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Solvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five‐membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)−H2O2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13C MAS NMR, two‐dimensional (2D) 1H−13C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five‐membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti‐Beta/H2O2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid‐phase epoxidation/hydration reactions over Ti(IV)−H2O2 system. [ABSTRACT FROM AUTHOR]

A series of SO42−/W−Zr catalysts with different W/Zr mole ratios were synthesized by solvent evaporation self‐assembly followed by impregnation of sulfuric acid. The catalysts were examined in the glycerol esterification with acetic acid, and fully characterized by XRD, BET, TEM, XPS, NH3‐TPD, H2O‐TPD and pyridine adsorption infrared spectroscopy. The results revealed that W/Zr mole ratio and calcination temperature significantly affected the structure, acidity and catalytic performance of the catalysts. SO42−/W−Zr(1:1)‐500 (with a W/Zr mole ratio of 1:1, calcined at 500 °C) exhibited the highest catalytic activity, which is mainly due to the fact that the catalyst had more acidic sites and good water tolerance. In addition, the catalyst also showed excellent recyclability, in five repeated runs the conversion of glycerol and yields of products remained stable. SO42−/W−Zr complex solid super acid catalysts with different Zr/Al mol ratios were synthesized by solvent evaporation self‐assembly followed by impregnation of sulfuric acid and used in the esterification of glycerol with acetic acid to glyceryl diacetate. SO42−/W−Zr(1:1)‐500 (with a W/Zr mole ratio of 1:1, calcined at 500 °C) exhibited high activity, selectivity, and excellent recyclability, owing to its abundant acidic sites and good water tolerance. [ABSTRACT FROM AUTHOR]

Solvent effects in catalytic reactions have received widespread attention as they can promote reaction rates and product selectivities by orders of magnitude. It is well accepted that the stable five-membered cyclic intermediates formed between the solvent molecules and Ti species are crucial to the alkene epoxidation in a heterogeneous Ti(IV)-H 2 O 2 system. However, the direct spectroscopic evidence of these intermediates is still missing and the corresponding reaction pathway for the alkene epoxidation remains unclear. By combining in situ 13 C MAS NMR, two-dimensional (2D) 1 H- 13 C heteronuclear correlation (HETCOR) NMR spectroscopy and theoretical calculations, the five-membered ring structures, where the protic solvents (ROH), and aprotic solvent (acetone), coordinate and stabilize the active Ti species, are identified for the first time over Ti-Beta/H 2 O 2 system. Moreover, the role of these cyclic intermediates in the alkene epoxidation/hydration conversion is clarified. These results provide new insights into the solvent effect in liquid-phase epoxidation/hydration reactions over Ti(IV)-H 2 O 2 system., (© 2024 Wiley-VCH GmbH.)