Cascade of Acid Sites and Oxygen Vacancy in Mo/Ga@ZSM-11 for Efficient Cracking of Lignin to Produce Alkylphenol

Abstract

The continuous directional cleavage of lignin provides a sustainable pathway for the synthesis of high-value alkylphenol chemicals. Herein, a multifunctional Mo/Ga@ZSM-11 catalyst and self-supplying hydrogen system were developed, 92.31 % of liquid products yield and 73.52 % of alkylphenol selectivity were achieved, and a good cyclic stability was maintained. Characterization results proved that Ga doped in the lattice gap of ZSM-11, lattice distortion and charge redistribution process generated more Si-O(H)-Ga sites and oxygen vacancies (OV), which provided ideal anchoring sites for active Mo species through covalent bond formation and strong metal-carrier interaction. The retention of terminal oxygen species MoO(H) and the emergence of electron rich Mo species were accompanied by the derivation of abundant Brønsted/Lewis acid sites (BAS/LAS) and OV. A series of model compound experiments and kinetic analysis proved that BAS promoted the activation of self-supplying hydrogen system and the rapid fracture of aliphatic C-O/C-C bonds under heat drive, while the presence of strong LAS and OV ensured the further fracture of side chain methyl group (CAr-OCH3) in phenolic intermediates. The design concept of multifunctional catalyst provides guidance for the continuous directional cracking of lignin to produce high-value chemicals.