Study On Aerobic Oxidation Of Ethylbenzene In Lique-Phase Catalyzed By Nitrogen Doped And Cobalt Supported Carbon Nanotubes

Carbon nanotubes（CNTs）have received widespread attentions for their significant performance and cost advantages in typical aromatic side chain liquid phase oxidation reactions.Previous studies have shown that CNTs have good catalytic activity in the liquid phase oxidation of ethylbenzene（EB）with O₂ as the oxidant,but the product selectivity needs to be improved.In order to further expand the application of CNTs in the EB liquid phase oxidation,this study improves the catalytic performance of CNTs in the EB liquid phase aerobic oxidation by doping N heteroatom and loading metal Co,and exploring its mechanism.The main research contents of this paper are as follows:（1）Nitrogen doped carbon nanotubes（NCNTs）were prepared and applied in the aerobic oxidation of EB in the liquid-phase.It was found that the catalytic activity was dependent on the amount of catalyst.When the amount of catalyst was very low,NCNTs could promote the oxidation of EB,but showed an inhibitory effect at a certain catalyst amount.Mechanism studies and DFT calculation results demonstrated that the process of abstraction ofα-H from EB molecule was inhibited in the presence of NCNTs,so that the oxidation of EB was inhibited at the stage of radical chain initiation.By adding tert-butyl hydroperoxide（TBHP）as a co-oxidant,the inhibition step was bypassed and peroxide radicals were generated,so that EB oxidation directly entered the stage of chain propagation,which significantly promoted the oxidation conversion of EB.With the addition of 30 wt%TBHP relative to EB,a higher catalytic performance with 46%EB conversion and 72%acetophenone（AcPO）selectivity were obtained.This study provides a new understanding of the EB catalytic oxidation by N-doped carbon nanomaterials.（2）Cobalt acetate and citric acid were used as the cobalt source and the carbon source for the carbon coating layer,respectively.The catalyst Co@C/CNTs was prepared by the method of impregnation and calcination of the aformentioned mixture and CNTs.The catalyst can effectively promote the catalytic oxidation of EB,and has a strong effect on the decomposition of phenethyl hydrogen peroxide（PEHP）and an excellent selectivity to AcPO.Under reaction conditions of 150 ^oC,2 MPa O₂,and 3 h,the solvent-free oxidation of EB by Co@C/CNTs with10 wt%Co loading dosage yielded 51.7%EB conversion and 79.6%AcPO selectivity.Furthermore,the influence of Co loading form and state on the reaction performance was studied.The activation energy of CNTs and Co@C/CNTs for EB conversion and various products formation were obtained,and the effect of catalysts on the product alcohol to ketone ratio were analyzed.These results showed that the low-valence Co was more conducive to the solvent-free catalytic oxidation of EB,and the carbon-coated Co could significantly promote the activation of O₂,and reduce the activation energy of EB conversion to AcPO and α-phenylethanol（PEA）,especially the promotion of AcPO.In addition,the catalyst displayed the excellent cycle stability.This research provides a new idea for the catalytic oxidation of EB by nano-carbon material supported metal catalysts.