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A significant role of MOFs as heterogeneous photocatalysts in enabling organic transformations. • Light harvesting Ru-polypyridyl complexes were incorporated into a semiconductor-like metal-organic framework (MIL-125). • Disclosing photoinduced electron transfer among photocatalysis. • The prepared Ru(bpy) 3 @MIL-125 exhibited good recyclability during reaction. Visible-light-driven selective photocatalytic organic synthesis has recently become a topic of great interest due to its environmental friendliness and sustainability. It is demanding for photocatalysis to utilize the wider range of light, such as visible light, and its performance is often plagued by the sluggish separation of photogenerated charge carriers. An approach is now reported to address these issues by incorporating light harvesting RuII-polypyridyl complexes into a semiconductor-type metal-organic framework (MIL-125). Delightedly, the obtained Ru(bpy) 3 @MIL-125 photocatalyst presents a remarkably stable and high photoactivity toward the selective oxidative coupling of amines under ambient air with visible light irradiation (λ > 440 nm). The mechanistic investigation unveiled that both effectively photoexcited electrons transfer from [Ru(bpy) 3 ]Cl 2 to MIL-125 and the interaction of C H bonds with superoxide radical (O 2 ·−) play a critical role in photo-catalyzing selective aerobic oxidative coupling of amines. This work highlights a significant role of MOFs as heterogeneous photocatalysts in photocatalytic organic transformations. [ABSTRACT FROM AUTHOR]

An oxygen-vacancies-engaged photocatalytic mechanism was proposed to address the poor photo absorption and sluggish electron-hole separation of TiO 2. Electrons and holes are fully utilized for nitrobenzene reduction coupled with benzyl alcohol oxidation under visible light irradiation. • Oxygen vacancies (OVs) were generated through surface complexation under mild condition. • Fully making use of the photogenerated charge carriers rapidly promoted its separation and transfer efficiency. • Disclosing photoinduced electron transfer among photocatalysis. • The prepared TiO 2 exhibited good recyclability. Defects can greatly optimize the solar light harvesting capability and electronic structure of oxide materials. However, it remains challenging to achieve a defect engineering strategy under mild conditions. Meanwhile, the simultaneous exploitation of photogenerated holes (h+) and electrons (e−) to promote both photooxidation and photoreduction in a coupled system has rarely been reported. For the first time, we reveal an oxygen-vacancies-mediated photocatalytic strategy in which the electrons and holes are fully utilized for nitrobenzene reduction coupled with benzyl alcohol oxidation. The oxygen vacancies (OVs) generated in situ on the surface of TiO 2 greatly extend light absorption into the visible region and promote the photogenerated electron transport for efficient photocatalysis. The experimental and theoretical results together indicate that chemisorption on the TiO 2 surface decreases the oxidation potential of benzyl alcohol and causes an upward shift in its HOMO, which facilitates the oxidation reaction of benzyl alcohol to benzaldehyde. The in situ generated surface OVs also act as a bridge to enable the trapping and transferring of the photoinduced electrons to the nitrobenzene. This work provides a new perspective of utilizing the chemisorption between the reactant and catalyst to achieve a defect engineering strategy for synergetic photocatalysis. [ABSTRACT FROM AUTHOR]

This study demonstrated a dye-sensitized TiO 2 -polyoxometalate system (denoted TiO 2 -(PW 12 -TH) 8 , where PW 12 = PW 12 O 40 3− and TH = thionine) for selective oxidation of alcohols under visible light. The results showed that various substituted alcohols were transformed into their corresponding aldehydes with high selectivity. Due to more efficient electrons transfer, large surface area, and enhanced visible light absorption, the photocatalytic activity of TiO 2 -(PW 12 -TH) 8 was superior to any other dye-sensitized system reported to date. The response in the photocurrent-time curves over several on/off cycles of intermittent irradiation showed good reproducibility. The photocurrent response of TiO 2 -(PW 12 -TH) 8 was much higher than that of TiO 2 /TH (physical mixture of TiO 2 and TH), SiO 2 -(PW 12 -TH) 8 or P25-(PW 12 -TH) 8 (P25 = Degussa P25), attributed to the more efficient transfer and longer lifetime of photoexcited electrons. This photocatalytic process confirmed that efficient electron transfer during photocatalytic oxidation plays a vital role in determining the reaction conversion and obtaining good selectivity. Electron paramagnetic resonance (EPR) spectra and radical scavenging experiments proved that superoxide radicals and electrons were the main reactive species in the proposed system, the absence of hydroxyl radicals and holes is demonstrated to be the key of high reaction selectivity. [ABSTRACT FROM AUTHOR]

The generation of hydroxyl radicals (HO ) by H 2 O 2 decomposition over solid catalysts (a Fenton-like reaction) will play an important role in the design of new processes for water treatment. More specifically, the understanding of H 2 O 2 decomposition on Au nanoparticles (NPs) is crucial for the optimization of the structure of active sites and the evaluation of cytotoxicity of Au NPs. Here, the kinetic behavior of H 2 O 2 decomposition over supported Au NPs was investigated in a buffer solution at pH ∼ 6.8. Over a range of H 2 O 2 concentrations, the decay of H 2 O 2 followed a pseudo-first-order kinetic rate law with an apparent activation energy of 142 kJ/mol. The observed rate constant was linearly increased from (3.0 ± 1.0) × 10 −3 to (66.7 ± 2.3) × 10 −3 min −1 with the increase in the Au NPs concentration. Further increase in the surface concentration of H 2 O 2 may reduce the HO generation efficiency. A dual intermediate model was proposed for the generation mechanism of HO . [ABSTRACT FROM AUTHOR]

• Multilayered wrinkled C 3 N 4 nanosheets is obtained via thermal-control synthesis. • The catalyst displays excellent selectivity, recycling stability, long-term durability, notable generality. • Cocatalysis of O 2 − and 1O 2 results in the unprecedented activity in sulfide oxidation. • The electron photoexcitation is valid under the competitive formation of charge carriers and excitons. Incorporating visible light into sulfide oxidation is an emerging desirable strategy to produce versatile sulfoxides. We introduce the design and synthesis of multilayered wrinkled C 3 N 4 nanosheets and demonstrate their unprecedented sulfide oxidation activity. Due to the wrinkled surfaces with a large S BET (208.6 m2g−1), wrinkled C 3 N 4 nanosheets exhibit a sensitive optical response, facilitating the electron photoexcition. Layer structure confinement enables robust e−-h+ interactions and valid photoexcited excitons formation, allowing rapid 1O 2 reactive species production. Integrating the sensitive optical response with robust e−-h+ interactions, photoexcited electrons and excitons are jointly produced, giving large yields of ⋅O 2 − and 1O 2 reactive species that are conductive to O 2 − and 1O 2 cocatalysis with an activity that is up to 33-fold that of bulk C 3 N 4. In the cocatalysis mechanism, both O 2 − and 1O 2 , can produce peroxysulfoxide intermediates, resulting in target sulfoxides. This is the first report on sulfide oxidation via O 2 − and 1O 2 cocatalysis and a promising study on catalyst exploitation for high-efficiency and high-selectivity production process. [ABSTRACT FROM AUTHOR]

• DFT calculations were performed on selective autocatalyzed α -alkylation of ketones with alcohols. • Ketones are not only the reactants, but also are the initiators that facilitate the formation of the catalytic aldehydes. • Reaction temperature and alcohol concentration govern the production selectivity. • Dioxygen can further enhance the ketone product selectivity. Base-promoted transition-metal-free α -alkylation of ketones with alcohols is an efficient, practical, and green method for the formation of new C C bonds. Here, we present a DFT study on NaOH/KOH-promoted selective autocatalyzed α -alkylation of ketones with alcohols. For the production of alkylated alcohol, the disodium alkoxide species Na1D is the mediator, and the transformation involves four stages: (I) aldehyde formation; (II) aldol condensation; (III) chalcone reduction to generate an alkylated ketone and an aldehyde; and (IV) reduction of the alkylated ketone to produce an alkylated alcohol. Stage I only occurs at the beginning of the reaction, and the subsequent reaction proceeds via the catalytic cycle cyc-Na involving stages II, III, and IV. The energetic span and the turnover frequency (TOF) of cyc-Na are 35.2 kcal/mol and 5.7 × 10 - 7 1/s, respectively. For the production of alkylated ketone, the dipotassium alkoxide species K1D is the mediator, and the transformation includes dioxygen-assisted oxidation of alkylated alcohol (stage V) and the above four stages. Stage I only takes place initially, too, but the subsequent reaction has two selectable channels. The main channel is the catalytic cycle cyc-K consisting of stages II and III. The energetic span and the TOF of cyc-K are 29.5 kcal/mol and 8.8 × 10 - 5 1/s, respectively. The side channel involves stages II, III, IV, and V, in which the apparent activation energy (AAE) is 34.1 kcal/mol. The calculations present the TOF-determining intermediates and the TOF-determining transition state, and uncover the essence of autocatalysis and the origins of the product selectivity. One important finding is the alkylated ketone selectivity may be enhanced by adding a small quantity of aldehyde corresponding to the alcohol reactant and lowering the reaction temperature. [ABSTRACT FROM AUTHOR]

Abstract: α-Mn2O3 nanocrystals with uniform morphology prepared by calcining a self-assembled Mn3O4 precursor have proved active (ca. 0.14moleculenm-2 s-1 at 153°C) toward CO oxidation at low temperatures. The reaction orders with respect to CO and O2 were measured in the temperature range 100–190°C. Operando and in situ Raman spectroscopy are used to determine the near-surface structure of α-Mn2O3 nanocrystals during the adsorption and oxidation of CO for the first time. A surface phase transformation from α-Mn2O3 to Mn j O k (1< j <2, 1< k <3, and 1< k/j <1.5) intermediate species was observed in gaseous CO with the change in temperature. In addition, with the combination of the temperature-programmed desorption of O2, temperature-programmed surface reaction of CO oxidation, operando Raman spectra, and kinetics parameters, we conclude that the oxidation of CO may proceed through the Langmuir–Hinshelwood mechanism (<200°C) to the Mars–van Krevelen mechanism (>350°C) with increasing reaction temperature. In particular, the adsorbed oxygen is deduced to be responsible for CO oxidation at lower temperatures. [Copyright &y& Elsevier]

Abstract: Mechanistic study of the preferential CO oxidation was carried out over a Pt(1.0wt.%)/NaY zeolite catalyst from 300 to 523K by combination of kinetics and spectroscopy. The mechanism of CO oxidation at 300K was proposed on the basis of spectroscopic study, and the activity at low temperatures was assumed to originate from small Pt clusters. The analysis of XPS and TEM revealed that metallic state of Pt was rather stable after the reaction. The kinetics suggests a Langmuir–Hinshelwood mechanism in the oxygen-limited low-rate branch (O2 adsorption/dissociation is strongly depressed by adsorbed CO), being responsible for CO oxidation in H2-rich gas in the temperature range of 423–523K. In situ DRIFT spectra show that the Pt surface is dominated by linearly bound CO species, and the presence of H2 leads to a significant red-shift of the C frequency, which indicates a Had-induced modification of the Ptnot just a coverage-dependent frequency shift. Consequently, CO oxidation was significantly enhanced in H2-rich gas. [Copyright &y& Elsevier]

Abstract: H2O2 synthesis directly from H2 and O2 over supported Pd–Pt alloy catalysts was carried out using a semibatch reactor under ambient conditions. As compared to pure Pd, the performance of Pd–Pt catalysts was enhanced significantly. The promotional role of Pt was studied systematically by using in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (DRIFTS), quantitative powder X-ray diffraction (XRD), X-rays photoelectron spectroscopy (XPS), and temperature-programmed desorption of H2/O2 (H2/O2-TPD). The spectra of DRIFT, XPS, and XRD demonstrate the formation of Pd–Pt alloy particles, which surfaces are enriched by Pt accompanying with possible electron transfer from Pd to Pt. The addition of Pt into Pd phase was proposed to impact on reactants adsorption, stabilization of intermediates such as OOH and OH radicals, and the formation and decomposition of H2O2. [Copyright &y& Elsevier]