Modulation of Brønsted and Lewis Acid Centers for Ni _x Co _{3− x} O ₄ Spinel Catalysts: Towards Efficient Catalytic Conversion of Lignin

Rational design and construction of catalysts with regulable active sites for selective cleavage of lignin to produce aromatic monomers remain challenging. Herein, the authors report a new strategy for tuning the active sites of tetrahedral centers (Lewis acid sites) and octahedral centers (Brønsted acid sites) in Ni x Co 3− x O 4 through tailoring the non‐stoichiometric ratio of Ni and Co. The ratio of Ni and Co is experimentally optimized for the optimal acidic activity of catalytic cracking of lignin when x = 0.2. The Ni 0.2 Co 2.8 O 4 catalysts achieve an outstanding catalytic conversion (up to 81 wt%) for the lignin cleavage and excellent selective cleavage into aromatic monomers (up to 90.30 wt%), which is mainly attributed to the optimized electron rearrangement, adjustable active sites, and synergistic effect between these two active sites. This work provides a new concept to rationally design solid acid catalysts for the efficient conversion of lignin.