Catalytic glycerol dehydration on mixed oxides of CuO/Fe2O3/Al2O3: Insights about surface chemistry.
Dehydration of glycerol, acetol, oxides, Cu-Fe-Al, mechanism.
As an alternative to the use of fossil fuels, biofuels have become consolidated in the international market. In this sense, biodiesel has become an excellent route, but in its synthesis the by-product glycerol is generated. The conversion of glycerol into products with higher added value stimulates the application of different possibilities involving heterogeneous catalysis. In this work, the application of a series of oxide catalysts composed of Fe-Al-Cu was tested. XRD results indicate nanometer diameter, Raman, Mössbauer and XPS spectroscopy suggest the presence of phases present based on Fe2O3, Al2O3 and CuO, in addition to 27Al NMR indicating the octahedral coordination of Al2O3. The FTIR with pyridine adsorption revealed high Lewis acidity in the entire series of catalysts. The TPR showed the range of reduction of the Fe3+ and Cu2+ sites, indicating the appropriate temperature range for pretreatment. The adsorption/desorption of N2 indicated the presence of macropores, while the porous morphology was observed by SEM and TEM images. Regarding the performance of the catalysts, the best condition had a conversion of 98% of glycerol and 84% of selectivity in the formation of acetol with 28% of coke according to TG. The interaction between the different Lewis acid sites involved in the mechanisms for the formation of acetol and coke on the catalyst surface are discussed. Thus, the synergy between the different active sites obtained in the pre-treatment with H2, based on DFT calculations, indicates that the presence of Cun+ drastically increases the selectivity in the formation of acetol, a more important characteristic than the high Lewis acidity.