Restraining deactivation of β-zeolite by modifying with MgAl2O4 spinel in gas-phase glycerol dehydration

Abstract

MgAl2O4 dispersed on HBEA zeolite with different spinel contents were successfully synthesized and their glycerol dehydration performances were presented. The different solids were characterized by XRD, infrared (IR) and Raman spectroscopy, N2 physisorption, SEM-FEG, acidity by TPD-NH3 and DRIFTS-pyridine adsorption. It was not possible to observe the spinel phase in the diffractograms due to its high dispersion, while the reflections of the HBEA were evidenced in the different samples. The Raman and infrared spectra suggested the presence of stretches concerning the MgAl2O4 spinel. N2 isotherms and low-angle XRD indicated that the pore structure and textural properties were altered after impregnation, but the micro-mesoporosity of zeolite was maintained. The HBEA morphology did not undergo significant changes by modification with spinel and the metals are evenly distributed according to SEM and EDS spectral mapping. The addition of spinel on zeolite caused a change in the acidic properties of HBEA related to the type, number and strength of the sites according to the TPD profiles and the DRIFTS spectra. The 2% of MgAl2O4 on HBEA catalyst exhibited the best catalytic performance due to the effects of its acidic and textural properties, reaching 60% of glycerol conversion, 66% of acrolein selectivity in 6 h and 16% of coke deposited in 10 h, restricting deactivation compared to pure zeolite. The reaction pathway for the different products formed depending on the type of acid site were detailed in the proposed mechanism and correlated with electrostatic potential maps as well as the reactions for coke formation were described according to compounds identified by GC-MS after coke extraction.