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Catalytic Combustion over Me-hexaaluminate (Me=Mn, Fe, Co, Ni) Catalysts

Author: KongJiHong
Tutor: SunLuShi；XiangJun
School: Huazhong University of Science and Technology
Course: Thermal Power Engineering
Keywords: Catalytic combustion hexaaluminate co-precipitation catalytic activity NH3
CLC: O643.36
Type: Master's thesis
Year: 2011
Downloads: 26
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Abstract


The main advantages of catalytic combustor are ultra-low emissions of nitrogen oxides （NOX）, carbon monoxide （CO） and unburned hydrocarbons （UHC）, and to stabilise combustion of low heating value gas （such as coal/biomass gasified gas, coal-bed gas） at relatively low temperatures. Catalytic combustion of gas is one of the most promising processes to produce environmentally clean energy. However, the utilization is prevented by development of catalyst life. Nowadys, the research of catalytic combustion focuses on how to prepare the catalysts own low ignition temperature and high-temperature stable.In this work,hexaaluminate catalysts LaMeAl11O19（Me=Mn、Fe、Co、Ni、NiCe）were prepared by co-precipitation method. The catalysts were characterized by means of XRD, BET, XPS, in-siut DRIFT and the catalyst activity in the catalytic combustion of simulating gasified biomass （3%CO、2%H2、1%CH4、500ppmNH3、balance N2） was test in a tubular quartz reactor. The effect of diffrent transition-metal ions substiuttion on catalytic structure and combustion activity was investgiated.It is found that the percursosr were aclcined at 1200℃for 4 hours leads to the formation of a final monophasic materials with a MP structure and maintain high surface areas. In these structures, the valence state of La, Al and O is respectively La3+, Al3+, O2-. As far as trnasition metalions is concerned, the introduecd Fe ions is trivalent, Co and Ni ions is both dvialent, whereas the Mn ions is either dvialent or tvriaient.The prepared substituted hexaaluminate catalysts are active in the catalytic combustion. In particular the Fe- and Mn-substituted samples show the highest activity in the combustion of methane, which is the least active biogas fuel. Ni-substituted samples have the maximum burning rate, and doping of Ce can obviously improve catalytic activity. The oxidation of NH3 follows closely that of CO for all catalysts. Generally the selectivity for NOX is proportional to the oxidation activity of the catalyst and ammonia contained in the biogas is oxidized to N2 but large amounts of NO are also formed, and little NO2 is formed under high tempreture. In whole process of combustion, the concertration of N2O is digit ppm. The results of in-situ DRIFT and combustion test show that ammonia contained in the gas is oxidized by an imide （NH） mechanism, in which the first step yields NH, and then the NH reacts with atomic oxygen （O） to form nitroxyl （HNO） and further conversion to N2 or nitrous oxide （N2O）, or NH could even react with molecular O2 to produce nitric oxide （NO）.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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