Preparation Of Heteroatom Doped Carbon Materials And Catalytic Performance Of Their Palladium-supported Catalysts For Phenol Hydrogenation

Heteroatom doped carbon materials represent modified morphology,electronic structure and physicochemical properties.N-doped nanocarbon materials are the most widely studied and have been proved to be good metal-free catalysts and supports of metals.Compared with nitrogen,it is difficult to incorporate larger atoms,such as sulfur and phosphorus,into the lattice of carbon materials,especially for multi-walled carbon nanotubes with small specific surface area.The content of sulfur in S-doped multi-walled carbon nanotubes was usually as low as 1%according to literature reports.Therefore,the highly controllable method for doping sulfur and phosphorus remains challenging.This thesis aims to present a facile method for doping sulfur and other heteroatom on fluorinated carbon nanotubes（FCNTs）.Furthermore,the metal-support interaction（MSI）between palladium and heteroatom doped CNTs was studied.Its effect on the selective hydrogenation performance of phenol was evaluated.The main research contents are as follows:（1）It has been found that the high temperature defluorination process of FCNTs introduced a large number of defects,which is beneficial to heteroatom doping.And the sulfur content of the S@FCNTs can be further improved by optimizing the pyrolysis deposition conditions such as heating method,deposition time,and injection rate.The reason why fast heating of FCNTs achieved high-efficiency sulfur doping is that fast heating shortens the residence time,and strengthens the coupling between defluorination of FCNTs which producing a large number of vacancies and the incorporation of sulfur atoms.And this method can be extended to dope N,P,N&S,N&P on carbon nanotubes.（2）Pd nanoparticles（NPs）were supported on S,N,N&S,P,N&P doped CNTs by sodium borohydride reduction.The effects of support-doping on Pd NPs size and electronic structure were investigated by XRD,TEM,CO-stripping and XPS.It was found that Pd NPs with a smaller dimension,narrower size distribution,and more active sites were obtained on S@FCNTs.Moreover,support-doping promotes the electron transfer from Pd NPs to supports leading to the electron deficiency of Pd NPs.And the electron-deficient property of Pd NPs supported on S@FCNTs is the most obvious,indicating that the MSI between palladium and sulfur is the strongest.（3）The selective hydrogenation of phenol was used as a model reaction to investigate the effect of support-doping on the catalytic performance of palladium catalysts.It was found that at 353 K and 1.1 atm H₂,the palladium catalysts showed good selectivity to cyclohexanone,while Pd NPs supported on S@FCNTs exhibit excellent activity and stability.The TOF of the reaction was correlated with the electronic structure of the Pd NPs,showing that electron-deficient Pd NPs are more likely to obtain high activity by promoting adsorption of the intermediate product.In the meantime,DFT calculation suggests that there is a strong interaction between Pd NPs and S,and Pd NPs preferentially interacts with graphitic sulfur.