Development of a New Ceramic Substrate with Gas Flow Control Functionality

摘要

Emission regulations in many countries and regions around the world are becoming stricter in reaction to the increasing awareness of environment protections, and it has now become necessary to improve the performance of catalytic converters to achieve these goals. A catalytic converter is composed of a catalytically active material coated onto a ceramic honeycomb-structured substrate. Honeycomb substrates play the role of ensuring intimate contact between the exhaust gas and the catalyst within the substrate's flow channels. In recent years, high-load test cycles have been introduced which require increased robustness to maintain low emissions during the wide range of load changes. Therefore, it is extremely important to increase the probability of contact between the exhaust gas and catalyst. To achieve this contact, several measures were considered such as increasing active sites or geometrical surface areas by utilizing substrates with higher cell densities or larger volumes. These measures, however, led to greater consumption of precious metals and decreased vehicle power by increasing pressure losses. Therefore, a new concept substrate, which focuses on gas flow redistribution, has been developed to overcome these negatives. The key points of this development include a compound cell structure design which consists of a higher cell density area in the center portion of the substrate completely surrounded by a lower cell density area and optimization of the cell design for each portion to improve the efficiency of the catalytic converter. As a result, this newly developed honeycomb substrate shifts the trend line relationship of catalytic performance and pressure loss to a higher level. In addition, it reduces precious metal usage, as well as the volume of catalytic converters while maintaining catalytic performance equivalent to that of a conventional honeycomb substrate (400 cell density).