Studies of the interactions of H2 and CO with Pd/TiO2 and TiO2-promoted Pd/SiO2

The interactions of H2 and CO with PdSiO2, PdTiO2, and titania-promoted PdSiO2 have been investigated using temperature-programmed desorption and temperature-programmed surface reaction. In the presence of TiO2, as a support or promoter, a portion of the TiO2 is reduced to TiOx moieties which decorate the surfaces of the Pd particles. These species cause a suppression in chemisorption of H2 and CO, the magnitude of which is a function of the catalyst reduction temperature. The TiOx moieties have little influence on distribution of H2 adstates but cause a noticeable change in CO adstates. Decoration of Pd by TiOx moieties also aids the dissociation of CO, and raises thereby the activity for CH4 synthesis relative to that for PdSiO2.