Interfacial Bonding Stabilizes Rhodium and Rhodium Oxide Nanoparticles on Layered Nb Oxide and Ta Oxide Supports

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• 作者：Megan E. Strayer ; Jason M. Binz ; Mihaela Tanase ; Seyed Mehdi Kamali Shahri ; Renu Sharma ; Robert M. Rioux ; Thomas E. Mallouk
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 16, 2014
• 年：2014
• 卷：136
• 期：15
• 页码：5687-5696
• 全文大小：594K
• 年卷期：v.136,no.15(April 16, 2014)
• ISSN：1520-5126

文摘

Metal nanoparticles are commonly supported on metal oxides, but their utility as catalysts is limited by coarsening at high temperatures. Rhodium oxide and rhodium metal nanoparticles on niobate and tantalate supports are anomalously stable. To understand this, the nanoparticle鈥搒upport interaction was studied by isothermal titration calorimetry (ITC), environmental transmission electron microscopy (ETEM), and synchrotron X-ray absorption and scattering techniques. Nanosheets derived from the layered oxides KCa₂Nb₃O₁₀, K₄Nb₆O₁₇, and RbTaO₃ were compared as supports to nanosheets of Na-TSM, a synthetic fluoromica (Na_0.66Mg_2.68(Si_3.98Al_0.02)O_10.02F_1.96), and 伪-Zr(HPO₄)₂路H₂O. High surface area SiO₂ and 纬-Al₂O₃ supports were also used for comparison in the ITC experiments. A Born鈥揌aber cycle analysis of ITC data revealed an exothermic interaction between Rh(OH)₃ nanoparticles and the layered niobate and tantalate supports, with 螖H values in the range 鈭?2 kJ路mol^鈥? Rh to 鈭?7 kJ路mol^鈥? Rh. In contrast, the interaction enthalpy was positive with SiO₂ and 纬-Al₂O₃ supports. The strong interfacial bonding in the former case led to 鈥渞everse鈥?ripening of micrometer-size Rh(OH)₃, which dispersed as 0.5 to 2 nm particles on the niobate and tantalate supports. In contrast, particles grown on Na-TSM and 伪-Zr(HPO₄)₂路H₂O nanosheets were larger and had a broad size distribution. ETEM, X-ray absorption spectroscopy, and pair distribution function analyses were used to study the growth of supported nanoparticles under oxidizing and reducing conditions, as well as the transformation from Rh(OH)₃ to Rh nanoparticles. Interfacial covalent bonding, possibly strengthened by d-electron acid/base interactions, appear to stabilize Rh(OH)₃, Rh₂O₃, and Rh nanoparticles on niobate and tantalate supports.