Improved Activity and SO₂ Resistance by Sm-Modulated Redox of MnCeSmTiO_x Mesoporous Amorphous Oxides for Low-Temperature NH₃-SCR of NO

Abstract

The selective catalytic reduction (SCR) technique that converts NO x from the outlet of industrial boilers at low temperature (<200 °C) requires catalysts that possess both the oxidization property of NO x and the adsorption ability to NH 3 . However, owing to unsuitable redox capacity, most NH 3 -SCR catalysts such as MnO 2 /TiO 2 and MnO 2 −CeO 2 /TiO 2 suffer from poor activity and N 2 selectivity and SO 2 poisoning. Benefiting from constructing mesoporous MnCeSmTiO x amorphous mixed oxides by the coprecipitation method, enhanced SO 2 -tolerant lowtemperature NH 3 -SCR performance was achieved. The MnCeSm-TiO x catalysts have an amorphous and mesoporous structure with a BET surface area of 214 m 2 •g −1 . The NO conversion could reach nearly 100% at 140−320 °C and maintain >90% at 400 °C and a gas hourly space velocity of 80,000 h −1 . The selectivity of N 2 could be maintained at ≈100% at 100−320 °C and stay at >90% up to 400 °C. Besides, the MnCeSmTiO x catalyst preserves higher catalytic performance after introducing H 2 O and SO 2 compared with the catalysts without adding Sm. The redox properties, acidic properties, and reaction intermediates of catalysts were analyzed by X-ray photoelectron spectroscopy, hydrogen temperatureprogrammed reduction, ammonia temperature-programmed desorption, oxygen temperature-programmed desorption, pyridine-IR, thermogravimetry−differential scanning calorimetry, and diffuse reflectance infrared Fourier transform. The synergistic effect of the Lewis acid sites and oxidation catalytic sites of mixed oxides serves for the conversion of NO to N 2 by following the Langmuir− Hinshelwood mechanism. Doping Sm into MnCeSmTiO x can increase oxygen vacancies and transfer electrons to Mn 4+ and Ce 4+ , which facilities the formation of active adsorbed NO 2 , bidentate nitrate, and bridging nitrate intermediates and suppresses SO 2 poisoning by inhibiting the oxidation of SO 2 by Mn 4+ and Ce 4+ . Our work could be beneficial to modulate the redox capacity of active sites on NH 3 -SCR catalysts so that NO x can be eliminated in complex flue gas at low temperatures.

Identifying the Fe3Mn3O8 phase as a superior catalyst for low-temperature catalytic oxidation of formaldehyde in air

“…5a and b) and all fitted with three peaks: Mn 4+ (∼643.5 and ∼655.2 eV), Mn 3+ (∼641.8 and ∼653.5 eV), and Mn 2+ (∼640.5 and 652.2 eV). 28,41,42 Even the previous XRD results did not show the presence of the Mn 4+ species, and XPS could detect Mn 4+ on the catalyst surface. The (Mn 3+ + Mn 4+ )/Mn (via peak area) ratios of these samples showed an ascending trend and then a descending trend with the increasing amount of introduced Fe element.…”

Recent advances in heighten sulfur resistance of SCR catalysts: A review

“…S4). Wang et al [54] also demonstrated the superiority of the Sm modified catalyst. Compared with catalysts without Sm, mesoporous MnCeSmTiOx mixed oxides maintained higher catalytic performance after H2O and SO2 were added by suppressing the oxidation of SO2 by Mn 4+ and Ce 4+ .…”

A Green CeO2−WO3/TiO2 Medium‐Low Temperature de‐NOx Catalyst for Selective Catalytic Reduction of NOx with NH3

“…Specifically, the bonds marked u' and v' represent the 3d 10 4f 1 states of Ce 3 + initial electronic, and the bands marked u, u'', u''', v, v'' and v''' represent the 3d 10 4f 0 states of the Ce 4 + . [51,52] According to reports in the literature, [53] the high content of Ce 3 + contributes to formed more oxygen vacancies and promoted adsorption of HN 3 . For the sulfur-treated catalyst, the content of Ce 3 + had slightly decreased, this phenomenon demonstrated that there was charge transfer between Ce 3 + and Ce 4 + in the SCR process, the conversion between Ce 4 + and Ce 3 + also related to the storage and release of oxygen from CeO 2 .…”