Low Temperature NOx Adsorber Catalyst Regeneration
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Solution Overview
Problem
Current exhaust gas treatment systems for lean-burn engines face inefficiencies in reducing nitrogen oxides (NOx) emissions, particularly during the 'cold start' period when catalytic activity is low, and existing NOx adsorbers struggle with regeneration efficiency and hydrothermal stability.
Innovation Solution
A Low-Temperature NOx Adsorber (LT-NA) catalyst composition is developed, comprising palladium ion-exchanged zeolites doped with platinum nanoparticles, which enhances NOx adsorption and desorption efficiency, maintaining performance even after hydrothermal aging when combined with a diesel oxidation catalyst (DOC).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LNT catalysts are used for NOx trapping, then NOx can be stored under lean conditions, but the reaction rate is very slow when temperature is below 200°C, rendering the catalyst inefficient for trapping of cold-start NOx emission
Solution Approach 1:
The patent changes the chemical parameters of the catalyst by incorporating specific metal components (precious metals like Pt, Pd, Rh and base metals like Fe, Cu, Zn) in optimized ratios. This modifies the catalytic activity to enable effective NOx trapping at lower temperatures, directly addressing the slow reaction rate issue during cold start
Solution Approach 2:
The invention uses a composite catalyst structure combining multiple metal components with alumina support. The synergistic interaction between different metals (e.g., precious metals for oxidation and base metals for storage) creates enhanced catalytic performance that overcomes the limitations of single-component catalysts at low temperatures
2Reliability
If rich purge is used to regenerate the LNT catalyst, then trapped NOx can be released and reduced to N2, but this reduces fuel economy
Solution Approach 1:
The catalyst is designed to utilize the engine's own exhaust conditions for regeneration. By optimizing the catalytic activity, the system can perform regeneration during normal lean operation or mild rich excursions, reducing the need for dedicated fuel-rich purge events and thereby improving fuel economy
Solution Approach 2:
The invention changes the operational parameters by enabling regeneration at lower temperatures and with smaller rich excursions. The optimized metal composition allows the catalyst to become active at lower temperatures, reducing the fuel penalty associated with regeneration events
3Reliability
If SCR catalyst components are used for converting NOx to N2, then effective conversion can be achieved at temperatures above 200°C, but they do not exhibit sufficient activities at lower temperature regions during cold start
Solution Approach 1:
The patent modifies the temperature parameter by incorporating metals with low-temperature catalytic activity. The specific metal composition enables the catalyst to function effectively at temperatures as low as -30°C to 200°C, expanding the operational temperature range compared to traditional SCR catalysts
Solution Approach 2:
The invention creates a composite material system that combines the NOx storage capability of LNT with the conversion efficiency of SCR. The multi-metal composition provides both trapping function at low temperatures and conversion function, eliminating the need for separate components and ensuring effectiveness across the full temperature range
4Reliability
If LNT catalyst operates under cyclic lean and rich exhaust conditions, then NOx can be trapped and subsequently released, but the system requires external fuel injection or transient rich conditions to induce regeneration
Solution Approach 1:
The catalyst is designed to automatically perform regeneration using the engine's normal operation cycles. By optimizing the metal composition, the system can utilize brief transient rich conditions that naturally occur during engine operation, eliminating the need for complex external control systems or dedicated regeneration modes
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 LT-NA catalyst composition effectively adsorbs NOx at low temperatures and releases it at elevated temperatures, improving regeneration efficiency and maintaining NOx desorption profiles, thus addressing the challenges of low-temperature catalytic activity and hydrothermal stability.
Implementation Method 1
palladium component, wherein at least a portion of the first palladium component is ion-exchanged in the first zeolite
Implementation Method 2
The LT-NA catalyst composition effectively adsorbs NOx at low temperatures
Implementation Method 3
platinum nanoparticles, which enhances NOx adsorption and desorption efficiency
Implementation Method 4
catalytic NOx oxidation and reduction
Implementation Method 5
releasing trapped NOx at elevated temperatures (>200° C.) when downstream catalytic components become effective
Data Source
AI summary
The present disclosure provides Low Temperature NOx-Absorber (LT-NA) catalyst compositions, catalyst articles, and an emission treatment system for treating an exhaust gas, each including the LT-NA catalyst compositions. Further provided are methods for reducing a NOx level in an exhaust gas stream using the LT-NA catalyst articles. In particular, the LT-NA catalyst compositions include a first zeolite, a first palladium component, and a plurality of platinum nanoparticles. The LT-NA catalyst compositions exhibit enhanced regeneration efficiency with respect to NOx adsorption capacity, even after hydrothermal aging.