Abstract
Sodium (1–10 wt.%)-promoted 1 wt.% Pt/TiO 2 catalysts were prepared by a co-impregnation method and tested for the water gas shift (WGS) reaction under differential reaction conditions. Significantly higher intrinsic activity is achieved with 2–4 wt.% Na addition, when 2–4 layers of NaO x are deposited on the support and the Pt particles are partially covered by NaO x , with moderate surface basicity and exposed Pt surface areas. In addition to the physical coverage, XPS data suggest that interactions between Pt and NaO x may occur by Pt electron donation to O in NaO x through Pt–O–Na. The strong metal–promoter interactions provide highly active sites for the WGS reaction at the periphery of the Pt–NaO x interface and also inhibit Pt particles from sintering. Optimal 4 wt.% Na (Na/Pt = 34) improves the intrinsic reaction rate and turnover frequency of Pt/TiO 2 at 300 °C by 8 and 11 times, respectively, and appears to be significantly higher than reported in the literature. The catalysts were characterized by X-ray diffraction, N 2 adsorption, CO chemisorption, transmission electron microscopy, H 2 temperature-programmed reduction, CO 2 temperature-programmed desorption, and X-ray photoelectron spectroscopy.
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