Effect of preparation method on the performance of Fe-Ag/Al₂O₃ catalyst in the selective catalytic reduction of NO with propene

Previous works demonstrated that the Fe-Ag/Al₂O₃ catalyst could efficiently reduce NO into N₂ by propene with a good resistance towards H₂O and SO₂. In this work, the effect of preparation method on the performance of Fe-Ag/Al₂O₃ 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 SO₂. 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/Al₂O₃/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 Al₂O₃ work together to achieve a large surface area and an intense interaction between Fe and Ag on the resultant DP-Fe/Ag/Al₂O₃/CM catalyst, forming the bimetal AgFeO₂ oxide and displaying the best reducibility. In terms of the PG method, the prepared GR-Fe/Ag/Al₂O₃ catalyst is powdery and shows the largest surface area; however, without cordierite serving as the monolithic support, Ag₂O and Fe₃O₄ exist as separate oxides together with a hint of elemental Ag. As a result, the GR-Fe/Ag/Al₂O₃ 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 Al₂O₃; in fact, individual Ag₂O and Fe₃O₄ agglomerate on the catalyst surface and no AgFeO₂ species is detected. Therefore, the DP-Fe/Ag/CM catalyst, with the surface area of only 1/4 of that for Fe-Ag/Al₂O₃/CM-SGI, exhibits the poorest activity in the SCR of NO by propene.