Chemisorption of CO, NO and H2 on Transition Metal-Titania Thin Film Model Catalysts

摘要

Chemisorption on thin film models of Rh/TiO2 and Pt/TiO2 catalysts before and after encapsulation with TiOx (1.0 < x < 1.2) is reported. TiOx blocks adsorption sites and induces new desorption states. A CO desorption peak, assigned to CO on Rh atoms perturbed by TiOx, is observed at 325 K after adsorption at 120K on a TiOx-covered Rh/TiO2 surface. CO adsorbed at 285 K onto the encapsulated Rh/TiO2 surfaces shows a new 685 K CO desorption state attributed to an activated form of CO with a weakened C-O bond. NO desorbs from clean Rh overlayers with a profile most like Rh(110). On encapsulated Rh surfaces N2O is the major desorption product. Compared to bulk Pt, desorption experiments show suppressed H2 adsorption capacity for thin (<2 ML) Pt layers in contact with, but not encapsulated by, TiOx. For thin layers of Pt on fully oxidized TiO2 layers there is no reduction of H2 chemisorption. The results suggest bonding between Ti and Pt which affects H2 chemisorption even though no Pt surface sites are blocked.