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Promoting functions of H2 in diesel-SCR over silver catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
48633 46516 2007 6 PDF Available
Title
Promoting functions of H2 in diesel-SCR over silver catalysts
Abstract

During the selective reduction of NOx over silver, the known promoting effect of H2 has been found to vary with the nature of the hydrocarbon reductant. The promoting effect is more pronounced when the reductants are short-chain alkanes, such that the steady-state NOx conversion at low temperature follows the order: n-C8H18 > n-C10H22 > n-C12H26 > GTL-fuel > ultra-low sulphur diesel fuel. This reactivity pattern is almost the reverse of that observed in the absence of H2, where the initial activity is higher for the longer, more reactive alkanes. It has become clear that silver can initially achieve very high NOx conversion irrespective of the reductant speciation when H2 is present, but the beneficial effect can be negated (when diesel fuels are used as reductants) by deposition of carbon-rich surface species. By optimising the fuel injection strategy (i.e., the hydrocarbon:NOx ratio), the promoting effect can be made to dominate, even at relatively low concentrations of H2 (300–600 ppm), which could be produced in an exhaust gas by re-calibrating the engine. When diesel fuel is the reductant, we suggest that a key function of H2 is to enhance the formation of NO2, which is very effective at oxidising the carbon-rich species at low temperatures, so allowing the good initial activity to be maintained.

Keywords
Hydrocarbon-SCR; Silver; Hydrogen; Diesel fuel
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 77, Issues 1–2, 30 November 2007, Pages 29–34
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
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