Catalytic and DRIFTS study of the WGS reaction on Pt-based catalysts

VIGNATTI, CHARITO; AVILA, MARÍA SOL; APESTEGUÍA, CARLOS R.; GARETTO, TERESITA

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2010 vol. 75 p. 7302 - 7312

0360-3199

The wateregas shift (WGS) activity of Pt/SiO2, Pt/CeO2 and Pt/TiO2 catalysts was studied byin-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Samples containeda similar amount of Pt, between 0.34 and 0.50%, and were characterized byemploying a variety of physical and spectroscopic techniques. The catalyst activities wereevaluated through both CO conversion versus temperature and CO conversion versus timetests. The DRIFTS spectra were obtained on stream during the WGS reaction at increasingtemperatures, from 303 to 573 K. Reduced ceria was the only active support and promotedthe WGS reaction on surface bridging OH groups that react with CO to form formateintermediates. Pt/SiO2 was more active than CeO2 and catalyzed the WGS reaction througha monofunctional redox mechanism on metallic Pt sites. The CO conversion turnover ratewas more than one order of magnitude greater on Pt/CeO2 than on Pt/SiO2 showing that thereaction proceeds faster via a bifunctional metal-support mechanism. Platinum on Pt/CeO2increased the concentration of OH groups by increasing the ceria reduction extent and alsoprovided a faster pathway for the formation of formate intermediates in comparison toCeO2 support. Pt/TiO2 catalysts were clearly more active than Pt/CeO2. The WGS reactionon Pt/TiO2 was catalyzed via a bifunctional metal-support mechanism, probably involvingthe activation of CO and water on the metal and the support, respectively. The role ofplatinum on Pt/TiO2 was critical for promoting the reduction of Ti4þ ions to Ti3þ whichcreates oxygen vacancies in the support to efficiently activate water.