부산대학교 도서관

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/0926-3373(96)00029-X Byline: Karen M. Adams, John V. Cavataio, Robert H. Hammerle Abstract: European Stage III emissions requirements will be difficult to meet for diesel passenger cars if lean NO.sub.x catalysts are not available. Current prototype lean NO.sub.x technology for diesels consists of Pt based and Cu zeolite catalysts. Both types have been examined for this study. The former is most active at low temperatures, approximately 190-250[degrees]C. The latter has optimum activity at higher temperatures, usually above 350[degrees]C. Maximum flow reactor activity of 40-55% NO.sub.x conversion (25 000-50 000/h space velocity) has been measured for Pt catalysts using a synthetic feedgas. During the MVEuro2 driving cycle, 35-40% of mass NO.sub.x has been emitted at inlet catalyst temperatures from 120 to 200[degrees]C. These temperatures fall below optimum temperatures for current Pt based lean NO.sub.x catalysts. For temperatures above 350[degrees]C, where Cu zeolite catalysts are active, one vehicle has emitted ca. 30% of mass NO.sub.x during MVEuro2. These high temperatures are achieved during high speed, hard acceleration driving; although attained briefly during the MVEuro2 cycle, these high temperature emissions could be a critical contribution under customer driving conditions. Effects of sulfur dioxide (SO.sub.2) and space velocity (SV) have been investigated as part of a strategy to optimize NO.sub.x removal with lean NO.sub.x catalysts. Elimination of feedgas SO.sub.2 can lower NO.sub.x light off temperature for both Pt and Cu zeolite. Some Pt catalysts do not show this behavior. Additional evaluation of a Cu zeolite catalyst demonstrates that poisoning by feedgas SO.sub.2 is reversible during evaluation or aging. This result suggests that if sulfur could be removed from diesel fuel, aged Cu zeolite catalysts could be practical. Decreasing space velocity will help NO.sub.x removal over Pt by (i) lowering NO.sub.x light off temperature, (ii) lowering the temperature at which peak NO.sub.x conversion occurs, (iii) increasing the level of peak NO.sub.x conversion, and (iv) widening the temperature window for NO.sub.x reduction. For Cu zeolite, decreasing space velocity can help mainly by lowering NO.sub.x light off temperature and temperature where maximum NO.sub.x conversion starts. Both increased catalyst volume and sulfur removal provide Pt catalysts with a NO.sub.x temperature window that coincides better with low temperatures where most NO.sub.x mass is emitted. SV effects on lean NO.sub.x reduction are explained by discussion of possible mechanistic features. Author Affiliation: Ford Motor Company, Scientific Research Laboratories, MD 3179, P.O. Box 2053, Dearborn, MI 48121, USA Article History: Received 6 October 1995; Revised 23 January 1996; Accepted 23 January 1996