Kinetics evidence for oxidized-site ensemble effects in surfactant-modified vanadium phosphorus oxide catalysts for n-butane oxidation

Abstract

Selective oxidation of n-butane to maleic anhydride (MA) is fundamentally limited by the activity-selectivity trade-off, and the origin of selectivity control remains debated. Here we show that surfactant-mediated modification of vanadium phosphorus oxide catalysts can shift the reaction network toward MA by suppressing competing carbon oxides (CO_x) formation. We establish a kinetic framework that explains this selectivity shift through coupled redox-site balance and product-branching kinetics. Kinetic analysis identifies the CO_x to MA branching parameter (𝛾) as a key descriptor of intrinsic selectivity and reveals that MA formation requires an ensemble instead of an isolated site. These results provide direct kinetic evidence that MA selectivity is governed not only by the electronic properties of the redox sites, but also by ensemble-dependent transition-state formation on the site domains. This work offers both a mechanistic interpretation and a practical model for the ensemble effect that influences MA yield in n-butane oxidation.