A Control over Hydrogenation Selectivity of Furfural via Tuning Exposed Facet of Ni Catalysts

Selective hydrogenation of biomass to value-added products plays a crucial role in the development of renewable energy resources. Herein, two heterogonous Ni catalysts supported on mixed metal oxides (MMO) were prepared via structural topological transformation from hydrotalcites (LDHs) precursors with carbonate or nitrate in interlayer region (denoted as Ni/MMO-CO3 and Ni/MMO-NO3), which were featured by highly exposed Ni(111) facets as well as multifacets with abundant steps/vacancies, respectively. Interestingly, the selectivity of furfural hydrogenation can be switched by using these two catalysts: Ni/MMO-NO3 exhibits a high selectivity (97%) to furfural alcohol (FOL) (hydrogenation product of C=O bond), whereas Ni/MMO-CO3 shows an exclusive selectivity (99%) toward tetrahydrofurfuryl alcohol (THFOL, hydrogenation product of both C=O and furan ring). A combination study including high-resolution transmission electron microscopy (HRTEM), extended X-ray analysis fine structure (EXAFS), and in situ CO-IR confirms a large proportion of steps/edges of Ni nanoparticles in Ni/ MMO-NO3 catalyst, which suppresses the adsorption of the furan ring and only facilitates activated adsorption of the C=O group. In contrast, a high exposure of Ni(111) plane in Ni/MMO-CO3 promotes activated adsorption of both furan ring and C=O group, resulting in the production of THFOL. In situ FT-IR measurements and DFT calculations reveal that the adsorption configuration of substrate plays a key role in determining the hydrogenation pathway and selectivity. This work provides a feasible approach for a control over hydrogenation selectivity of biomass molecules by tuning the surface microstructure of metal catalysts.