Rationally designed novel multifunctional poly(ionic liquid)s for ultra-selective valorization of Yiwu lignite to monocyclic aromatic compounds

Abstract

The selective valorization of lignite into monocyclic aromatic compounds (MCACs) is extremely challenging due to its chemical inertness and geometrical complexity. The catalytic efficiency of lignite valorization into MCACs over solid acids is significantly reduced by the presence of H2O resulting in the leaching and deactivation of acid sites. Moreover, the precise fabrication of poly(ionic liquid)s (PILs) containing Brønsted-Lewis acidic sites, well-defined mesoporous channels, and hydrophobicity remains a considerable challenge. Herein, a novel hydrophobic mesoporous PILs with strong Brønsted-Lewis acid sites was successfully constructed by a synergistic regulation-induced copolymerization strategy for the first time. More exotically, the resultant multifunctional PILs was found to be ultra-efficient catalyst for the selective valorization of Yiwu lignite (YL) into MCACs with 23.5 wt.% yield, which is the highest yield reported for lignite catalytic valorization by precious metal-free catalysts under mild conditions. The co-catalysis mechanisms of YL valorization into MCACs over the multifunctional PILs are confirmed by characterization methods and the synergistic catalysis mechanisms are as follows: (1) hydrophobic micro-environment: the hydrophobic micro-environment created by hydrophobic block is favorable for preventing the leaching and deactivation of Brønsted-Lewis acid sites; (2) mesoporous confinement: the well-defined mesoporous channels strengthen the adsorption amount of H2 and increases the concentration of substrates; (3) synergistic catalytic active hydrogen transfer of Brønsted-Lewis acid sites: Brønsted-Lewis acid sites synergistically promote H2 heterolysis to the mobile H+ and immobile H−, and then the resulting mobile H+ transfers to oxygen atom in lignite to produce MCACs via C–O bond cleavage. This work not only sheds some light on developing the multifunctional solid acid catalysts, but also demonstrates an efficient catalyzing method to produce lignite-based MCACs by co-catalysis of Brønsted-Lewis acidic sites, mesoporous confinement, and hydrophobic micro-environment.