近年來，又愈來愈多有關汽機車尾氣在富氧條件下之NOx去除的研究，因為富氧的條件下去除汽機車尾氣可以節省油料的消耗。NOx 在富氧的條件下被觸媒所吸附儲存；而在缺氧的條件之下, 被儲存的NOx 會被還原成無害的N2。本研究利用濕式含浸法與反應沉澱法合成去除NOx的觸媒。在觸媒中加入可以作為吸附用的鹼土族（Ba，Sr）以作為吸附NOx之成分。另外再加入Ce與La作為提供氧氣儲存的成分。在鑑定樣品的物理性質上，藉掃描式電子顯微鏡與穿透式電子顯微鏡觀察顆粒大小；由氮吸附、脫附分析測定表面積；另外，對觸媒進行循環測試（cycle test），測試其吸附能力與反應性，並探討溫度對觸媒吸附力的影響與研究觸媒的吸附耐力測試。由實驗結果得知，利用反應沉澱法合成去除NOx的觸媒，雖然有極相同的成果，但由於反應沉澱法較為費時，而濕式含浸法在合成上較為簡便，故我們選用濕式含浸法。由一系列的濕式含浸法所得的觸媒比較，含有Ce的觸媒有較高的NO吸附能力；從實驗所得的圖形，可以知道被吸附的NO是由丙烯(C3H6)所還原而得氮氣。另外，比較Ce與La的效果，可以得知在反應一開始時，Ce的效果遠比La佳，因為La在一開始時吸附效果為零。但做耐力測試的結果，Ce與La有極相同的成果。由循環測試及耐力測試的結果作探討比較，我們得到最好的觸媒是利用濕式含浸法所配製的Pt2.5Ce30.5Ba33.4Al100 與 Pt2.5Ce22.5Ba41.7Al100，其中下標數字代表重量比。我們把濕式含浸法的觸媒做描式電子顯微鏡與穿透式電子顯微鏡分析，發現其顆粒為不規則與不均勻的聚集，顆粒大小約0.1μm到5.0μm，且為不規則的形狀，而且分散度不佳。 The performance and durability of NOx storage catalyst were studied. The catalysts were used to reduce nitrogen oxides from lean-burn condition. There are increasing interests in car engines in the lean-burn condition to improve fuel economy. In the catalysts, NOx emitted from an engine at lean A/F operation was stored and this stored NOx was reduced at rich-burn operation. The incipient-wetness impregnation and precipitation methods were used to synthesize the catalysts. The properties of the catalysts were characterized by scanning electron microscopy, transmission electron microscopy, N2 sorption. The catalysts were tested by the lean-rich cycle. The effects of reaction temperature for storage capacity and duration were also tested. To investigate the storage capability of the catalyst, the samples were prepared with different alkaline-earth metal additives and different rare-earth metal oxides. Comparing the effects of preparation methods between incipient-wetness impregnation and precipitation, both samples had similar storage capability, but the incipient-wetness impregnation was more convenient to synthesize the samples. Therefore, this method was used in this study. The transient experiments comprise a storing phase using a lean NO/O2/N2/C3H6/CO gas mixture, and a regeneration phase where the O2 flow was switched off. The De-NOx catalysts consisted of nonuniform aggregates of very small and distinct particles. The catalysts containing barium had better storage capability and duration. On the other hand, the catalyst containing cerium had a higher NO storage capability than that having no cerium.
