The reduction process of copper-zinc oxide-(allumina) methanol catalysts

CuO-ZnO-Al2O3 catalysts at different copper and zinc contents were obtained by thermal decomposition of hydroxycarbonate precursors at 350°C in air. They were characterized by using X-ray diffraction, diffuse reflectance spectroscopy and surface area determination. We find disticnt CuO and ZnO phases whose particle sizes, determined by XRD line broadening, are in the range 65-90 Å for CuO and around 100 Å for ZnO in the binary CuO/ZnO systems. For pure CuO the particle dimensions are higher View the MathML source. For the three component oxide, CuO|ZnO|Al2O3=60|30|10, the particle sizes of both CuO and ZnO phases are around 60 Å. The BET surface areas are around 70 m2/g for the two components oxides, ~40 for pure CuO and for the three component systems. The reduction of the copper oxide (CuO) has been studied by in situ XRD. The reduction to metallic copper proceeds through the formation of intermediate Cu2O which is present together with metallic copper even at relatively high extents of reduction. It has also been observed that the reduction process is much slower in the three component system than for pure CuO or the two component, CuO-ZnO, system. The presence of alumina in intimate contact with CuO and ZnO (due to the preparation conditions of the precursors) thus seems to hinder the reduction of the Cu2+ species (to Cu+ or Cuo) and to prevent the nucleation of both cuprous oxide and metallic copper partcles.