Segmented SCR Catalyst for Cold Start NOx Control
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Solution Overview
Problem
Current Selective Catalytic Reduction (SCR) systems for reducing NOx emissions from diesel engines are inefficient during the cold start period due to the minimal temperature requirement for urea decomposition and SCR catalyst activity, which exceeds the initial cold start emissions period.
Innovation Solution
A catalyst article with a two- or three-zone configuration, including a passive NOx adsorber (PNA) and an ammonia slip catalyst (ASC) combined with a diesel oxidation or exotherm catalyst, where the PNA is located upstream to trap NOx at low temperatures and assist in controlling ammonia slip, CO, and HC emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SCR catalyst is used, then NOx conversion efficiency is improved at high temperatures, but NOx reduction performance deteriorates during cold start period
Solution Approach 1:
The catalyst is divided into multiple functional zones: a first zone containing a passive NOx adsorber (PNA) for cold start operation, and a second zone containing an SCR catalyst for high-temperature operation. This segmentation allows each zone to specialize in different temperature ranges, resolving the contradiction between cold start and high-temperature performance.
Solution Approach 2:
The passive NOx adsorber in the first zone performs preliminary NOx trapping during cold start conditions before the SCR catalyst becomes active. This preliminary action stores NOx on the PNA, which is then released and reduced when the SCR catalyst reaches operating temperature, ensuring continuous NOx control across all temperature conditions.
2Reliability
If SCR catalyst activity is enhanced for better NOx reduction, then operating temperature requirement increases, but cold start emissions control worsens
Solution Approach 1:
The catalytic system is segmented into a low-temperature active first zone with PNA and a high-temperature optimized second zone with SCR catalyst. This allows the SCR catalyst to be designed for high-temperature efficiency without compromising cold start performance, as the PNA handles low-temperature NOx trapping independently.
Solution Approach 2:
The invention changes the operational parameters of different catalyst zones to match their optimal temperature ranges. The PNA operates effectively at low temperatures with different kinetic characteristics, while the SCR catalyst operates at higher temperatures with optimized parameters for maximum NOx conversion efficiency, resolving the temperature-performance contradiction.
3Reliability
If multiple catalyst functions are integrated into separate components, then each function performs optimally, but system complexity and space requirements increase
Solution Approach 1:
The invention merges the PNA and SCR catalyst functions into a single integrated catalyst article with two zones on one substrate. This combining approach maintains the optimal performance of each function while reducing system complexity and space requirements compared to using separate components, as the two zones are positioned sequentially on the same substrate structure.
Solution Approach 2:
The catalyst article is designed as a multi-functional universal component that performs both cold start NOx trapping (PNA function) and high-temperature NOx reduction (SCR function) within a single device. This multi-functionality eliminates the need for multiple separate components, reducing system complexity while maintaining comprehensive emissions control performance across all operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces NOx emissions during the cold start period without compromising NOx conversion and N2 selectivity, improving fuel economy and engine power output by integrating SCR, ASC, and DOC functionalities into a compact space.
Implementation Method 1
The PNA can provide the additional benefit of assisting with controlling NH3 slip as well as CO and HC emission
Implementation Method 2
an ammonia slip catalyst (ASC) comprising a platinum group metal on a support and a first SCR catalyst
Implementation Method 3
The reduction of NOx to N2 is particularly problematic because the exhaust gas contains enough oxygen to favor oxidative reactions instead of reduction. Notwithstanding, NOx can be reduced by a process commonly known as Selective Catalytic Reduction (SCR).
Implementation Method 4
a catalyst selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC)
Data Source
AI summary
A catalyst article including a substrate with an inlet side and an outlet side, a first zone and a second zone, where the first zone includes a passive NOx adsorber (PNA), and an ammonia slip catalyst (ASC) comprising a platinum group metal on a support and a first SCR catalyst; where the second zone includes a catalyst selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC); and where the first zone is located upstream of the second zone. The first zone may include a bottom layer with a blend of: (1) the platinum group metal on a support and (2) the first SCR catalyst; and a top layer with a second SCR catalyst, the top layer located over the bottom layer.