Effect Of Manganese Oxides On Cumene Oxidation Of Carbon Nanotubes And Nitrogen-doped Carbon Material

The selective oxidation of aromatics to produce ketones,alcohols and peroxides in the liquid phase is an crucial chemical process,in which using carbon-based materials as catalysts shows the high catalytic performance and the advantages of low cost.In this study,the oxidation of cumene was used as the probe reaction,and carbon material was used as the carrier to regulate its catalytic oxidation of cumene by loading manganese oxide or doping nitrogen.By doing so,the reaction kinetics and reaction mechanism inflecned by the interactions between carbon material and manganese oxide or nitrogen dopant were further revealed.The main research contents and results of this paper are as follows:（1）Carbon nanotube（CNTs）supported manganese dioxide（MnO₂/CNTs）catalyst was prepared by a simple one-pot synthesis method and used in the oxidation of cumene.The results show that the catalytic activity can be effectively improved by loading manganese oxide on CNTs.Among these catalysts,the conversion of cumene over 21.23-MnO₂/CNTs reached73.44%,the selectivity of 2-phenyl-2-propyl alcohol（PP）reached 59.06%,and the initial reaction rate of cumene was 345.99 mmol/g/h,which was much higher than that over CNTs or MnO₂ as catalysts alone.Combined with the simulation calculation,it was found that the introduction of MnO₂ nanoparticles on CNTs could promote the decomposition of cumyl hydroperoxide（CHP）into acetophenone（AP）and PP.While,AP was more favorable to be generated than PP,due to the strong synergistic effect between MnO₂ particles and CNTs.By establishing a kinetic model of the reaction,the influences of the loading of MnO₂ particles on the rate-determining step,reaction rate constant and activation energy of the elementary reaction were analyzed.The results showed that the homolytic cleavage of CHP was the rate-determining step and plays a significant role in the reaction process.The loading amount of MnO₂ particles significantly promoted the elementary step,especially in promoting the generation of PP.This study provides a new understanding of the synergistic effect of MnO₂and CNTs on the oxidation of cumene.（2）Nitrogen-doped CNTs（MnO₂/NCNTs and MnO/NCNTs）loaded with MnO_x and nitrogen-doped mesoporous carbon coated with manganese oxides（Mn@NMC）were synthesized by formamide solvothermal method and high temperature pyrolysis method,respectively.The activity over these catalysts were much higher than that of CNTs,which was not resulted from the synergistic effect of MnO₂ and NCNTs.Comprehensive characterizations and performance evaluation analysis showed that MnO_x and nitrogen dopant could both improve the catalytic activity of cumene and promote the decomposition of CHP.The catalytic conversion of cumene is similar over the catalysts with the same dosage.（3）Based on the problem that the conversion rate reached the equilibrium and was difficult to be improved catalyzed by NCNTs in the oxidation of cumene for a certain period of time,the products from the reaction was evaluated in affecting the reaction.It was found that there was a by-product（formic acid）dislaying an inhibitory effect on the oxidation of cumen.Theoretical calculation also showed that the pyridine nitrogen species on the surface of carbon materials acted as the active sites to adsorb formic acid,which inhibited the reaction.Herein,how to exclude the influence formic acid and further improve the conversion rate of cumen is still on the road.