Study On Carbon Based Nano Catalytic Materials And Enhancement Of Reaction Process By High Gravity Technology

In the development of modern science,the research of catalytic reaction is one of the most active fields in the scientific community,which has become the source and power to promote the development of energy,materials and chemical industry.Over the last few years,metal-based catalytic materials,such as platinum,ruthenium,palladium and other precious metals,have shown excellent catalytic performance in many catalytic reactions.However,there are many problems for metal catalysts,such as limited resources,expensive prices,environmental pollution,and so on,which limit their large-scale commercial application.With the development of green chemistry and sustainable chemistry,the application of metal-free materials as catalysts has been gradually recognized and explored.Among them,the metal-free catalysts represented by carbon nano materials have been found to be used in many kinds of catalytic reactions requiring the participation of metals,which is expected to replace the traditional metal-based catalysts.At present,in the field of carbon nanomaterials catalysis,the research is mainly in the preparation of new carbon nanomaterials,the identification of active sites,and the exploration of catalytic process.However,the catalytic reaction system of carbon materials as catalysts is mostly heterogeneous process,and the catalytic performance is obviously affected by the mixing efficiency between different phases.There are some problems in the conventional reactor,such as weak mixing effect and poor interphase transfer effect.The high gravity technology is a typical chemical process strengthening technology.It can greatly enhance the inter phase mass transfer efficiency by using the centrifugal force generated by rotation to simulate the high gravity environment.Thus,this thesis explores the influence of the structure of carbon-based nano materials on the catalytic reaction performance,studies the process law of metal-free catalytic reaction system under different reaction conditions,and proposes a new process of carbon-based metal-free catalytic reaction enhanced by high gravity technology.The main work is as follows:(1)Cheap commercial graphite and sulfur powder was used as raw materials,a 3.4 wt.%sulfur doped graphite sheet(SG)metal-free nano material was prepared by ball-milling method.The prepared SG can be used as metal-free catalyst for the oxidation of benzyl alcohol to benzyl alcohol.Under the optimum reaction conditions,reaction temperature of 80℃,catalyst doage of 2 mg SG,and reaction time of 3 hours,the conversion of benzyl alcohol and the selectivity of benzaldehyde are 18.2%and 96.8%,respectively.When it is used to catalyze the reduction of p-nitrophenol to p-aminophenol,the apparent reaction rate constant is 0.02874 min-1,the apparent activation energy is 24.21 kJ mol-1,the reaction entropy is-146.34 kJ mol-1 K-1,and the reaction enthalpy is 21.57 kJ mol-1.The structure of doped carbon materials is optimized by density functional theory calculation.It is found that when sulfur atom was doped into the carbon skeleton,it will cause the rearrangement of electron cloud,which is conducive to the improvement of catalytic activity.Based on the study of reaction kinetics,the reaction mechanism of metal-free catalytic oxidation and reduction was proposed;(2)MgO nanoparticles with controllable morphology was used as template and catalyst,multi layers nitrogen doped graphite tube metal-free materials can be prepared by chemical vapor deposition method.The length of graphite tube is in the range of 10-20 μm,and the average diameter is about 500 nm.In the process of electrocatalytic oxygen reduction and electrocatalytic oxygen evolution,double layers graphite tube has higher positive initial potential,half wave potential,and limiting current density than those of single wall graphite tube,and it has better dual function activity.In addition,when it used as the support of electrocatalyst in the synthesis of ammonia.The effect of hydrophobicity of the catalyst on the catalytic performance was explored.Under-0.4 V overpotential,the NH3 yield was the highest,whose value was 2.24 μg h-1 mg cat.-1.Meanwhile,the double layers graphite tube structure with hydrophobic outer layer could effectively improve the selectivity of the electrocatalyst synthesis of ammonia;(3)A three-dimensional nitrogen doped graphene-Ni composite monolithic catalyst was synthesized by using graphene oxide and urea as nitrogen source and nickel foam as template.The catalyst can efficiently promote the reduce process of nitrobenzene to aniline.The apparent activation energy is calculated as 30.50 kJ mol-1.Based on the reaction kinetics datas,the Langmuir-Hinshelwood adsorption-reaction model was used to fit the reaction system.The fitting error between the final model value and the experimental value were less than 10%.Moreover,A metal-free nitrogen doped graphene foam monolithic catalyst,which could be used to catalyze nitrobenzene reduction was prepared by the hydrothermal synthesis coupling freezing-drying method.The pore size of the prepared monolithic catalyst is about 100 nm;(4)A new process of carbon-based metal-free catalytic reaction enhanced by high gravity technology was promoted.When the reaction temperature was 60℃,the conversion of benzyl alcohol increased from 5.56%under normal gravity(1 g)to 20.86%under 279 g,and the selectivity remain unchanged.The reduction of nitro aromatic compounds was carried out in a rotating tube type high gravity reactor.The apparent rate of the reaction under high gravity of 6484 g was six times than that of in the conventional gravity environment.According to the result of CFD simulation,we find that the higher the high-gravity level is,the faster the surface renewal rate will be,thus improving the surface reaction effect.