鈣鈦礦觸媒結合非熱電漿以儲存與還原NOx之可行性探討;Storage and reduction of NOx via combining nonthermal plasma and perovskite-type catalyst

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Title:	鈣鈦礦觸媒結合非熱電漿以儲存與還原NOx之可行性探討;Storage and reduction of NOx via combining nonthermal plasma and perovskite-type catalyst
Authors:	魏彤軒;Wei, Tong Syuan
Contributors:	環境工程研究所
Keywords:	氮氧化物;NOx儲存與還原;非熱電漿;柴油引擎;鈣鈦礦觸媒;Nitrogen oxides (NOx);NOx storage and reduction (NSR);diesel engine;Perovskite-type caralysts
Date:	2017-08-02
Issue Date:	2017-10-27 16:23:47 (UTC+8)
Publisher:	國立中央大學
Abstract:	Lean-burn 引擎具有較高之燃燒效率與低二氧化碳排放之優點，逐漸被廣泛應於重型柴油引擎及輕型柴油引擎。其排放氣體含有NOx及過多的氧氣，若沒有適當處置將會導致嚴重的NOx汙染。NOx被公認為重要的空氣汙染物，因為它會使環境及人體健康造成嚴重的影響。因此如何有效地還原NOx排放已經成為一個重要的議題。由於目前汽機車所使用之三元觸媒操作於過多氧氣條件下無法有效地將NOx還原成N2。NOx儲存與還原(NOx storage and reduction, NSR)已經被提出用於lean burn引擎中還原NOx。傳統NSR觸媒為Pt/BaO/Al2O3，此觸媒熱穩定性較薄弱，於低溫條件下(<400oC)無法有效將NOx還原成N2。最近，perovskite-type觸媒被考慮應用在NSR上，因為Perovskite-type觸媒具有較高的熱穩定性且活性能與貴金屬觸媒相比。因此，本研究是使用perovskite-type 觸媒去取代貴金屬觸媒並擔載於BaO/Al2O3探討NOx儲存能力。另外於Rich burn條件下結合非熱電漿(non-thermal plasma)探討低溫條件下NOx之還原能力。在Lean burn條件下之結果顯示SrKMn0.8Co0.2O4/BaO/Al2O3 (SKMCBA)觸媒於NO濃度200 ppm、反應溫度400oC、空間流速30,000 h-1、氧氣含量5%下具有最佳之NOx吸附能力(214 μmol/g)，但隨著氧氣含量提高，觸媒對NOx吸附能力明顯下降；另外若僅添加CO2或H2O(g)添加至系統中會降低觸媒對NOx吸附能力，但同時添加CO2及H2O(g)至系統中，可以減少NOx吸附之負面影響。在Rich burn條件下結合電漿還原NOx結果顯示16 kV電壓下就足以將NOx脫附並還原成N2(78%)；若氣氛通入加熱(150oC)之電漿系統中N2選擇性可以達83%；若加入1-2%之H2、CO、C3H6當作還原劑於加熱(150oC)之電漿系統中，N2之選擇性皆能達到85%以上。整體而言，非熱電漿結合本研究之perovskite-type觸媒能有效於低溫條件下脫附NOx並還原成N2。;Diesel engine has the advantage of high energy efficiency and it has been widely applied in industry and transportation. However, it can cause the severe emission of NOx if not properly treated. NOx is considered as an important air pollutant because it causes devastating effects on environment and human health. Hence, how to effectively reduce NOx emission has become an important issue. The concept of NOx storage and reduction (NSR) has been proposed to reduce NOx emission. The mechanisms of NSR over catalysts during lean/rich cycles can be generally divided into several steps: (1) oxidation of NO into NO2; (2) NOx (NO and NO2) sorption on the alkali and/or alkaline-earth sites in the form of nitrites or nitrates; (3) reducing agents (such as H2, CO, CxHy) evolution from the rich exhaust gas; (4) NOx release from the nitrite or nitrate sites; (5) NOx reduction to N2 . Traditionally, Pt/BaO/Al2O3 has been used for NSR. Recently, perovskite-type catalysts are considered for this application because their activities are comparable to noble metal catalysts for NSR. In this study, perovskite-type catalysts are used to replace noble metal catalysts, further perovskite is supported on BaO/Al2O3 to evaluate the NOx storage and reduction capability. The physicochemical properties of the catalysts (LSCBA, LSMCBA, SKMCBA, SKMCeB, SKCNBA) were characterized by XRD, SEM and BET, and the results indicate that 5 perovskites prepared possess good crystal phase, pore structures and specific surface area. SKMCBA shows good NOx storage capacity (NSC) (about 214 μmol/g ) compared to previous studies due to the high efficiency in adsorbing NO2. Various operating parameters which may affect NOx removal are also evaluated via a lab-scaled experimental setup for NSR, and the mechanisms are elucidated.
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