Nickel-based spinel-modified multi-dimensional pore molecular sieves co-catalyze the directional preparation of aromatics from lignin pyrolysis

In response to the key challenges such as the complexity of deoxidation pathways and the low selectivity of aromatics commonly encountered in lignin catalytic conversion, this study proposes an innovative nickel-based spinel-modified multi-dimensional pore molecular sieve composite catalyst. By precisely regulating the cross-scale pore topology and enhancing the synergy between active components and the support, the catalyst integrates three functionalities-efficient deoxidation, directional aromatization, and coking inhibition. Experimental results demonstrate that NiAl 2 O 4 @MCM-41(7:1), which features a two-dimensional hexagonal straight pore structure, achieves a monocyclic aromatic hydrocarbons (MAHs) selectivity of 54.46%, attributed to its unique confined diffusion characteristics. This performance significantly surpasses that of NiAl 2 O 4 @SBA-15 with a two-dimensional through-pore structure and NiAl 2 O 4 @KIT-6 with a three-dimensional cubic pore structure. When the mass ratio of NiAl 2 O 4 to MCM-41 was optimized to 3:1 (NiAl 2 O 4 @MCM-41(3:1)), the spatial matching effect of the interfacial active sites was maximized, further increasing the selectivity of MAHs to 63.04%. In-situ infrared dynamic analysis reveals a spatiotemporal cascade catalytic mechanism: lignin macromolecules are first cleaved into oxygen-containing intermediates at the NiAl 2 O 4 sites outside the pores, followed by directional demethoxylation and dehydroxylation reactions within the confined pores of the molecular sieve. Besides, the stability of the catalyst was systematically evaluated. This process enables in-situ removal of coke precursors and efficient regulation of aromatic hydrocarbon formation pathways. This strategy offers a novel paradigm for the dynamic synergy of multiple active sites in biomass catalytic transformation.