Novel Exhaust After Treatment Catalyst
The diesel engines are more efficient than their gasoline powered counterparts, and their widespread use in vehicles could significantly reduce fuel consumption. However, diesel engines have a serious drawback, which is their relatively high emissions of particulate matter (PM) and nitrogen oxides (NOx)(EPA, 2002). During cold starts, the emission of volatile organic compounds (VOCs) is also a concern. Recently, there have been significant breakthroughs in diesel particulate filters, however, the cost effective control of NOx and VOC emissions (during cold starts) remains unresolved. Reducing the emissions of these contaminants is critical for diesel engines to be widely accepted in the U.S. automotive fleet. The Department of Energy in a partnership with an industry association called the U.S. DRIVE Partnership (Driving Research and Innovation for Vehicle efficiency and Energy sustainability) has issued the “150⁰C Challenge” where they predict that “light-off temperatures of ~150ºC will be required to meet emission regulations for new engines used to meet vehicle fuel economy standards.” The light-off temperature is the temperature at which the catalytic activity of the exhaust after-treatment system increases to 50% conversion for hydrocarbons (HC), CO and NOx. In this diesel exhaust after-treatment research and development program, TDA worked to improve the catalyst formulation and reduce the catalyst cost without negatively impacting its activity. An improved reactor system was designed and assembled for simultaneously testing the destruction of CO, NOx and VOCs to provide a high-fidelity simulation of diesel exhaust conditions. Included in this new reactor system was an improved analysis methodology that utilized an MKS Multigas Model 2030 FTIR analyzer for the simultaneous on-line measurement of several exhaust components (NO, NO2, SO2, CO, and VOCs from C1–C7). This new system allowed TDA to evaluate various formulations under representative conditions and facilitated rapid analyses (up to 1 Hz measurements) for the study of transient conditions such as those encountered during cold-starting and rapid acceleration. In addition to small-scale catalyst screening in packed bed operation, the new reactor system was designed to accommodate catalysts prepared over monoliths and other engineered structures. Our catalyst development work reduced the CO and HC light-off temperatures to as low as 25⁰C and 65⁰C, respectively. This is important because the Clean Diesel VI Consortium led by Southwest Research Institute (SwRI) identified low temperature VOC oxidation capability as one of the most pressing issues in the further advancement of the LNC and diesel exhaust after-treatment systems. For NOx abatement, our strategy was to separate the conversion of NOx to N2 to 2 steps: 1) NO to NO2 and 2) NO2 to N2. Pt-based catalysts that showed excellent oxidation activity for CO and HC also showed >70% conversion of NO to NO2 at 150⁰C. However, no catalysts showed >50% conversion of NO2 to N2 (or direct conversion of NOx to N2) at temperatures below 350ºC. Our goal had been to achieve total catalytic NOx reduction with a light-off temperature of <150⁰C. A new type of material for NOx conversion was explored; the catalysts were metal-organic frameworks (MOFs). With the correct deposition procedure our MOFs could be optimized for CO and HC destruction at <150ºC. Several coated MOFs were tested including some tests where MOFs were combined with low temperature oxidation catalysts. The best experiment showed over 500 hours of performance at 150ºC with the conversion of CO and C2H4 at nearly 100% while maintaining ~15-20% total NOx conversion.
- Research Organization:
- TDA Research, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0009219
- OSTI ID:
- 1439885
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- TDA-2983-F; TDA-2983-F
- Country of Publication:
- United States
- Language:
- English
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