| In the coal mine, the volume fraction of methane, which is the main combustible component, is about 0.1~5%. If the low-concentration methane is directly discharged into the atmosphere without ulmost utilization, serious environmental problem and resource waste would have been occurred. Due to the difficulty in conventional combustion, the catalytic combustion technology, which can decrease the light-off temperature and maintain the stable combustion of low-concentration methane, has been widely used. Cu catalyst has a good industrial application prospect because of its good catalytic activity and low price. However, the impurities in low-concentration methane, such as SO2, have some effects on the catalytic combustion reaction over Cu catalyst. Mainwhile, it has further reseach to improve the combustion of low-concentration methane with SO2 over Cu based catalyst by adding assistant into catalyst. Consequently, it has important academic significance and value in industrial application that combustion characteristic, mechanism of sulfur poisoning and improvement measure of low-concentration methane with SO2 over Cu based catalyst are being studied.In the paper, a series of Cu based catalysts have been prepared, and the effects of internal and external diffusion of catalytic reaction have been investigated in the fixed bed reactor. Then, the effects of the internal and external diffusion and the dilution between catalysts have been eliminated experimentally. My work researched the effect of SO2(volume fraction, 0~0.02 %) on the catalytic combustion characteristics of low-concentration methane(volume fraction, 3 %), and analyzed the cause of catalyst deactivation with some characterization methods. Then, the article introduced the Ni to Cu based catalyst in order to improve the performance of the catalyst. The effects of the content of Ni on the characteristics of stability of sulfur poisoning have been studied seriously, and the reason of improved performance has been analyzed by a series of characterization technology.It is found in the research that SO2 in the feed gas can cause the decrease of activity and stability of Cu/gamma-Al2O3 catalyst, and the characteristic temperatures of methane catalytic combustion will increase in some degree. At the same time, the SO2 concentration fluctuation will exacerbate this phenomenon. The reason for this is that the presence of SO2 in the feed gases results to the agglomeration and the accumulation of sulfur on the surface of Cu/γ-Al2O3 catalysts. Sulfur is in the form of sulfate, which mainly contains copper sulfate(Cu SO4). Under the condition of oxygen enrichment, the copper sulfate, formed by the absorption of SO2 and Cu2+ on the oxygen ions, attaches to the surface of catalysts and ends up forming a hard shell, which decreases the active sites and the specific surface area, hinders the adsorption of methane molecules on the active sites, and inhibits the catalytic reaction. The addition of Ni to Cu based catalyst increased the catalyst activity and stability of resistance to sulfur poisoning, and the activation energy of catalytic reaction decreased. With the increase of Ni content, the improved effect was more obvious. Due to the formation of Ni Al2O4 spinel, the stability of Cu catalysts increased with the Ni content. Weaker adsorption of SO2 and less retention time of CO2 on the surface of Cu catalysts contributed by the decrease of Lewis acidity due to Ni Al2O4 spinel were the reasons of high performance of Cu catalysts.This paper systematically studied the sulfur poisoning mechanism of Cu/ gamma-Al2O3 catalyst and the reasons why the addition of Ni improved the performance of Cu/ gamma-Al2O3 catalyst, which provides a theoretical guidance for the combustion of low-concentration with SO2 over Cu/ gamma-Al2O3 catalyst, and it helped the practical engineering application of low concentration coal-bed gas... |
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