Toward a thermodynamic framework for identifying and quantifying chemical synergism in heterogeneous systems

• Establishes thermodynamic criteria for chemical synergism • Distinguishes cooperative stabilization from apparent non-additivity • Links interfacial irreducibility with measurable amplification • Provides a concise framework for heterogeneous systems Chemical synergism is widely invoked to explain performance enhancement in heterogeneous catalytic and multiphase engineering systems, yet the term is frequently used without rigorous physicochemical criteria, leading to confusion between genuine cooperative effects and simple kinetic or structural improvements. This work establishes explicit thermodynamic criteria for chemical synergism and introduces a cooperative stabilization concept linking interfacial irreducibility with measurable non-additivity. Chemical synergism is defined as arising exclusively in heterogeneous systems where cooperative interfacial interactions generate stabilized ternary or higher-order entities irreducible to independent binary contributions. Within this formulation, amplification of measurable properties (rate, selectivity, yield, or efficiency) is interpreted as a manifestation rather than a definition of synergism. Representative literature examples are critically reassessed to distinguish true cooperative equilibria from apparent enhancements caused by dispersion or transport effects. Operational descriptors are introduced to enable consistent comparison of non-additive behavior across systems. By providing explicit criteria and engineering interpretation, the framework supports rational catalyst and process design while preventing misclassification of performance amplification as chemical synergism. Distinction between apparent performance enhancement and genuine chemical synergism in heterogeneous systems. Non-additive behavior may arise without cooperative stabilization. Here, chemical synergism is interpreted as arising from heterogeneous environments where interfacial ternary or higher-order entities are thermodynamically stabilized. The scheme provides a conceptual basis for distinguishing cooperative effects from apparent amplification.