The NiO-Fe2O3 modified rice husk char catalysts for catalytic hydrothermal cracking of heavy oil at low temperatures

Heavy oil has the characteristic of high viscosity. Research on efficient and eco-friendly methods to reduce viscosity plays a crucial role in the sustainable utilization of global heavy oil resources. In this study, a biochar-based catalyst, NiO/Fe₂O₃-KRHC, was successfully prepared using KOH-modified rice husk char (KRHC) via the impregnation method. The RHC, KRHC, and catalyst were analyzed using multiple characterization techniques. The findings showed an increased abundance in the pore structure of the rice husk char after modification with KOH. The catalyst exhibited good thermal stability and strong acid sites. The catalyst activity was evaluated through the catalytic viscosity reduction experiment. The NiO/Fe₂O₃-KRHC catalyst demonstrated a satisfactory viscosity reduction effect at 185–245 ℃. Specifically, the NiO/Fe₂O₃-KRHC catalyst reduced the viscosity by 81.81 % at 230 ℃. The optimal reaction time for the catalyst was 24 h. The biochar-based catalyst demonstrated excellent performance in reducing viscosity at low to medium temperatures. The contact between transition metal oxides and heavy oil molecules facilitated the formation of coordination complexes, leading to the breakage of molecular chains and hydrogen bonds. Among them, the breakage of C-S bonds was the key reason for the reduction of viscosity. These findings will provide a reference for applying biomass-based catalysts to reduce the viscosity of heavy oil.