Gold supported CeO 2 /Al 2 O 3 catalysts for CO oxidation: influence of the ceria phase
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Catalysis Letters Vol. 102, Nos. 3–4, August 2005 ( 2005) DOI: 10.1007/s10562-005-5871-5
Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase Miguel A´ngel Centeno*, Cristina Portales, Ignacio Carrizosa, and Jose´ Antonio Odriozola Institute de Ciencia de Materiales de Sevilla, Centro Mixto CSIC-Universidad de Sevilla, Avda Americo Vespuccio s/n, 41092 Sevilla, Spain
Received 3 March 2005; accepted 27 April 2005
A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, SBET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid. KEY WORDS: gold catalysts; CO oxidation; CeO2/Al2O3 catalysts.
1. Introduction In the last years, the use of gold supported catalysts for oxidation reactions has been widely improved [1–6]. In particular, a large number of works has focussed on the high catalytic activity of gold catalysts towards low temperature CO oxidation [7,8]. The catalytic performance of gold strongly depends on the particle size, in such a way that smaller the particles higher the activities [1]. Typically, gold particles lower than 4 nm are needed for a good activity. On the basis of this observation, most of the studies focussed on the preparation of catalyst with supported gold nanoparticles as small as possible [9, 10]. On the other hand, the nature of the support is also a key factor. In this sense it has been proved that when a reducible transition metal oxide such as Fe2O3 or MnO2 is used as support, the catalytic performances of the gold catalyst for CO oxidation are improved, due to the support ability of provide reactive oxygen to the gold particles [11]. CeO2 is one of these ‘‘active’’ supports, Ceria has a high oxygen storage capacity and well known catalytic and redox properties, On the other hand, it is a structural promoting component which enhances metal dispersion and participates in the stabilisation against thermal sintering of other common used supports, as alumina [12]. In a previous work we have demonstrated that CeO2/Al2O3 is a suitable support for obtaining well dispersed and active gold catalyst for CO and volatile organic compounds oxidation [13,14]. The objective of this work is to demonstrate that in the case of low loading gold supported ceria/alumina catalysts, where the metallic *To whom correspondence should be addressed. E-mail: [email protected]
particles are far away one from another and the oxygen transportati
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