Promotion effect with dispersed Fe-Ni-S catalyst to facilitate hydrogenolysis of lignite and heavy residue

[Display omitted] •Iron incorporation into nickel sulfide promotes H2 dissociation.•Dispersed Fe4.5Ni4.5S8 catalyst was synthesized purposively.•Synergies were observed in hydrogenolysis of lignite and heavy residue.•Dispersibility of solid residues was improved. Nickel sulfide is regarded as one of the most promising substitutes for the best-performing disposable molybdenum catalyst in the hydrogenolysis of lignite and heavy residue, but its practical application is hindered severely by insufficient catalytic activity and a prohibitively large dosage. Herein, we report that the issues of activity and cost of nickel sulfide can be addressed simultaneously by employing a combination of iron incorporation and a dispersing strategy via oil-soluble ligands. Motivated by first-principles calculations where iron incorporation in nickel sulfide would lead to a better activity towards the rate-limiting step of hydrogenolysis compared with nickel sulfide alone, we successfully prepared a well-dispersed Fe-Ni-S catalyst by coordinating active metal salts with carboxylate ligands and a subsequent essential sulfurization. The synthesized Fe-Ni-S catalyst outperformed not only the monometallic nickel catalyst but also the commercial molybdenum catalyst in the hydrogenolysis of lignite and heavy residue, and exhibited a high conversion efficiency, hydrogen consumption, hydrogen/carbon product atomic ratio, and dispersibility of solid residues, with an economic nickel dosage of as low as ~250 μg·g−1. Structural changes of raw coal and solid residues further confirmed the role of the Fe-Ni-S catalyst in facilitating the hydrogenolysis of lignite and heavy residue.