Reaction distributions in diesel emissions catalysts

了解柴油排放催化剂目前的预测表明，相对于汽油发动机，用于乘用车的柴油发动机将会增加。巧合的是，世界上大多数国家即将出台的环境政策都要求大幅减少柴油发动机尾气中的氮氧化物和颗粒物排放。为了满足这些需求，人们正在开发新技术。其中一项技术是NOX储存/还原（NSR），其中NOX以硝酸盐的形式储存在催化剂上，并定期还原为N2。另一种是催化微粒过滤器，其中微粒物质（烟灰）被捕获在过滤器上并定期氧化成二氧化碳。这两种技术都打破了传统的催化剂性能表征，因为不需要进行与稳态相关的操作，而且反应动力学、表面物质和温度具有明显的轴向分布。为了成功地建模、控制和优化氮氧化物减少和颗粒去除，需要了解这些参数梯度。我们就柴油排放控制提出的短期目标包括：-发展“噪音感应强”循环的机制描述；-评价硫与NSR催化剂体系的相互作用；烟灰氧化在烟灰过滤器上的传播演示。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在柴油发动机上实施噪音感应和烟尘过滤技术，并显著减少废气排放。此外，如果NSR技术确实被证明是有效的，那么它也适用于稀燃汽油发动机，这将导致二氧化碳排放的减少和燃料的节省，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.