Selective hydrogenation of acetylene over Pd/CeO 2
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RESEARCH ARTICLE
Selective hydrogenation of acetylene over Pd/CeO2 Kai Li, Tengteng Lyu, Junyi He, Ben W. L. Jang (✉) Department of Chemistry, Texas A&M University Commerce, PO Box 3011, Commerce, TX 75429, USA
© Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Five hundred ppm Pd/CeO2 catalyst was prepared and evaluated in selective hydrogenation of acetylene in large excess of ethylene since ceria has been recently found to be a reasonable stand-alone catalyst for this reaction. Pd/CeO2 catalyst could be activated in situ by the feed gas during reactions and the catalyst without reduction showed much better ethylene selectivity than the reduced one in the high temperature range due to the formation of oxygen vacancies by reduction. Excellent ethylene selectivity of ~100% was obtained in the whole reaction temperature range of 50°C–200°C for samples calcined at temperatures of 600°C and 800°C. This could be ascribed to the formation of PdxCe1 – xO2 – y or Pd-O-Ce surface species based on the X-ray diffraction and X-ray photoelectron spectroscopy results, indicating the strong interaction between palladium and ceria. Keywords selective hydrogenation, acetylene, Pd/CeO2, strong interaction
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Introduction
Ethylene from petrochemical cracking and distillation contains small quantities of acetylene (0.5%–2%), which could poison the Ziegler-Natta catalyst used for downstream ethylene polymerization. So these trace amounts of acetylene must be removed [1–3]. Palladium is the industrially used metal catalyst for selective hydrogenation of acetylene in ethylene stream. However, supported Pd catalyst is generally hampered by its limited selectivity at high acetylene conversion because the increase in acetylene conversion also accelerates the hydrogenation rate of acetylene and ethylene to the undesirable hydrogenation product, ethane [4]. While the low selectivity to ethylene could be due to the strong adsorption of reactants and products on contiguous Pd sites, low coordination Pd Received August 31, 2019; accepted November 23, 2019 E-mail: [email protected]
atoms have been generally regarded as the most active sites for selective acetylene hydrogenation [5]. Therefore, downsizing Pd nanoparticles to sub-nano clusters or single atoms should enhance the efficiency of supported noble metal catalysts. Meanwhile, efficient catalysts with trace amounts of noble metals may be more feasible for practical applications [6]. Ceria is one of the most extensively used material in redox reactions due to its facile oxygen storage/release behavior [7–11]. Recently, it has been found to act as a remarkable stand-alone catalyst in the selective hydrogenation of alkynes to alkenes [12–14]. Vilé et al. [14] reported for the first time the superior performance of ceria in the hydrogenation of alkynes. The degree of surface reduction impacts on the lattice structure through the formation of oxygen vacancies, which are detrimental for the hydrogenation performance. Density functional theory sim
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