Electrocatalytic ORR-coupled ammoximation for efficient oxime synthesis

State-of-the-art technology for cyclohexanone oxime production typically demands elevated temperature and pressure, along with the utilization of expensive hydroxylamine sulfate or oxidants. Here, we propose an electrochemistry-assisted cascade strategy for the efficient cyclohexanone ammoximation under ambient conditions by using in situ cathode-generated green oxidants of reactive oxygen species (ROS) such as OOH* and H2O2. This electrochemical reaction can take place at the cathode, achieving over 95% yield, 99% selectivity of cyclohexanone oxime, and an electron-to-oxime (ETO) efficiency of 96%. Mechanistic analysis reveals that, in addition to the direct ammoximation by in situ-generated OOH* by electrocatalytic ORR, Ti-MOR also play a major role in capturing OOH* directly and converting the in situ-generated H2O2 to OOH*, thus accelerating the ORR-coupled cascade production of cyclohexanone oxime. This work paves a mild, economical, and sustainable energy-efficient electrocatalytic route for the oxime production using oxygen, ammonium bicarbonate, and cyclohexanone.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.