Oxidative Dehydrogenation Of Methanol On Nanocarbon Catalysts

Metals(mainly transition metals and precious metals)or metal oxide catalysts used in the field of traditional industrial catalysis have poor sustainability and serious environmental pollution issues etc,which has stimulated researcher’s interests in exploring and investigating green sustainable catalytic systems.Nanocarbon,as a novel type of non-metallic catalysts,has been widely used in many gas or liquid phase chemical reactions due to its low cost,high activity,strong stability,anti-carbon deposition and large-scale production,exhibiting the possibility to substitute metal-based catalysts.Nanocarbon catalysis has gradually become a hot research topic in the field of catalysis and green chemistry.Nanocarbon materials are applied in a wide variety of catalytic reactions,mainly concentrating on the reactions of redox type(dehydrogenation/hydrogenation).Large efforts are currently focused on the development of new high-performance catalysts and the evaluation of apparent activity,and has achieved fruitful results.However,the research on the mechanism of nanocarbon catalytic reaction is relatively rare.The key issue in the mechanistic studies in carbon catalyzed oxidative dehydrogenation reaction,such as:active site characterization and quantification,reaction kinetics model,molecular scale reaction mechanism and catalyst structure-activity relationship,are divergent in the related field.The lack of research on these basic problems not only hinders the researchers to further understand the nature of nanocarbon catalysis,but also limits the rapid development of high-performance nanocarbon catalyst design and fabrication.Therefore,we designed and synthesized a carbon material model catalyst with specific chemical composition and single functional group,and applied it into the research of methanol oxidative dehydrogenation reaction mechanism in this thesis.The in-situ infrared spectroscopy measurement confirmed the transformation of active sites,and the mass spectrometry captured the intermediate and product,and the isotope labeled experiments proved explored methanol oxidative dehydrogenation rate-determining step.Finally,the feasibility of the oxygen functional group was determined by modifying the carbon nanotubes with oxygen functional groups via plasma technique.The main contents include:(1)We realized the synthesis of a novel conjugated monomer having specific composition and single functional group(ketonic carbonyl group)through Yamamoto coupling reaction of 3,6-dibromophenanthrene and 1,3,5-tribromobenzene.The polymer is used as a model for carbon catalysts for the catalytic mechanism study of methanol oxidative dehydrogenation.In situ infrared information gives direct evidence of the transformation of the active site structure during the catalytic process.Combining with in-situ infrared,mass spectrometric captured the structure of intermediates and other measurements monitored the reaction process and kinetics of oxidative dehydrogenation of methanol and kinetic analysis,The catalytic reaction mechanism depending on the redox cycle of ketonice carbonyl/phenolic hydroxyl groups is proposed,and the entire catalytic reaction process can be divided into a hydrogen abstraction step and a reoxidation step.(2)The modified multi-walled carbon nanotubes were treated by oxygen plasma and applied in the oxidative dehydrogenation of methanol.Characterization by SEM,TEM,TG,Raman shows that the multi-walled carbon nanotubes treated by oxygen plasma have an increased surface oxygen content.At the same time,the analysis on the Ols XPS shows that the oxygen content on the surface of the treated multi-walled carbon nanotubes is increased,and the content of the ketonic carbonyl group,which serves as active sites for the reaction,is also increasing.Subsequently,the activity test of the oxidative dehydrogenation reaction of methanol was carried out.After the oxygen plasma treatment,the catalytic activity of multi-wall carbon nanotube(the conversion rate of methanol and the selectivity of formaldehyde)is improved.