A comparative study of the H2-assisted selective catalytic reduction of nitric oxide by propene over noble metal (Pt, Pd, Ir)/γ-Al2O3 catalysts

• H2 enhances NO conversion of the Pt-, Pd- and Ir-catalyzed C3H6-SCR of NOx.
• H2-induced de-NOx enhancement follows the sequence: Pt > Ir > Pd.
• A two-maxima NO conversion pattern is obtained on Pt and Pd, instead of one on Ir.
• A synergy between H2 and C3H6 is revealed over Ir, boosting the deNOx performance.

The impact of H2 as additional reducing agent on the SCR of NO with C3H6 in excess oxygen, was comparatively explored over low noble metal loading (0.5 wt%), Pt/γ-Al2O3, Pd/γ-Al2O3, Ir/γ-Al2O3 catalysts. To gain insight into the role of H2, the reactions NO + C3H6 + O2 (R#1), NO + C3H6 + O2 + H2 (R#2), NO + H2 + O2 (R#3) were employed. In respect to propene oxidation, the Pd > Pt > Ir sequence was obtained under R#1, since they exhibit complete conversion at 220, 250, 325 °C, respectively; all metals exhibit moderate deNOx performances (XNO, <40%). H2 co-presence (R#2) promotes both the NO and C3H6 conversions, which is valid in the whole temperature interval investigated (50–400 °C), being more substantial for Pt/γ-Al2O3 and Ir/γ-Al2O3, less beneficial for Pd/γ-Al2O3. A two-maxima feature is obtained on XNO pattern (at ∼100 and ∼230 °C) of Pt and Pd during R#2. The low temperature maximum −attributed to NO reduction by H2- is substantially more pronounced on Pt than Pd, offering XNO ∼90% and SN2 ∼85%; the high temperature maximum—attributed to NO reduction by C3H6—is higher by ∼15% on both Pt and Pd, in respect to the values obtained during R#1, while SN2 remained unaffected. Different XNO pattern with one maximum is obtained over Ir, implying a synergistic interaction between H2 and C3H6. This synergy is accompanied by a substantial widening of the NO reduction window toward lower temperatures and a considerable increase on both XNO,max and SN2 (from XNO ∼30% with SN2 ∼55% during R#1 to XNO ∼70% with SN2 ∼95% during R#2). The specific features of all reactions and metals employed are comparatively discussed.

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