The Study Of Catalytic Performance And Mechanism For Nanocarbon Materials In Gas Phase Reaction

Carbon nanotubes (CNTs) with their unique physical and chemical properties can be used as catalysts in various catalytic reactions and seems to be a promising candidate for metal catalysts widely applying in catalysis. Researches have indicated that surface properties of carbon materials played a significant role in their catalytic activities. In this thesis, based on the requirements of the gas phase catalytic reaction, we tune the surface structure of carbon materials, design and synthesize three kinds of nanocarbon catalysts with different concentrations of surface defects, functional groups and heteroatoms. They are also used as catalysts in catalytic methane decomposition (CMD), selective oxidation of acrolein and allyl alcohol, and show good catalytic performances. The results are summarized as follows:(1) Nanodiamond (ND) with varied graphitic layer thickness and different amount of surface defects was fabricated through adjusting the calcined temperature. These catalysts exhibited good resistance to carbon deposition and catalytic stability in CMD reaction, and obtained a by-product with few-layered graphene structure. The structure-performance correlation of ND annealed at different temperatures in CMD reaction was studied and we are inclined to recognize the unsaturated edges or vacancies in graphene sheet as the active sites. Combining with the theoretical simulation and experimental results, it was proposed that CMD was a multi-step process.(2) CNTs selectively functionalized by concentrated nitric acid and oxygen have been systematically characterized and used as catalysts for catalytic selective oxidation of acrolein (ACR). This study indicated that this oxidation method facilitated generating more surface active oxygen groups and improving the catalytic performances greatly. The best acrylic acid (AA) formation in all samples was40.8%. Through a systematic design to selectively remove the oxygen functional groups on the oxidized CNTs surface, the CNTs catalysts were performed in ACR. The epoxy and lactone groups were determined as active sites for the acrolein oxidizing to AA. It was also proved by the well correlation between the AA formation rate and the amount of active oxygen groups. Based on the kinetic tests and performance results, we explained the reaction pathway and proposed a possible mechanism for ACR.(3) A series of nitrogen modified carbon nanotubes (N-CNT) with adjustable nitrogen content were synthesized for catalytic application in selective oxidation of allyl alcohol. The results showed that N-CNT exhibited a better performance than other nitrogen-free carbon materials. The surface chemistry and structural properties were investigated by using various characterization methods. The excellent catalytic activity was related to the incorporation of nitrogen atom rather than surface area, and increased with the increasing of surface nitrogen content. Based on the performance results, kinetic tests and theoretical background, it was proved that graphitic nitrogen species was pivotal in the allyl alcohol selective oxidation reaction. In addition, we explained the reaction pathway and proposed a possible mechanism for this reaction.