Intra-catalyst CH4 oxidation pathways on a Pd/Al2O3/CeZrOx-based commercial catalyst and implications on NOx conversion profiles for a natural gas vehicle exhaust under lambda modulation

Dhruba J. Deka; Josh A. Pihl; Calvin R. Thomas; William P. Partridge

doi:10.1016/j.cej.2023.144803

Intra-catalyst CH₄ oxidation pathways on a Pd/Al₂O₃/CeZrO_x-based commercial catalyst and implications on NO_x conversion profiles for a natural gas vehicle exhaust under lambda modulation

Dhruba J. Deka, Josh A. Pihl, Calvin R. Thomas, William P. Partridge

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

Abstract

The performance of a three-way catalyst (TWC) in natural gas-powered vehicles is enhanced by periodic changes in air-to-fuel ratio (λ-modulation). The reaction networks and sequences inside the catalyst that facilitate such enhanced performance have not been extensively investigated. This work applied intra-catalyst measurements (SpaciMS) to analyze the transient spatiotemporal gas concentrations inside a Pd-based TWC to establish relationships between CH₄, NO_x, CO and H₂ conversion pathways. Steam reforming and partial oxidation were revealed to be the main CH₄ conversion routes. The cyclic rich-lean conditions combined with the oxygen storage capacity (OSC) of the TWC generate reduced and oxidized zones that are constantly moving within the catalyst, changing the dominant chemical reactions occurring on the surface. In the reduced zones, OSC is depleted while CH₄ is converted through steam reforming and NO_x is converted through reactions with H₂, CO, and other surface-bound reducing fragments formed by CH₄ conversion. In the oxidized zones, OSC is replenished, CH₄ is converted by partial oxidation, and H₂, CO, and NH₃ are oxidized. The length of lean-rich phases impacts the catalyst performance significantly; too short or too long of a rich or lean phase can lower the overall conversion of reactive species. An inhibition of CH₄ conversion was observed during the rich phase possibly due to CO-poisoning of active sites. The intra-catalyst measurements revealed that the catalyst consists of three distinct reaction zones and their lengths vary with modulation conditions. Various modulation frequencies, amplitudes, λ-centers, and temperatures were investigated which allowed an understanding of how these parameters affect the reaction zones and catalyst utilization. Understandings from this work can enable adaptive λ-control strategies to optimize the overall TWC performance over a range of vehicle operating conditions.

Original language	English
Article number	144803
Journal	Chemical Engineering Journal
Volume	472
DOIs	https://doi.org/10.1016/j.cej.2023.144803
State	Published - Sep 15 2023

Funding

This research was supported in part by the DOE Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) and used resources at the National Transportation Research Center, a DOE-EERE User Facility at Oak Ridge National Laboratory. We thank Petr Kočí, Tomáš Hlavatý and Martin Isoz of the University of Chemistry and Technology, Prague, for their work with DJD and WPP developing the practically noninvasive Fast-SpaciMS capillary sampling configuration used here; that work is referenced here [37] and we are working on a related publication. We thank Michael Harold‘s group at University of Houston for valuable discussions and insights. We thank DOE VTO Program & Technology Managers: Gurpreet Singh, Siddiq Khan, and Ken Howden for supporting the project. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).

Keywords

Lean-Rich cycling
Methane oxidation catalyst
Methane steam reforming
NO abatement
SpaciMS
Three-way catalyst

Access to Document

10.1016/j.cej.2023.144803

Cite this

@article{628483887d12442081295ea68a9405df,

title = "Intra-catalyst CH4 oxidation pathways on a Pd/Al2O3/CeZrOx-based commercial catalyst and implications on NOx conversion profiles for a natural gas vehicle exhaust under lambda modulation",

abstract = "The performance of a three-way catalyst (TWC) in natural gas-powered vehicles is enhanced by periodic changes in air-to-fuel ratio (λ-modulation). The reaction networks and sequences inside the catalyst that facilitate such enhanced performance have not been extensively investigated. This work applied intra-catalyst measurements (SpaciMS) to analyze the transient spatiotemporal gas concentrations inside a Pd-based TWC to establish relationships between CH4, NOx, CO and H2 conversion pathways. Steam reforming and partial oxidation were revealed to be the main CH4 conversion routes. The cyclic rich-lean conditions combined with the oxygen storage capacity (OSC) of the TWC generate reduced and oxidized zones that are constantly moving within the catalyst, changing the dominant chemical reactions occurring on the surface. In the reduced zones, OSC is depleted while CH4 is converted through steam reforming and NOx is converted through reactions with H2, CO, and other surface-bound reducing fragments formed by CH4 conversion. In the oxidized zones, OSC is replenished, CH4 is converted by partial oxidation, and H2, CO, and NH3 are oxidized. The length of lean-rich phases impacts the catalyst performance significantly; too short or too long of a rich or lean phase can lower the overall conversion of reactive species. An inhibition of CH4 conversion was observed during the rich phase possibly due to CO-poisoning of active sites. The intra-catalyst measurements revealed that the catalyst consists of three distinct reaction zones and their lengths vary with modulation conditions. Various modulation frequencies, amplitudes, λ-centers, and temperatures were investigated which allowed an understanding of how these parameters affect the reaction zones and catalyst utilization. Understandings from this work can enable adaptive λ-control strategies to optimize the overall TWC performance over a range of vehicle operating conditions.",

keywords = "Lean-Rich cycling, Methane oxidation catalyst, Methane steam reforming, NO abatement, SpaciMS, Three-way catalyst",

author = "Deka, {Dhruba J.} and Pihl, {Josh A.} and Thomas, {Calvin R.} and Partridge, {William P.}",

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doi = "10.1016/j.cej.2023.144803",

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Intra-catalyst CH₄ oxidation pathways on a Pd/Al₂O₃/CeZrO_x-based commercial catalyst and implications on NO_x conversion profiles for a natural gas vehicle exhaust under lambda modulation. / Deka, Dhruba J.; Pihl, Josh A.; Thomas, Calvin R. et al.
In: Chemical Engineering Journal, Vol. 472, 144803, 15.09.2023.

Research output: Contribution to journal › Article › peer-review

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AU - Partridge, William P.

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