Infrared Study of Benzene Hydrogenation on Pt/SiO 2 Catalyst by Co-adsorption of CO and Benzene
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Catalysis Letters Vol. 105, Nos. 3–4, December 2005 (Ó 2005) DOI: 10.1007/s10562-005-8684-7
Infrared study of benzene hydrogenation on Pt/SiO2 catalyst by co-adsorption of CO and benzene Ching-Shiun Chena,*, Jarrn-Horng Linb, Hsiu-Wei Chenc, and Chien-Yuan Wangc a
Center for General Education, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan Tao-Yuan 33302 Taiwan, Republic of China Center of Research and Technology, Tzu Hui Institute of Technology, 367, San Ming Road, Nanjou Shiang, Ping Tung 92641 Taiwan, Republic of China c Department of Chemistry, National Sun Yat-Sen University, 70 Lien Hai Road, Kaohsiung 80424 Taiwan, Republic of China
b
Received 27 June 2005; accepted 23 August 2005
FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen and benzene on a Pt/SiO2 catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO2 includes: an a peak at 2091 cm)1, a b peak at 2080 cm)1 and a c peak at 2067 cm)1 indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO2. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of benzene hydrogenation. KEY WORDS: benzene hydrogenation; CO adsorption; FTIR; Pt/SiO2.
1. Introduction Hydrogenation of benzene is readily catalyzed by Pt and is assumed to be a very important process in industry, however less attention has been given addressing the relationship between the adsorption sites of benzene and hydrogen on the Pt catalyst surface. Several papers have studied benzene adsorption geometry by co-adsorption of CO and benzene on single crystal Pt surfaces, indicating that the carbon ring of benzene was parallel to the surface and centered over bridge sites [1–3]. Thomas et al. have studied temperature programmed desorption of co-adsorption of H2/ C6H6 on Pt(110), suggesting that benzene could partially block hydrogen adsorption and that benzene hydrogenation only occurred when hydrogen was adsorbed on top of the benzene adlayer [4]. Moreover, benzene hydrogenation did not occur when benzene was dosed onto a hydrogen covered surface [4]. Nevertheless, these results of studies on well-characterized single crystal surfaces do not seem to entirely reflect the behavior during benzene hydrogenation on Pt catalysts, since many defect sites may exist on the surface of a catalyst system to influence benzene hydrogenation. The main goal of this paper is to understand the relationship between hydrogen and benzene on an actual Pt catalyst system. In the present study, we use CO as a probe molecule to determine preferred adsorption sites of hydrogen and benzene on Pt/SiO2 catalysts because CO is an ideal probe molecule for vibrational spectroscopy * To whom correspondence should be addressed. E-mail: [email protected]
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