Catalytic Hydrogenation of C<sub>2</sub>H<sub>2</sub> over Amorphous CeNi<sub>2</sub>H<i><sub>x</sub></i> and Crystalline CeNi<sub>2</sub>: Effects of Hydrogen-Induced Amorphization and Oxidation

The catalytic hydrogenation of acetylene over crystalline CeNi2 and amorphous CeNi2Hx 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 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 CeNi2 and provided complete conversion of acetylene at 125°C. Both the crystalline CeNi2 and 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.