Figure - available from: Royal Society Open Science
This content is subject to copyright.
Source publication
HRF5015, a perfluorosulfonic acid resin catalyst with unique pore structures, was investigated in the catalytic self-condensation of cyclohexanone under mild conditions. The morphology of HRF5015 was characterized by transmission electron microscopy (TEM) and atomic force microscope (AFM), and the reaction mechanism was studied by in situ diffuse r...
Similar publications
The development of rechargeable lithium−oxygen (Li−O2) batteries with high specific energy is essential to satisfy increasing energy consumption. It is critical to understand the dynamic process and detailed pathways during cell operation, which will allow us to control the reaction, suppress the formation of byproducts, and optimize battery perfor...
Citations
... In the case of the aldol condensation catalysts, a broad variety of heterogeneous alternatives has been explored, e.g. hydrotalcite and other layered oxides based ones [98, , zeolites [16,101,[172][173][174][175][176][177][178][179][180][181][182][183][184][185][186] , acidic ion-exchange resins [180,[187][188][189][190][191][192][193] , and amine functionalized materials . So far, the latter have yielded the most promising results. ...
... Other acidic aldol condensation catalysts are acidic ion-exchange resins, e.g. commercial acid resins Amberlite® and Amberlyst®, which provide high aldol condensation product yields, with TOFs in the order of 10 −4 -10 −3 s −1 [180,[187][188][189][190][191][192][193]219] . Mild deactivation can sometimes occur due to accumulation of large condensation products inside the pores, which necessitates a regeneration step [187][188][189] . ...
During the past two decades, new insights have driven the development and optimization of aminated materials as aldol condensation catalysts. Amines, either primary or secondary, facilitate the reaction via an enamine mechanism. If the spatial placement with respect to the amine allows it, weak acid sites such as silanols or hydroxyls, can cooperate as hydrogen bond donors and aid in proton transfer steps. Furthermore, the reaction environment, i.e., support and solvent and their mutual interactions, is also a key determining factor. In particular, co-feeding small amounts of water suppresses the formation of inhibiting and site-blocking species. However, silica-based materials are susceptible to hydrolysis. This led to the development of water tolerant (bio)polymer supported amine catalysts which also exhibit selective component enrichment properties, opening up opportunities for further catalyst development.
A series of TiO2/Al2O3 catalysts for cyclohexanone condensation have been prepared by impregnation method. Various characterization techniques, including XRD, BET, SEM, FT-IR, NH3-TPD, and Py-IR were applied to characterize their physical properties and chemical structures. The results show that the acidity of the TiO2/Al2O3 catalysts are all come from L-acid. In addition, the effects of reaction parameters such as TiO2 loading dosage, amount of cyclohexane, catalyst dosage, particle mesh, agitation rate, temperature and time were examined. The optimal reaction conditions were 40 ~ 60 particle mesh, 8% catalyst dosage, 393.15 K reaction temperature, 300 r/min agitation rate for 120 min with the conversion of cyclohexanone is 29.11% and close to 100% ultrahigh selectivity. Five cycles of reaction suggested the activity and selectivity of the catalyst did not change obviously and had potential industrial application value. Finally, the reaction kinetics was evaluated in cyclohexane under the reaction conditions of particle mesh 40 ~ 60 and 8% catalyst dosage and absence removing water produced, indicating the cyclohexanone self-condensation reaction was a second-order reaction.
A rapid, cheap and feasible new approach was used to synthesize the Mg0.375Fe0.375Al0.25-LDH in the presence of tetramethylammonium hydroxide (TMAH), as a nontraditional hydrolysis agent, applying both mechano-chemical (MC) and co-precipitation methods (CP). For comparison, these catalysts were also synthesized using traditional inorganic alkalis. The mechano-chemical method brings several advantages since the number of steps and the energy involved are smaller than in the co-precipitation method, while the use of organic alkalis eliminates the possibility of contaminating the final solid with alkaline cations. The memory effect was also investigated. XRD studies showed Fe3O4 as stable phase in all solids. Regardless of the alkalis and synthesis methods used, the basicity of catalysts followed the trend: mixed oxides > parent LDH > hydrated LDH. The catalytic activity of the catalysts in the Claisen–Schmidt condensation between benzaldehyde and cyclohexanone showed a linear dependence to the basicity values. After 2 h, the calcined sample cLDH-CO32−/OH−-CP provided a conversion value of 93% with a total selectivity toward 2,6-dibenzylidenecyclohexanone. The presence of these catalysts in the reaction media inhibited the oxidation of benzaldehyde to benzoic acid. Meanwhile, for the self-condensation of cyclohexanone, the conversions to mono- and di-condensed compounds did not exceed 3.8%.
