Efficient transformation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system over single-site titanium BEA zeolite

Ti x SiBEA zeolites prepared by a two-step post-synthesis method are applied in the liquid-phase Baeyer-Villiger oxidation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system. Such method of ε-caprolactone synthesis offers the application of milder reaction conditions with the catalytic system which transforms cyclic ketones into lactones in the presence of molecular oxygen and aldehyde. They are the source of in situ peracid formation. The Ti incorporation into SiBEA involves the formation of Ti(IV) (OSi) 4 as main species and small numbers of Ti(III) (OSi) 3 –O(H)–Si sites having Brønsted and Lewis acid properties. The acidity is a key factor for efficient transformation of cyclohexanone to ε-caprolactone in the BV oxidation depending on the titanium oxidation state and environment. Among all of the studied catalysts, the highest catalytic activity is observed for Ti 2.0 SiBEA zeolite. The active catalyst of the studied BV oxidation reaction is bi-functional, possessing both the acidic and redox properties, catalyzing different reaction stages. • The incorporation of Ti into the SiBEA framework evidenced by FTIR and NMR. • DR UV–vis and XPS showed the presence of framework tetrahedral Ti(IV). • Ti(IV) (OSi) 4 sites appeared as main redox centres. • Ti(III) (OSi) 3 –O(H)–Si sites possessed both Brønsted and Lewis acid properties. • The Ti x SiBEA catalysts applied in BV oxidation reaction have bifunctional character.