Dependence on size of supported Rh nanoclusters in the decomposition of ethanol

Yu-Yao Hsia^1*, Meng-Fan Luo¹

¹Department of physics, National Central University, Taoyuan, Taiwan

* Presenter:Yu-Yao Hsia, email:siab1144775@gmail.com

To produce renewable hydrogen as a clean source for fuel cell, catalysts play a crucial role in the reaction of ethanol, which can be readily obtained from fermentation of biomass. Rhodium (Rh), as catalysts, have been widely used and alloyed with platinum (Pt) to improve the catalytic properties. The adsorption and decomposition of ethanol on the surfaces of Rh(100) and Rh(111), as single-crystal model systems, have been studied. However, ethanol decomposition on oxide-supported Rh nanoclusters, as a realistic model system, has been little investigated. We herein present our investigation of the catalyzed reaction of ethanol on Rh clusters supported on ordered thin film of Al2O3/NiAl(100), under ultrahigh vacuum (UHV) conditions and with temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Upon the adsorption of monolayer ethanol at 120 K, ethoxy (CH3CH2O*) was readily produced via the scission of O-H bond. The ethoxy decomposed predominantly via Cα-H bond cleavage and produced surface acetaldehyde (CH3CHO*), which was followed by the further decomposition to yield CH4, CO, H2, and surface carbon. Another pathway of ethoxy decomposition produced oxometallacycle (CH2CH2O*) via Cβ-H bond cleavage, leading to the formation of formaldehyde (CH2O), as a minor product, via C-C bond scission. For Rh clusters diameter <1.5 nm and height <0.6 nm, the reaction probabilities, measured by the ratios of quantities of the produced species (such as H2, CH4, and CO) to the total adsorbed monolayer ethanol, increased with decreasing size.

Keywords: Ethanol decomposition, Rh nanoclusters, Cluster chemistry