Plasma Catalytic CH₄ Oxidation To CH₃OH Over Ni-based Catalyst

The selective activation and orientable conversion of methane are considered as the"holy grail"in catalysis.The direct oxidation of CH₄ to CH₃OH with molecular oxygen（O₂）as oxidant is a challenging subject.In this thesis,a novel dielectric barrier discharge（DBD）reactor with circulating water as the grounding electrode has been used to generate CH₄/O₂ plasma,aiming to oxidize CH₄ to CH₃OH by O₂.Furthermore,the effects of supported metal catalysts have been studied,and Ni-based catalysts exhibit the best performance.The results and conclusions are shown as follows:1.By investigating the reaction conditions of CH₄/O₂ plasma,it was found that the high methanol selectivity can be realized in the case of short residence time and low discharge power.In addition,the reaction pathway for production of CH₃OH and other by-products in CH₄/O₂ plasma were predicted based on 0D modelling（ZD-Plaskin）.2.The influence of metal catalysts on the methanol synthesis by CH₄/O₂ plasma has been studied,and Ni/γ-Al₂O₃ catalysts with 10 wt.%metal loading exhibited best performance on plasma catalytic CH₄ oxidation to CH₃OH,with 6.4%CH₄ conversion and 50.0%CH₃OH selectivity.3.The Ni/Al₂O₃ catalyst was characterized by XRD,XRF,TPR,XPS,HRTEM,HADDF-STEM and N₂ physisorption,and the results showed that highly dispersed NiO phase（β-NiO）,which has strong interaction withγ-Al₂O₃ support,played an important role in plasma catalytic CH₄ oxidation to CH₃OH.In addition,based on the in-situ plasma diagnosis,there are abundant high reactive groups such as CH₃ and O（¹D）in CH₄/O₂ plasma,and Ni/γ-Al₂O₃ catalyst could adsorb more H free radicals on the catalysts surface.In conclusion,by combining plasma modelling,catalyst characterization and plasma diagnosis,it is believed thatβ-NiO is the active sites,and the interaction between plasma gas phase species and active sites play an important role in promoting CH₃OH synthesis.