Bimetallic Au-Pd alloy catalysts for N ₂O decomposition: Effects of surface structures on catalytic activity

Highly dispersed and well-homogenized Au-Pd alloy nanoparticles with average particle sizes of ∼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 N ₂O 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 N ₂O decomposition because they function as the active sites for the elementary step of N ₂O decomposition into N ₂ and oxygen adatom, which becomes the rate-determining step over the Au-Pd alloy catalysts.