Effect of the support on the hydrodeoxygenation of m-cresol over molybdenum oxide based catalysts

Abstract

The hydrodeoxygenation (HDO) of m-cresol was investigated over supported molybdenum oxide catalysts at 340 °C under 4 MPa as total pressure. All catalysts were fully characterized using several techniques such as atomic absorption, N2 physisorption, XRD, H2-TPR, NH3-TPD, Raman spectroscopy, TEM analysis and oxygen chemisorption. It was noted that the reducibility of molybdenum species depends on the support used and follows the same order than the one determined from the HDO activity, i.e. MoOx/Al2O3 > MoOx/SBA–15 > MoOx/SiO2. In addition, the use of an ordered mesoporous silica support (SBA-5) or an acidic support (Al2O3) favored significantly the dispersion of MoOx particles compared to SiO2. Under these experimental conditions, m-cresol transformation underwent through two parallel deoxygenation routes which involved either the direct CO bond scission leading to toluene (DDO route), or the total hydrogenation of the aromatic ring yielding mainly to a mixture of methylcyclohexene isomers (HYD route). Regardless of the support used, the DDO route was always predominant. A reaction mechanism was proposed to explain the formation of toluene, the main product observed from HDO of m-cresol. To explain the formation of this aromatic, a selective adsorption through the oxygen atom of the phenolic reactant on oxygen vacancies, acting as HDO active sites, was proposed.