Interface engineering of Fe/TiO2 derived from kaoline impurities for selective 5-hydroxymethylfurfural hydrogenation to 2,5-dihydroxymethylfuran: The effect of Fe2+-Ov-Ti4+ sites synergy

Biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-dihydroxymethylfuran (DHMF) is a pivotal process in biomass valorization, however, it is hindered by the high cost of noble metal catalysts and environmental hazards posed by toxic copper-chromium systems. Herein, we report an unexpected discovery that naturally occurring Fe-Ti impurities in kaolinite act as a highly efficient heterogeneous catalyst for this reaction, challenging the conventional notion that impurities are detrimental to catalytic performance. Through hydrothermal synthesis and controlled reduction, Fe species are highly dispersed on the TiO 2 rutile surface, forming a synergistic Fe 2+ -oxygen vacancy-Ti 4+ (Fe 2+ -O v –Ti 4+ ) interface. The catalyst exhibits outstanding activity and selectivity under mild conditions (50 °C, 0.6  MPa H 2 ), achieving 97.6 % HMF conversion and 93.3 % DHMF selectivity, significantly outperforming catalysts based on kaolin and pure TiO 2 . Kinetic analysis reveals an apparent activation energy of 50.14  kJ/mol and a near first-order dependence on HMF concentration. Combined DFT calculations and in situ DRIFTS spectra confirm that the Fe 2+ -O v interface facilitates the adsorption of the HMF aldehyde group (adsorption energy −0.56  eV) and lowers the energy barrier for H 2 dissociation to 0.06  eV, enabling highly selective C=O hydrogenation. Moreover, the reaction benefits from the strong polarity of water and the hydrogen-bonding capacity, which further enhances catalytic performance. The catalyst retains over 90 % activity after 10 cycles, demonstrating excellent stability. This work not only provides a sustainable route for high-value utilization of kaolin-associated metal impurities, but also offers theoretical insights into the rational design of non-precious metal catalysts for biomass transformation.