Mesoporous silicas of MCM-41 type modified with iron species by template ion-exchange method as catalysts for the high-temperature NH3-SCR process – Role of iron species aggregation, silica morphology and associated reactions

Abstract

Mesoporous silica of MCM-41 type with cylindrical and spherical morphology was synthesized and modified with iron species by template ion-exchange (TIE) method. Methanol solutions of FeCl2 and [Fe3(OCOCH3)7·OH·2 H2O]NO3, used as iron precursors, resulted in deposition of this metal in highly dispersed and aggregated forms, respectively. The obtained samples were characterized with respect to chemical composition - iron loading and surfactant content in non-calcined silicas (ICP-OES, TG-DSC), texture (low-temperature N2 sorption, XRD), morphology (SEM-EDS), form and aggregation of deposited iron species (UV–vis DRS, XRD, SEM-EDS), surface acidity (NH3-TPD) and reducibility of deposited iron species (H2-TPR). Iron modified silicas presented a very good catalytic performance in the high-temperature NH3-SCR process (effective operation in the range of 350–475 °C), however the specific catalytic activity depends on the morphology of the silica samples as well as the form and aggregation of deposited iron species. Moreover, the reactions associated with the NH3-SCR process, such as NO to NO2 oxidation and direct ammonia oxidation were studied.