Catalysis for heavy oil upgrading: Hydrocracking, fluid catalytic cracking, and process synergy

Heavy-oil conversion is limited by low H/C ratios, heteroatom, metals, and asphaltene-driven instability. This review critically compares hydroprocessing/hydrocracking and fluid catalytic cracking (FCC) from a molecular-to-refinery perspective. It links feed composition, saturates, aromatics, resins, and asphaltenes (SARA) association, and molecular characterization to catalyst accessibility, sediment formation, coke evolution, and catalyst-reactor performance. The complementary roles of hydrogen addition and carbon rejection are assessed with cross-unit integration and industrial constraints (catalyst management, feed tolerance, solids handling, stability, and operability). Three unresolved challenges are identified: the working active phase of dispersed catalysts, morphology-dependent coke deactivation, and transferability of mechanistic models across variable oil matrices. Molecular and data-driven models may support refinery decisions but require uncertainty-aware validation under industrially relevant conditions.