Preferential oxidation of CO in a hydrogen-rich stream over Au/MOx/Al2O3 (M = La, Ce, and Mg) catalysts.

The preferential oxidation of CO (CO-PROX) under excess hydrogen over Au/MO x /Al 2 O 3 (M = La, Ce, and Mg) catalysts was investigated. All catalysts were prepared by a deposition-precipitation method with urea and characterized with inductively coupled plasma-atomic emission spectroscopy, N 2 physisorption, temperature-programmed reduction, X-ray diffraction, transmission electron microscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. The catalytic activity of the supported gold catalysts was found to be dependent on the promoter, and decreased in the order: Au/La 2 O 3 /Al 2 O 3 > Au/CeO 2 /Al 2 O 3 > Au/MgO/Al 2 O 3 > Au/Al 2 O 3 . The catalytic activity of the Au/La 2 O 3 /Al 2 O 3 catalyst depended on the pretreatment conditions, i.e., reduction with aqueous NaBH 4 , thermal reduction with H 2 , and calcination with O 2 . This indicates that the oxidation state of gold is an important factor in the activity of the catalyst, and that metallic gold is more suitable than its oxidized form for this reaction. XPS results revealed that the treatment with aqueous NaBH 4 resulted in more negative charge in gold particles than that of conventional thermal reduction under H 2 . Smaller gold particles appeared to be favorable for the low-temperature CO-PROX activity of the Au/La 2 O 3 /Al 2 O 3 catalysts, which showed stable CO-PROX performance, even in the presence of CO 2 . [ABSTRACT FROM AUTHOR]