Removal of NOx over LaMnO۳ and LaMn۰.۷۵A۰.۲۵O۳ (A=Cu, Fe &Zn) perovskite Nanocatalysts

چکیده مقاله

With the increasing concerns about environmental protection, the control of NOx emissions has become important and efficient methods are required in order to meet more stringent regulations. One effective technique for reduction of NOx to N2 is selective catalytic reduction (SCR) with ammonia. As it has been well established in literature, the structure and properties of catalyst play the main effects on NH3-SCR of NOx. The main catalytic systems applied in NH3-SCR of NOx are: I) M-Supports (M: Transitional and noble metals, Supports: Zeolites, Active Carbon, Alumina), II) metal oxides and composite mixed oxides. Perovskite oxides are mixed oxides with the general formula of ABO3. Lanthanides usually occupy the A-site position, and the first row transition metals are at the B-site. A-site and B-site replacements mainly affect the amount and the nature of adsorbed oxygen, and would modify the catalytic behavior of perovskites. The objectives of this work were to develop some nanocrystalline LaMnO3 and LaMn0.75A0.25O3 (A=Cu, Fe & Zn), obtained by sol gel combustion method toward NOx removal by NH3-SCR. The structure and surface properties of prepared perovskites were investigated by XRD, FT-IR and SEM. The NH3-SCR tests were performed in a fixed bed reactor with a feed gas mixture consisting NO, NH3, O2 and Ar as balance. It was observed that with the rise of reaction temperature, the NOx conversion of prepared perovskites increases and the N2 selectivity extremely decrease. The LaMnO3 exhibited a quite low activity at different temperatures. The NOx conversion improved due to partial substitution of Fe3+ by B cation, which may have been caused by the synergistic effects between Mn and Fe. The following order was observed for performance of catalysts: LaMn0.75Fe0.25O3> LaMn0.75Cu0.25O3> LaMn0.75Zn0.25O3> LaMnO3. The temperature for 50% NOx conversion (T50%) on LaMn0.75Fe0.25O3 was 250 ºC.