“…These results show that V sites reduced by the reaction of NH 4 + (Brønsted acid site) with NO are re-oxidized, and remaining ammonia species move to Brønsted acid sites which are adjacent to redox V sites, then they react with NO by the re-oxidized V sites again. According to the previous reports on supported vanadium-based catalysts, Brønsted acid sites are not directly involved in the catalytic cycle and they play a role in an NH 3 pool to supply NH 3 to the Lewis acid sites 20 , 52 . In the case of bulk tungsten-substituted vanadium oxide catalyst, Brønsted acid site (B) would be located next to redox-active V 5+ site and it would directly react with NO as following reduction half-cycle: Fig.…”
NH3-SCR (selective catalytic reduction) is important process for removal of NOx. However, water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH3-SCR at a low temperature (100–150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W-substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5–20 vol% water) NO conversion at 150 °C (250 ppm NO, 250 ppm NH3, 4% O2, SV = 40000 mL h−1 gcat−1). Lewis acid sites of W-substituted vanadium oxide are converted to Brønsted acid sites under a wet condition while the distribution of Brønsted and Lewis acid sites does not change without tungsten. NH4+ species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V5+ sites at 150 °C. The high redox ability and reactivity of Brønsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor.
“…These results show that V sites reduced by the reaction of NH 4 + (Brønsted acid site) with NO are re-oxidized, and remaining ammonia species move to Brønsted acid sites which are adjacent to redox V sites, then they react with NO by the re-oxidized V sites again. According to the previous reports on supported vanadium-based catalysts, Brønsted acid sites are not directly involved in the catalytic cycle and they play a role in an NH 3 pool to supply NH 3 to the Lewis acid sites 20 , 52 . In the case of bulk tungsten-substituted vanadium oxide catalyst, Brønsted acid site (B) would be located next to redox-active V 5+ site and it would directly react with NO as following reduction half-cycle: Fig.…”
NH3-SCR (selective catalytic reduction) is important process for removal of NOx. However, water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH3-SCR at a low temperature (100–150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W-substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5–20 vol% water) NO conversion at 150 °C (250 ppm NO, 250 ppm NH3, 4% O2, SV = 40000 mL h−1 gcat−1). Lewis acid sites of W-substituted vanadium oxide are converted to Brønsted acid sites under a wet condition while the distribution of Brønsted and Lewis acid sites does not change without tungsten. NH4+ species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V5+ sites at 150 °C. The high redox ability and reactivity of Brønsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor.
“…In addition, the characterization peaks at 1460 and 875 cm −1 for both AC and (P/Ti-1/2)15@AC were intensified possibly because of the adsorbed NH 3 dehydrogenation process ( Fig. 3b, d), which was reported as the controlling step of denitrification 45,46 . On the basis of the XPS results, the additional surface oxygen of the sample after the SCR reaction increased by 4.66% and 0.94% of AC and (P/Ti-1/2)15@AC (Table 3).…”
Activated coke (AC) has great potential in the field of low-temperature NO removal (DeNOx), especially the branch prepared by blending modification. In this study, the AC-based pyrolusite and/or titanium ore blended catalysts were prepared and applied for DeNOx. The results show blending pyrolusite and titanium ore promoted the catalytic performance of AC (Px@AC, Tix@AC) clearly, and the co-blending of two of them showed a synergistic effect. The (P/Ti-1/2)15@AC performed the highest NO conversion of 66.4%, improved 16.9% and 16.0% respectively compared with P15@AC and Ti15@AC. For the (P/Ti-1/2)15@AC DeNOx, its relative better porous structure (SBET = 364 m2/g, Vmic = 0.156 cm3/g) makes better mass transfer and more active sites exposure, stronger surface acidity (C–O, 19.43%; C=O, 4.16%) is more favorable to the NH3 adsorption, and Ti, Mn and Fe formed bridge structure fasted the lactic oxygen recovery and electron transfer. The DeNOx of (P/Ti-1/2)15@AC followed both the E–R and L–H mechanism, both the gaseous and adsorbed NO reacted with the activated NH3 due to the active sites provided by both the carbon and titanium.
“…For K-a-MnO 2 ,i tw as first treated with NH 3 /N 2 for 30 min and then followed by purging with N 2 for 30 min at 150 8 8C (Figure 4c;S upporting Information, Figure S15 a), the peaks appearing at 1419 and 1300 cm À1 were attributed to coordinated NH 3 bound to Lewis acid sites, [13] whereas no obvious bonds linked to Brønsted acid sites were observed. It is noteworthy that the amide species ( À NH 2 )r esulting from dehydrogenation of adsorbed NH 3 was also detected (1540 cm À1 ), [14] which can react directly with gaseous or weakly adsorbed NO to form NH 2 NO and finally decompose into N 2 and H 2 O. After switching the gas atmosphere to NO + O 2 ,c oordinated NH 3 (1419 and 1300 cm À1 )a nd the amide species ( À NH 2 )w ere decreased rapidly within 5min.…”
The unexpected phenomenon and mechanism of the alkali metal involved NH3 selective catalysis are reported. Incorporation of K+ (4.22 wt %) in the tunnels of α‐MnO2 greatly improved its activity at low temperature (50–200 °C, 100 % conversion of NOx vs. 50.6 % conversion over pristine α‐MnO2 at 150 °C). Experiment and theory demonstrated the atomic role of incorporated K+ in α‐MnO2. Results showed that K+ in the tunnels could form a stable coordination with eight nearby Osp3
atoms. The columbic interaction between the trapped K+ and O atoms can rearrange the charge population of nearby Mn and O atoms, thus making the topmost five‐coordinated unsaturated Mn cations (Mn5c, the Lewis acid sites) more positive. Therefore, the more positively charged Mn5c can better chemically adsorb and activate the NH3 molecules compared with its pristine counterpart, which is crucial for subsequent reactions.
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