NH3 Regeneration of Sulfur Poisoned Pt/Al2O3

dc.contributor.advisorHarold, Michael P.
dc.contributor.committeeMemberBalakotaiah, Vemuri
dc.contributor.committeeMemberGrabow, Lars C.
dc.contributor.committeeMemberLouie, Stacey M.
dc.contributor.committeeMemberBrankovic, Stanko R.
dc.creatorFang, Chenhao
dc.date.createdDecember 2023
dc.description.abstractSulfur poisoning is a ubiquitous challenge in diesel emission control. The commercial Ammonia Slip Catalyst (ASC) is composed of an NH3 oxidation function (Pt/Al2O3) and a selective catalytic NOx reduction function (Cu/zeolite). This report focuses on the impact of sulfur in the form of SOx (x = 2, 3) on the performance of a low loading Pt/Al2O3 (0.1 wt.% Pt/Al2O3) monolith catalyst characteristic of the oxidation function of the ASC. Sulfur that accumulates in the form of sulfates and bisulfates significantly decreases the Pt/Al2O3 catalytic oxidation activity. However, during the ensuing temperature ramp mimicking engine warmup the presence of NH3 serves to regenerate the S-poisoned catalyst. A mechanism involving sulfate formation in the form of Al2(SO4)3 at low temperature, followed by reaction with NH3 forming (NH4)2SO4 and its subsequent decomposition at elevated temperature is postulated to explain the restoration of the ASC activity. A combination of light-off experiments, temperature-programmed reaction, and DRIFTS measurements corroborate the mechanism. NH3 reacts with some of the aluminum sulfate formed during sulfur-aging process, forming ammonium sulfate. Under a temperature ramp, the ammonium sulfate decomposes, releasing NH3 and SO2, leading to the recovery of the catalytic activity. Since NH3 regeneration method works pretty well for the low loading Pt/Al2O3 catalyst, it is of interest to see if this method is applicable to high loading Pt/Al2O3 catalyst. The impact of SOx (x = 2, 3) on the activity of high loading Pt/Al2O3 is examined for the oxidations of sulfur dioxide (SO2), propylene (C3H6) and nitric oxide (NO). Flow reactor studies of the high loading Pt/Al2O3 before and after sulfation are conducted. The effectiveness of NH3 as a regenerant to remove accumulated sulfur species at low to moderate temperature is investigated. A combination of steady state reaction, temperature programmed desorption (TPD) and temperature programmed 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.
dc.description.departmentChemical and Biomolecular Engineering, William A. Brookshire Department of
dc.format.digitalOriginborn digital
dc.identifier.citationPortions of this document appear in: Fang, Chenhao, and Michael P. Harold. "Low temperature NH 3 regeneration of a sulfur poisoned Pt/Al 2 O 3 monolith catalyst." Catalysis Science & Technology 13, no. 23 (2023): 6718-6732.
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectsulfur poisoning, regeneration
dc.titleNH3 Regeneration of Sulfur Poisoned Pt/Al2O3
dcterms.accessRightsThe full text of this item is not available at this time because the student has placed this item under an embargo for a period of time. The Libraries are not authorized to provide a copy of this work during the embargo period.
thesis.degree.collegeCullen College of Engineering
thesis.degree.departmentChemical and Biomolecular Engineering, William A. Brookshire Department of
thesis.degree.disciplineChemical Engineering
thesis.degree.grantorUniversity of Houston
thesis.degree.nameDoctor of Philosophy


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