Structural effects of Na promotion for high water gas shift activity on Pt-Na/TiO2

• Published in: Journal of catalysis 2011-02, Vol.278 (1), p.123-132
• Main Authors: XINLI ZHU, MIN SHEN, LOBBAN, Lance L, MALLINSON, Richard G
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Chemical reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2010.11.023

Intrinsic reaction rate and turnover frequency of water gas shift reaction at 300°C are improved 8 and 11 times, respectively, for Pt/TiO2 catalyst with optimal Na loading (Na/Pt=34). Characterizations reveal the strong metal-promoter interactions between Pt and NaO x are responsible for the significant improvement in activity and stability. Display Omitted Research highlights Addition of optimal Na to Pt/TiO2 improves TOF of WGS by 11 times at 300°C. Strong metal-promoter interactions between Pt and NaOx create highly active sites. The highly active sites are located at the periphery of the Pt-NaOx interface. NaOx covers Pt partially, with moderate surface basicity and exposed Pt surface areas. Electronic interactions occur by Pt electron donation to O in NaOx . Sodium (1-10wt.%)-promoted 1wt.% Pt/TiO2 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 2-4wt.% 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 4wt.% Na (Na/Pt=34) improves the intrinsic reaction rate and turnover frequency of Pt/TiO2 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, N2 adsorption, CO chemisorption, transmission electron microscopy, H2 temperature-programmed reduction, CO2 temperature-programmed desorption, and X-ray photoelectron spectroscopy. [PUBLICATION ABSTRACT]