Insights into the WOx Coverage-Dependent Location and Oxidation State of Noble Metals Supported on Tungstated Oxides: The Case of Rh/WOx鈥揅e0.62Zr0.3

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• 作者：Thomas Bonnotte ; Rachel P. Doherty ; C茅line Sayag ; Jean-Marc Krafft ; Christophe M茅thivier ; Micka毛l Sicard ; Fr茅d茅ric Ser ; Cyril Thomas
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：April 10, 2014
• 年：2014
• 卷：118
• 期：14
• 页码：7386-7397
• 全文大小：533K
• 年卷期：v.118,no.14(April 10, 2014)
• ISSN：1932-7455

文摘

Noble metals-promoted tungstated oxides have been shown to be profitable in a wide variety of catalytic reactions of environmental interest but to be detrimental in the hydrogenation of aromatics. The origin of the deleterious effect of tungstates on the hydrogenation performance of noble metals is still being debated. To provide further insights into this, the location and the oxidation state of Rh were investigated as a function of the W surface density (0鈥?0 W/nm²) of Rh/WO_x鈥揅e_0.62Zr_0.38O₂ (Rh/W鈥揅Z) catalysts after high-temperature reduction. For that purpose, a thorough characterization of the oxide phases was performed through N₂-sorption, X-ray diffraction, Raman spectroscopy, NO_x temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS), whereas the metallic phases were characterized by low-temperature H₂ chemisorption, XPS, N₂ Fourier transform infrared spectroscopy and benzene hydrogenation. It was found that Rh deposited on both tungstates and CZ, and did not sinter with increasing W surface densities. The observed linear decrease in the Rh hydrogenation performance of the WO_x-promoted Ce_0.62Zr_0.38O₂ below pseudo monolayer coverage of CZ (4.8 W/nm²_CZ) was assigned to a strong metal support interaction effect between the Rh particles and the nonreducible underlying WO_x phase, resulting in the formation of electron-deficient Rh species (Rh^未+).