Effect of WO ₃ and Fe ₂ O ₃ Additives on H ₂ ‐SCR Over Pt/SiO ₂ ─Al ₂ O ₃ Catalysts: An Operando DRIFTS Investigation

ABSTRACT Low‐loaded 0.3 wt.% Pt/SiO 2 ─Al 2 O 3 catalysts, either unmodified or modified with WO 3 or Fe 2 O 3 , were investigated to elucidate the reaction pathways and mechanistic features of the NO X selective catalytic reduction by hydrogen (H 2 ‐SCR) over a wide temperature range. At low temperatures (50–100°C), catalytic activity is governed by H 2 activation, which is significantly enhanced by WO 3 addition, whereas Fe 2 O 3 inhibits NO reduction and consequently suppresses low‐temperature N 2 O formation. In the intermediate temperature range (80–200°C), distinct H 2 ‐SCR behaviors are linked to the reactivity of in situ–formed NH 3 toward residual NO X . This NH 3 ‐SCR type pathway is strongly promoted by WO 3 , while Fe 2 O 3 hampers NH 3 activation at low temperature, leading to increased NH 3 slip. However, this reaction pathway remains limited to a narrow temperature window, as it requires the presence of unconverted NO X . At higher temperatures (> 150°C), the NH 3 + O 2 reaction, previously identified as the dominant deNO X route, is largely unaffected by the addition of WO 3 or Fe 2 O 3 . Moreover, the undesired N 2 O formation in this high temperature range originates not only from the ammonia oxidation route, but a possible contribution from the decomposition of ammonium nitrate–like surface species was also evidenced.