Browse Publications Technical Papers 2005-01-1082
2005-04-11

Hydrocarbon Selective Catalytic Reduction Using a Silver-Alumina Catalyst with Light Alcohols and Other Reductants 2005-01-1082

Previously reported work with a full-scale ethanol-SCR system featuring a Ag-Al2O3 catalyst demonstrated that this particular system has potential to reduce NOx emissions 80-90% for engine operating conditions that allow catalyst temperatures above 340°C. A concept explored was utilization of a fuel-borne reductant, in this case ethanol “stripped” from an ethanol-diesel micro-emulsion fuel. Increased tailpipe-out emissions of hydrocarbons, acetaldehyde and ammonia were measured, but very little N2O was detected. In the current increment of work, a number of light alcohols and other hydrocarbons were used in experiments to map their performance with the same Ag-Al2O3 catalyst. These exploratory tests are aimed at identification of compounds or organic functional groups that could be candidates for fuel-borne reductants in a compression ignition fuel, or could be produced by some workable method of fuel reforming. A second important goal was to improve understanding of the possible reaction mechanisms and other phenomena that influence performance of this SCR system. Test results revealed that diesel engine exhaust NOx emissions can be reduced by more than 80%, utilizing ethanol as the reductant for a space velocity near 50,000/h and catalyst temperatures between 330 and 490°C. Similar results were achieved for 1-propanol, 2-propanol and 1-butanol, with a (desirable) shift to a lower temperature range seen for the primary alcohols. Heavier alcohols and other oxygenated organics were also tested as reductants showing a range of less successful results. Non-oxygenated hydrocarbons and the selected secondary and tertiary alcohols proved to be very poor reductants for this system. Some discussion concerning the possible mechanisms behind the results is offered.

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