Highly efficient catalytic hydrocracking of East Inner Mongolia lignite and lignite-related model compounds through selective cleavage of aryl C-O bonds

Highly efficient catalytic hydrocracking of lignite through selective cleavage of aryl C-O bonds to produce valuable fuels and chemicals is a prospective but challenging approach. Catalytic hydrocracking reactions of lignite and lignite-related model compounds were performed over a Ni-based catalyst. The results demonstrated that the aryl C-O bonds in benzyl phenyl ether and dinaphthyl ether were preferentially cleaved and the resulting aromatic monomers were subsequently hydrogenated with continuous optimization of reaction conditions. Moreover, a complete conversion of model compounds and 100 % selectivity of monomeric products were achieved. The density functional theory calculations unraveled that the stable horizontal adsorption of both benzene rings in benzyl phenyl ether at Ni sites can reduce the electron cloud density around ether-oxygen bonds and weaken their dissociation energy, facilitating the dominant cleavage of aryl C-O bonds. Component analyses and structural characterizations indicated that aromatic hydrocarbons were mainly produced (50.02 %) after catalytic hydrocracking of lignite through the selective cleavage of C-O bonds, effective removal of oxygen-containing structure and cracking of side chain groups on aromatic rings. Most significantly, this study proposed the probable mechanism that H⁺ species originating from the heterolytic cleavage of H₂ and H···H were the main active hydrogen species, committing to cracking C-O bonds, while H···H species were tendentious for subsequent hydrogenation of aromatic rings.