New Mn-TiO 2 aerogel catalysts for the low-temperature selective catalytic reduction of NO x

A new series of Mn-based catalysts (Mn-TiO 2 , Ce-Mn-TiO 2 , Mn-TiO 2 -SO 4 2 – , and Ce-Mn-TiO 2 -SO 4 2– ) were successfully elaborated using the sol–gel method associated with supercritical drying approach for the low-temperature NO-SCR by NH 3 . The physicochemical properties of aerogel powders were examined by XRD, N 2 -Physisorption at 77 K, NH 3 -TPD, H 2 -TPR, and DRUV-Vis spectroscopy. It was shown that all the catalysts develop essentially the diffraction peaks of TiO 2 anatase phase and are characterized by a nanometer size (ranging between ~5 and 9 nm), developed mesoporous texture, high surface area (S BET > 104 m 2 /g) and large porosity (V PT > 0.24 cm 3 /g). The incorporation of Ce and/or SO 4 2– influences differently the structural, textural, acidic, and redox properties of Mn-derived sol–gel catalysts and consequently affects their SCR activity. High NO conversions (>75%) into essentially N 2 O are obtained at low temperatures (150–270 °C) over Mn-TiO 2 and Ce-Mn-TiO 2 aerogel systems. The addition of sulfate modifies the nature of Mn species and noticeably reduces the low-temperature reactivity of catalysts ( T < 300 °C). However, it induces, thanks to the contribution of many strong acid sites, a substantial increase of the NO conversion into N 2 at higher temperatures ( T > 300 °C) leading to highly active and N 2 -selective Mn-TiO 2 -SO 4 2– and Ce-Mn-TiO 2 -SO 4 2– sulfated catalysts. Above 90% NO conversion into N 2 (100%) was reached, in the NO-SCR by NH 3 , over the new Ce-Mn-TiO 2 -SO 4 2– aerogel catalyst, in the 450–500 °C temperature range.