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

Abstract

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 Ga^y+–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.