【作者】 李欢；

【导师】 杨剑；

【作者基本信息】 重庆大学 ， 材料与化工（专业学位）， 2024， 硕士

【摘要】 一氧化碳（CO）作为主要的大气污染物之一,对环境和人体健康构成了严重威胁。催化氧化法作为一种广泛采用且经济高效的CO脱除技术,其中催化剂是应用该技术的关键。虽然传统贵金属催化剂在低温CO氧化方面表现出色,但其高昂的成本限制了广泛应用。与之相比,钙钛矿型催化剂因其低成本和高催化活性成为替代贵金属催化剂的有力候选者。本课题组先前研究发现La-Mn基钙钛矿型催化剂在CO氧化反应中展现出优异性能,但鉴于环保治理的严峻形势,进一步对催化剂“降本增效”具有重要意义。本研究首先探索了FcarCS₃催化剂的结构调控策略,评估了制备条件对其催化效能的影响,并分析了催化剂的结晶过程。结果显示,柠檬酸用量对LaMnO₃催化剂在催化CO氧化反应中的性能具有决定性影响。确定最优制备条件为:前驱体溶液p H值为7、柠檬酸用量（柠檬酸与金属盐的摩尔比）为1.5、、焙烧温度为700℃、焙烧时间为4 h。催化剂结晶分为五个阶段,而形成完整钙钛矿结构的最低焙烧温度为700℃。在高温下,La与Mn氧化物之间的相互作用及化学反应是形成钙钛矿晶体结构的关键。为提高催化剂性能,本研究对LaMnO₃进行了A、B位掺杂改性。结果显示,A位掺杂Sr的La_0.6Sr_0.4Mn O₃催化剂在CO氧化反应中表现最优(T₉₀=180℃),而B位掺杂Cu的La Mn_0.6Cu_0.4O₃催化剂在低温下具有显著的活性(T₁₀<50℃),均优于原始LaMnO₃催化剂(T₁₀=112℃)。通过XRD、SEM、BET、XPS、TPR等多种表征手段的综合分析发现,A位掺杂改性主要通过改善织构特性和增强氧化还原性能来提升催化性能;B位掺杂改性则依赖于活性物质浓度的调整和低温氧化还原性能的提高。研究催化剂的反应机制对于优化其性能至关重要。本文通过分析LaMnO₃、La_0.4Sr_0.6Mn O₃和La Mn_0.6Cu_0.4O₃催化剂表面基团的变化,探讨了CO氧化反应的途径及机理。结果显示,这三种催化剂的CO氧化反应都遵循M-v K和E-R两种机制。在La_0.4Sr_0.6Mn O₃和La Mn_0.6Cu_0.4O₃催化剂中,M-v K机制更为关键,其反应途径为:预吸附的CO与晶格氧反应生成CO₂,随后CO₂分子脱附并在催化剂表面形成一个氧空位,然后气态O₂将催化剂表面重新氧化复原氧缺陷。而对LaMnO₃催化剂而言,E-R机制更为主导,其主要反应途径为:预先吸附的CO分子与催化剂表面进行电荷交换反应,形成CO₃碳酸盐中间体并分解生成CO₂产物。更多还原

【Abstract】 CO,as one of the main pollutants,poses a huge threat to ecological environment and human health.Ccatalytic oxidation is currently the most widely used and cost-effective technology,with catalysts being the core of those.Traditional precious metal catalysts have excellent low-temperature CO oxidation performance,but their high cost limits their widespread application.In comparison,perovskite-type catalysts have the advantages of low cost and high catalytic activity,and are currently one of the most promising choices to replace precious metal catalysts.In previous research,the La-Mn based perovskite-type catalyst has shown excellent performance in CO oxidation.However,it is of great significance to further"reduce costs and increase efficiency"of the catalyst in response to the increasingly severe environmental governance situation.In this study,the structural control methods of LaMnO₃ catalyst were investigated,the influence of preparation conditions on catalytic performance was explored,and the crystallization behavior of the catalyst was analyzed.The research results indicate that the amount of citric acid is the most significant factor affecting the catalytic oxidation performance of LaMnO₃ catalyst for CO.The optimal process parameters for the preparation of LaMnO₃ catalyst are as follows:the p H value of the precursor solution is7,the amount of citric acid（molar ratio of citric acid to metal salt）is 1.5,the calcination temperature is 700℃,and the calcination time is 4 hours.The crystallization process of the catalyst can be divided into five stages,and the lowest calcination temperature for the formation of a complete perovskite structure is 700℃.Under high-temperature conditions,the interaction and chemical reaction between La and Mn oxides are key factors in the formation of the perovskite crystal structure.To further enhance the catalytic performance of the catalyst,A and B-site doping modifications were conducted on the LaMnO₃ catalyst.The research results show that for La_0.6X_0.4Mn O₃（X=Sr,Ce,Ca）catalysts,A-site doping with Sr exhibits the best CO oxidation activity.Among them,the catalyst with a doping content of 0.6 shows the best catalytic activity(T₉₀=180℃).For La Mn_0.6Y_0.4O₃（Y=Co,Fe,Cu）catalysts,B-site doping with Cu shows excellent catalytic activity at low temperatures(T₁₀<50℃),which is significantly better than that of LaMnO₃ catalyst(T₁₀=112℃).Through comprehensive analysis of characterization results such as XRD,SEM,BET,XPS,and TPR,it was found that the improved catalytic performance of A-site-doped catalysts is mainly attributed to the improvement of textural properties and enhancement of redox performance,while for B-site-doped catalysts,it mainly depends on the variation of active species concentration and enhancement of low-temperature redox performance.Studying the reaction mechanism of the catalyst helps to discover performance optimization strategies.In this study,by investigating the surface functional groups changes of LaMnO₃,La_0.4Sr_0.6Mn O₃,and La Mn_0.6Cu_0.4O₃ catalysts,the pathway and reaction mechanism of CO oxidation on the catalyst surface were analyzed.The research results show that the CO oxidation reactions on the surfaces of the three catalysts simultaneously follow both M-v K and E-R mechanisms.For La_0.4Sr_0.6Mn O₃ and La Mn_0.6Cu_0.4O₃ catalysts,the M-v K mechanism plays a more important role,with the reaction pathway:the pre-adsorbed CO reacts with lattice oxygen to form CO₂,followed by the desorption of CO₂ molecules and the formation of an oxygen vacancy on the surface of the catalyst,and then gaseous O₂ re-oxidizes the surface of the catalyst to recover the oxygen defect.For LaMnO₃ catalyst,the E-R mechanism dominates,and the main reaction pathway is:the pre-adsorbed CO molecules react with the catalyst surface in a charge exchange reaction to form CO₃^2-carbonate intermediates and decompose to produce CO₂ products.更多还原