Study on the fuel-reforming-assisted hydrocarbon selective catalytic reduction over silver/alumina catalyst

This study aims to assess the feasibility of fuel-reforming-assisted hydrocarbon selective catalytic reduction (HC-SCR) over 2 wt % Ag/Al ₂O₃ catalyst. For this purpose, the effects of reduction agents and the presence of hydrogen on NO_x reduction over silver catalyst were tested, and, after catalytic partial oxidation (CPOx) reforming performances were studied, the DeNO_x performance of reformate-assisted HC-SCR was investigated. Although normal heptane/octane/ dodecane showed better NO_x reduction rates at 300 and 350 °C than the other C₂-C₄ range hydrocarbons, the performances were still unpractical at the temperature range similar to actual diesel exhaust. To enhance the low temperature activity of the Ag/Al₂O₃ catalyst, CPOx reforming was tested and applied in the SCR system. By the addition of CPOx products to the HC-SCR reactor, NO_x reduction performance was increased to a great extent especially in the low temperature range between 200 and 400 °C. For the reductant condition of C/N = 6 + CPOx/N = 6 without water, about 52.5% of NO_x reduction was recorded over C₃H₆-SCR at 300 °C, whereas nearly zero DeNO _x efficiency was measured when only C₃H₆ was present in the reactants. Also, it was found that C/N = 6 + CPOx/N = 6 showed the better NO_x reduction efficiency than C/N = 3 + CPOx/N = 9. Together with the hydrogen model gas tests results, it implies that there is an optimum hydrogen to hydrocarbon ratio in terms of low-temperature activity enhancement assuming that the total amount of fuel used in CPOx-assisted HC-SCR is the same. In addition, inhibition effect by water was reduced to an extent by CPOx products. C₃H₆-SCR was deactivated so seriously that no NO_x conversions were measured at 300 and 400 °C in the presence of water vapor. However, through the addition of CPOx products to the C₃H₆-SCR reactants, NO_x reduction was increased to 20% at 300 °C and 25% at 400 °C.