Copper oxide and niobium pentoxide supported on silica-alumina: Synthesis, characterization, and application on diesel soot oxidation

Copper oxide and niobium pentoxide were supported on silica-alumina by two methods: co-impregnation and sequential impregnation, with CuO:Nb2O5 ratios of 1:10 and 1:1. These new materials showed different characteristics according to the preparation method. The copper and niobium precursors totally decomposed after treatment at 300 degrees C for 6 h. The materials prepared by sequential impregnation exhibited lower thermal stability than the analogous ones prepared by co-impregnation based on the Nb2O5 transition phase. Whereas that transition occurs at about 1356 degrees C in the absence of CuO, it occurs at 1340 and 1290 degrees C using the co-impregnation and sequential processes, respectively. In addition, the materials with a CuO:Nb2O5 ratio of 1:1 and copper oxide content > 2 wt% did not present that transition phase. This indicates a strong influence of CuO over Nb2O5 crystallites. XRD studies confirmed this interaction, showing the patterns of Cu and Nb oxides (for most of the samples prepared by both methods) and the presence of a third component (copper niobium oxide) on the samples with CuO content >= 10 wt% when calcined at 800 degrees C for 6 h. FTIR, DRIFTS, and FT-Raman studies provided additional evidence of that interaction, which occurs not only on the surface hydroxyl groups of silica-alurnina, but also on the surface hydroxyl groups of niobium pentoxide. The application of CuO/Nb2O5/SiO2-Al2O3 materials in the oxidation of diesel soot particulates is promising; mixtures of the catalyst with a model particulate (Printex (R) U) lowered the oxidation temperature from 622 to 518 degrees C. (c) 2007 Elsevier Inc. All rights reserved.