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

Abstract

Copper oxide and niobium pentoxide were supported on silica-alumina by two methods: co-impregnation and sequential impregnation, with CuO:Nb 2O 5 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 °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 Nb 2O 5 transition phase. Whereas that transition occurs at about 1356 °C in the absence of CuO, it occurs at 1340 and 1290 °C using the co-impregnation and sequential processes, respectively. In addition, the materials with a CuO:Nb 2O 5 ratio of 1:1 and copper oxide content >2 wt% did not present that transition phase. This indicates a strong influence of CuO over Nb 2O 5 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 °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-alumina, but also on the surface hydroxyl groups of niobium pentoxide. The application of CuO/Nb 2O 5/SiO 2-Al 2O 3 materials in the oxidation of diesel soot particulates is promising; mixtures of the catalyst with a model particulate (Printex ® U) lowered the oxidation temperature from 622 to 518 °C.