| With the global warming and energy issues becoming more and more serious throughout the world, the conversion of natural gas (mainly methane) as the feedstock for the production of highly valuable chemicals and/or clean fuels has become one of the hot fields in the word. Cold plasma, an effective technique for activating methane molecular, has received considerable attention in recent years. In this work, by using dielectrical barrier discharge (DBD) plasma technology, studies on the preparation and modification of highly efficient catalysts for methane conversion and the direct methane conversion were investigated.An experimental investigation has been conducted first to examine the characteristics of the dielectrical barrier discharge plasma at atmospheric pressure. Active species in Ar, CH4 and O2 plasma were analyzed with the diagnosis technique of optical emission spectroscopy (OES), active species of CH, Ha, Hp, Hy and O were observed in plasma. At the same time, the electron excitation temperature and electron density, the key parameters of DBD plasma, were measured, and the effects of input voltage and feed flowrate on the electron excitation temperature were also investigated. It was found that the excitation transfer is a very important process in DBD plasma at atmospheric pressure.The Ni/La2O3/γ-Al2O3 catalysts prepared using DBD plasma treatment method exhibited a much better activity for CH4/CO2 reforming in comparison with the untreated samples. The conversion of CH4 and CO2 over plasma treated sample are 90.1% and 91.3% at 650℃, while, at the same temperature, they are 80.3% and 81.2%, respectively, over the plasma untreated sample. At the same methane conversion, the reaction temperature with plasma treated Ni-based catalysts is at least 30～80℃lower. It was observed from various characterizations that the plasma treated samples displayed the smaller particle size of Ni, better high temperature sintering resistance, and higher exposed Ni concentration, the promoted catalytic performance was ascribed to high dispersion and enrichment of Ni on the surface of catalysts induced by plasma. It was found that both the addition of promoter to Ni-based catalyst and plasma treatment is useful to enhance the resistance to carbon deposition.Rare earth-doped copper-based catalysts were prepared by using DBD O2 plasma treatment for lean methane catalytic combustion. The results showed that the plasma treated Cu-based catalyst revealed excellent stability and superior activity for methane catalytic combustion, the reaction temperature with plasma treated sample is at least 25～35℃lower.. The preliminary studies showed that the higher metal dispersion induced by plasma treatment and greater surface oxygen mobility enhanced by doping of rare earth elements improved the catalytic performance.In this paper, partial oxidation of methane to methanol in a plasma-catalytic system was explored. The results of the combination of DBD with Mo/CuO/γ-Al2O3 catalyst showed that the introduction of catalyst to plasma zone has helped to promote the conversion of methane to methanol at lower temperature of 50～300℃. The effects of catalyst on methanol yield were investigated. The methane conversion percentage and methanol yield during 30 min were 35.5% and 3.62% over Mo/CuO/γ-Al2O3 catalyst at 150℃with 36.6 kJ/L of specific input energy. Meanwhile, combined with products analysis, the mechanisms of methanol synthesis in plasma-catalytic system were also discussed.
|
PDF Full Text Request