Abstract
A 2 wt.% Ag/γ-Al 2O 3 catalyst was studied for the ethanol selective catalytic reduction of NO x from 200 to 550°C and space velocities between 30,000 h -1and 140,000 h -1. Peak NO x conversions reached 85% at 400°C, and an activation energy was determined to be 57 kJ/mol with a feed of ethanol to NO x or HC 1/NO x = 3. Up to 80% of the NO is oxidized to NO 2 at 250°C, but overall NO x conversion is only 15%. Interestingly, ethanol oxidation occurs at much lower temperatures than NO x reduction; at 250°C, ethanol oxidation is 80% when flowing ethanol + NO + O 2. This increased reactivity, compared to only 15% when flowing only ethanol + O 2, combined with the observation that NO is not oxidized to NO 2 in the absence of ethanol illustrates a synergistic relationship between the reactants. To further investigate this chemistry, a series of DRIFTS experiments were performed. To form nitrates/nitrites on the catalysts it was necessary to include ethanol in the feed with NO. These nitrates/nitrites were readily formed when flowing NO 2 over the catalyst. It is proposed that ethanol adsorbs through an ethoxy-intermediate that results in atomic hydrogen on the surface. This hydrogen aids the release of NO 2 from Ag to the gas-phase which, can be subsequently adsorbed at γ-Al 2O 3 sites away from Ag. The disappearance of these nitrates/nitrites at higher temperatures proceeds in parallel with the increase in NO x reduction reactivity between 300 and 350°C observed in the kinetic study. It is therefore proposed that the consumption of nitrates is involved in the rate determining step for this reaction.
Original language | English |
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Pages (from-to) | 166-177 |
Number of pages | 12 |
Journal | Catalysis Today |
Volume | 184 |
Issue number | 1 |
DOIs | |
State | Published - Apr 30 2012 |
Funding
Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program under contract DE-AC05-00OR22725 with UT-Battelle, LLC.The contribution of W.L. Johnson II was supported in part by an appointment to the Oak Ridge National Laboratory Postdoctoral Research Associates Program administered jointly by the Oak Ridge Institute for Science and Education and the Oak Ridge National Laboratory.
Funders | Funder number |
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Oak Ridge National Laboratory | |
U.S. Department of Energy | |
Office of Energy Efficiency and Renewable Energy | DE-AC05-00OR22725 |
Oak Ridge National Laboratory | |
Oak Ridge Institute for Science and Education |
Keywords
- (Ag/Al O )
- Ethanol selective catalytic reduction of NO (ethanol SCR NO )
- Lean NO reduction
- Silver alumina