Reduction kinetics of CuO in CuO/ZnO/ZrO2 systems

Abstract

Reduction of copper oxide in the CuO/ZnO/ZrO₂ system, which is an oxide precursor of the catalysts active in the synthesis of methanol from CO₂ and H₂, was investigated. Preparations with varying CuO contents were obtained by co-precipitation or complexing the components with citric acid; also modifying additives (MgO, MnO) were introduced. The prepared materials were characterised by determining their surface area (BET), the active surface of Cu using the method of reactive adsorption of N₂O, the size of the CuO crystallites by XRD line broadening, the surface composition by XPS, and the kinetics of reduction using TPR, XRD and gravimetric methods. It was found that the reduction of CuO was an autocatalytic consecutive reaction and that the intermediate product was amorphous Cu₂O. The autocatalytic effect is due to facilitated dissociation of H₂ on the metallic copper formed. Water formed during the reaction hinders the reduction by blocking the hydrogen adsorption centres. Changes in preparation methods, CuO content, as well as introduction of additives, affect the rate of the CuO reduction mainly by morphological changes: content of the amorphous CuO phase, size of the CuO crystallites and its surface segregation.