Preparation Of Nickel And Iron Based Catalysts Using Dielectric Barrier Discharge Plasma

The social progress and development leads to a dramatic increase of energy consumption,and serious environmental pollution problem.How to enhance the utilization efficiency and reduce waste emission has become a serious problem that needs to be solved immediately.Catalysts,as one of the most important joint in energy utilization clathrates,their traditional synthesis methods and conventional performance can't meet the increasing demand for energy utilization.There is an urgent need for the chemical industry to develop new synthesis route and new types of catalysts.Taking advantage of the low temperature feature of plasma,and the bombardment of high energy electrons and highly active ions,plasma treatment is capable of preparing catalysts in a way that no common treatment methods can be achieved.Previous studies have shown that plasma treatment can influence catalyst particle size and structure.In this dissertation,based on previous studies,DBD plasma treatment effect on the particle size and structure control over nickel based and iron based catalysts were thoroughly discussed,the mechanism for the enhanced performance in the reactions for these plasma treated catalysts are also investigated.As an important methane conversion process,stream reforming of methane?SRM?reaction is responsible for the industrial hydrogen and syngas production.Nickel based catalysts are the most widely used catalysts for SRM reaction,but the high coke formation amount is a serious problem.In this dissertation,DBD plasma was applied to decompose nickel nitrate to prepare Ni/SiO₂ catalyst.Compared with the conventional calcination method,the plasma treated catalyst showed high activity and low coke formation amount in the SRM reaction at low steam to methane ratio.According to the characterization results,the high energy electron bombardment effect of plasma treatment can modify the catalyst structure by generating more closed packed facets,less defects and enhancing metal-support interaction.Moreover,the low temperature feature of non-thermal plasma treatment can effectively control the nickel particles at an average size of 5 nm,which is much smaller than the thermally calcined¹0 nm particles.All these factors help the catalyst reducing methane decomposition rate and increasing carbon gasification rate in the SRM reaction,which as a result led to high activity and enhanced coke resistance.Fischer-Tropsch synthesis?FTS?,which uses syngas as reactants,is one of the most important downstream reactions of SRM in the methane clathrates.Compared with cobalt based catalysts,iron based catalysts are widely used because of their low cost and wider applicability.In this dissertation,activated carbon spheres were applied as template to synthesis iron precursor catalyst,and used DBD plasma treatment to remove carbon template and synthesize iron based FTS catalysts.The results showed that plasma treatment is a fast and efficient way to remove template,its carbon removal efficiency was almost 6 times faster than thermal calcination.The results also showed that the micro-combustion during DBD plasma treatment and the reduction effect of carbon template removal reduced part of the Fe³⁺ions into Fe²⁺,generating magnetite phase in the catalyst.This magnetic property of the catalyst made it easier to be extracted from other phases.The electron bombardment effect of DBD plasma treatment also modified the electronic structure of iron based catalyst,leading to a much higher carbonization degree during the FTS process,so that the activity and light olefin selectivity were greatly improved.During catalyst synthesis process,catalyst support has a huge impact on the structure of the active phase.By using DBD plasma gas phase synthesis,the influence of DBD plasma treatment on crystal nucleation and growth can be studied without the support effect.In this dissertation,nickel nanoparticles were synthesized in the gas phase using coaxial DBD plasma reactor,and the plasma influence on the crystal nucleation and growth was discussed.The particle size control could be achieved by changing the precursor concentration,residence time and the geometry of plasma setup.Compared with the conventional synthesis methods,plasma gas phase synthesis can effectively avoid the introduction of impurities,and control particle size in a more convenient way.Then based on the coaxial DBD plasma setup,the potential of reactor scale-up and the scale-up effect were studied,and principles for scaling up were also proposed.Based on these principles,the volume of the plasma reactor was scaled up to9 times higher than before,which laid the foundation for industrial application.