Reaction distributions in diesel emissions catalysts

目前的预测表明，相对于汽油发动机，乘用车用柴油发动机将增加。巧合的是，世界大部分地区即将出台的环境政策将显著降低柴油发动机的尾气NOX和颗粒物排放。为了满足这些需求，正在开发新的技术。一种这样的技术是NOX存储/还原(NSR)，其中NOX以硝酸盐的形式存储在催化剂上，并定期还原为氮气。另一种是催化颗粒过滤器，颗粒物(烟尘)被捕获在过滤器上，并定期氧化为二氧化碳。这两种技术与传统的催化剂性能表征技术不同，没有与稳态相关的操作，反应动力学、表面物种和温度有显著的轴向分布。为了成功地模拟、控制和优化NOX减少和颗粒物去除，需要了解这些参数梯度。我们提出的关于柴油排放控制的短期目标包括：-开发NSR循环的机理描述；-评估硫与NSR催化剂系统的相互作用；以及-展示煤烟氧化在煤烟过滤器上的传播。这项研究工作的一个规划目标是开发和验证实验方法，以评估催化反应过程作为催化剂系统内轴向位置的函数。该项目的成功将促进NSR和烟尘过滤器技术在柴油发动机上的实施，并产生显著更清洁的废气。此外，如果NSR技术被证明是有效的，那么它也适用于稀燃汽油发动机，这将导致二氧化碳排放减少和燃料节省，从而抑制当前的燃料需求。

UNDERSTANDING DIESEL EMISSIONS CATALYSTS      Current predictions indicate that diesel engines for passenger vehicles will increase relative to gasoline engines. Coincidentally, upcoming environmental policy throughout most of the world is imposing significant decreases in tailpipe NOX and particulate emissions from diesel engines. New technologies are being developed to meet these demands. One such technology is NOX storage/reduction (NSR) where NOX is stored as nitrates on a catalyst and periodically reduced to N2. Another is catalyzed particulate filters, where particulate matter (soot) is trapped on a filter and periodically oxidized to CO2. With both of these technologies, there is a break with traditional catalyst performance characterization in that there is no steady-state related operation and there are significant axial distributions of reaction kinetics, surface species and temperature. These parameter gradients need to be understood in order to successfully model, control and optimize NOX reduction and particulate removal. Our proposed, short-term objectives with respect to diesel emission control include: - the development of a mechanistic description of the NSR cycle; - evaluation of the interaction of sulfur with the NSR catalyst system; and - demonstration of the propagation of soot oxidation on a soot filter. A programmatic goal of this research effort is the development and validation of experimental methodologies for evaluating catalytic reaction processes as a function of axial position inside a catalyst system. The success of this program will facilitate the implementation of NSR and soot filter technologies onto diesel engines and result in significantly cleaner exhaust. Furthermore, if the NSR technology does prove effective, it is then applicable to lean-burn gasoline engines as well, which would result in CO2 emissions reductions and fuel savings thereby dampening current fuel demands.