Applied and Fundamental Studies of LNT-SCR Dual-layer Monolithic Catalysts for Lean NOx Emission Control
type: CreativeWork
description: The increasingly stringent both greenhouse gas (GHG) and tailpipe NOx emission standards have driven the continuous improvement of commercial deNOx technologies, NOx reduction & storage (NSR, also referred to as lean NOx trap (LNT)) and selective catalytic reduction (SCR) technologies. This dissertation conducts applied and fundamental studies of coupled LNT-SCR dual-layer catalysts with the aim of expanding the operating temperature window of a conventional NSR system at lower cost. This is accomplished by a systems approach to identify the influencing factors such as catalyst composition and architecture, types of reducing agents, operating and regeneration strategies, as well as synergistic interactions between the LNT and SCR. We start with performance evaluation of dual-layer catalysts under different regeneration conditions such as H2 alone, CO/H2 mixture and a simulated diesel exhaust containing the CO/H2/C3H6 mixture. Spatial analyses of NH3 yield and NOx conversion along the LNT monolith identify the upstream zone as major NH3 generator and NOx reducer, especially at temperatures exceeding 300 oC. Zoning of either or both the SCR and LNT having a dual-layer structure enables an increase in the low-temperature (200-250 oC) NOx conversion, and minimizes the high temperature (300-400 oC) conversion loss caused by the SCR diffusion resistance and undesired NH3 oxidation by the LNT. The hydrocarbon (HC) reductant leads to an alternative LNT-SCR synergy to classical NH3-pathway; a LNT-assisted HC-SCR pathway. The LNT promotes the formation of partially oxidized HC intermediates during the rich purge which are otherwise difficult to be generated by the Cu-zeolite layer at low temperatures. These activated intermediates can be captured and utilized by the SCR catalyst via HC-SCR during the ensuing lean phase. This pathway plays a major role at low temperatures (<= 225 oC) using the simulated diesel exhaust feed. We investigated the steady-state and transient effect…
abstract: The increasingly stringent both greenhouse gas (GHG) and tailpipe NOx emission standards have driven the continuous improvement of commercial deNOx technologies, NOx reduction & storage (NSR, also referred to as lean NOx trap (LNT)) and selective catalytic reduction (SCR) technologies. This dissertation conducts applied and fundamental studies of coupled LNT-SCR dual-layer catalysts with the aim of expanding the operating temperature window of a conventional NSR system at lower cost. This is accomplished by a systems approach to identify the influencing factors such as catalyst composition and architecture, types of reducing agents, operating and regeneration strategies, as well as synergistic interactions between the LNT and SCR. We start with performance evaluation of dual-layer catalysts under different regeneration conditions such as H2 alone, CO/H2 mixture and a simulated diesel exhaust containing the CO/H2/C3H6 mixture. Spatial analyses of NH3 yield and NOx conversion along the LNT monolith identify the upstream zone as major NH3 generator and NOx reducer, especially at temperatures exceeding 300 oC. Zoning of either or both the SCR and LNT having a dual-layer structure enables an increase in the low-temperature (200-250 oC) NOx conversion, and minimizes the high temperature (300-400 oC) conversion loss caused by the SCR diffusion resistance and undesired NH3 oxidation by the LNT. The hydrocarbon (HC) reductant leads to an alternative LNT-SCR synergy to classical NH3-pathway; a LNT-assisted HC-SCR pathway. The LNT promotes the formation of partially oxidized HC intermediates during the rich purge which are otherwise difficult to be generated by the Cu-zeolite layer at low temperatures. These activated intermediates can be captured and utilized by the SCR catalyst via HC-SCR during the ensuing lean phase. This pathway plays a major role at low temperatures (<= 225 oC) using the simulated diesel exhaust feed. We investigated the steady-state and transient effect…
author: Zheng, Yang
language: eng
keywords: Lean NOx traps, Selective catalytic reduction (SCR), NOx reduction
date published: 2015-12
date modified: 2026-07-24T02:32:27Z
provider: University of Houston
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Houston

PropertyValue
property ID: Handle
value: https://hdl.handle.net/10657/5451