Surface and Catalytic Properties of the CuO/Al2O3 System as Influenced by Treating with Trace Amounts of MoO3

Abstract

A CuO/Al2O3 solid containing 0.2 mol% CuO (0.2CuO/Al2O3) and three MoO3-doped variants of this material were all prepared via the wet impregnation method, the amount of dopant added to the CuO/Al2O3 solid being 0.25, 1.0 or 2.0 mol% MoO3, respectively. All the samples prepared were heated in air to 350, 450 or 600°C, respectively, before being cooled to room temperature and stored. X-Ray studies of these materials showed that the undoped (pure) solid calcined at 350°C exhibited all the diffractions lines associated with the AlO(OH) and CuO phases with an excellent degree of crystallinity. Doping the pure solid resulted in the effective progressive decrease in the degree of crystallinity of both the above-mentioned phases to an extent proportional to the amount of dopant added. Increasing the calcination temperature of the pure and doped solids to 650°C led to a significant decrease in the degree of ordering of CuO due to the formation of poorly crystalline γ-Al2O3 having a much better dispersion power relative to AlO(OH). The specific surface areas of the various samples were found to decrease progressively as the amount of dopant added was increased, especially for samples calcined at 650°C. Increasing the calcination temperature of the pure sample within the range 350–650°C led to a small increase in their catalytic activities in H2O2 decomposition. In contrast, MoO3 treatment followed by calcination of the resulting materials in the range 350–650°C resulted in a significant increase in their catalytic activities in the same catalytic reaction. The maximum increase in the catalytic activity at 30°C attained values of 720%, 735% and 976% for the doped solids calcined at 350, 450 and 650°C, respectively. In contrast, however, such doping brought about a progressive measurable decrease in the catalytic activity of the treated solids towards CO oxidation by O2 when this latter reaction was conducted over the temperature range 150–250°C.