Engineered Dynamic Co2+ Sites Resolve the Complete Reaction Network for C(sp3)–H Oxidation

Abstract

The dynamic evolution of active sites under operating conditions fundamentally dictates catalytic performance, yet state-of-the-art studies remain confined to passive observation, i.e., they are unable to intervene in detrimental dynamics or translate beneficial ones into universal design principles. Here, we report a precisely engineered core–shell Co@Co3O4 catalyst that utilizes a reversible solid-state redox equilibrium (Co0(s) + 2Co3+(s) ↔ 3Co2+(s)) during toluene oxidation, a benchmark transformation for the activation of inert C(sp3)–H bonds. Operando XAFS and XPS results reveal that the dynamically generated Co2+ species correlate directly with catalytic activity. Systematically integrated operando characterizations, DFT calculations, and control experiments establish Co2+ as a multifunctional center that activates toluene via electronic donation and concurrently facilitates O2 activation at surface oxygen vacancies, initiating a reactive oxygen species cascade (O2(g) → •O2–(ads) → •OH(ads)) that drives a dual-channel oxidation mechanism through low-energy-barrier routes. The catalyst achieves a turnover frequency of 33.8 h–1 (surpassing reported catalysts by 4- to 360-fold) with 90% selectivity in batch operation. We further establish a continuous-flow toluene oxidation system, which delivers a turnover number of 45425 and a space-time yield of 362.3 g·gcat–1·h–1 over 260 h of stable operation, producing ca. 3.25 kg of benzoic acid. The dynamic active site paradigm demonstrates broad utility, as evidenced by the successful oxidation of 42 aromatic alkanes and its application in the synthesis of a cholesteric liquid crystal intermediate.