Selective catalytic reduction of NO by hydrogen (H2-SCR) on WON-promoted CezZr1-zO2 solids

The selective catalytic reduction of NOx by H-2 (H-2-SCR) under strongly oxidizing conditions (520 ppm NOx/1% H-2/5% O-2/10% CO2/He; NO:NO2-4:1-9:1) in the 150-600 degrees C range has been studied over 3 wt-% W-promoted Ce02-Zr02 solids (85 wt-% Ce02-15 wt-% Zr02 (CeZr), and 17 wt-% CeO2-83 wt-% Zr (ZrCe) synthesised by a proprietary method) for the first time. The highest NOx conversion (XN0, = 54%) was obtained on the W-ZrCe (Zr-rich) solid at 300 degrees C (GHSV of 51,000 h-1), whereas N2 -selectivity was in the 77-92%-range over both W-ZrCe (Zr-rich) and W-CeZr (Ce-rich) catalysts. Significantly higher integral specific rates (RNo, ja,mol NO m-2 mm-1) were estimated on the W-ZrCe (Zr-rich) catalyst compared to the W-CeZr (Ce-rich) one in the 250-350 degrees C range. The formation of adsorbed NO under 0.1% NO/10% 02/He gas treatment at 25 degrees C followed by H-2/O-2-TPSR experiments revealed that at least two different kinds of active NOx of low concentration (4-7 mu mol g(-1)) were formed on both catalysts, whereas other inactive (spectator) NOx species formed were of larger concentration (>160 ji,mol UV-vis/DRS studies revealed that deposition of 3 wt-% Won ZrCe (Zr-rich) mixed metal oxide following calcination at 600 degrees C resulted in the formation of both polymeric WOx and WO3 clusters, whereas on CeZr (Ce-rich) only the latter phase (W6+) was seen. Large differences in the concentration (p,mol m-2) and strength of surface acid sites between the W-CeZr and W-ZrCe solids were revealed after performing NH3-TPD and NH3-DRIFTS. These results were found to correlate with the specific H2-SCR rate (Ilmol m-2 min) obtained for the two solids. In particular, the surface acid sites on W-ZrCe and W-CeZr solids were found to be 5.96 and 2.76 mu mol m(-2), respectively, whereas the specific reaction rate was 0.14 and 0.046 mu mol m(-2) min at 300 and 250 degrees C, at which maximum rates were observed, respectively. (C) 2014 Elsevier B.V. All rights reserved.