Catalytic activities of noble metal atoms on WO(3) (001): nitric oxide adsorption

Using first-principles density functional theory calculations within the generalized gradient approximation, we investigate the adsorption of NO molecule on a clean WO(3)(001) surface as well as on the noble metal atom (Cu, Ag, and Au)-deposited WO(3)(001) surfaces. We find that on a clean WO(3) (001) surface, the NO molecule binds to the W atom with an adsorption energy (E(ads)) of −0.48 eV. On the Cu- and Ag-deposited WO(3)(001) surface where such noble metal atoms prefer to adsorb on the hollow site, the NO molecule also binds to the W atom with E(ads) = −1.69 and −1.41 eV, respectively. This relatively stronger bonding of NO to the W atom is found to be associated with the larger charge transfer of 0.43 e (Cu) and 0.33 e (Ag) from the surface to adsorbed NO. However, unlike the cases of Cu-WO(3)(001) and Ag-WO(3)(001), Au atoms prefer to adsorb on the top of W atom. On such an Au-WO(3)(001) complex, the NO molecule is found to form a bond to the Au atom with E(ads) = −1.32 eV. Because of a large electronegativity of Au atom, the adsorbed NO molecule captures the less electrons (0.04 e) from the surface compared to the Cu and Ag catalysts. Our findings not only provide useful information about the NO adsorption on a clean WO(3)(001) surface as well as on the noble metal atoms deposited WO(3)(001) surfaces but also shed light on a higher sensitive WO(3) sensor for NO detection employing noble metal catalysts.