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.