COMBINED TEMPERATURE-PROGRAMMED REDUCTION (TPR)-TEMPERATURE-PROGRAMMED DESORPTION (TPD) STUDY OF SUPPORTED PLATINUM CATALYSTS

Successive temperature-programmed desorption (TPD) after temperature-programmed reduction (TPR) (Combined TPR-TPD) was performed in order to characterize supported platinum catalysts (Pt/SiO2, Pt/Al2O3, Pt/ZrO2 and Pt/TiO2) as well as to judge the validity of the apparent TPR profiles. In successive H-2-TPD runs obtained after cooling in the absence of hydrogen from 450-degrees-C to room temperature, the hydrogen desorption peak was observed only for the Pt/TiO2 sample, indicating that the hydrogenic species were kept on Pt/TiO2 sample, while no hydrogenic species were retained on the other samples after TPR up to 450-degrees-C. For both Pt/Al2O3 and Pt/TiO2 samples, hydrogen spillover seemed to proceed. Hydrogen incorporation during TPR was greater for Pt/TiO2 than for the others. This hydrogen spillover causes an overestimation of the consumed H-2/Pt value determined by the apparent TPR profile for Pt/TiO2. For Pt/SiO2 and Pt/ZrO2 samples, the apparent TPR profiles were mostly due to a reduction of the supported Pt oxides. For the Pt/TiO2 sample, the hydrogen incorporation/emission at different temperatures during TPR was investigated. To generate SMSI states, desorption of the spiltover hydrogen is suggested to play a significant role; the role of hydrogen incorporation/emission in the generation of SMSI states is also discussed.