刘剑勋¹，王旭东²，姜若兰¹，赵心怡¹，干良然¹，刘 伟¹，亓海强¹，王仲鹏¹

（1. 济南大学 水利与环境学院，山东 济南 250022；2. 山东省枣庄生态环境监测中心，山东 枣庄 277800）

收稿日期：2023-11-09，修回日期：2024-02-24，上线日期：2024-04-19。

基金项目：国家自然科学基金项目，编号：21777055；山东省自然科学基金项目，编号：ZR2023MB100，ZR2021MB063。

第一作者简介：刘剑勋（1999—），男，硕士生，研究方向为环境功能材料开发与应用。E-mail：ljxxx1111@163. com。

通信作者简介：王仲鹏（1978—），男，教授，博士，科技部国家火炬计划专家，山东省优秀中青年科学家，山东省科技人才，博士生导师，研究方向为大气污染控制与催化技术。E-mail：chm_wangzp@ujn. edu. cn。

摘要：【目的】 提高 NO_x催化剂在中低温条件下的 NO_x储存还原能力，实现高效 NO_x储存还原。【方法】 采用甘氨酸辅助溶液燃烧法制备钙钛矿型La_0.5Sr_0.5CoO₃（LSC）催化剂，通过多种表征手段对催化剂的理化性质进行表征，研究甘氨酸与硝酸根物质的量比、煅烧温度等制备条件对催化剂理化性质、 NO_x储存性能以及催化剂的抗硫性和水热稳定性的影响。【结果】 所制备的 LSC 催化剂在 300 ℃条件下的 NO_x吸附、储存性能显著提高。当物质的量比为 1. 6、煅烧温度为700 ℃时，制得的LSC催化剂具有良好的NO_x吸附能力（A=1 889 µmol·g^-1）和NO_x储存能力（S=1048µmol·g^-1 ）；并且该催化剂经硫化及水热老化后仍保持良好的NO_x吸附、储存能力（A=1 434 µmol·g^-1，S=1 262 µmol·g^-1 ）。【结论】该催化剂具有较大的比表面积、较强的NO氧化能力以及存在适量的表面SrCO₃物相，使其具有良好的NO_x储存性能。

关键词：溶液燃烧法；钙钛矿；氮氧化物储存；甘氨酸

Abstract

Objective To enhance the NO_x storage and reduction capacity of NO_x catalysts under medium and low temperature conditions and achieve efficient NO_x storage and reduction performance， the development of an efficient and cost-effective catalyst for medium and low temperature NO_x storage and reduction is crucial.

Methods In this study， the perovskite La_0.5Sr_0.5CoO₃（LSC） catalyst was synthesized utilizing the glycine-assisted solution combustion method. The physicochemical properties of the catalyst were comprehensively characterized through various analytical techniques. The impact of preparation parameters， including the molar ratio of glycine to nitrate and calcination temperature， on the NO_x storage performance of the catalyst was systematically investigated. Furthermore， the sulfur resistance， hydrothermal stability， and NO_x storage mechanism of the LSC catalyst during NO_x storage were thoroughly examined.

Results and Discussion Based on the aforementioned characterization and experimental findings， the NO_x desorption curve depicted in Fig. 9 illustrated that altering the amount of glycine led to a shift in the temperature of the catalyst desorption peak towards higher values， consequently enhancing the stability of nitrate species. Specifically， at a glycine-to-nitrate ratio （φ） of 1.6， the catalyst exhibited the lowest desorption peak temperature， indicative of less stable nitrate species prone to releasing NO_x species. The order of NO_x adsorption capacity （A） and NO_x storage capacity （S） of the catalyst was as follows： LSC-1.6 > LSC-2.4 > LSC-0.8. Upon reaching equilibrium adsorption of NO_x，the concentrations of NO and NO₂ in the atmosphere remained stable. The relative NO₂ reduction （R_NO2） of the catalyst followed the sequence：φ=1.6（65%）>φ=2.4（51%）>φ=0.8（49%）. Notably， the LSC catalyst synthesized with φ=1. 6 exhibited the highest S，A，and R_NO2， attributed to its large specific surface area， robust NO oxidation capacity， and the presence of appropriate SrCO₃ species. Furthermore， the NO_x desorption curve in Fig. 10 revealed a shift of the catalyst desorption peak towards lower temperatures with increasing calcination temperature， indicating decreased stability of nitrate species at higher calcination temperatures. Specifically， the catalyst prepared at a calcination temperature of 700℃ exhibited reduced SrCO₃ content but possessed a larger specific surface area， pore volume，strong NO oxidation capacity， and effective reduction performance， thereby demonstrating good activity. The R_NO2 values were observed in the following order：700 ℃（63%），800 ℃（44%）， and 600 ℃（41%）. The NO_x storage phase in the LSC catalyst comprised perovskite and SrCO₃， with an appropriate amount of SrCO₃ species favoring NO_x adsorption and storage. However，an excessive presence of SrCoO_x could inhibit the active Sr-Co sites， thereby diminishing the NO_x storage capacity of the catalyst.Hydrothermal aging resulted in an increased SrCoO_x phase and a decreased SrCO₃ phase on the catalyst surface， consequently reducing its NO_x storage performance. Nonetheless， it's noteworthy that nitrate species formed on the surface of SrCO₃ exhibited high thermal stability， thereby maintaining excellent NO_x storage performance even after hydrothermal aging.

Conclusion 1） Under different φ values and calcination temperatures， the prepared LSC catalysts primarily exhibited perovskite crystalline phases， accompanied by a minor presence of SrCO₃ and SrCoO_x crystalline phases. Notably， when φ was set to 1.6 and the calcination temperature was 700 ℃， the prepared LSC catalyst demonstrated the highest capacity for NO_xadsorption and storage. The catalysts displayed a loose and porous structure with a spongy morphology. 2） The NO_x storage phase in the LSC catalyst primarily comprised perovskite and SrCO₃. The capacity for NO_x storage was significantly influenced by the presence of SrCO₃ species within the perovskite structure. An optimal quantity of SrCO₃ species was favorable for NO_x adsorption and storage. However， excessive content of SrCoO_x could result in the coverage of Sr-Co active sites， thereby impeding contact between the active site and the reaction gas， ultimately leading to a reduction in the NO_x storage capacity of the catalyst. 3）After vulcanization， all LSC catalysts exhibited a pure perovskite structure， with no presence of sulfur-containing species. Following hydrothermal aging， the LSC catalyst primarily comprised the perovskite crystal phase， accompanied by a small amount of SrCO₃ and SrCoO_xheterophase. The hydrothermal aging process promoted the growth of the perovskite structure and SrCoOxphase， while inhibiting the growth of the SrCO₃ phase. The NO_x sorption and desorption reaction demonstrated that varying degrees of decline in the NO_x adsorption capacity （A） and relative NO₂ reduction （R_NO2） of the catalysts post vulcanization and hydrothermal aging. Nevertheless， the LSC catalyst still exhibited strong resistance to both vulcanization and hydrothermal aging， retaining a high NO_xstorage capacity after both vulcanization and hydrothermal aging， with A values of 1 434 and 1 262 µmol·g^-1， respectively.

Keywords：solution combustion method； perovskite； NO_x storage； glycine

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