Surface Reconstruction Of Nanocatalysts Based On Selectively Photochemical Transformation Of Active C-H And C-C Bonds

Catalytic reactions usually occur on catalysts surface. Therefore, the catalytic activity, selectivity, and stability of certain catalysts largely depend on their surface properties. Nanocatalysts are special catalysts that have been explored for decades, and they have unique activity for C-H and C-C bond activation and utilization. The present thesis will include the following aspects.First, we found that mesoporous TiO2is an efficient photocatalyst for benzyl alcohol selective oxidation into benzaldehyde under visible light irradiation. Usually TiO2can only be activated by UV light, however, due to the hybridization of the molecular orbital of benzyl alcohol with O2p orbital of TiO2, some donor levels can be introduced in the forbidden band, resulting in the narrowing of the band gap. Consequently, electron-hole pairs will be formed on these donor levels with visible light irradiation. The holes are able to oxidize absorbed benzyl alcohols into benzaldehydes, while benzaldehydes have limited interaction with TiO2and they are apt to desorb from TiO2surface. Therefore, the donor levels are disappeared, leading to the pristine band gap intact. The resulting controllable hole generation is thus termed as self-adjustable photo-oxidation system.Second, under anaerobic conditions, we found that the surface of TiO2experienced reconstruction during benzyl alcohol oxidation under visible light. Plenty of oxygen vacancies are formed, and hydrogen atoms are grafted onto the surface oxygen atoms, both of which lead to the narrowing of the band gap of TiO2, making itself visible light responsive. The resulting surface reconstructed TiO2has some acceptor levels just below the conduction band, thus it can be served as promising visible light photocatalyst for oxidation and reduction purposes.Third, it is found that reactive oxygen species resulted from the UV induced photochemical reaction can be used to break the C-C bond of acetonitrile, generating CN radicals.These radicals are able to react with Au or other transitional metals to form metal cyanides. This method has been demonstrated to be green, versatile and convenient, which potentially can replace the conventional cyaniding strategy. The AuCN oligomers derived from this photocyanation method showed promising catalytic activity during annulation of salicylaldehyde with phenylacetylene to afford isoflavanones.Fourth, by employing the similar photocyanation strategy, we used H2O2as a new reactive oxygen species generator to pattern Pt/C electrode with CN groups. The resulting CN patterned Pt/C catalysts hold a much enhanced methanol tolerate ability during oxygen reduction reactions.Last, we found that FeCl3-CH3CN complex can be used to efficient oxidation of acetaldehyde into acetic acid at room temperature, which proceeds rather rapidly and follows the enzymatic-like Michaelis-Menten kinetics, ased on the catalytic results, spectro-scopic evidences and successive DFT calculations, a reactant-initiated, putative mononuclear non-heme iron-oxygen complex,[FeCl(MeCN)4(O)]2+, is proposed as the active oxidizing species to conduct the room temperature reaction with relatively high TOF values (～1.2s-1). Finally, the putative iron-oxygen complexes are employed to the selective oxidation of benzyl alcohol under ambient conditions.