In-situ XPS study of zirconium oxide promoted by platinum and sulfate ion

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) study of adsorbed CO were performed to characterize the states of the platinum particles supported on the sulfate ion-treated zirconium oxide (S024−-ZrO2) after reduction with hydrogen. Presence of the sulfate ion strongly suppressed the reducibility of the platinum particles as well as the chemisorptive capacity for CO. The platinum particles consisted mainly of platinum cations (mixture of platinum oxide and platinum sulfate) after reduction with hydrogen at 673 K; the concentration of metallic platinum phase was low. The low reducibility of the dispersed platinum particles present as platinum cations on the SO24−-ZrO2 support is interpreted by the redox metal-support interaction (RMSI), which is caused by the acidic properties of the S024−-ZrO2 support and results in a slow nucleation of the platinum particles. The states of sulfur were also measured by XPS, and the partial conversion of the S6+ (sulfate ion) to S2− species on hydrogen treatment is concluded to occur by the metal-catalyzed mechanism involving spiltover hydrogen atoms resulting from the dissociation of a hydrogen molecule on the metallic platinum.