Activity of copper–cerium–zirconium catalysts in oxidation of hydrogen

Abstract

We have studied the catalytic properties in oxidation of hydrogen for copper-cerium oxide systems deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300-1000°C. We have shown that the catalytic activity of the samples obtained depends on the specific surface area of the original supports and the amount of reduced copper within the composition of the catalyst. In samples whose support has high specific surface area, the content of reduced metallic copper is greater and the catalytic activity is higher.Fine purification of hydrogen-containing fuel to remove CO impurities (down to 10-100 ppm) is needed because of the poisoning effect of carbon monoxide on platinum particles contained in the electrodes of proton exchange membrane (PEM) fuel cells. An advantage of the catalytic CO oxidation method is its relative simplicity compared with adsorption/diffusion methods and its low hydrogen losses compared with the catalytic hydrogenation method, when not only CO but also CO 2 contained in the hydrogen-rich mixture is involved in the reaction [1]. Hydrogen losses can be generally avoided if we use a catalyst that selectively oxidizes only CO. A comparative study of copper-cerium oxide systems deposited on chemically different oxide supports has shown that catalytic compositions based on zirconium dioxide exhibit the highest selectivity in CO oxidation in hydrogen-rich mixtures [2]. In [3,4], we studied the catalytic properties of nanosized zirconium dioxide and copper-cerium-zirconium catalysts obtained on its basis, in the reaction of CO oxidation (including selective oxidation in hydrogen-rich gas mixtures). We showed that the highest CO conversions were observed not only in samples characterized by high dispersity and extended surface area but also on catalysts with low specific surface area and supports with large particle sizes. At the same time, during oxidation of CO in excess hydrogen, the selectivity decreased as the specific surface area increased and the zirconium dioxide particle sizes decreased in copper-cerium-zirconium oxide catalysts, which was connected with involvement of hydrogen in the oxidation process. In order to establish the reason for the high selectivity of the catalysts, in this work we studied the effect of the structural and texture characteristics of zirconium dioxide on the catalytic properties of the copper-cerium-zirconium oxide catalysts obtained in the undesirable reaction of hydrogen oxidation. We varied the particle size and the specific surface area of the supports based on yttrium-stabilized zirconium dioxide by controlling their calcination temperature. EXPERIMENTALFor the studies on oxidation of hydrogen, we used copper-cerium-zirconium oxide catalysts which had already been previously tested in selective oxidation of CO in hydrogen-rich mixtures [4]. The procedure for preparing the original catalysts is described in detail in [4]. As the supports for the copper-cerium systems, we used yttrium-stabilized zirconium dioxide (3.4 mole % Y 2 O 3 /...