Titania–Samarium–Manganese Composite Oxide for the Low-Temperature Selective Catalytic Reduction of NO with NH₃

Abstract

A novel Ti-doped Sm–Mn mixed oxide (TiSmMnO x ) was first designed for the selective catalytic reduction (SCR) of NO x with NH3 at a low temperature. The TiSmMnO x catalyst exhibited a superior catalytic performance, in which NO x conversion higher than 80% and N2 selectivity above 90% could be achieved in a wide-operating temperature window (60–225 °C). Specially, the catalyst also showed high durability against the large space velocity and excellent SO2/H2O resistance. Ti incorporation can efficiently inhibit MnO x crystallization and tune the MnO x phase during calcination at a high temperature. Subsequently, a high specific surface area as well as an increased amount of acid sites on the TiSmMnO x catalysts were produced. Further, the reducibility of the Sm-doped MnO x catalyst was modulated, facilitating NO oxidation and inhibiting NH3 nonselective oxidation. Consequently, a superior SCR activity was achieved at a low temperature and the operating temperature window of the TiSmMnO x catalyst was significantly widened. These findings may provide new insights into the reasonable design and development of the new non-vanadium catalysts with a high NH3-SCR activity for industrial application.

Iron-Based Composite Oxide Catalysts Tuned by CTAB Exhibit Superior NH3–SCR Performance

“…These results suggested that the intrinsic properties governing the direct oxidation of NO were different from that of NH 3 oxidation. Combined with the results listed in Table 4, it can be deduced that surface oxygen plays a crucial role in NO oxidation to NO 2 over the Fe-M catalysts [6,57,58].…”

“…For metal oxide NH 3 -SCR catalysts, generally, surface oxygen (O α ) is important for the oxidation of NO to NO 2 , thus promoting the "fast-SCR" reaction at low-temperature [6,57,58]. In addition, the over-oxidation of NH 3 accounted for the decreased NO x conversion at high temperatures [1,13,16,63,64].…”

Understanding the role of redox properties and NO adsorption over MnFeOx for NH3-SCR

“…The promotion by the redox properties will cause the operational temperature window shifting to lower temperatures, and the increase in acidity facilitates the NH 3 adsorption at high temperatures. 49,64 Hence, tuning the redox properties and acidity is an efficient strategy to achieve high activity. Doping has been widely applied in catalyst design because it significantly affects the chemical state and structure of the catalysts.…”

“…The NO 2 contributed to the low temperature NH 3 -SCR via a "fast-SCR reaction" (NO + NO 2 + NH 3 → 2N 2 + 3H 2 O). 49 Hence, NO oxidation and NH 3 oxidation were investigated and the results are shown in Fig. 7 and S3 (ESI †).…”

Recent progress of low-temperature selective catalytic reduction of NOx with NH3 over manganese oxide-based catalysts

“…Compared with single MnO x catalysts, Sm-Mn composite catalysts exhibited superior N 2 selectivity. 67,68 Plenty of studies had shown that the reaction after Sm doping mainly proceeded via the E-R mechanism, in which -NH 2 was the key intermediate. There was a large electronegativity difference between Sm 2+ and Mn 4+ , and Sm 2+ would preferentially lose electrons.…”