The selective aerobic oxidation of alcohols to aldehydes is an important industrial challenge due to the easy further overoxidation of these products to acids and esters. The most common industrial methods require organic radicals such as 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO) for the selective conversion of alcohols to carbonyl compounds with the formation of TEMPOH, which can be regenerated back to TEMPO by oxygen over metal complexes. The high cost and difficulties related to the separation of complexes prompted us to develop heterogeneous catalysts by coordinating TEMPO over acid sites in zeolite BEA with encapsulated RuO2 nanoparticles. The catalyst demonstrates excellent activity, selectivity, and stability for the oxidation of alcohols to aldehydes. The analysis of the reaction mechanism confirms the activation of alcohols by TEMPO and the subsequent regeneration of TEMPOH by RuO2.
Ti 3 C 2 MXenes with different halogen modifications are prepared rapidly and efficiently by microwave molten salt method, and the MXene surface functional group modification is successfully achieved to address the problems of low purity, complex functional groups, and uncontrollable energy band structure of MXenes obtained by traditional liquid phase etching. Among them, the modification of the iodine (I) functional group onto the surface of Ti 3 C 2 changes the energy band structure and band gap, resulting in easier photoexcitation and more photogenerated carriers. The increased Fermi energy is closer to the conduction band, the decreased surface work function weakens the electron confinement ability. The photogenerated carriers can migrate to the surface of the material more easily with extended lifetime, so the activity of the catalyst is improved. Further, for gaseous monomeric mercury (Hg 0 ) photo-oxidative removal, Ti 3 C 2 -I 2 exhibits 85.5% efficiency of Hg 0 photo-oxidative removal under visible light. Based on the experimental characterization and density functional theory calculations, a mechanism for the photooxidative removal of Hg° from Ti 3 C 2 -I 2 MXene is proposed, which provides a valuable strategy for studying Ti 3 C 2 MXenes in the field of photocatalysis.
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