Abstract
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.
Highlights
NH3-selective catalytic reduction (SCR) is important process for removal of NOx
Tungstensubstituted vanadium oxide was synthesized by the oxalate method using ammonia metavanadate, ammonia metatungstate, and oxalic acid
The stability of the catalysts was increased by the addition of tungsten because bulk WO6 units connected vanadium oxide layers
Summary
NH3-SCR (selective catalytic reduction) is important process for removal of NOx. water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. 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 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 the catalytic cycle is less affected by water vapor. Vanadium (V) oxide-based catalysts (V2O5/TiO2, V2O5–WO3/ TiO2) have been used as industrial catalysts for stationary boiler systems because they show high N2 selectivity, good thermal stability, and low SO2 oxidation activity to SO32. Their high working temperature limits the latitude of the deNOx process. Many studies have been carried out to develop low-temperature SCR catalysts such as metal oxide-based materials (V, Mn, Cr, Cu, W, Ce, and Fe)[1,5,6,7,8,9,10] and ion-exchanged zeolite (Cu-ZSM-5, Fe-ZSM-5, Cu-CHA, and Cu-SSZ-13)[1,11,12,13,14,15,16,17]
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