Contribution of Different NbOx Species in the Hydrodeoxygenation of 2,5-Dimethyltetrahydrofuran to Hexane

Hydrodeoxygenation (HDO) is significant for the upgrading of biomass, bio-oil, and biomass-derived compounds to fuels due to their abundant oxygen atoms. It is reported that Pd, Pt supported on Nb-based materials is excellent for the HDO reaction of raw biomass and biomass-derived compounds because NbOx species has a strong ability to activate C-O bonds in the previous studies. Here, we try to clarify which are the active NbOx centers, isolated, oligomer or low-coordinated species by using Pd/Nb-doped SBA-15 as the catalyst and 2,5-dimethyltetrahydrofuran (DMTHF) as the model compound. Nb-doped SBA-15 with tunable Nb content is prepared by glycerol-assisted one-pot hydrothermal method. These Nb-doped SBA-15 and Pd-loaded catalysts are characterized by XRD, N-2 sorption, TEM/SEM, diffuse reflectance ultraviolet-visible spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy. The performance of Pd/Nb-doped SBA-15 catalysts is found to be depended on the state of Nb species in SBA-15. The catalyst with low Nb loading possessing lower Nb coordination numbers can adsorb the oxygen atom of DMTHF and hence promote the cleavage of C-O bond of DMTHF. A higher turnover frequency of the catalysts based on Nb content and Lewis acid site can be obtained in catalysts with low Nb loading.