Hexacoordinate Ti-Anchored Single-Atom Pd Catalyst for High-Efficiency Cyclohexanone Ammoximation with H₂ and O₂

Integrating Pd or its alloys with titanosilicate zeolites enables the production of cyclohexanone oxime through the ammoximation reaction of cyclohexanone with H₂ and O₂ instead of relying on H₂O₂ produced in advance. To address the inefficient utilization of precious metals and the suboptimal Ti activity in existing composite catalysts, we innovatively employed Ti-MWW zeolite as a support to develop a brand-new bifunctional catalyst Pd@Ti-MWW-PI through a one-step synthesis, constructing a unique active site where piperidine-modified Pd single atoms are anchored on the hexacoordinated framework-Ti via the Pd-O-Ti bond. This catalyst with an ultralow Pd loading of 0.02 wt % attains a record cyclohexanone oxime formation rate of 13000 mol mol_Pd^–1 h^–1 and demonstrates exceptional stability in continuous fixed-bed operation, sustaining cyclohexanone oxime selectivity greater than 99% for more than 2500 h. Notably, this work, utilizing water as the solvent, marks a significant stride toward environmentally sustainable green chemistry and bolsters the practical feasibility of H₂/O₂-mediated ammoximation.