Grantee Research Project Results
Final Report: Zero Ammonia Catalysts for Abatement of NOx and Other Species With Waste Minimization
EPA Contract Number: 68D03020Title: Zero Ammonia Catalysts for Abatement of NOx and Other Species With Waste Minimization
Investigators: White, James H.
Small Business: Eltron Research & Development Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $69,997
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)
Description:
The purpose of this Phase I research project was to investigate the applicability of new catalyst compositions for effecting the ammonia-free removal of nitrogen oxides from the exhausts of combustion sources. Of particular interest was identification of catalysts that retained significant activity in the presence of SO2 and water. Work performed involved investigation of both reagentless abatement of NOx and reduction by an aliphatic hydrocarbon (ethylene), representative of an average or typical incompletely oxidized species in diesel exhaust, for example. A number of catalysts were screened for activity under both regimes of conditions. Preferred candidates were identified and initial optimization was performed.
Specific objectives that were addressed by Eltron Research, Inc., during Phase I are summarized as follows:
• Synthesize heterogeneous catalysts of composition (A1-x'A'x')1-y(Cu1-xCox)y(SO4)2-d or Sr2-xLaxGa2-y-zFeyCuz(SO4)5±d by either: (1) calcining the initial stoichiometric sulfates and oxides; (2) coprecipitating a mixed-metal sulfate from aqueous solution; (3) coprecipitating the analogous metal sulfide, followed by calcination in air; or (4) synthesizing the metal oxide, followed by conversion to metal sulfate. Synthesize supported metal (Cu or Co) oxides by incipient wetness impregnation of selected supports followed by x-ray diffraction (XRD) analysis to determine phase purity and crystallographic lattice constants.
• Experimentally determine correlations between catalyst activity towards NOx decomposition under reagentless conditions and correlations with catalyst physical parameters such as: (1) metal-oxygen bond energy; (2) crystallographic phase present; (3) catalyst lattice parameters; (4) calculated catalyst electronic considerations such as d-orbital occupancy and calculated Fermi level position; and (5) general experimental operating conditions including the concentrations of CO, CO2, SO2, H2O, O2, and hydrocarbon (C3H8 or C3H6). Selection of preferred catalysts was assisted by a statistical analysis approach.
• For a preferred defined catalyst composition, identify correlations between NOx decomposition activity and the procedure used for catalyst preparation.
• Experimentally identify preferred honeycomb supports for immobilizing catalysts for subsequent application and performance evaluation.
These objectives were successfully met during Phase I. Namely, identified catalysts displayed both reagentless activity and activity for reduction of nitrogen oxides under oxidizing conditions and in the presence of water and sulfur dioxide. Activity obtained under these conditions was sufficient for practical application. Initial results obtained by testing in diesel exhaust were extremely promising.
Summary/Accomplishments (Outputs/Outcomes):
During Phase I, the following objectives were achieved:
• Synthesized selected metal sulfate and supported metal oxide catalysts by conventional co-precipitation, impregnation, and ceramic (metal oxides) techniques.
• Obtained XRD patterns; elemental analysis by energy dispersive x-ray spectroscopy; and surface area, pore size distribution, and total pore volume using nitrogen physisorption for selected catalyst candidates.
• Screened a total of 27 catalyst candidates for activity under both reagentless conditions and in the presence of a hydrocarbon (ethylene) reductant representative of the chemistry and reducing power of incompletely oxidized constituents (e.g., CO) of diesel exhaust. Incorporated SO2 and water into a simulated exhaust stream to test effects of these exhaust constituents on candidate activities.
• Identified a subset of the above catalyst candidates consisting of 13 candidates exhibiting measurable activity towards decomposition or hydrocarbon reduction of NO and NO2. Determined reagentless activity of these materials. Identified the best candidate as a supported copper oxide displaying the removal of 21 percent of 1,000 ppm NO in 2.9 percent O2 at 7,000 h-1.
• Determined the activities of five catalysts selected from the above down-selected catalysts for the reduction of NO + NO2 by ethylene. Down-selected from the above subset to two candidates.
• Determined activity of the above two candidates as a function of oxygen content, NO concentration, space velocity, temperature, and ethylene concentration.
• Identified variants of the above preferred two down-selected catalysts possessing superior activity under the greatest range of conditions. Determined activity as a function of support and active metal (or metal oxide).
• Evaluated preferred catalysts and their variants as a function of time online for up to 30 hours under 1,000 ppm NO, 2.9 percent O2, 3.1 percent H2O, and 200 ppm SO2. Activity was persistent for three of the candidates, and activity of two of the candidates actually increased over time.
• Optimized the resulting variants to obtain maximum NO + NO2 removal and minimal NO2 production. Identified one variant that yielded 47 percent conversion of NO + NO2 at 300°C and 50,000 h-1 in 1,000 ppm NO, 2.9 percent O2, 3.1 percent H2O, and 200 ppm SO2 when an equimolar level of ethylene was used. The same material yielded up to 83 percent removal of NOx with excess ethylene. Up to 63 percent conversion of 400 ppm NO was obtained. This material was identified as possessing activity practical for employment in diesel engine exhaust.
• Performed gas chromatographic (GC) analysis of products evolved from the preferred catalyst under both reagentless conditions and those employed using an ethylene reductant. Correlation between NO + NO2 converted and nitrogen evolved was observed. N2O was not observed, possibly being below the detection limit of the GC employed. Residual ethylene was not measurable, and CO2 was invariably produced when C2H4 was employed.
• Incorporated the preferred catalyst using a dip-coater onto a cordierite monolith possessing 400 cells/inch and several metal monoliths with 200 cells/inch. Obtained catalyst coatings of between 1 and 2 g on each 1-inch diameter by 2-inch length monolith.
• Fabricated an aluminum holder for incorporating three monoliths in series into the exhaust of a one-cylinder diesel engine.
• Performed initial tests of coated monoliths using three of the metal monoliths in the aluminum chamber described above. Obtained 47 percent removal of NO (mean inlet concentration equaled 340 ppm) from the diesel exhaust at 250ºC and 155,000 h-1.
In summary, selected new catalyst materials were identified that possess activity and stability appropriate for employment in diesel engine exhausts. Initial testing in diesel engine exhaust showed that a preferred material possessed practical and potentially interesting activity for the abatement of nitrogen oxides in diesel exhausts.
Conclusions:
Work performed during Phase I identified new catalyst materials demonstrating exceptional activity for the conversion of nitrogen oxides into nitrogen without the use of ammonia. Materials demonstrated reagentless (direct decomposition) activity and were much more effective for the reduction of NOx using a hydrocarbon reductant. The preferred materials converted all of the excess measurable ethylene into CO2 and were effective even with sub-stoichiometric levels (molar hydrocarbon/NO ratio less than 1) of hydrocarbon. The preferred materials displayed performance that was practical in both bench experiments using simulated exhaust and in experiments using diesel engine exhaust, and gave performance impressive enough to justify further investigation and development of the catalysts. Activity under practical conditions was comparable to or greater than that reported in the literature with more expensive catalysts.
Supplemental Keywords:
air pollution, zero ammonia catalysts, NOx abatement, nitrogen oxides, hydrocarbon, diesel engine, sulfur dioxide, SO2, emissions control technology, exhaust after-treatment, mobile sources, x-ray diffraction analysis, small business, SBIR., RFA, Scientific Discipline, Air, Waste, INDUSTRY, POLLUTANTS/TOXICS, Sustainable Industry/Business, POLLUTION PREVENTION, air toxics, cleaner production/pollution prevention, waste reduction, Environmental Chemistry, Air Pollutants, Chemicals, Analytical Chemistry, Economics and Business, Industrial Processes, Incineration/Combustion, Environmental Engineering, Nitrogen Oxides, metal nitride catalysts, combustion byproducts, Nox, catalytically stablizied incineration, waste minimization, hazardous air pollutants, air pollution control, airborne organics, combustion emissions, VOCs, clean technology, VOC removal, emission controls, combustion technology, emissions control, air pollution control technology, combustion, catalytic combustion, incineration, nitrogen oxides (Nox), Volatile Organic Compounds (VOCs), air emissionsThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.