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

Surface reactivity toward H2 and CO using a pulse method was investigated for Al2O3, In2O3–Al2O3 and Ga2O3–Al2O3. It was found that reduction by either CO or H2 and reoxidation by O2 occurred reversibly on In2O3–Al2O3. Although the surface of Ga2O3–Al2O3 was hardly reduced by H2, CO consumption and CO2 formation was observed on exposure to CO. Mass spectroscopic analysis revealed the formation of H2 from injection of CO pulses on Ga2O3–Al2O3, while small amounts of H2 were detected on In2O3–Al2O3. The formation of H2 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 + 1/2H2) is proposed.