Sulfur poisoning and NH3 regeneration of Pt/Al2O3: oxidations of SO2, NH3, NO and C3H6 as probe reactions

Abstract

The impact of SO_x (x = 2, 3) on the activity of a model diesel oxidation catalyst (DOC: Pt/Al₂O₃) is examined for the oxidations of sulfur dioxide (SO₂), nitric oxide (NO), and propylene (C₃H₆). Flow reactor studies conducted of the Pt/Al₂O₃ washcoated monolith before and after sulfation quantify the detrimental deactivation. Subsequent exposure of the poisoned catalyst to NH₃ without and with O₂ enables the assessment of its effectiveness as a regenerant. A combination of steady state reaction, temperature programmed desorption (TPD) and reaction (TPR), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) are conducted to characterize the poisoning and regeneration processes. Mechanistic explanations are proposed consistent with DRIFTS-identified surface species. The findings suggest a potential mitigation strategy for restoring the activity of Pt/Al₂O₃ in diesel emission control. The effectiveness of the activation restoration strategy is in the order of NH₃ oxidation > SO₂ oxidation > C₃H₆ oxidation > NO oxidation.