The synergistic effect between Ru single-atomic sites and nanoclusters during catalytic hydrotreatment of fast pyrolysis liquids from lignocellulosic biomass

Catalytic hydrotreatment is a promising technique to upgrade pyrolysis liquids (PLs) with undesired properties into intermediate that can be co-processed with vacuum gas oil in FCC refinery. Highly active catalysts are key in such a process. In this study, a ruthenium-based catalyst possessing both single-atomic and nanocluster sites supported on hierarchically porous nitrogen-doped carbon (Ru_1+NPs/HPNC) was prepared by a two-step alcohol reduction method. Catalytic performance was evaluated for both model compound vanillin (VL) and PLs in a batch autoclave. The model compound study showed that Ru_1+NPs/HPNC exhibited excellent intrinsic activity in VL hydrogenation, with a TOF of 26.9 s⁻¹, which is approximately 3 times higher than that of Ru₁/HPNC (8.4 s⁻¹) and Ru_NPs/HPNC (8.8 s⁻¹), and 6 times that of Ru/AC (4.2 s⁻¹). Catalytic hydrotreatment of PLs indicated that Ru_1+NPs/HPNC possessed the best activity regarding to the highest H/C ratio (mild hydrotreatment: 1.33; deep hydrotreatment: 1.29) and the lowest TG residue (mild hydrotreatment: 14.4 wt%; deep hydrotreatment: 6.5 wt%) of the product oils. To obtain understanding of the synergistic effect between single-atoms and nanoclusters, the adsorption of VL and H₂ on the catalyst was examined by ATR-FTIR and DFT calculations. The results revealed that VL is preferentially adsorbed and activated on the single-atomic sites, while the H₂ is preferentially dissociated on the nanocluster sites. Based on these findings, a plausible mechanism is proposed. This study offers new ideas for developing better-performing catalysts for catalytic hydrotreatment of PLs.