Regulating the crystal phase of Pd/Nb2O5 for vanillin selective HDO at room temperature

Constructing heterogeneous catalysts with high efficiency and stability to achieve biomass HDO under comparatively mild conditions is an arduous challenge. Crystal phase of metal oxides supports could affect the geometric and electronic properties, causing the variation of catalytic performance. Herein, a series of Pd/Nb2O5 catalysts of pseudohexagonal crystal phase (Nb2O5-TT), orthorhombic phase (Nb2O5-T) and monoclinic phase (Nb2O5-H) are prepared through regulating the annealing temperature. Impressively, Pd/Nb2O5-T catalyst showed amazing catalytic performance of 100% conversion and 98.9% selectivity of 2-methoxy-4-methylphenol (MMP) at room temperature (25℃) within 30 min, superior than Pd/Nb2O5-TT, Pd/Nb2O5-H and other Pd-based catalysts that had been reported. Besides, the Pd/Nb2O5-T perform robust stability and maintain its high activity after ten times recovery experiment. This catalytic system is also suitable for different kinds of aldehydes compounds at room temperature, exhibiting the high activity and selectivity towards deoxygenated products. Based on the characterizations and experimental validations, it has confirmed that the strong metal-support interaction (SMSI) effect generates via electron transfer between Pd species and Nb2O5-T support, where in situ reduction of PdO occurred during the reaction, generating active interfacial Pd-O-Nb sites and accelerating the breaking of C-O bonds. The insights of this work provide a guiding direction for the future design of highly selective heterogeneous catalysts by crystal phase modulation engineering.