Preparation of Au/MgxAlO hydrotalcite catalysts for CO oxidation

Gold catalysts of CO oxidation, supported on a solid base of MgxAlO (x = Mg/Al molar ratio) hydrotalcite, were prepared by a modified deposition precipitation method. The effect of various parameters that are involved in the preparation of catalysts were studied, including the pH and the concentrations of HAuCl4 in the initial solution, the Mg/Al molar ratio and the calcination temperature of the MgxAlO support as well as the calcination temperature of the Au/MgxAlO catalyst. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS) analyses. The pH and the HAuCl4 concentrations in the initial solution. and the Mg/Al molar ratio of MgxAlO affected the pH in the final solution, and determined the real gold loading in the resulting catalyst. The calcination temperatures of the MgxAlO support and the Au/MgxAlO catalyst dominated the ratio of gold states (Au3+/Au-0) on the catalyst. The optimal catalyst, 2%Au/Mg2AlO(100), was obtained using the following preparation parameters: (1) 1 x 10(-3) M HAuCl4, (2)pH 2 (without adjusting pH) in the initial solution, (3) Mg/Al = 2 Mg2AlO) calcined at 100 degrees C as a support and (4) 2%Au/Mg2AlO catalyst calcined at 100 degrees C. This investigation confirms that not only gold loading of the catalyst is important, the ratio of gold states (Au3+/Au-0) is also critical in determining the activity of the catalyst for CO oxidation. (c) 2007 Elsevier B.V. All rights reserved.