Selective catalytic reduction of NO by H2 in O2 on Pt/BaO/Al2O3 monolith NOx storage catalysts☆
Selective catalytic reduction of NO by H2 in O2 on Pt/BaO/Al2O3 monolith NOx storage catalysts☆
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DOI：
10.1016/j.apcatb.2007.11.038
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发表时间：
2008-06
影响因子：
22.1
通讯作者：
R. D. Clayton;M. Harold;V. Balakotaiah
中科院分区：
文献类型：
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作者：
R. D. Clayton;M. Harold;V. Balakotaiah
在一系列Pt、Pt/BaO和BaO整体式催化剂上进行了NO选择性催化还原的稳态实验，考察了原料组成、温度和催化剂组成对起燃、NOx转化率和产物分布的影响。NO和H2之间的反应产生含有N2 O、NH3和N2的混合物，其组成是催化剂温度和进料中NO/H2比的函数。NO抑制反应在低温下所揭示的起燃温度和支持动力学数据。NOx的转化在空速低于90，000 h − 1和高于100°C时完成，Pt负载量超过1.27wt.%。在低温和O2浓度下，NO-H2反应主要生成N2 O，H2（NO）为正（负）级。NO-H2体系的起燃温度取决于这些动力学以及Pt负载。补充的理论分析阐明选定的动力学趋势和Pt负载对转化率与温度的趋势的影响。NO-H2-O2数据用唯象反应网络模型进行了解释。特别关注的是氨的生产和消费，这是传统的氮氧化物储存和减少（NSR）过程中的一个有问题的副产品。NH3是一个主要的产品在O2不足的条件下，典型的丰富的脉冲在NSR，而N2和N2 O是主要产品在较高的O2浓度（贫条件）。NH3氧化在170-180°C下在Pt催化剂上点燃;在点燃状态下产生N2、NO、NO2和N2 O的混合物，其组成对NH3/O2进料比和温度敏感。实验涉及进料含有H2，NH3，和NO显示完全H2转化和可忽略的净NH3转化。对于超过150°C的温度，三种组分的等摩尔混合物导致通过H2完全还原NO，而NH3的转化可以忽略不计。在330°C以上观察到NH3的分解，但在动力学上被H2抑制。Pt和Pt/BaO催化剂的比较揭示了类似的稳态行为。与Pt和Pt/BaO催化剂相比，BaO催化剂表现出不可忽略但较低的活性和不同的产物分布。
Comprehensive steady-state experiments of the selective catalytic reduction of NO on a series of Pt, Pt/BaO, and BaO monolithic catalysts have been carried out to evaluate the light-off, NOxconversion and product distribution features as a function of the feed composition, temperature and catalyst composition. The reaction between NO and H2produces a mixture containing N2O, NH3, and N2, the composition of which is a function of the catalyst temperature and NO/H2ratio in the feed. NO inhibits the reaction at low temperatures as revealed by light-off temperature and supporting kinetic data. NOxconversions were found to be complete at space velocities below 90,000h−1and above 100°C for Pt loadings exceeding 1.27wt.%. At low temperature and O2concentration the NO–H2reaction mainly produces N2O and is positive (negative) order in H2(NO). The light-off temperature of the NO–H2system is dictated by these kinetics as well as the Pt loading. Complementary theoretical analyses elucidate selected kinetic trends and the effect of Pt loading on the conversion versus temperature trends. The NO–H2–O2data are interpreted with a phenomenological reaction network model. Particular attention focused on the production and consumption of ammonia, a problematic byproduct during conventional NOxstorage and reduction (NSR). NH3is a major product under O2deficient conditions typical of the rich pulse in NSR, while N2and N2O are the main products at higher O2concentrations (lean conditions). NH3oxidation ignites on Pt catalysts at 170–180°C; in the ignited state a mixture of N2, NO, NO2and N2O is produced, the composition of which is sensitive to the NH3/O2feed ratio and temperature. Experiments involving a feed containing H2, NH3, and NO show complete H2conversion and negligible net NH3conversion. For temperatures exceeding 150°C an equimolar mixture of the three components results in complete NO reduction by H2with negligible conversion of NH3. The decomposition of NH3is observed above 330°C but is kinetically inhibited by H2. A comparison of the Pt and Pt/BaO catalysts reveals similar steady-state behavior. The BaO catalyst exhibited a non-negligible but lower activity and a different product distribution than the Pt and Pt/BaO catalysts.