Surface characterization of alumina-supported catalysts prepared by sol-gel method.: Part II.: Surface reactivity with CO

Surface reactivity toward H-2 and CO using a pulse method was investigated for Al2O3, In2O3-Al2O3 and Ga2O3-Al2O3. It was found that reduction by either CO or H-2 and reoxidation by O-2 occurred reversibly on In2O3-Al2O3. Although the surface of Ga2O3-Al2O3 was hardly reduced by H-2, CO consumption and CO2 formation was observed on exposure to CO. Mass spectroscopic analysis revealed the formation of H-2 from injection of CO pulses on Ga2O3-Al2O3, while small amounts of H-2 were detected on In2O3-Al2O3. The formation of H-2 on Ga2O3-Al2O3 was also evidenced by Fourier transform infrared (FT-IR) spectroscopy. Namely, when Ga2O3-Al2O3 was exposed to CO at elevated temperatures above 573 K, the IR band assignable to Gay+-H species was detected at 1997 cm(-1). A reaction model in which the reaction of CO with basic hydroxy groups occurs on the surface of Ga2O3-Al2O3 (CO+OH --> CO2+1/2H(2)) is proposed.