Catalyst–Support Interactions in Carbon–Inorganic Hybrid Catalysts for Biomass Valorization: Interfacial Chemistry, Stability, and Regeneration

Carbon–inorganic hybrid catalysts offer tunable surface chemistry, high active-phase dispersion, improved electron and mass transport, and enhanced opportunities for catalyst recovery and regeneration. Their performance in biomass valorization, however, depends strongly on the physicochemical interactions established at the interface between the carbonaceous support and the inorganic catalytic phase. This review examines catalyst–support interactions in hybrid systems based on biochar, activated carbon, graphene-related materials, carbon nanotubes, and hydrothermal carbons combined with metals, metal oxides, zeolites, layered double hydroxides, ferrites, perovskites, and related inorganic phases. The roles of surface functional groups, defects, oxygen vacancies, acid–base interactions, charge transfer, metal anchoring, confinement, and strong metal–support interactions are critically evaluated using an evidence hierarchy that distinguishes correlation from mechanistic proof. Particular emphasis is placed on quantitative links between interfacial descriptors and catalytic activity, selectivity, stability, coke resistance, sintering, leaching, and regenerability. Applications in hydrolysis, dehydration, esterification, transesterification, hydrogenation, hydrodeoxygenation, reforming, pyrolysis-vapor upgrading, and the conversion of lignocellulosic intermediates into fuels and platform chemicals are compared. A focused levulinic-acid-to-γ-valerolactone case study is used to extract transferable design rules from quantitative literature data. Spectroscopic, microscopic, thermal, electrochemical, in situ, and operando methods are compared, together with kinetic and computational approaches. Finally, the review identifies current limitations in standardization, realistic feedstocks, continuous processing, material closure, techno-economic assessment, life-cycle assessment, and scale-up, and proposes a minimum reporting framework for predictive design of durable carbon–inorganic catalysts for circular biorefineries.