Surface Ir-Ti Alloy Formed via Strong Metal − Support Interaction over Ir/TiO₂

The strong metal-support interaction and its chemical nature was examined over a Ir/TiO₂ catalyst, constructed by dispersing 2 nm Ir colloids on the {001} facets of anatase TiO₂. Air-calcination of the Ir/TiO₂ sample led to the oxidation of Ir particles into IrO_x clusters. Upon H₂-reduction at 573 K, the IrO_x species were reduced into metallic with a prominent character for H₂-chemisrption. As further raising the temperature to 673–773 K for H₂-reduction, strong metal-support interactions occurred pronouncedly and the amounts of chemically adsorbed hydrogen dropped significantly. Spectroscopic and microscopic analysis found that the formation of surface Ir-Ti alloys on the Ir particles dominated the metal-support interactions, rather than the traditional encapsulation of the metal particles by TiO_x overlayers. The surface Ir-Ti alloy, thus formed, promoted the selectivity for hydrogenating the C = O bond in acetophenone by altering the adsorption model of the C = O bond in the substrate.