In Situ DRIFTS Study of the Low Temperature Selective Catalytic Reduction of NO with NH3 over MnOx Supported on Multi-Walled Carbon Nanotubes Catalysts

Abstract

MnO x supported on multi-walled carbon nanotubes (MWCNTs) catalysts were prepared by the pore volume impregnation method and used for low-temperature selective catalytic reduction (SCR) of NO with NH 3 . Based on the previous study, 10 wt.% loading MnO x /MWCNTs were then selected for investigation of the reaction mechanism by in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (in-situ DRIFTS). The important intermediates in the SCR of NO x process at 210°C were discussed based on the DRIFTS results. Furthermore, the NH 3 -SCR reaction pathways over MnO x /MWCNTs catalysts were proposed. The results showed that NH 4 + species on Brønsted acid sites and coordinate ammonia species on Lewis acid sites existed during the SCR reaction. NH 4 + species was more active than coordinate ammonia species over the catalysts at 210°C. Most of NO x ad-species would react with NH 3 ad-species. However, nitrite species, bidentate and monodentate nitrates contributed to the SCR reaction over the catalysts mostly. Two possible reaction pathways were proposed. One was that NO x ad-species could react with NH 4 + to form intermediate of NH 4 N 2 O 4 (a), NH 4 NO 2 (a) or NH 4 NO 3 (a), then to produce N 2 and H 2 O as the final products. The other pathway was that NH 3 was initially adsorbed on active site and NH 2 was formed, then NH 2 reacted with NO x ad-species to produce intermediate NH 2 NO 2 or NH 2 NO 3 which were unstable and would decompose into N 2 and H 2 O.

In situ FT-IR study of highly dispersed MnO x /SAPO-34 catalyst for low-temperature selective catalytic reduction of NO x by NH 3

“…Although, the Mn-based catalysts exhibit high activities in a low temperature range, there are obvious differences in LT SCR catalytic activity [8,10,24,25], and related mechanism studies have been carried out in detail [17,18,26]. The properties of the support should not be neglected [27][28][29].…”

“…To gain insight into the NH 3 -SCR reaction over Mn-based catalysts, many reaction mechanism studies have been performed [17][18][19][20]. According to most reported reaction pathways, the initial step is considered to be the adsorption of NH 3 on the Lewis acid sites of the catalysts to form coordinated NH 3 and -NH 2 , and then they can react either with aerial NO through the Eley-Rideal (E-R) mechanism or active nitrite intermediates adsorbed on the surface of the catalysts through the Langmuir-Hinshelwood (L-H) mechanism [21,22].…”

Characterization and SCR Performance of Nano-Structured Iron-Manganese Oxides: Effect of Annealing Temperature

“…Selective catalytic reduction (SCR) has been proved to be an effective technology for the reduction of NO x by NH 3 over different catalysts due to its high efficiency and economic efficiency (Yu, 2015;Jiang et al, 2017;Yu et al, 2017). Among these catalysts, V 2 O 5 /TiO 2 in combination with MoO 3 and WO 3 has been commercialized in consequence of its high catalytic reactivity, including NO conversion, N 2 selectivity and resistance to sulfur poisoning, and mechanical strength.…”

Effect of Ce/Y Addition on Low-Temperature SCR Activity and SO2 and H2O Resistance of MnOx/ZrO2/MWCNTs Catalysts

“…As shown in Figure 8, the spectrum of all fresh catalysts exhibited three characteristic peaks at 3440 cm −1 , corresponding to the vibration of -OH units [39][40][41]; at 1645 cm −1 , which was ascribed to the stretching vibration of C=C on the surface of MWCNTs [42]; and a broad peak in the 1000-400 cm −1 range, which was attributed to the stretching vibration of metallic oxide groups (Me-O-Me) [43,44]. Compared to the fresh catalysts, a peak around 1102 cm −1 , assigned to the SO 4 2− species, appeared after reacting with SO 2 [6,45].…”