Research On Preparation Of Mn Low-temperature SCR DeNO_x Catalyst By Combustion Method

Selective catalytic reduction?SCR?technology is one of the current mainstream deNOx technologies.With the improvement of environmental protection requirements for cement,waste incineration and other industries,the demand and requirements for low-temperature SCR catalysts have increased.At present,the V-Ti catalyst is the main commercial catalyst.However,V-Ti catalyst not only can't meet the current low-temperature requirements but also has environmental problems such as recycling difficulties.Therefore,it is urgent to develop new SCR catalysts suitable for low temperature.As far as the research of low-temperature SCR technology at home and abroad is concerned,it is mainly faced with problems such as low temperature activity,narrow temperature window,current method not suitable for large-scale industrial production,and unclear reaction mechanism.Aiming at the above problems,this paper proposes a new method of combustion for preparing Mn-based low-temperature SCR catalyst.And besides,systematically studies the preparation of SCR catalyst by combustion method and explores the preliminary process of this method.In this paper,the catalyst prepared by combustion method was compared with the hydrothermal method.The characteristics of the catalyst prepared by combustion method was investigated through a series of characterizations.According to the results,?1?The pore structure of the Mn-based low-temperature SCR deNOx catalyst prepared by the combustion method is a foamed structure,which can effectively increase the residence time of the gas inside the pores,and form an adsorption desorption curve different from that of the hydrothermal preparation catalyst;?2?The catalyst prepared by the combustion method has a larger specific surface area and a smaller grain size,thereby having higher catalytic activity;?3?Mn ion have higher surface valence state and more Ce³⁺ion prepared by combustion,so that the catalyst has more acidic sites,which is conducive to better low-temperature reduction ability;?4?The MnO_x-CeO₂catalyst prepared by the combustion method and the hydrothermal method has various crystal forms of MnO_x on the phase,the combustion method is mainly Mn₃O₄,and the hydrothermal method is mainly Mn₂O₃.In order to investigate the influence mechanism of different MnO_x crystal forms on the catalytic performance of SCR catalysts,the stability and adsorption energy of various MnO_x crystal forms were studied by density functional theory.Secondly,in this paper,the effect of precursor pH on the structure and properties of MnO_x-CeO₂ catalyst was studied for the combustion process parameters.Through chemical calculation and experimental verification,the optimum Mn/Ce ratio is 6:1,and the precursor solution is around pH=5.The results show that:?1?In the preparation of sol,Mn ions need to be fully complexed at pH above 5;?2?with the increase of ammonia addition,the specific surface area of the catalyst increases,and the foaming condition is excellent.?3?As the amount of ammonia added increases,the self-propagating combustion temperature of the dry gel will gradually increase;?4?The increase of combustion temperature will cause the crystal form of Mn₂O₃ to Mn₃O₄.Through the systematic research in this paper,a new method for preparing Mn-based low-temperature SCR catalyst by combustion method is proposed.Compared with the previously reported preparation methods of Mn-based SCR catalysts,the method can form a unique pore structure,more acidic sites and a more low-temperature reducing surface capable of performing SCR reaction at a lower temperature.In addition,the preliminary process of the combustion method has been explored to lay the foundation for future industrial application.Finally,the Mn-Ce/TiO₂ low temperature deNOx catalyst with TiO₂ as carrier was prepared by combustion method,and the catalytic activity of the catalyst was tested.The results show that the MnO_x?6?-CeO₂?SA?/TiO₂ low-temperature deNOx catalyst prepared by combustion method with MnO_x addition content of 5wt%can achieve more than 90%deNOx efficiency at 150°C,which is better than MnO_x prepared by hydrothermal method.The research in this thesis shows that compared with the previously reported preparation methods of Mn-based SCR catalysts,the new preparation process of combustion method can form unique pore structure,more acidic sites,and stronger low temperature reduction.According to this thesis,the experimental research and theoretical investigation of the preparation process of combustion method have a good significance for the industrialization of low temperature deNOx catalyst.