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

摘要

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 deg 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 deg C in the absence of CuO,it occurs at 1340 and 1290 deg 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 Nb2Os 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 deg 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/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 deg C.