关键词: 催化加氢, 丙酸甲酯, 活化, 钌, 镧

Abstract:

We prepared a 4%Ru-9%La/γ-Al₂O₃ catalyst by impregnation method and characterized it using X-ray diffraction(XRD) ,X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalyst was used for the hydrogenation of methyl propionate. The effects of solvent, inorganic salt additive, steric as well as electronic factors of the substrate on the hydrogenation of a carboxylic ester were investigated. We found that both water and the Co(NO₃)₂ additive obviously improved the hydrogenation of methyl propionate, the conversion of the substrate and the selectivity for propanol. The promotional effects of water and Co²⁺ are attributed to polarization of the C=O bond in the carboxyl group of the substrate molecule by the formation of a hydrogen bond between water and the carboxylic group and the coordination of Co²⁺ to the carboxylic group. This is favorable for an attack on the carbon atom of the carboxyl group by the activated hydrogen. Similarly, the electron -withdrawing group in the substrate molecule also caused the high positive charge of carbon in the carboxyl group. The highly positive charged carbon is beneficial for the hydrogenation reaction. In addition, an increase in the steric hindrance of the substrate molecules was not favorable for the adsorption of the substrate on the catalyst and, therefore, the reaction rate decreased.

Key words: Catalytic hydrogenation, Methyl propionate, Activation, Ruthenium, Lanthanum