Catalytic Hydrogenation of C₂H₂ over Amorphous CeNi₂H_x and Crystalline CeNi₂: Effects of Hydrogen-Induced Amorphization and Oxidation

抄録

The catalytic hydrogenation of acetylene over crystalline CeNi₂ and amorphous CeNi₂H_x was investigated. CeNi₂ was found to undergo a transformation to an amorphous phase after exposure to 0.35 MPa hydrogen at 25°C. Both crystalline CeNi₂ and amorphous CeNi₂H_x without exposure to air showed minimal catalytic activity. These results indicated that the hydrogen-induced amorphization of CeNi₂H_x does not result in an increase of catalytic activity and that the absorbed hydrogen in CeNi₂H_x was minimally active. After exposure to air, both materials were found to catalyze the hydrogenation of acetylene, suggesting that surface oxidation was a prerequisite. Amorphous CeNi₂H_x also exhibited higher catalytic activity than crystalline CeNi₂ and provided complete conversion of acetylene at 125°C. Both the crystalline CeNi₂ and amorphous CeNi₂H_x were characterized by X-ray photoelectron spectroscopy, thermogravimetry-differential thermal analysis and transmission electron microscopy. Amorphous CeNi₂H_x was more readily oxidized and formed a dense surface nanostructure that provided superior catalytic activity. Amorphous CeNi₂H_x is evidently a better catalytic precursor for acetylene hydrogenation than crystalline CeNi₂.