Nature of Rh Oxide on Rh Nanoparticles and Its Effect on the Catalytic Activity of CO Oxidation
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Nature of Rh Oxide on Rh Nanoparticles and Its Effect on the Catalytic Activity of CO Oxidation Sun Mi Kim • Kamran Qadir • Bora Seo Hu Young Jeong • Sang Hoon Joo • Osamu Terasaki • Jeong Young Park
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Received: 16 June 2013 / Accepted: 9 August 2013 / Published online: 4 September 2013 Ó Springer Science+Business Media New York 2013
Abstract Surface oxide layers formed on transition metal catalysts are well known as one of the controlling factors in enhancing or suppressing the catalytic activity of metal catalysts. We investigated the growth of a surface oxide layer on two sizes of Rh metal nanoparticles (NPs) as a function of UV–ozone (UV/O3) dosing as well as how the oxide layer formed on the surface of the Rh NPs affects the catalytic activity for CO oxidation. Monodisperse Rh NPs were synthesized via one-pot polyol reduction using poly(vinylpyrrolidone) as a capping agent. Varying the concentration of the Rh precursors controlled the size of the NPs. The changes that occurred as a function of UV/O3 dosing were characterized using X-ray photoelectron spectroscopy, which showed that the oxidation state increased with increasing surface modification time. The catalytic activity and activation energy of the two-dimensional Rh NPs arrays were measured as the UV/O3
S. M. Kim K. Qadir O. Terasaki J. Y. Park Graduate School of EEWS (WCU) and NanoCentury KI, KAIST (Korea Advanced Institute of Science and Technology), Daejeon 305-701, Republic of Korea S. M. Kim K. Qadir J. Y. Park (&) Center for Nanomaterials and Chemical Reactions, Institute for Basic Science, Daejeon 305-701, Republic of Korea e-mail: [email protected] B. Seo S. H. Joo School of Nano-Bioscience and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan 689-798, Republic of Korea H. Y. Jeong UNIST Central Research Facilities and School of Mechanical & Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan 689-798, Republic of Korea
exposure time increased. Our reaction studies indicate that the turnover rate of CO oxidation on the Rh NPs is enhanced as the quantity of the surface oxide layer formed during UV/O3 surface treatment increases, indicating that the oxides grown on the surface of the Rh metal are catalytically active. These results suggest an intriguing way to tune catalytic activity via engineering of the nanoscale surface oxide. Keywords Surface oxide layer CO oxidation Rh nanoparticles Oxidation state UV–ozone (UV/O3) dosing Catalytic activity
1 Introduction Technologically relevant catalysts have complex chemistry, which make it challenging to understand and, hence, control the involved processes and chemical reaction steps at atomic scale. Thus, less structurally complex systems, or ‘model systems’, such as single crystals, nanoparticles (NPs) arrays deposited on two-dimensional (2D) supports or dispersed on three-dimensional oxide supports, have been extensively investigated. This has resulted in addit
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