2012 Volume 55 Issue 1 Pages 57-66
The kinetic study on the effect of O2 concentration in the selective catalytic reduction (SCR) of nitrogen oxide (NOx) by ammonia (NH3) was systematically carried out at temperatures below 200 °C over Fe- and Cu-loaded beta zeolites. The large difference was observed in the effect of O2 concentration over the two catalysts: for the Fe-loaded beta zeolite, the NO conversion increased considerably with the O2 concentration. On the other hand, for the Cu-loaded beta zeolite, increasing the concentration of O2 did not have a significant impact. In addition, the temperature dependence of the apparent reaction orders was investigated. The apparent reaction order of O2 decreased with an increase in the reaction temperature, being 0.9 at 150 °C and 0.4 at 200 °C for the Fe-loaded beta zeolite, and 0.2 at 125 °C and 0.1 at 175 °C for the Cu-loaded beta zeolite. The fact that the degree of the reduction in the reaction order of O2 was consisted with that of the increase in the reaction order of NH3 when the reaction temperature was increased strongly suggests that adsorbed NH3 inhibits the adsorption of O2.
