Enzyme-like mechanism of selective toluene oxidation to benzaldehyde over organophosphoric acid-bonded nano-oxides

An Investigation of N-Hydroxyphthalimide Catalyzed Aerobic Oxidation of Toluene without Metal Ions in Liquid Phase: Effect of Solvents and Phase Transfer Catalysts

The selective oxidation of toluene to yield value-added oxygenates, such as benzyl alcohol, benzaldehyde, and benzoic acid, via dioxygen presents a chlorine-free approach under benign conditions. Metal-free catalytic processes are preferred to avoid metal ion contamination. In this study, we employed N-hydroxyphthalimide (NHPI) as a catalyst for the aerobic oxidation of toluene to its oxygenated derivatives. The choice of solvent exerted a significant impact on the catalytic activity and selectivity of the catalyst NHPI at reaction temperatures exceeding 70 °C. Notably, hexafluoroisopropanol substantially enhanced the selective production of benzaldehyde. Furthermore, we identified didecyl dimethyl ammonium bromide, featuring two symmetrical long hydrophobic chains, as a potent enhancer of NHPI for the solvent-free aerobic oxidation of toluene. This effect is ascribed to its unique symmetrical structure, extraction capabilities, and resistance to thermal and acid/base conditions. Based on the product distribution and control experiments, we proposed a plausible reaction mechanism. These findings may inform the industrial synthesis of oxygenated derivatives from toluene.

Recent Approaches for Cleaving the C─C Bond During Ethanol Electro-Oxidation Reaction

Direct ethanol fuel cells (DEFCs) play an indispensable role in the cyclic utilization of carbon resources due to its high volumetric energy density, high efficiency, and environmental benign character. However, owing to the chemically stable carbon-carbon (C─C) bond of ethanol, its incomplete electrooxidation at the anode severely inhibits the energy and power density output of DEFCs. The efficiency of C─C bond cleaving on the state-of-the-art Pt or Pd catalysts is reported as low as 7.5%. Recently, tremendous efforts are devoted to this field, and some effective strategies are put forward to facilitate the cleavage of the C─C bond. It is the right time to summarize the major breakthroughs in ethanol electrooxidation reaction. In this review, some optimization strategies including constructing core-shell nanostructure with alloying effect, doping other metal atoms in Pt and Pd catalysts, engineering composite catalyst with interface synergism, introducing cascade catalytic sites, and so on, are systematically summarized. In addition, the catalytic mechanism as well as the correlations between the catalyst structure and catalytic efficiency are further discussed. Finally, the prevailing limitations and feasible improvement directions for ethanol electrooxidation are proposed.

COx hydrogenation to methanol and other hydrocarbons under mild conditions with Mo3S4@ZSM-5

The hydrogenation of CO₂ or CO to single organic product has received widespread attentions. Here we show a highly efficient and selective catalyst, Mo₃S₄@ions-ZSM-5, with molybdenum sulfide clusters ([Mo₃S₄]ⁿ⁺) confined in zeolitic cages of ZSM-5 molecular sieve for the reactions. Using continuous fixed bed reactor, for CO₂ hydrogenation to methanol, the catalyst Mo₃S₄@NaZSM-5 shows methanol selectivity larger than 98% at 10.2% of carbon dioxide conversion at 180 °C and maintains the catalytic performance without any degeneration during continuous reaction of 1000 h. For CO hydrogenation, the catalyst Mo₃S₄@HZSM-5 exhibits a selectivity to C₂ and C₃ hydrocarbons stably larger than 98% in organics at 260 °C. The structure of the catalysts and the mechanism of CO_x hydrogenation over the catalysts are fully characterized experimentally and theorectically. Based on the results, we envision that the Mo₃S₄@ions-ZSM-5 catalysts display the importance of active clusters surrounded by permeable materials as mesocatalysts for discovery of new reactions.

Oxyfunctionalization of Benzylic C-H Bonds of Toluene Mediated by Covalently Anchored Co-Schiff Bases

Oxyfunctionalization of toluene to value-added benzaldehyde, benzyl alcohol and benzoic acid is of great significance. In this work, Co-Schiff bases were immobilized on commercial silica gel by covalent anchoring, and resulting catalysts were used to catalyze the oxidation of toluene in the presence of the cocatalyst N-hydroxyphthalimide (NHPI). The catalysts exhibited excellent textural and structural properties, reliable bonding and a predomination of the cobaltous ions. The catalyst synthesized by diethylamino salicylaldehyde (EASA) possessed a grafting density of 0.14 mmol/g and exhibited a toluene conversion of 37.5%, with predominant selectivities to benzaldehyde, benzyl alcohol and benzoic acid under solvent-free conditions. It is concluded that the effect of ligands on their catalytic performance might be related to their electron-donating or -withdrawing properties.

Study on the Alternative Solvent of Methylbenzene in the Total Acid Number Titration of Current Jet Fuels

Evaluation of the acidic characteristics of a jet fuel, especially for the total acid number (TAN), is of great significance to ensure flight safety. Methylbenzene is commonly used as the titration solvent; however, it is poisonous and harmful to the environment. It is highly desirable to develop an alternative solvent for methylbenzene to extract the acidic compounds from the jet fuel during the determination of the TAN. Here, we develop a desirable alternative solvent of a mixed ethanol-water solution with the volume ratio of ethanol to water of 99:1, which exhibits a value of TAN similar to that of the solvent of methylbenzene in potentiometric titration and acid-base titration methods. The TAN value derived from the different titration solvents was in the order of 2.96 μg KOH g^-1 (V _cyclohexane/V _isopropanol/V _water = 100:99:1) > 2.68 μg KOH g^-1 (V _{methylbenzene}/V _isopropanol/V _water = 100:99:1) ≈ 2.6 μg KOH g^-1 (V _{absolute ethanol}/V _water = 99:1) > 2.34 μg KOH g^-1 (V _isopropanol/V _water = 99:1). The current report presents a nontoxic and eco-friendly alternative solvent for methylbenzene, which may open up an avenue for evaluating the TAN of jet fuels.