Hydrogen Promotes The Selective Catalytic Reduction Of NO_x By N-C₄H₈ Over Ag/Al₂O₃ Catalysts

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) by n-C4H8 in the assistance of H2 (n-C4H8-H2-SCR) was investigated over Ag/Al2O3 catalysts (0-5 wt.% Ag). The n-C4H8-H2-SCR was conducted by feeding a gas mixture of 1000 ppm NO,1000 ppm n-C4H8,5000 ppm H2,10% O2 and N2 balance with a total flow rate of 200 ml/min to a fixed bed reactor loading desired amount of catalyst. The effect of H2 on n-C4H8-SCR was studied. The results showed that the addition of H2 significantly promoted NOx reduction by n-C4H8 in the low temperature range. With the decrease of GHSV from 48000 h"1 to 9600 h-1, NOx conversion remarkably increased at the reaction temperature ranged from 200℃to 250℃, especially over the Ag/Al2O3 catalysts containing 1.5-2 wt.% of Ag. At GHSV = 9600 h-1, the activity of Ag/Al2O3 influenced by the loading amount of Ag was studied. It indicated that the 2%Ag/Al2O3 is most active in the investigated catalysts, over which, as high as 88% of NOx in the feeding gas was reduced at 250℃. Furthermore, the 2%Ag/Al2O3 gave high NOx reduction selectivity and displayed substantial catalytic stability at the reaction conditions. In the catalytic durability test at 250℃, no deactivation of the catalyst could be found with time on stream. Therefore, the 2%Ag/Al2O3 catalyst can be considered to be suitable for the n-C4H8-H2-SCR at low temperature (250℃).For the 2%Ag/Al2O3 catalyst, the dependence of NOx conversion upon the concentration of n-C4H8 and H2 in the feeding gas was also studied at the reaction temperature of 250℃. The results showed that the NOx conversion markedly increased with the increase of n-C4H8 concentration from 0 to 1000 ppm and the increase of H2 concentration from 0 to 5000 ppm. Nevertheless, when the concentration of H2 further increased from 5000 ppm, less enhanced NOx conversion was observed.