Final Report: Low-Cost Retrofit Emissions Control in Off-Road SourcesEPA Contract Number: EPD10023
Title: Low-Cost Retrofit Emissions Control in Off-Road Sources
Investigators: White, James H.
Small Business: Eltron Research & Development Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $69,999
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: SBIR - Emission Reductions and Biofuels , Small Business Innovation Research (SBIR)
This Phase I program addressed the development and demonstration of a heterogeneous catalyst for promoting the post-combustion removal of NOx from diesel sources without the use of supplemental fuel, ammonia, or urea. This approach is advantageous when compared to selective catalytic reduction (SCR), for example, in that atom economy is improved (stoichiometric ammonia or other reagents are unnecessary) and the costs of reagents eliminated. Additionally, application to area (mobile or small, widespread) sources is far more attractive than the alternative SCR, SNCR, and NSR processes. It was anticipated that the proposed approach would achieve project objectives by utilizing selected metal nitrides as supports for metals and/or metal oxides. Heterogeneous catalyst candidates for this application were selected on the basis of previous results which were, in turn, identified on the basis of optimal oxygen and NOx binding as well as combustion activity or efficient reagent (i.e., CO or hydrocarbons for passive catalytic reduction) utilization for application under net oxidizing conditions, which is appropriate for effectively promoting NOx reduction in the exhausts of real combustion sources. Phase I identified novel catalyst materials that when used in monolithic form, demonstrated useful activity in real diesel exhaust and were estimated to be more cost effective than existing approaches for retrofit applications in non-highway (off-road) diesel sources.
Key Phase I findings were as follows:
- Validated previous bench (simulated exhaust) results obtained with silicon nitride supported metal.
- Synthesized existing Eltron catalyst compositions and derivatives of these compositions using wetness impregnation methods.
- By screening catalyst candidates in simulated exhaust (400 ppm NO, 400–600 ppm ethylene, 8%O2, and 3% H2O at 250oC and 112,500h-1), identified optimal compositions. A non-crystalline main group nitride material proved to be the best catalyst support.
- Preferred supported metal catalyst materials gave up to 70% conversion of NOx under the above conditions, far better than any other material. Preferred metal oxide materials gave up to ~37% NOx conversion under the same conditions.
- Temperature dependence of catalyst activity in diesel exhaust was investigated between 250 and 400oC. Supported metal and supported metal oxides both gave a temperature window in which activity was essentially constant. For example, the best supported metal catalyst gave a maximum conversion at ~360oC of ~36% and a minimum of 32% at 250oC.
- Lead candidate catalyst materials were optimized for activity. Little improvement was obtained with the metal oxide system.
- The 3 best catalyst candidates were incorporated onto metal (fecralloy) honeycomb monoliths.
- Monoliths were tested under fixed conditions (i.e., fixed load of 1000W) in the exhaust of a single cylinder, four stroke diesel engine. Preferred candidates identified on the basis of activity exhibited and catalyst adherence to monolith.
- Preferred candidate monoliths were evaluated as a function of engine load, temperature, distance from the engine, and time on-line. The best candidate monolith identified incorporated a supported metal catalyst and displayed NOx conversion of more than 38% without activity loss over 16 hours. One monolith was cumulatively used in diesel exhaust for up to 21.75 hours without major activity loss.
- Average NOx emissions over the range 0 to 1.75kW were less than < 1.5g/bhp • h.
- Use of a supported metal catalyst with biodiesel gave essentially the same overall performance as that obtained with low sulfur diesel.
- Cost of monolith catalyst was estimated to be only about one-fifth that of existing diesel NOx abatement approaches.
The most significant observations of Phase I were thus the identification of the most active metal catalyst to date and tentative evidence of longevity. Additionally, reduction of NOx emissions from a real non-highway diesel source to within some EPA standards (Tier 3) was realized.
Results of Phase I strongly support the concept proposed, i.e., metal nitride supported metals and metal oxides as passive NOx catalysts for non-highway diesel applications. Activity obtained and reasonable cost suggest that further development is warranted, particularly when combined with other emerging technologies.