Effects of promotion of TiO2 with alkaline earth metals on the chemisorptive properties and water-gas shift activity of supported platinum catalysts

The effects of promotion of TiO2 with Group II alkaline earth metals on the chemisorptive properties and water-gas shift (WGS) activity of dispersed platinum have been investigated over Pt/TiO2(x%MO) catalysts of variable promoter type (M = Mg, Ca, Sr, Ba) and loading (x = 0-4 wt.%). DRIFTS experiments carried out using CO as a probe molecule showed that the presence of calcium does not affect appreciably adsorption on sites located on the surface of Pt crystallites, but results in the development of new, low-frequency bands in the v(CO) region attributed to the creation and population of sites with increased electron density located at the metal-support interface. Results of H-2-TPD experiments indicated a weakening of the adsorption strength of these sites toward hydrogen with increasing CaO content. Catalytic performance tests and kinetic measurements showed that activity of alkaline earth metal-promoted catalysts depends appreciably on the nature and loading of the promoter, as well as on the calcination temperature employed for the preparation of doped TiO2 supports. Optimal results were obtained for Pt catalyst supported on TiO2 promoted with 1-2 wt.% CaO, the specific activity of which is 2-3 times higher, compared to that of the unpromoted catalyst. Optimized catalysts are characterized by increased activity and excellent stability under realistic reaction conditions and may be used efficiently in practical applications, provided that promoter loading, calcination temperature and operating conditions are properly selected. (C) 2010 Elsevier B.V. All rights reserved.