Downstream SCR Catalyst for Diesel NOx Conversion
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Solution Overview
Problem
Current diesel particulate filters with high SCR catalyst loadings face challenges in managing backpressure while maintaining effective NOx conversion, especially under varying temperatures and exposure to deleterious exhaust components, which affects fuel efficiency and catalyst durability.
Innovation Solution
A system comprising a particulate filter with a first SCR catalyst and a downstream substrate with a second SCR catalyst, optimized for reduced catalyst loading to achieve balanced NOx conversion and backpressure, utilizing catalyst compositions like zeolites with a CHA structure and mixed oxides of V2O5, WO3, and TiO2, to ensure efficient NOx reduction across a range of temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high SCR catalyst loading is used in the particulate filter, then NOx conversion effectiveness is improved, but backpressure increases excessively affecting fuel efficiency
Solution Approach 1:
The exhaust treatment system is divided into two distinct stages: a particulate filter with low SCR catalyst loading (0.1-2.5 g/in³) for primary NOx conversion, and a downstream substrate with additional SCR catalyst for secondary NOx reduction. This segmentation allows each component to operate at optimized loading levels, preventing excessive backpressure while achieving comprehensive NOx treatment.
Solution Approach 2:
The system transitions from a single-point catalyst loading approach to a distributed spatial arrangement across two components. By spreading the catalyst loading across the particulate filter and downstream substrate, the system achieves effective NOx conversion without concentrating excessive catalyst mass in one location that would cause prohibitive backpressure.
2Reliability
If high SCR catalyst loading is used to maintain NOx conversion, then catalytic activity is improved, but catalyst durability decreases due to exposure to deleterious exhaust components
Solution Approach 1:
Different regions of the exhaust treatment system have different catalyst loading characteristics. The particulate filter maintains relatively low catalyst loading to minimize exposure to deleterious components during the high-temperature regeneration process, while the downstream substrate provides additional catalytic capacity. This local differentiation protects catalyst durability while maintaining overall activity.
Solution Approach 2:
The system design anticipates the damaging effects of high-temperature regeneration and deleterious exhaust components by distributing catalyst loading across two components. This distribution acts as a cushion, preventing any single catalyst zone from suffering excessive degradation, thereby extending overall catalyst durability.
3Loss of energy
If reduced catalyst loading is used in the particulate filter, then backpressure is controlled, but NOx conversion effectiveness may be compromised
Solution Approach 1:
The exhaust treatment process continues effectively across two sequential stages. The particulate filter performs initial NOx conversion with low catalyst loading and controlled backpressure, followed by a downstream substrate that continues the NOx reduction process. This continuous action ensures comprehensive NOx treatment without requiring excessive catalyst loading in any single component.
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 system achieves NOx conversion rates of 50-100% with a backpressure increase of less than 25%, maintaining catalytic activity and durability, even at high temperatures, while minimizing the risk of catalyst degradation and fuel efficiency loss.
Implementation Method 1
a particulate filter coated with a least a first catalyst effective to promote selective catalytic reduction ('SCR') of NOx by a reductant
Implementation Method 2
a substrate coated with at least a second SCR catalyst
Implementation Method 3
Oxidation catalysts that contain platinum group metals, base metals and combinations thereof are known to facilitate the treatment of diesel engine exhaust by promoting the conversion of both HC and CO gaseous pollutants and some proportion of the particulate matter through oxidation of these pollutants to carbon dioxide and water
Implementation Method 4
oxidation catalysts that contain platinum group metals (which are typically dispersed on a refractory oxide support) promote the oxidation of nitric oxide (NO) to NO2
Data Source
AI summary
Emissions treatment systems and methods for treating an engine exhaust gas stream containing NOx and particulate matter are disclosed including a particulate filter comprising a first SCR catalyst for NOx conversion a second SCR catalyst for NOx conversion on a substrate disposed downstream of the particulate filter. The system NOx conversion and the system back pressure increase lie within a targeted operational window.