Abstract:
Previous works demonstrated that the Fe-Ag/Al
2O
3 catalyst could efficiently reduce NO into N
2 by propene with a good resistance towards H
2O and SO
2. In this work, the effect of preparation method on the performance of Fe-Ag/Al
2O
3 catalyst in the selective catalytic reduction (SCR) of NO with propene was investigated. Three typical methods, viz., physical grinding (PG), direct impregnation (DI) and sol-gel-impregnation (SGI), were comparatively used to load the active components on the supports. The results indicate that all the catalysts prepared by these three methods display good tolerance towards water vapor and SO
2. However, they are rather different in the denitration efficiency; the maximum NO removal efficiency of the catalysts prepared by three methods follows the order of SGI (100%) > PG (62%) > DI (58%). Various characterization results reveal that the catalytic performance of Fe-Ag/Al
2O
3/CM was mainly related to the porous surface and Fe-Ag interaction. By using the SGI approach, the primary support of cordierite and the secondary support of Al
2O
3 work together to achieve a large surface area and an intense interaction between Fe and Ag on the resultant DP-Fe/Ag/Al
2O
3/CM catalyst, forming the bimetal AgFeO
2 oxide and displaying the best reducibility. In terms of the PG method, the prepared GR-Fe/Ag/Al
2O
3 catalyst is powdery and shows the largest surface area; however, without cordierite serving as the monolithic support, Ag
2O and Fe
3O
4 exist as separate oxides together with a hint of elemental Ag. As a result, the GR-Fe/Ag/Al
2O
3 catalyst shows poor reducibility due to the lack of porous surface to facilitate the Fe-Ag interaction. In contrast, the DP-Fe/Ag/CM catalyst prepared using the DI method shows rather poor dispersion of Fe and Ag due to the absence of the secondary support of Al
2O
3; in fact, individual Ag
2O and Fe
3O
4 agglomerate on the catalyst surface and no AgFeO
2 species is detected. Therefore, the DP-Fe/Ag/CM catalyst, with the surface area of only 1/4 of that for Fe-Ag/Al
2O
3/CM-SGI, exhibits the poorest activity in the SCR of NO by propene.