Synergistic metal-acid catalysis over mesopore-confined SiW/Ni-MCM-41 for lignin-to-aromatics valorization

A composite catalyst that combines acid and metal catalysis has been developed. • Selectivity of up to 83.12 % toward MAHs achieved in lignin pyrolysis. • Heating rate affects routes and activation energy in catalytic lignin conversion. • SiW affords B acid sites while Ni centers stabilize intermediates and inhibit coking. To address the challenges of complex deoxygenation pathways and low monoaromatic hydrocarbon (MAHs) selectivity in the catalytic conversion of lignin, a series of SiW/Ni-MCM-41 metal–acid bifunctional catalysts were synthesized via an incipient wetness impregnation method. The effects of silicotungstic acid (SiW) loading ratios on the physicochemical properties of the catalysts and their performance in lignin catalytic pyrolysis were systematically investigated. Characterization results revealed that both SiW and Ni species were highly dispersed on the surface of the MCM-41 support, with interactions between them. With increasing SiW loading, specific surface area and pore volume decreased, Brønsted acid proportion increased, and total acid sites decreased mainly due to Lewis acid loss, enabling Brønsted/Lewis acid balance tuning. Catalytic performance evaluation demonstrated that the catalyst with a SiW-to-Ni-MCM-41 mass ratio of 1:2 exhibited the optimal lignin conversion (80.25 %) and MAHs selectivity (83.12 %), alongside excellent universality in substrate extension experiments. Kinetic analysis indicated that the apparent activation energy is heating-program dependent. In-situ FTIR confirmed that the Brønsted acid sites provided by SiW promoted deoxygenation and alkylation reactions, the Ni metal centers assisted deoxygenation and stabilized the aromatic ring structure via hydrogen-transfer-related pathways, while inhibiting condensation and coking side reactions to a certain extent; and the mesoporous MCM-41 framework provided a highly dispersed environment and a possible confinement-like effect, collectively driving the efficient conversion of lignin into monoaromatic hydrocarbons. This study provides a novel design strategy for metal–acid synergistic catalysts in the field of high-value conversion of lignin. Download: Download high-res image (144KB) Download: Download full-size image