. The chemisorptions of H-2 and CO as well as the IR spectra of CO adsorption show that with increase of the Au/Pd ratios the surface Pd atoms are separated by gold atoms gradually until totally isolated at Au/Pd >= 0.95, which indicates the formation of Pd single atoms at higher Au/Pd ratios. The chemisorption of O-2 shows that both the adsorption heat and the saturation uptake decrease with an increase of Au/Pd ratio, suggesting alloying Pd with gold will facilitate the desorption of oxygen adatoms as O-2, which is generally the rate-determining step for N2O decomposition reaction. Theoretical investigations using periodic DFT methods confirm the tunable O-2 desorption ability by alloying Pd with Au and indicate that contiguously located Pd sites are indispensable for N2O decomposition because they function as the active sites for the elementary step of N2O decomposition into N-2 and oxygen adatom, which becomes the rate-determining step over the Au-Pd alloy catalysts.