Improving catalytic aquathermolysis of heavy oil using a tri-metal supported zeolite catalyst

A hierarchical zeolite-supported trimetallic catalyst (Mo/Co/Ni-ZSM-5) was synthesized via incipient wetness impregnation and evaluated for the hydrothermal upgrading of heavy oil. The catalytic system was designed to integrate acidic cracking functionality with metal-mediated hydrogenation under aquathermolysis conditions. Mono- and bimetallic counterparts were investigated for comparison. Among all tested catalysts, Mo/Co/Ni-ZSM-5 exhibited the highest hydrogenation activity and viscosity-reduction efficiency. Under optimized conditions (280 °C, 24 h, oil-to-water ratio of 7 : 3, and catalyst loading of 1.0 wt%), the heavy-oil viscosity decreased by 75.7%. Saturates, aromatics, resins, and asphaltenes (SARA) fractionation revealed an increase in saturates and aromatics and a reduction in resins and asphaltenes, accompanied by a significant reduction in sulfur and nitrogen contents. Spectroscopic analyses (FT-IR, ¹H-NMR, and GC-MS) demonstrated that catalytic upgrading proceeds via the fragmentation of condensed aromatic cores and deep hydrogenation. Crucially, the active hydrogen is supplied by a newly clarified dual-source pathway: tetralin acts as the primary donor, while high-temperature water serves as a synergistic hydrogen source via the catalytic water-gas shift reaction (WGSR). This combined active hydrogen supply ensures effective radical termination and prevents secondary condensation. Kinetic analysis indicated a low apparent activation energy of 16.87 kJ mol^-1, confirming the high catalytic efficiency of the trimetallic system. These results elucidate the synergistic roles of metal-acid bifunctionality, hierarchical porosity, and the complex catalytic function of water in heavy-oil aquathermolysis, providing practical guidance for the rational design of multifunctional catalysts.