Bulk tungsten-substituted vanadium oxide for low-temperature NOx removal in the presence of water.

NH-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 NH-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 NH, 4% O, SV = 40000 mL h g). 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. NH species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V 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.