Slurry-phase　hydrocracking　is　an　effective　technology　for　the　conversion　of　heavy　oils　to　clean　and　light　fuels.　Herein,　trialkylmethylammonium　molybdate　ionic　liquids　(ILs)　with　multiple　long-chain　alkyl　groups　were　designed,　and　applied　as　the　oil-soluble　precursors　of　dispersed　metal　catalysts　for　slurry-phase　hydrocracking.　The　molybdate　ILs　were　synthesized　through　a　two-　or　three-step　route　from　readily　available　reagents　under　mild　conditions.　The　chemical　structure　and　sulfidation　behavior　of　molybdate　ILs　were　characterized　first.　The　performance　of　molybdate　ILs　for　hydrogenation　was　then　evaluated　with　phenanthrene　as　the　model　compound.　The　dispersed　MoS2　catalysts　in-situ　produced　in　the　model　system　were　isolated　and　characterized　to　explain　the　different　performance　of　oil-soluble　precursors.　The　performance　of　molybdate　ILs　for　slurry-phase　hydrocracking　of　heavy　oils　was　finally　investigated.　To　figure　out　the　favored　routes　for　the　conversion　of　heavy　oils,　the　reaction　rate　constants　were　also　calculated　based　on　an　established　kinetical　model.　©　2022　Elsevier　Ltd