钙钛矿型La_(0.5)Sr_(0.5)CoO_(3)催化剂的制备及其NO_(x)储存性能

Preparation of La_(0.5)Sr_(0.5)CoO_(3) perovskite catalyst and its performance for NO_(x) storages

【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_(0.5)Sr_(0.5)CoO_(3)(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=1889µmol·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=1434µmol·g^(-1),S=1262µmol·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。

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_(0.5)Sr_(0.5)CoO_(3)(LSC)catalyst was synthesized utilizing the glycine-assisted solution com⁃bustion 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).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 NO_(2) in the atmosphere remained stable.The relative NO_(2) reduction(RNO2)of the catalyst followed the sequence:φ=1.6(65%)>φ=2.4(51%)>φ=0.8(49%).Notably,the LSC catalyst synthesized withφ=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 SrCO_(3) 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 calcina⁃tion temperature of 700℃exhibited reduced SrCO_(3) 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.Hydrother⁃mal aging resulted in an increased SrCoO_(x) phase and a decreased SrCO_(3) phase on the catalyst surface,consequently reducing its NO_(x) storage performance.Nonetheless,it is worth noting that nitrate species formed on the surface of SrCO_(3) exhibited high ther⁃mal stability,thereby maintaining excellent NO_(x) storage performance even after hydrothermal aging.Conclusion 1)LSC catalysts prepared under variousφvalues and calcination temperatures predominantly exhibited perovskite crystalline phases,with minor traces of SrCO_(3) and SrCoO_(x) crystalline phases.Notably,whenφwas set to 1.6 and calcination temperature to 700℃,the catalyst demonstrated the highest capacity for NO_(x) adsorption 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 NO_(x) storage capacity was significantly influenced by the presence of SrCO3 species within the perovskite structure,with an optimal quantity of SrCO_(3) species favorable for NO_(x) adsorption and storage.However,excessive SrCoO_(x) content could obstruct active Sr-Co sites,reducing contact with the reaction gas,and diminishing NO_(x) storage capacity.3)After vulcanization,all LSC catalysts exhibited a pure perovskite structure without sulfur-containing species.Following hydrothermal aging,the catalyst primarily comprised the perovskite crystal phase,with a small amount of SrCO_(3) and SrCoO_(x)het⁃erophase.While hydrothermal aging promoted the growth of the perovskite structure and SrCoO_(x) phase,it inhibited SrCO_(3) phase growth.Despite declines in NO_(x) adsorption capacity(A)and relative NO_(2) reduction(R_(NO2))post-treatment,the LSC catalyst maintained strong resistance,and retained high NO_(x) storage capacity,with A values of 1434 and 1262μmol·g^(-1) after vulcanization and hydrothermal aging,respectively.