Promoting effect of corn stalk on the aquathermolysis of low-asphaltene heavy oil over Ni–Mo/Al₂O₃ catalysts

Biomass-assisted aquathermolysis is a promising strategy for in situ upgrading of heavy oil. Supported Ni–Mo/Al₂O₃ catalysts with different Ni/Mo molar ratios were synthesized and evaluated for the aquathermolysis of low-asphaltene Karamay heavy oil. Ni₃–Mo₇/Al₂O₃ showed the highest upgrading efficiency, owing to its favorable mesoporous structure, balanced acid strength distribution and suitable reducibility. The cooperative effect between corn stalk and Ni₃–Mo₇/Al₂O₃ was systematically investigated. Under the best conditions within the investigated range, a viscosity reduction rate of 57.34% was achieved with 2 wt% corn stalk and 1.5 wt% catalyst at 300 °C for 24 h. Group composition and elemental analysis indicated that corn stalk promoted the conversion of polar fraction into saturates, increased the atomic H/C ratio, and decreased sulfur and nitrogen contents. The average molecular weight decreased from 535.1 to 482.7 g·mol −1 , and the boiling-range distribution shifted toward lighter fractions. 1 H NMR indicated suppressed aromatization/condensation and increased aliphatic hydrogen. XPS revealed reaction-induced surface evolution of Ni 3 –Mo 7 /Al 2 O 3 , with lower-valence Mo and sulfide/oxysulfide species more evident in the corn-stalk-assisted system. GC–MS analysis of aqueous-phase products suggested that biomass-derived oxygenates may participate over Ni Mo active sites through hydrogen transfer, deoxygenation, and carbon-chain scission, thereby stabilizing radicals, suppressing secondary polycondensation, and enhancing upgrading.