Regulating the nanoscale intimacy of metal and acidic sites in Ru/γ-Al2O3 for the selective conversions of lignin-derived phenols to jet fuels

The catalytic interfaces between metals and acidic sites in Ru/γ-Al 2 O 3 were regulated by TFMSA modification, which can dramatically improve the catalytic performance of the metal–acid catalyst for HDO conversion of lignin to jet fuels. Catalytic hydrodeoxygenation (HDO) of biomass-derived oxy-compounds to advanced hydrocarbon fuels usually requires bifunctional catalysts containing metals and acidic sites. The appropriate tuning of metal and/or acidic active sites at interfaces of bifunctional catalysts can significantly improve catalyst activity and product selectivity. Here, 4-trifuoromethyl salicylic acid (TFMSA), as a hydrothermal stable organic acid, was employed to tailor the bifunctional interface of Ru/γ-Al 2 O 3 to enhance the catalytic performance on converting lignin-derived phenols to jet fuel range cycloalkanes. More than 80% phenol was converted into cyclohexane at 230 °C for 1 h over Ru/γ-Al 2 O 3 modified by TFMSA, which was about three times higher than that over unmodified Ru/γ-Al 2 O 3 . X-ray diffraction (XRD), Transmission electron microscope (TEM), H 2 chemisorption, and energy dispersive X-ray spectroscopy (EDS) elemental mapping results indicated that Ru nanoparticles and TFMSA were well distributed on γ-Al 2 O 3 , and a nanoscale intimacy between Ru and TFMSA was reached. Meanwhile, Fourier transform infrared spectroscopy after pyridine adsorption (Py-FT-IR) analysis proved that Brønsted acidic sites on the catalytic interfaces of TFMSA modified Ru/γ-Al 2 O 3 had been improved. Moreover, the kinetic and density functional theory (DFT) results suggested that the synergistic effects of adjacent Ru nanoparticles and acidic sites were crutial for promoting the rate-limiting conversion step of phenol HDO to cyclohexane.