Transition metal-containing MgFe ex-LDH mixed oxides, effective catalysts in the hydrodeoxygenation of benzyl alcohol

Abstract

Several M-MgFe-LDH precursors were prepared via co-precipitation and then calcined at 500 °C to yield the corresponding M-MgFeO mixed oxide catalysts, which were tested in the hydrodeoxygenation (HDO) of benzyl alcohol. The prepared LDH contained Mg and Fe in a mol ratio of 3:1 and 10 at% M with respect to cations, where M = Ni, Co, Ag and Cu. The Cu-MgFeO mixed oxide gave the best results, therefore we proceeded with the preparation of a Cu(x)-MgFeO series, where x = 2.5–20 at% Cu. The prepared solids were characterized by powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed reduction with H2, temperature-programmed desorption of CO2 and energy dispersive X-ray spectroscopy. We studied the influence of the nature of the transition metal M on the activity and selectivity of the catalysts and, for the Cu-containing samples, the influence of Cu loading, reaction time and reaction temperature on their performance in the HDO reaction of benzyl alcohol. With 93.8% conversion and 93.8% selectivity towards toluene at 230 °C, 3 h reaction time and under a hydrogen pressure of 5 atm, the Cu(10)-MgFeO catalyst proved to have the best performance in the studied reaction. Therefore, its stability and reusability were checked. We also proposed a sequence of reactions for the entire HDO process, based on a reverse Mars-van Krevelen mechanism driven by oxygen vacancies formed on the catalyst surface.