Taming Strong Metal–Support Interactions to Generalize Gold–Zinc Oxide Catalysts in Oxidative Coupling

Strong metal–support interactions (SMSI) are at the cutting edge of catalysis research, yet their size-dependent nature remains both widespread and subject to ongoing debate. Here, we report the discovery of bell-shaped size-dependent SMSI, and we establish its structure–SMSI–performance relationship in oxidative C–H/O–H coupling reactions. Using Au/ZnO as a prototypical catalyst, we develop a thermodynamic equilibrium model that quantitatively captures the size-dependent surface energy and tension disparities, identifying the particle size ratio as the descriptor for bell-shaped encapsulation dynamics. Larger Au particles with a higher surface energy are prone to wetting by smaller ZnO particles, triggering lattice oxygen spillover to form Au–O species that accelerate the rate-limiting hemiacetal β-H elimination. Simultaneously, residual oxygen vacancies serve as frustrated Lewis pairs, synergizing with Au–O to replenish hemiacetals and complete the catalytic cycle. This dual promotional mechanism overcomes the oxygen activation bottleneck in traditional Au catalysts, achieving state-of-the-art performance of 94.6% aldehyde conversion and 97.0% ester selectivity. The obtained structure–SMSI relationships are applicable to Ir/ZnO and Rh/ZnO catalysts, with similar SMSI–performance relationships extending to various aldehyde substrates, including saturated, unsaturated, and aromatic. These generalizable relationships lay a strong foundation for the strategic design and manipulation of SMSI states.