Selective catalytic reduction of NO x over Ag/Al2O3 using various bio-diesels as reducing agents

Abstract

The effect of bio-diesel compounds (vegetable methyl and ethyl laurate and hexadecane) as reducing agents on the selective catalytic reduction of NO x over a 2 wt.% Ag/Al 2 O 3 was investigated. These components were found to have a two-fold effect on the SCR over Ag/Al 2 O 3 . First, the reduction activity below 400°C was higher with bio-diesel than with n-octane, which is a representative compound for fossil fuels. This effect is attributed to the presence of the ester group in these molecules. However, the conversion above 400°C decreased sharply and was considerable lower than with n-octane. The most interesting observation was found when the reduction efficiency of bio-diesel components was tested in the presence of hydrogen. The well known low temperature boosting effect of hydrogen was visible not only at lower temperatures, but also above 400°C. Mechanistically the observation is extremely interesting and indicates that hydrogen effect cannot directly be connected to reduction of surface nitrates, which can be operative only at low temperature domain.

Lean NO x Reduction with Various Bio-Diesels as Reducing Agents

“…Similar behavior with higher low temperature activity and lower high temperature activity was observed by Arve et al [3] on Ag/Al 2 O 3 when methyl and ethyl laurate were compared to n-octane. This decrease in activity at higher temperature could be connected to increased non-selective oxidation of the hydrocarbon due to the high oxygen content of the esters.…”

“…For an engine running on an alternative fuel, it is thus essential to investigate the effect on the catalyst performance with this fuel compared to conventional diesel. However, only a limited amount of research has been published on HC-SCR when used with bio-diesel and synthetic diesel fuels [3][4][5][6][7][8].…”

Assessing the effect of reducing agents on the selective catalytic reduction of NOx over Ag/Al2O3 catalysts

“…9,10 It is clear that the nature of the reducing agent has a strong effect on SCR catalytic activity. In the literature it has been reported 2,3,[11][12][13][14][15][16][17] that oxygenated molecules, such as alcohols, give improved catalyst performances compared to hydrocarbons, which is thought to originate from competitive adsorption effects between reducing agent molecules and water, the latter being able to inhibit the catalyst sites. 2,3,18 This is indeed a plausible explanation, although it has to be said that, according to our knowledge, there is little experimental evidence to support it.…”

Dependence of the catalytic activity of Ag/Al2O3 on the silver concentration in the selective reduction of NO x with n-hexane in the presence of H2

“…However, many of the above studies were carried out in the presence of relatively high concentrations of Н 2 (>4000 ppm) [9][10][11][12][13]. Therefore, there are serious difficulties in the practical use of this reaction because the real concentration of Н 2 in the operation of a die sel engine does not exceed 1000 ppm.…”