New Mn-TiO2 aerogel catalysts for the low-temperature selective catalytic reduction of NOx

A new series of Mn-based catalysts (Mn-TiO2, Ce-Mn-TiO2, Mn-TiO2-SO42–, and Ce-Mn-TiO2-SO42–) were successfully elaborated using the sol–gel method associated with supercritical drying approach for the low-temperature NO-SCR by NH3. The physicochemical properties of aerogel powders were examined by XRD, N2-Physisorption at 77 K, NH3-TPD, H2-TPR, and DRUV-Vis spectroscopy. It was shown that all the catalysts develop essentially the diffraction peaks of TiO2 anatase phase and are characterized by a nanometer size (ranging between ~5 and 9 nm), developed mesoporous texture, high surface area (SBET > 104 m2/g) and large porosity (VPT > 0.24 cm3/g). The incorporation of Ce and/or SO42– 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 N2O are obtained at low temperatures (150–270 °C) over Mn-TiO2 and Ce-Mn-TiO2 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 N2 at higher temperatures (T > 300 °C) leading to highly active and N2-selective Mn-TiO2-SO42– and Ce-Mn-TiO2-SO42– sulfated catalysts. Above 90% NO conversion into N2 (100%) was reached, in the NO-SCR by NH3, over the new Ce-Mn-TiO2-SO42– aerogel catalyst, in the 450–500 °C temperature range.