Synergistic interaction between Ni single atoms and nanoparticles for selective cleavage of C-O bonds in lignin without external hydrogen

Selective cleavage of C-O bonds is a pivotal step for converting lignin into value-added chemicals, yet the development of efficient catalysts for mild-conversion remains a formidable challenge. Herein, a novel bi-Ni metal catalyst (Ni NPs-SAs /NC) composing of Ni single atoms (SA) and Ni nanoparticles (NP) was synthesized by pyrolysis strategy and employed for lignin hydrogenolysis without external hydrogen gas. Due to the high reactivity of Ni NPs-SAs /NC, various lignin model compounds (α-O-4, β-O-4 and 4-O-5, etc.) were fully converted into aromatic monomers at low temperature (200 ℃) and autogenous pressure, and the selectivity of aromatic monomers was as high as 86.3 %. Structural characterization and theoretical calculations indicated that the excellent catalytic performance of Ni NPs-SAs /NC catalysts was attributed to the synergistic effect of Ni SA and NP sites. Specifically, isopropanol was adsorbed at the Ni NP site and generates active hydrogen, and the Ni SA site adsorbed and activated the C-O bonds. The active hydrogen spillover from the Ni NP site to the Ni SA site enabled the cleavage of the C-O bond of lignin under mild conditions. This work may pave the way for developing high-performance non-noble metal catalysts with exceptional reactivity and selectivity for the valorization of lignin.