Understanding the promoter effect of bifunctional (Pt, Ni, Cu)-MoO3-x/TiO2 catalysts for the hydrodeoxygenation of p-cresol: A combined DFT and experimental study

Abstract

The effect of Pt, Ni, and Cu promoters on the partial reduced MoO3-x/TiO2 catalysts for the hydrodeoxygenation (HDO) reaction of p-cresol was investigated through experiments and density functional theory (DFT) calculations. The MoO3-x/TiO2 was firstly prepared and then Pt, Ni, or Cu precursor was introduced. The mixed Mo4+, Mo5+, and Mo6+ states were identified by XPS. The HR-TEM and TEM-EDX images suggest that the MoO3-x becomes amorphous and is well-dispersed on TiO2 supports leading to direct contact of the metal on MoO3-x/TiO2. The HDO of p-cresol under a low hydrogen pressure (5 bar) at 300 °C showed the %conversion as the following order: Pt-MoO3-x > Ni-MoO3-x > Cu-MoO3-x > MoO3-x. DFT results explained the differences of catalytic performance of the catalysts and the role of the promoters in enhancing the H2 activation. The high electronegativity and density of state near the Fermi level are responsible for the high catalytic performance of Pt-MoO3-x/TiO2, which shows barrierless for H2 dissociation and allows this catalyst to be active under a milder reaction temperature and pressure. These results deepen the fundamental understanding of the role of the promoters toward the key reaction step in HDO, which is beneficial for guiding the development of catalysts for biomass conversion.