Desidratação catalítica do glicerol sob óxidos mistos de CuO/Al2O3/MxOy (MxOy = ZnO ou Fe2O3): estudo sobre a química de superfície

Abstract

As an alternative to the use of fossil fuels, biofuels have consolidated in the international market. In this sense, biodiesel has become an excellent route, however, in its synthesis, the by-product glycerol is generated. The conversion of glycerol into higher added value products stimulates the application of different possibilities involving heterogeneous catalysis. In this work, the application of a series of oxide catalysts based on Fe, Al, Cu and another on Zn, Al and Cu was tested. XRD results indicate nanometric diameter and the presence of ZnO, Al2O3 and CuO oxides. Raman, Mössbauer and XPS spectroscopy suggest the presence of phases based on Fe2O3, Al2O3 and CuO. The 27Al NMR indicates an octahedral coordination of Al2O3. Whereas materials made of Zn present tetra, penta and hexa coordination in alumina. FTIR with pyridine adsorption revealed high Lewis acidity across the Fe catalyst series. The TPR exhibited the reduction range of the Fe3+ and Cu2+ sites, indicating the appropriate temperature range for pretreatment. N2 adsorption/desorption indicated the presence of micro-mesopores, while the porous morphology was visually observed by SEM and TEM images. Regarding the performance of the catalysts, the best material was Fe10Al90Cu with 60% glycerol conversion and 92% selectivity in the formation of acetol with 17% coke according to TG. The interaction between the different Lewis acid sites involved in the mechanisms for acetol and coke formation on the catalyst surface are discussed. Thus, the synergy between the active sites obtained in the pre-treatment with H2, based on the surface maps ρ(r) and V(r), obtained by calculations via density functional theory, indicating that the presence of Cun+ increases dramatically the selectivity in the formation of acetol, a more important characteristic than the high Lewis acidity.