The effect of ceria content on the properties of Pd/CeO2/Al2O3 catalysts for steam reforming of methane |
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| Affiliation: | 1. Department of Chemical Engineering, Universidade Federal de São Carlos, C.P. 676, 13565-905 São Carlos, SP, Brazil;2. Department of Chemistry, Universidade Federal de São Carlos, C.P. 676, 13565-905 São Carlos, SP, Brazil;3. Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria;4. FEQ, Universidade Federal de Uberlândia, Av. João Naves de Ávila, 2160, bloco 1K-CEP, 38400-902 Uberlândia, MG, Brazil;5. Instituto Nacional de Tecnologia—INT, Av. Venezuela 82, CEP 20081-310 Rio de Janeiro, RJ, Brazil;1. Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, China;2. College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China;1. Institute of New Energy and Low-carbon Technology, Sichuan University, Chengdu 610064, China;2. College of Chemical Engineering, Sichuan University, Chengdu 610064, China;3. Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, F-59000 Lille, France;4. College of Chemistry, Sichuan University, Chengdu 610064, China;5. Institute of Atmospheric Environment, Chongqing Academy of Environmental Science, Chongqing 401147, China;1. Dipartimento Politecnico, Università di Udine and INSTM, via del Cotonificio 108, 33100 Udine, Italy;2. Chemistry Division, Brookhaven National Laboratory, Upton, NY 11973, USA;3. Chemistry Department, Stony Brook University, Stony Brook, NY 11794, USA;4. Institute of Energy Technologies, Department of Chemical Engineering and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Eduard Maristany 10-14, 08019 Barcelona, Spain;1. Department of Chemical and Pharmaceutical Sciences, ICCOM-CNR URT Trieste, Consortium INSTM Trieste Research Unit, University of Trieste, via L. Giorgieri 1, 34127 Trieste, Italy;2. Charles University in Prague, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovičkách 2, 18000 Prague, Czech Republic;3. Elettra-Sincrotrone Trieste SCpA, Strada Statale 14, km 163.5, 34149 Basovizza, Trieste, Italy;4. IOM, Strada Statale 14, km 163.5, 34149 Basovizza, Trieste, Italy;5. Department of Chemical and Biomolecular Engineering, University of Pennsylvania, 311A Towne Building, 220 South 33rd Street, Philadelphia, USA;1. Leibniz Institute for Catalysis at the University of Rostock, Albert-Einstein-Str. 29a, D-18059 Rostock, Germany;2. Electron Microscopy Center, Strempelstr. 14, University Medicine, D-18057 Rostock, Germany;1. Boreskov Institute of Catalysis SB RAS, Prosp. Akad. Lavrentieva 5, Novosibirsk 630090, Russia;2. Nikolaev Institute of Inorganic Chemistry SB RAS, Prosp. Akad. Lavrentieva 3, Novosibirsk 630090, Russia;3. Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia |
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| Abstract: | The effect of CeO2 loading on the surface properties and catalytic behaviors of CeO2–Al2O3-supported Pd catalysts was studied in the process of steam reforming of methane. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). The XRD measurements indicated that palladium particles on the surface of fresh and reduced catalysts are well dispersed. TPR experiments revealed a heterogeneous distribution of PdO species over CeO2–Al2O3 supports; one fraction of large particles, reducible at room temperature, another fraction interacting with CeO2 and Al2O3, reducible at higher temperatures of 347 and 423 K, respectively. The PdO species reducible at room temperature showed lower CO adsorption relative to the PdO species reducible at high temperature. In contrast to Pd/Al2O3, the FTIR results revealed that CeO2-containing catalyst with CeO2 loading ≥12 wt.% show lower ratio (LF/HF) between the intensity of the CO bands in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). This ratio was constant with increasing the temperature of reduction. The FTIR spectra and the measurement of Pd dispersion suggested that Pd surface becomes partially covered with ceria at all temperature of reduction and with increasing ceria loading in Pd/CeO2–Al2O3 catalysts. Although the PdO/Al2O3 showed higher Pd dispersion compared to that of CeO2-containing catalysts, the addition of ceria resulted in an increase of the turnover rate and specific rate to steam reforming of methane. The CH4 turnover rate of Pd/CeO2–Al2O3 catalysts with ceria loading ≥12 wt.% was around four orders of magnitude higher compared to that of Pd/Al2O3 catalyst. The increase of the activity of the catalysts was attributed to various effects of CeO2 such as: (i) change of superficial Pd structure with blocking of Pd sites; (ii) the jumping of oxygen (O*) from ceria to Pd surface, which can decrease the carbon formation on Pd surface. Considering that these effects of CeO2 are opposite to changes of the reaction rate, the increase of specific reaction rate with enhancing the ceria loading suggests that net effect results in the increase of the accessibility of CH4 to metal active sites. |
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