Fibrous Tubular LaMnO₃ Perovskite Prepared By Electrospinning For Aerobic Oxidation Of Benzyl Alcohol To Benzaldehyde

The liquid phase selective oxidation of benzyl alcohol to benzaldehyde using a solid catalyst with oxygen as the oxidant is a"green,environmentally friendly and sustainable"process route.However,the low solubility of molecular oxygen in organic solutions limits its adsorption and activation efficiency on the catalyst,reducing the reaction activity significantly.For this reason,the design of a class of catalysts with high performance for molecular oxygen adsorption and activation is essential for the industrial application of this technology.A series of LaMnO₃-NFT catalysts with fibrous tubular shape using electrospinning were prepared in this work.It was found that the correlation between the physical and chemical properties such as metal ion valence,oxygen vacancies of the catalysts and the catalytic activity of benzyl alcohol oxidation was systematically investigated,and a reasonable reaction mechanism was proposed,which can be used for the future preparation of high-performance perovskite oxide catalysts.Catalyst preparation and its performance in catalytic molecular oxygen selective oxidation of benzyl alcohol to benzaldehyde can provide theoretical basis and reference for future research.The main studies are as follows:LaMnO₃-NFT with a fibrous tubular morphology showed excellent performance in catalyzing the selective oxidation of benzyl alcohol to benzaldehyde:the reaction reacted at low temperature（50℃）for 3 h and the conversion of benzyl alcohol reached 81.4%,which was about 14%more than the LaMnO₃-bulk catalyst prepared by the sol-gel method.H₂-TPR,O₂-TPD and TEM characterization confirmed that the redox ability,oxygen vacancy content,and the ability to adsorb molecular oxygen of LaMnO₃-NFT are all closely related to its fibrous tubular morphology,which in turn affects its ability to adsorb and activate reactants and improve the reactivity.Based on the successful preparation of LaMnO₃-NFT,the content of La was modulated.By varying the La content,a series of La_xMnO₃ catalysts with different La/Mn ratios were synthesized.Among them,the La_0.90MnO₃ sample exhibited the best catalytic activity.The low content of La can,on the one hand,induce the conversion of Mn³⁺to Mn⁴⁺and the generation of oxygen vacancies to improve the oxidation capacity of the catalyst;on the other hand,it can also reduce the enrichment of La on the catalyst surface and expose more Mn active sites,thus improving the reaction activity.Finally,the La_1-xK_xMnO₃ catalysts were synthesized by doping of K⁺at the La³⁺site.According to the principle of electroneutrality,the substitution of low valence K⁺at La³⁺can lead to an increase in the Mn chemistry valence or the creation of oxygen vacancies,improving the oxidation capacity of the catalyst to achieve the effect of defects with the La site.The results show that at 5%of the K doping level(i.e.:La_0.95K_0.05MnO₃),the sample exhibited the best catalytic benzyl alcohol oxidation activity:up to 93.6%benzyl alcohol conversion at 50℃,atmospheric pressure,20μL benzyl alcohol and 50 m L/min O₂ flow rate.