Reaction and Transport Coupling in Multi-Functional Catalysts for Selective Oxidation of Ammonia to Nitrogen

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dc.contributor.advisorHarold, Michael P.
dc.contributor.committeeMemberLuss, Dan
dc.contributor.committeeMemberGrabow, Lars C.
dc.contributor.committeeMemberBrankovic, Stanko R.
dc.contributor.committeeMemberKumar, Ashok
dc.creatorDhillon, Pritpalsingh
dc.date.accessioned2020-01-03T05:46:00Z
dc.date.createdDecember 2019
dc.date.issued2019-12
dc.date.submittedDecember 2019
dc.date.updated2020-01-03T05:46:01Z
dc.description.abstractA multi-functional catalytic reactor (popularly known as “Ammonia Slip Catalyst (ASC)” or “AMOx”) comprising Pt/Al2O3 and Cu or Fe-exchanged zeolite is utilized for selective oxidization of NH3 to N2 in the diesel engine emission control system. Pt catalyzes the oxidation of NH3 to four products (N2, N2O, NO, NO2) while the metal-exchanged zeolite concurrently catalyzes the selective catalytic reduction of NO/NO2 with NH3, directing the product mixture towards N2. The state-of-the-art ASC has a dual-layer washcoat architecture with a bottom layer of Pt/Al2O3 and a top layer of Cu/SSZ-13. As emission control catalysts experience degradation under the severe operating conditions which can negatively impact the product distribution and conversion. The first part of this dissertation study elucidates the effect of hydrothermal aging on the performance of a Pt/γ-Al2O3, Cu/SSZ-13 and dual-layer washcoated monolith used for oxidation of ammonia. The catalysts was subjected to a feed stream containing H2O at 550 oC for over 250 hours and performance was measured at discrete intervals as it was progressively aged. In the next part of this study, the enhanced mass transport phenomenon coupled with multi-functional catalytic reactions in ASC is investigated. Earlier works have shown that pore diffusion can be limiting in ASC. we used sacrificial agents (polymer, yeast) to increase the porosity of washcoat for ASC. The sacrificial agents are removed by oxidation generating pores to increase the washcoat macroporosity. Steady state reaction experiments showed a noted increase in NH3 conversion while testing NH3 oxidation the dual-layer ASC with negligible change in N2 selectivity. Modeling and analysis of ASC catalysts is presented using 1 + 1 dimensional reactor model containing tuned multi-step kinetic formulations to simulate ASC performance for understanding and optimization. We also describe a systematic study to identify the ASC architecture and composition that optimize the trade-off between conversion and selectivity. The in-house synthesized ASC samples span the single layer Pt/Al2O3, conventional dual-layer Pt/Al2O3 + Cu/SSZ-13, uniform single layer of mixed Pt/Al2O3 + Cu/SSZ-13, and a hybrid design comprising a bottom layer of mixed Pt/Al2O3 + Cu/SSZ-13 and a thin top layer of Cu/SSZ-13.
dc.description.departmentChemical and Biomolecular Engineering, Department of
dc.format.digitalOriginborn digital
dc.format.mimetypeapplication/pdf
dc.identifier.citationPortions of this document appear in: Dhillon, Pritpal S., Michael P. Harold, Di Wang, Ashok Kumar, and Saurabh Joshi. "Hydrothermal aging of Pt/Al2O3 monolith: Washcoat morphology degradation effects studied using ammonia and propylene oxidation." Catalysis Today 320 (2019): 20-29. And in: Dhillon, Pritpal S., Michael P. Harold, Di Wang, Ashok Kumar, and Saurabh Y. Joshi. "Enhanced transport in washcoated monoliths: Application to selective lean NOx reduction and ammonia oxidation." Chemical Engineering Journal 377 (2019): 119734. And in: Dhillon, Pritpal S., Michael P. Harold, Di Wang, Ashok Kumar, and Saurabh Y. Joshi. "Modeling and analysis of transport and reaction in washcoated monoliths: Cu-SSZ-13 SCR and dual-layer Cu-SSZ-13+ Pt/Al 2 O 3 ASC." Reaction Chemistry & Engineering (2019).
dc.identifier.urihttps://hdl.handle.net/10657/5651
dc.language.isoeng
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.subjectAmmonia Oxidation
dc.subjectSelective catalytic reduction (SCR)
dc.titleReaction and Transport Coupling in Multi-Functional Catalysts for Selective Oxidation of Ammonia to Nitrogen
dc.type.dcmiText
dc.type.genreThesis
local.embargo.lift2021-12-01
local.embargo.terms2021-12-01
thesis.degree.collegeCullen College of Engineering
thesis.degree.departmentChemical and Biomolecular Engineering, Department of
thesis.degree.disciplineChemical Engineering
thesis.degree.grantorUniversity of Houston
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

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