DRIFTS study of γFe₂O₃ nano‐catalyst for low‐temperature selective catalytic reduction of NO_x with NH₃

Abstract

The catalysts used in the selective catalytic reduction (SCR) of NOx with NH3 were prepared from γFe2O3 nanoparticles. The NH3‐SCR activity measurement was carried out in a fixed bed reactor. The adsorption characteristics of γFe2O3 nano‐catalysts to NH3 and NO were studied with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Experimental activity measurement indicated that γFe2O3 used as a SCR de‐NOx catalyst exhibited excellent low‐temperature SCR de‐NOx performance. The DRIFTS measurements showed that there existed both NH4+ bonded to Brønsted acid sites and coordinated NH3 bonded to Lewis acid sites on the catalyst surface. Coordinated NH3 was the main adsorption product. O2 promoted H‐abstraction from coordinated NH3 to form NH2 species, as well as O2 greatly enhancing the adsorption of NO on the catalyst surface to form nitrate species and absorbed NO2. Possible reaction paths with the γFe2O3 catalyst were proposed as follows: the SCR process mainly formed NH2 from H‐abstraction of coordinated NH3 which reacted with NO to form N2 and H2O at high and medium temperatures. At low temperatures, however, the formation of adsorbed NO2 resulted from NO oxidation by O2 over Fe3+ sites played an important role. NH4NO3 and (NH4+)2NO2 as the key intermediate products reacted with NO to form N2 and H2O at low temperatures.

The utilization of red mud waste as industrial honeycomb catalyst for selective catalytic reduction of NO

“…The results were also consistent with previous reports about the competition reaction between NH 3 -SCR and NH 3 -SCO (NH 3 -selective catalytic oxidation) [8,23,24]. The -NH 2 intermediate species [25,26] activated by NH 3 preferentially reacted with NO at the lower NH 3 concentration. With the increase in NH 3 /NO ratio, the oxidation of NH 3 was enhanced, resulting in the lack of NH 3 to react with NO.…”

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

“…Figure S14. In situ DRIFTs of NH3 desorption over (A) SO4 2-/CeZr and (B) 1.5Fe/SO4 2-/CeZr catalysts after exposure to a flow of 500 ppm NH3 for 1 h at 30 °C, Related to Figure 3.For SO4 2-/CeZr catalysts, NH4 + (1691, 1473,1440 cm -1 ) and NH3 (1357 cm -1 ) species appear SO4 2-/CeZr catalysts after NH3 adsorption, and gradually reduce with the increased temperature and only few NH4 + species reserve at 250 o C and 300 o C. Similarly, NH4 + (1684,1472,1433 cm -1 )(Liang et al, 2016) and NH3 (1601 cm -1 ) adsorb on 1.5Fe/SO4 2-/CeZr catalysts and gradually reduce with the increased temperature and few NH4 + and NH3 species remain above 250 o C. These results indicate that adsorbed NHx species are not stable above 250 o C.…”

“…For SO4 2-/CeZr, bidentate nitrates (1555 cm -1 ) (Hu et al, 2015) and M-NO2 (1363 and 1328 cm -1 ) species appear after the adsorption of NO+O2, and these species gradually decrease and vanish after introducing NH3 for 30 min. Meanwhile, NH4 + species (1680 cm -1 ) (Liang et al, 2016) increase with continuous introduction of NH3. For 1.5Fe/SO4 2-/CeZr catalysts, N2O4 (1696 cm -1 ) , bidentate nitrates (1559 cm -1 ) and M-NO2 (1376 cm -1 ) species appear after the adsorption of NO+O2, and these species gradually decrease within 5 min after introducing NH3.…”

Formation of Nitrogen Mono Oxide (NO) during Iron Ore Sintering Process

“…Si and Al could hardly effect the thermal migration of fuel-N. [10][11][12][13] The researches of Liang H and Xu C. B both indicated that Fe 2 O 3 showed a reactivity to the removal of NO in the NO NO-CO-CO 2 -N 2 system. 14,15) K. Monticelli and Min Gan found that the calcium ferrite generated in the sintering process played a significant role in promoting the reaction between CO and NOx. K. Katayama believed the calcium ferrite formed by chemical reaction between adherent CaO on coke breeze surface and fine iron ore had effect on inhibiting NOx emission.…”