Synthesis of Cu-MxOy/Al2O3 (M = Fe, Zn, W or Sb) catalysts for the conversion of glycerol to acetol: effect of texture and acidity of the supports
Résumé
The purpose of this work is to study the relationships between the copper oxide structure, specific surface area, acidity of MxOy/Al2O3 (M = Fe, Zn, Wand Sb) supports and subsequently the catalytic proprieties of the solids. The samples were characterized by XRD, N-2 adsorption/desorption isotherms and microcalorimetry of NH3 adsorption. The XRD results (after and before reaction) of the Fe and Zn-containing solids present the formation of a copper-modified alumina structure (high dispersion of Cu species with a strong interaction with the support); however, it is not observed a copper-modified phase for the catalysts composed of W and Sb, since it was identified the isolated CuO phase (a lower dispersion of Cu with a poor interaction with the support). N-2 adsorption/desorption isotherms analysis shows that the copper-modified alumina samples are mesoporous materials and have a high surface area compared to the other catalysts, which did not presented a copper-modified phase. The catalytic tests ascribed that the presence of a copper-modified structure improves the activity, selectivity and mainly the stability for conversion of glycerol to acetol. W and Sb-based samples present low stability in glycerol transformation to acetol probably due to its acidity leading to formation of coke, blocking the active sites as a result of the low number of sites per area (low surface area) as well as the sintering of the copper phase. Thus, the results explain that the choice of metal elements in the solids composition affects its structural, textural, acidity proprieties and consequently the catalytic performance.