With the growing consumption of fossil fuel, the renewable biomass has drawn attention as the sustainable alternatives to bridge gaps in the supply of chemical fuel and feedstock. The NbOPO4 based catalyst presents a high activity for the direct production of liquid alkanes from a wide variety of raw woody biomass with excellent mass and carbon yields. By virtue of DFT calculation, we examined the crucial C–O bond breaking process of phenol and 1-butanol, which are the model compound of lignin and important intermediate in THF conversion, respectively. For 1-butanol conversion on NbOPO4, the calculation indicates that 1-butanol efficiently adsorbs on Nb5c with a corresponding adsorption energy of - 1.20 eV, indicating that NbOPO4 possesses a stronger binding ability. Subsequently, with the aid of the surface Nb5c, the C–O bond can break with each OH and butyl occupying a Nb5c site as the product; this process is strongly exothermic by 1.72 eV and gives a barrier of only 0.79 eV, implying its feasibility in both thermodynamics and kinetics. Notably, the widely used ReOx catalyst in biomass conversion was also tested for comparison. By comparing the energy profiles, it is conclusive that NbOPO4 demonstrates an inherently better performance for 1-butanol deoxygenation than Re2O7. Likewise, with respect to C–O bond cleavage of phenol, the high catalytic activity of NbOPO4 can be ascribed to better adsorption capability of surface Nb5c and a lower activation barrier in comparison to Re2O7. To understand the bond properties of M5c–O(OH), an electronic structure analysis was performed, which indicates a typical covalent bond character between O (or OH) and Nb5c (or Re5c). Therefore, the binding strength with O(OH) is mainly decided by the size and energy level of the d-orbital of Nb5c and Re5c cations. The projected density of states on the d-orbitals indicates that the d band of Nb5c near the Fermi level (EF) is more delocalised comparing to Re5c, and more importantly, the energy level of the highest occupied d bands is evidently higher for Nb5c with some metallic character across EF. Therefore, one can rationalise such a strong binding ability of NbOPO4 in facilitating deoxygenation reaction from these d bands features according to the frontier orbital theory.

Unraveling the catalytic origin of NbOPO4 catalyst in biomass conversion by density functional theory

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.