La0.6Sr0.4Co0.95Cu0.05O3添加銀作為電觸媒陰極材料進行模擬廢氣中氮氧化物分解之研究

Study of adding Ag in La0.6Sr0.4Co0.95Cu0.05O3 as cathode material of electrochemical-catalytic cell on decomposition of nitric oxide in simulated exhaust

游家棋(Chia-Chi Yu)

指導教授 ： 黃大仁

國立清華大學/工學院/化學工程學系/碩士(2012年)

摘要

柴油引擎(diesel engine)為富氧燃燒引擎(lean-burn engines)的富氧燃燒雖能提高燃料的使用效率，現今的氮氧化物(NOX)的處理技術須更努力尋找新方法來解決此問題，此研究新技術著重於電化學觸媒電池(electrochemical-catalytic cells, ECC)能夠在中低溫時，通入富氧燃燒排放之模擬廢氣，更有效將其NOX轉換形成無害的N2與O2，並且將未燃燒完全之碳氫化合物(hydrocarbon)氧化形成無害的CO2與H2O。
在電化學觸媒電池的陽極處通入還原性氣體H2，因為其無發電效果，故H2並不會減少，而在陰極處通入富氧燃燒之引擎廢氣，經由電觸媒反應後，分析其出口氣體。富氧燃燒引擎主要包括氮氧化物(NOX)、氧氣(O2)、二氧化碳(CO2)、水氣(H2O)、二氧化硫(SO2)，研究於不同NOX、CO2、H2O混和模擬廢氣通入電化學觸媒電池與觸媒是否會因為其electro-motive force(EMF)而在NOX轉化率有所差別，並在不同溫度下通入丙烯(C3H6)、丙烷(C3H8)。實驗結果證明NOX轉化率隨著氧濃度增加而上升，而CO2對於電觸媒與觸媒都有促進效果，而H2O會毒化觸媒導致NOX轉化率下降，而H2O對於電觸媒則是有增進的效果，而在不同溫度下，由於NOX低濃度為表面擴散(surface diffusion)，故NOX轉化率隨著溫度越高而增加，NOX高濃度則是受到EMF的影響，隨著溫度上升，EMF轉化率下降，所以NOX的轉化率也隨之下降。
新式電觸媒為Zirconia tube，結構更為堅固，而且可以自由的升降溫，在不同NOX濃度下，其NOX轉化率也能展現出V curve，隨著通入NOX濃度上升而上升，而低濃度也隨著濃度下降轉化率上升。而不同氧濃度也能隨著氧濃度上升，EMF上升導致NOX的轉化率上升。而且隨著氧濃度的上升，N2 yield能夠有效的提升。在陰極不同的流速下，高流速表現出高N2 formation rate，低流速表現出高NO conversion。在高濃度NOX反應時，隨著溫度的下降，NOX轉化率明顯的提升，且操作溫度可以降至室溫反應，EMF的提升更表現出NOX的高轉化率。在長時間操作下，H2 flow與H2 stagnant的NO轉化率並不會差距太大，且通入不同氧濃度的情況下，模擬休息時通入20%O2，再通入原本NOX濃度，仍舊有高NO轉化率。在陽極積碳部分，在100oC積碳結果比未積碳前轉化率來的高，而在陽極通入He與H2所造成的EMF，是以H2的EMF較高，且NOX轉化率較佳。在CH4積碳部分，以600OC積碳4小時最佳，做V curve與不同氧濃度皆呈現高轉化率。

關鍵字

富氧燃燒引擎 ； 氮氧化物 ； 電化學催化觸媒電池

並列摘要

Diesel engine is a kind of lean-burn engines. Lean-burn engine can improve the efficiency of fuel using. Processing technology for nitric oxide should be more efforts to find new ways to solve this problem. The study of new technology is electrochemical-catalytic cells(ECC) that can used in low temperature. Inlet lean-burn engines exhaust gas can effective let nitric oxide transfer to nitrogen and oxides. And let not complete combustion of hydrocarbon transfer to carbon dioxide and water.
At ECC anode site inlet reducing gas which is hydrogen. Because of the ECC doesn’t generate power, the hydrogen will not be reduced. At ECC cathode site inlet exhaust gas, analysis the outlet gas which including NOX , O2, CO2, H2O and SO2 via reaction of ECC cathode. Study different the amount of NOX, CO2 and H2O inlet ECC that can be how much electro-motive force(EMF) is. EMF will improve the NOX conversion. At different temperature inlet propane and propene. The experiment show that NOX conversion increased with increasing oxygen concentration. In the catalytic site inleting H2O will decay the NOX conversion,but doesn’t occur in ECC. In low NOX concentration, the rate determine step(R.D.S.) is Nads diffusion. In high NOX concentration, the R.D.S. is rate equation. The NOX conversion increased with increasing NOX concentration.
The new electrochemical-catalytic cell is zirconia tube that the structure more hard then previously ECC. So it can free make thermal circle. At different NOX concentration, the NOX conversion is V curve with NOX concentration. The EMF and N2 yield increased with O2 concentration increasing. The different gas velocity at ECC cathode,the high gas velocity shows the high N2 formation rate;the low gas velocity shows the high NO conversion. And the high NOX concentration, the EMF increased with the temperature decreasing. At the anode site coking, at 100oC use the 1%CO coking 20 min that shows the high NOX conversion. The cause is that the coking carbon effectively increased the triple phase boundary(TPB).

並列關鍵字

NOx ； electrochemical-catalystic cell ； diesel engine

參考文獻

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