Abstract
A γ-AlOOH/γ-Al₂O₃ washcoat overlayer, applied to a PdO(Pt/CeO₂)/γ-AlOOH/γ-Al₂O₃ on cordierite (2MgO·2Al₂O₃·5SiO₂) mini-monolith catalyst (400 cells per square inch, 1 cm diameter × 2.5 cm length), is shown to reduce the impact of H₂O and SO₂ on the catalyst activity and stability during CH₄ oxidation at low temperatures (<500 °C). The washcoat overlayer covered the Pd (and Ce and Pt when present) and decreased the catalyst CH₄ oxidation activity in a dry feed gas (0.07 vol % CH₄, 8.5 vol % O₂, 0.06 vol % CO, 8 vol % CO₂) at a gas hourly space velocity (GHSV) of 36 000 h–¹. However, when H₂O (2, 5, and 10 vol %) and SO₂ (2 and 5 ppm) were added to the feed gas, the loss in catalyst activity was reduced and the catalyst stability was improved. The overlayer provided additional sites for both SOₓ and H₂O adsorption, thereby reducing their adsorption on the active phase of the catalysts, and consequently, the catalysts maintained higher activity in the presence of both SO₂ and H₂O over periods of up to 200 h.
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