Integrated SCR DPF with Oxygen Storage Catalyst
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional diesel exhaust treatment systems face challenges with SCR performance during start-up and early operation cycles, and they incur an inverse tradeoff between NOx reduction and filter regeneration efficiencies.
Innovation Solution
A diesel particle filter (DPF) with a coating that includes an SCR catalyst, an oxidation catalyst (OC), and an oxygen storage catalyst (OSC) is used, which promotes selective catalytic reduction of NOx, oxidation of hydrocarbons and carbon monoxide, and enhances filter regeneration, while maintaining NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SCR converter is placed downstream of a cDPF, then the SCR converter can reduce NOx emissions, but the thermal mass of the cDPF delays heat transfer and limits SCR performance during start-up and early operation cycles
Solution Approach 1:
The patent combines the SCR catalyst and OC/OSC catalysts into a single integrated particle filter device. The SCR catalyst is applied to the outer surface of the filter walls, while the OC and OSC catalysts are incorporated into the washcoat layer. This merging eliminates the thermal mass barrier of a separate cDPF, allowing the SCR function to activate immediately during start-up while maintaining both NOx reduction and soot oxidation capabilities in one component.
Solution Approach 2:
The integrated filter performs multiple functions simultaneously: particle filtration, soot oxidation (via OC and OSC), and NOx reduction (via SCR catalyst). The SCR catalyst reduces NOx to N2, while the OC oxidizes CO and HC, and the OSC stores and releases oxygen to support soot combustion. This multi-functionality in a single device resolves the contradiction by eliminating the need for separate heated components.
2Reliability
If an SCR catalyst is applied to a DPF to create an SCR filter, then NOx reduction is achieved, but there is an inverse tradeoff between NOx reduction efficiency and filter regeneration efficiency
Solution Approach 1:
The patent applies different catalysts to different locations and layers of the filter structure. The SCR catalyst is applied to the outer surface of the filter walls where it contacts the exhaust gas for NOx reduction, while the OC and OSC catalysts are incorporated into the washcoat layer that contacts trapped soot particles. This spatial differentiation allows both NOx reduction and efficient soot oxidation to occur simultaneously without interference.
Solution Approach 2:
The filter employs a composite catalytic system with three distinct catalyst components: SCR catalyst for NOx reduction, OC for oxidation of CO and HC, and OSC for oxygen storage and soot combustion support. These composite materials work synergistically, with the OSC providing oxygen to the OC for soot oxidation while the SCR catalyst concurrently reduces NOx, eliminating the inverse tradeoff between these functions.
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 improves NOx reduction and filter regeneration efficiencies, particularly during start-up and early operation cycles, by using a coating with SCR, OC, and OSC components, which work synergistically to enhance particle burn-off and oxidation of HC and CO constituents.
Implementation Method 1
an SCR catalyst, which, when in the presence of a reductant such as ammonia, promotes the selective catalytic reduction of NOx
Implementation Method 2
an oxidation catalyst (OC) component that promotes the oxidation of hydrocarbons and carbon monoxide
Implementation Method 3
an oxygen storage catalyst (OSC) component that alternates between adsorbing and storing oxygen and desorbing and releasing oxygen
Implementation Method 4
the catalytic coating serves to lower the activation energy for oxygen-based particle burn-off (soot combustion), thus decreasing the ignition temperature for soot trapped on the filter and improving regeneration behavior thereof
Data Source
AI summary
A particle filter for treating exhaust gases includes an SCR catalyst that, when in the presence of a reductant such as ammonia, promotes selective catalytic reduction of NOx; an active oxidation catalyst that promotes oxidation of hydrocarbons and carbon monoxide; and an oxygen storage catalyst that alternately stores and releases oxygen, enhances soot oxidation, and stores NOx at temperatures below optimal SCR functioning. The particle filter may be included in a system having an oxidation catalytic device (OCD) upstream of the particle filter, and optionally includes one or more SCR converters upstream and/or downstream of the particle filter, and/or an ammonia slip catalyst downstream of the particle filter. The system may further be adapted for operation under a high frequency injection fuel control with an OCD having substantial NOx storage material content, or an NSC for improving the efficiency tradeoffs between soot oxidation during filter regeneration and NOx reduction.