Catalytic Hydrogenation of C2H2 over Amorphous CeNi₂Hx and Crystalline CeNi₂: Effects of Hydrogen-Induced Amorphization and Oxidation

The catalytic hydrogenation of acetylene over crystalline CeNi₂and amorphous CeNi₂Hx was investigated. CeNi₂was found to undergo a transformation to an amorphous phase after exposure to 0.35 MPa hydrogen at 25°C. Both crystalline CeNi₂and amorphous CeNi₂Hx without exposure to air showed minimal catalytic activity. These results indicated that the hydrogen-induced amorphization of CeNi₂Hx does not result in an increase of catalytic activity and that the absorbed hydrogen in CeNi₂Hx 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 CeNi₂Hx also exhibited higher catalytic activity than crystalline CeNi₂and provided complete conversion of acetylene at 125°C. Both the crystalline CeNi₂and amorphous CeNi₂Hx were characterized by X-ray photoelectron spectroscopy, thermogravimetry-differential thermal analysis and transmission electron microscopy. Amorphous CeNi₂Hx was more readily oxidized and formed a dense surface nanostructure that provided superior catalytic activity. Amorphous CeNi₂Hx is evidently a better catalytic precursor for acetylene hydrogenation than crystalline CeNi₂.