鈀負載型稀燃NO_x存儲還原催化劑的制備及性能研究
發(fā)布時間：2019-02-14 07:24
【摘要】：稀薄燃燒技術(shù)是近幾十年提出的一種有效的機內(nèi)凈化技術(shù)。稀燃發(fā)動機具有燃油經(jīng)濟性好、燃燒效率高的特點,但由于較高的空燃比導(dǎo)致尾氣中NO_x含量升高且不易去除,NO_x已成為稀燃機動車尾氣中的主要污染物。NO_x存儲/還原(NSR)技術(shù)被認(rèn)為是稀燃發(fā)動機去除NO_x的最有效的方法之一,其中高活性的NSR催化劑是技術(shù)的關(guān)鍵。傳統(tǒng)的NSR催化劑Pt-BaO/Al2O3成本高,低溫活性和穩(wěn)定性較差,因此有必要開發(fā)更加經(jīng)濟高效的NSR催化劑。本文以組成可調(diào)變的類水滑石層狀納米材料為催化劑前驅(qū)物,制備出多活性位點、高分散的系列CuMgAlFe介孔復(fù)合氧化物以及貴金屬負載的系列Pd-K/CuMgAlFe新型NSR催化劑,采用XRD、BET、FT-IR、SEM、H_2-TPR等現(xiàn)代表征手段研究催化劑的晶相結(jié)構(gòu)、表面性質(zhì)、微觀形貌、孔結(jié)構(gòu)特性和氧化還原能力等理化性質(zhì),通過恒溫靜態(tài)NO_x吸/脫附、貧富燃循環(huán)動態(tài)實驗測試催化劑NO_x的存儲還原活性,利用原位紅外技術(shù)研究NO_x在催化劑表面的吸附物種和存儲路徑。主要工作和研究結(jié)果如下。采用共沉淀法制得過渡金屬Cu和Fe部分取代的類水滑石前驅(qū)物,通過焙燒獲得了以MgO為主晶相的介孔復(fù)合氧化物催化劑(CuMgAl、MgAlFe和CuMgAlFe)。該體系催化劑具有較高比表面積(160~180 m~2·g~(-1)),CuMgAl和CuMgAlFe催化劑表現(xiàn)出較高的氧化還原性能。Cu和Fe雙摻雜提高了催化劑的NO_x存儲能力,這與材料表面Cu物種和Fe物種的強相互作用有關(guān),CuMgAlFe催化劑在300oC恒溫靜態(tài)吸附NO_x時NO_x存儲量為216μmol·g-1。在CuMgAlFe催化劑上,NO_x存儲有兩種路徑: 亞硝酸鹽路徑‖和 硝酸鹽‖路徑。 亞硝酸鹽路徑‖:NO與Mg(Al)O載體上的堿性氧反應(yīng)生成亞硝酸鹽,隨后亞硝酸鹽被進一步氧化成硝酸鹽; 硝酸鹽‖路徑:NO在過渡金屬位點被氧化成NO_2,隨后溢流到臨近的Mg位點形成硝酸鹽。以類水滑石為前驅(qū)物,制備了貴金屬Pd負載的介孔復(fù)合氧化物催化劑(MgAl、PdMgAl和PdCuMgAl)。與MgAl樣品相比,Pd和Cu引入類水滑石層結(jié)構(gòu)大大提高了衍生復(fù)合氧化物催化劑的比表面積(160~190 m~2·g~(-1))和孔體積,這有助于反應(yīng)過程中氣體分子的擴散,也有利于PdO和CuO活性物種的分散;Pd和Cu同時負載對催化劑氧化還原能力的提升具有協(xié)同作用。Pd負載后提高了催化劑NO_x的存儲能力,這與孔結(jié)構(gòu)性質(zhì)的改善和氧化還原能力的提高有關(guān)。原位紅外研究發(fā)現(xiàn),300oC恒溫靜態(tài)吸附NO_x時,在MgAl催化劑上,NO_x全部以亞硝酸鹽的形式儲存,而在PdMgAl和PdCuMgAl催化劑上,硝酸鹽的存儲更占優(yōu)勢。在PdMgAl催化劑上,NO_x存儲遵循亞硝酸鹽路徑,而PdCuMgAl催化劑上,NO_x存儲則遵循硝酸鹽路徑,表明Pd和Cu的相互作用增強了催化劑的氧化還原能力和存儲能力。以CuMgAlFe復(fù)合氧化物為載體,通過浸漬法制備了Pd和K負載的多活性位點、高分散系列新型NSR催化劑(Pd/CuMgAlFe、K/CuMgAlFe和Pd-K/CuMgAlFe)。研究表明所有催化劑呈現(xiàn)MgO晶相,Pd和K共負載提高了表面PdO物種的可還原性。NO_x吸脫附實驗表明,K負載后提高了催化劑的NO_x存儲能力和存儲硝酸鹽物種的穩(wěn)定性,Pd-K/CuMgAlFe的NO_x存儲能力可達1766μmol·g-1。Pd和K共負載對增強NSR催化劑NO_x存儲能力具有協(xié)同作用,這可能與材料氧化還原性能的提高和堿性的改善有關(guān)。原位紅外表征發(fā)現(xiàn)NO_x在CuMgAl Fe和Pd/CuMgAlFe催化劑上存儲遵循亞硝酸鹽路線,最終存儲物種為硝酸鹽;K/CuMgAlFe催化劑上NO_x以大量亞硝酸鹽和硝酸鹽的形式存儲;Pd-K/CuMgAl Fe催化劑上,Pd和K共負載促進了表面亞硝酸鹽的分解。模擬汽車尾氣氣氛,在貧燃(120 s)和富燃(60 s)循環(huán)交替的動態(tài)條件下研究了催化劑的NSR性能,結(jié)果表明K/CuMgAlFe、Pd-K/Cu MgAlFe催化劑的NO_x去除率較高:150oC時NO_x平均去除率在70%左右,300oC和450oC時去除率均在85%以上。
[Abstract]:The lean combustion technology is a kind of effective internal purification technology that has been put forward in recent decades. The lean-burn engine has the characteristics of good fuel economy and high combustion efficiency, but because of higher air-to-air ratio, the content of NO _ x in the tail gas is increased and is not easy to be removed, and the NO _ x has become the main pollutant in the tail gas of the lean-combustion motor vehicle. The NO _ x storage/ reduction (NSR) technique is considered one of the most efficient methods for the removal of NO _ x from a lean burn engine, where the high activity NSR catalyst is the key to the technology. The traditional NSR catalyst Pt-BaO/ Al2O3 is high in cost, low in low-temperature activity and poor in stability, and therefore it is necessary to develop a more economical and efficient NSR catalyst. In this paper, a series of Pd-K/ CuMgAlFe-based NSR catalysts with a multi-active site, a high-dispersion series of CuMgAlFe mesoporous composite oxides and a noble metal load are prepared by using a composition-adjustable hydrotalcite-like layered nano-material as a catalyst precursor. The novel NSR catalyst is characterized by XRD, BET, FT-IR and SEM. The crystal phase structure, surface property, micro-morphology, pore structure and oxidation-reduction ability of the catalyst were studied by the modern characterization means such as H _ 2-TPR and the like, and the storage and reduction activity of the catalyst NO _ x was tested by the constant temperature static NO _ x suction/ desorption, the rich and poor combustion cycle dynamic experiment. The adsorption species and storage path of NO _ x on the surface of the catalyst were studied by in-situ IR technology. The main work and study results are as follows. A composite oxide catalyst (CuMgAl, MgAlFe and CuMgAlFe) with MgO as the main crystal phase was obtained by co-precipitation. The catalyst has a higher specific surface area (160 ~ 180 m ~ 2 路 g ~ (-1)), and the CuMgAl and CuMgAlFe catalysts show high redox properties. Cu and Fe double doping increase the NO _ x storage capacity of the catalyst, which is related to the strong interaction of the Cu species and the Fe species on the surface of the material. The amount of NO _ x stored at the constant temperature static adsorption of NO _ x at the constant temperature of 300oC is 216 & mu; mol 路 g-1. 鍦–uMgAlFe鍌寲鍓備笂,NO_x瀛樺偍鏈変袱縐嶈礬寰，
本文編號：2421968
[Abstract]:The lean combustion technology is a kind of effective internal purification technology that has been put forward in recent decades. The lean-burn engine has the characteristics of good fuel economy and high combustion efficiency, but because of higher air-to-air ratio, the content of NO _ x in the tail gas is increased and is not easy to be removed, and the NO _ x has become the main pollutant in the tail gas of the lean-combustion motor vehicle. The NO _ x storage/ reduction (NSR) technique is considered one of the most efficient methods for the removal of NO _ x from a lean burn engine, where the high activity NSR catalyst is the key to the technology. The traditional NSR catalyst Pt-BaO/ Al2O3 is high in cost, low in low-temperature activity and poor in stability, and therefore it is necessary to develop a more economical and efficient NSR catalyst. In this paper, a series of Pd-K/ CuMgAlFe-based NSR catalysts with a multi-active site, a high-dispersion series of CuMgAlFe mesoporous composite oxides and a noble metal load are prepared by using a composition-adjustable hydrotalcite-like layered nano-material as a catalyst precursor. The novel NSR catalyst is characterized by XRD, BET, FT-IR and SEM. The crystal phase structure, surface property, micro-morphology, pore structure and oxidation-reduction ability of the catalyst were studied by the modern characterization means such as H _ 2-TPR and the like, and the storage and reduction activity of the catalyst NO _ x was tested by the constant temperature static NO _ x suction/ desorption, the rich and poor combustion cycle dynamic experiment. The adsorption species and storage path of NO _ x on the surface of the catalyst were studied by in-situ IR technology. The main work and study results are as follows. A composite oxide catalyst (CuMgAl, MgAlFe and CuMgAlFe) with MgO as the main crystal phase was obtained by co-precipitation. The catalyst has a higher specific surface area (160 ~ 180 m ~ 2 路 g ~ (-1)), and the CuMgAl and CuMgAlFe catalysts show high redox properties. Cu and Fe double doping increase the NO _ x storage capacity of the catalyst, which is related to the strong interaction of the Cu species and the Fe species on the surface of the material. The amount of NO _ x stored at the constant temperature static adsorption of NO _ x at the constant temperature of 300oC is 216 & mu; mol 路 g-1. 鍦–uMgAlFe鍌寲鍓備笂,NO_x瀛樺偍鏈変袱縐嶈礬寰，
本文編號：2421968
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