Study on the Simultaneous Catalytic Removal of Diesel Soot Particulates and Nitrogen Oxides

本研究旨在开发一种新的柴油机尾气后处理催化系统，即同时去除NOx和柴油机微粒（PM）。钙钛矿型（ABO_3）、K_2NiF_4型（A_2BO_4）和尖晶石型（AB_2O_4）氧化物同时去除NOx和PM的催化活性显著依赖于A位和B位金属阳离子。总的来说，含Co和Mn的复合金属氧化物对NOx还原为N2的反应活性高，但选择性低，而含Cu和Fe的复合金属氧化物对NOx还原为N2的反应活性中等，选择性高。碱金属离子的加入，特别是K的加入，对提高催化剂的活性和选择性都是非常有效的。混合金属氧化物的NOx还原选择性上级过渡金属简单氧化物、它们的机械混合物和负载型Pt催化剂 ...更多信息 NOx和O_2。NO_2对降低颗粒物着火温度是有效的，O_2与NOx共存是促进NOx还原成N_2的必要条件。在此基础上，提出了一种可能的同时脱除NOx和PM的反应机理：O2将NO氧化为NO2，NO2解离吸附生成活性氧（O2<ad>），O2活化形成表面碳物种（中间体）<ad>，气态氧对中间体的进攻<0.9><0.1>。直接从真实的柴油机排气中捕集颗粒物后，在模拟的柴油机排气流中进行NOx-颗粒物的同时去除反应。这一结果有力地表明了本发明的同时去除NOx和PM的工艺在实际应用中的潜力。少

The present study has aimed to develop a new after-treatment catalytic system for diesel exhausts, socalled the simultaneous removal of NOx and diesel particulates (PM). The catalytic activity of perovskite-type (ABO_3), K_2NiF_4-type (A_2BO_4) and spinel-type (AB_2O_4) oxides for the simultaneous NOx-PM removal depended significantly on A- and B-site metal cations. Generally speaking, mixed metal oxides containing Co and Mn showed high activity but low selectivity to NOx reduction into N_2, while those containing Cu and Fe were excellent catalysts with moderate activity and high selectivity. The addition of alkali metal ions, especially K,was quite effective in promoting both the activity and selectivity. The mixed metal oxides were superior to transition metal simple oxides, their mechanical mixtures and supported Pt catalysts in the selectivity for NOx reduction.The mechanism of the simultaneous NOx-PM removal reaction was investigated by measuring the effect of gaseous composition … More of NOx and O_2. Nitrogen dioxide (NO_2) was effective for the ignition temperature of PM to decrease, and coexistence of O_2 with NOx was indispensable to enhance the NOx reduction into N_2. Based on the results, a possible reaction mechanism for the simultaneous NOx-PM removal was proposed which involves the oxidation of NO into NO_2 by O_2, the dissociative adsorption of NO_2 to give active oxygen species (O_<ad>), the formation of surface carbon species (intermediate) activated by O_<ad> and the attack of gaseous oxygen to intermediate.Honeycomb PM filter loaded with perovskite-type La_<0.9>K_<0.1>CoO_3 catalyst (catalytic filter) was prepared as a prototype of practical catalysts. After PM being trapped on the catalytic filter directly from the real diesel exhaust, the simultaneous NOx-PM removal reaction was performed in the flow of simulated diesel exhaust. The result strongly suggests the potentiality in the practical application of the present simultaneous NOx-PM removal process. Less