Integrated SCR-LNT Soot Filter for Lean Engine Emissions
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current emissions treatment systems for lean-burn engines face challenges in efficiently reducing NOx and CO emissions while minimizing platinum group metal usage and excess ammonia production, particularly in passive SCR systems.
Innovation Solution
A catalyzed soot filter with a specific arrangement of lean NOx trap and selective catalytic reduction catalysts on a porous wall flow substrate, optimizing the distribution and depth of platinum group metals like palladium and rhodium, and using zeolites for efficient NOx conversion and CO oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LNT catalyst is used for NOx reduction in lean-burn engines, then NOx conversion is improved, but platinum group metal loading increases significantly
Solution Approach 1:
The patent combines LNT and SCR catalysts into a single integrated catalyst system. The LNT component captures NOx during lean operation, while the SCR component reduces stored NOx using ammonia generated during rich operation periods. This merging allows the system to achieve high NOx conversion efficiency while using lower overall platinum group metal loading compared to separate LNT or SCR systems.
Solution Approach 2:
The catalyst system operates in periodic lean-rich cycles. During lean periods, the LNT component stores NOx; during rich periods, ammonia is generated and the SCR component reduces stored NOx. This periodic operation pattern enables efficient NOx control with reduced precious metal requirements by alternating between storage and reduction phases.
2Reliability
If separate LNT and SCR catalyst systems are used, then NOx reduction efficiency is improved, but device complexity increases
Solution Approach 1:
The patent integrates LNT and SCR catalysts into a single physical unit with multiple functional zones. The LNT catalyst (containing barium oxide and platinum group metals) and SCR catalyst (containing zeolite with copper or iron) are combined in one catalyst substrate, eliminating the need for separate catalyst housings and reducing system complexity while maintaining high NOx reduction efficiency.
Solution Approach 2:
The integrated catalyst system performs multiple functions within a single device: NOx storage during lean operation, ammonia generation during rich operation, and NOx reduction via SCR. This multi-functionality reduces the number of separate components needed while achieving comprehensive emissions control.
3Reliability
If ammonia storage is increased for passive SCR, then NOx conversion is improved, but excess ammonia production increases
Solution Approach 1:
The catalyst system incorporates feedback control through its dual-function design. The LNT component monitors and stores NOx levels, while the SCR component adjusts ammonia-based reduction based on stored NOx quantities. This feedback mechanism ensures ammonia is generated and consumed in balanced amounts, improving NOx conversion while minimizing excess ammonia slip.
Solution Approach 2:
The system recovers and utilizes ammonia generated during rich operation periods to reduce stored NOx during lean periods. By discarding harmful NOx and recovering useful ammonia in situ, the system achieves high conversion efficiency while minimizing excess ammonia production, as the ammonia is immediately consumed for NOx reduction.
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 achieves high NOx and CO conversion efficiency with reduced platinum group metal usage and minimal excess ammonia production, effectively addressing the limitations of existing systems in lean-burn engine emissions treatment.
Implementation Method 1
a lean NOx trap (LNT) catalyst... provided on a portion of the surface of the inlet channel walls and on at least a portion of the surface of the pores within the channel walls
Implementation Method 2
a catalyst for selective catalytic reduction (SCR)... extending from the outlet end to (100-x)% of the substrate axial length
Implementation Method 3
a porous wall flow substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of channels defined by internal walls of the wall flow substrate
Data Source
AI summary
The present invention relates to catalyzed soot filter (CSF), wherein the CSF comprises a porous wall flow substrate, a lean NOx trap (LNT) catalyst, and a catalyst for selective catalytic reduction (SCR), the wall flow substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of channels defined by internal walls of the wall flow substrate, wherein the plurality of channels comprise inlet channels having an open inlet end and a closed outlet end, and outlet channels having a closed inlet end and an open outlet end, wherein the LNT catalyst is provided on a portion of the surface of the inlet channel walls and on at least a portion of the surface of the pores within the channel walls underneath the surface of the channel walls coated with the LNT catalyst, wherein the portion of the inlet channel walls coated with the LNT catalyst extends from the inlet end to x % of the substrate axial length with 0 < x < 100, wherein the SCR catalyst is provided on a portion of the surface of the outlet channel walls and on at least a portion of the surface of the pores within the channel walls underneath the surface of the channel walls coated with the SCR catalyst, wherein the portion of the outlet channel walls coated with the SCR catalyst extends from the outlet end to 100-x % of the substrate axial length, as well as to a method of preparing the catalyzed soot filter, to an emissions treatment system containing the catalyzed soot filter, to a process for the treatment of exhaust gas emissions employing the catalyzed soot filter, and to the use of the catalyzed soot for the treatment of exhaust gas emissions.