Selective Catalytic Reduction Catalyst with Segmented Zeolite Layers
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Solution Overview
Problem
Current SCR systems face challenges with ammonia slip at higher temperatures and low NOx conversion efficiency at temperatures above 500°C, due to high ammonia storage capacity of chabazite catalysts and decreased activity of beta zeolites under hydrothermal conditions.
Innovation Solution
A selective catalytic reduction catalyst system is developed with a copper-loaded beta zeolite (Cu/beta) layer supported on a copper-loaded chabazite (Cu/CHA) layer, where the Cu/beta layer is pre-aged to reduce ammonia storage capacity and enhance NOx conversion efficiency at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper-loaded chabazite (Cu/CHA) is used as SCR catalyst, then ammonia storage capacity is improved, but ammonia slip increases at higher temperatures
Solution Approach 1:
The catalyst is divided into two distinct layers: a Cu/CHA layer for ammonia storage and a Cu/beta layer for NOx conversion. This segmentation allows each layer to perform its specialized function, with the Cu/beta layer preventing ammonia slip by converting NOx at high temperatures where Cu/CHA alone would cause ammonia emissions.
Solution Approach 2:
Different regions of the catalyst have different properties optimized for specific functions. The Cu/CHA layer provides high ammonia storage capacity, while the Cu/beta layer provides high-temperature NOx conversion activity. This local quality differentiation resolves the contradiction by placing each material where its specific properties are most beneficial.
2Productivity
If copper-loaded beta zeolite (Cu/beta) is used as SCR catalyst, then NOx conversion efficiency at high temperature is improved, but ammonia storage capacity decreases
Solution Approach 1:
The catalyst is segmented into functional layers where Cu/beta provides high-temperature NOx conversion and Cu/CHA provides ammonia storage. This allows the system to achieve both high productivity through Cu/beta and sufficient ammonia storage through Cu/CHA, resolving the contradiction between these two parameters.
3Productivity
If SCR catalyst operates at high temperature for filter regeneration, then NOx conversion efficiency is improved, but ammonia slip increases
Solution Approach 1:
The Cu/beta layer is specifically designed for high-temperature operation with optimal NOx conversion activity, while the Cu/CHA layer provides stable ammonia storage. This local quality differentiation ensures that at high temperatures during filter regeneration, the Cu/beta layer efficiently converts NOx without causing ammonia slip, while Cu/CHA maintains ammonia storage stability.
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 lower ammonia storage capacity and higher NOx conversion efficiency at temperatures typical of filter regeneration, maintaining catalytic activity over a wide temperature range, thus reducing tailpipe NOx emissions during diesel particulate filter regeneration.
Implementation Method 1
chabazite catalysts have a high capacity to store ammonia
Implementation Method 2
Selective catalytic reduction (SCR) systems of NOx by nitrogen compounds
Data Source
AI summary
A selective catalytic reduction (SCR) catalyst includes a support layer. A copper-loaded chabazite (Cu/CHA) layer is supported on the support layer. A copper-loaded beta zeolite (Cu/beta) is supported on the Cu/CHA layer. The Cu/beta may be hydrothermally pre-aged prior to use of the SCR catalyst in a vehicle. The pre-aged Cu/beta is essentially free of phosphorous (P), calcium (Ca), zinc (Zn), sodium (Na), potassium (K), magnesium (Mg), iron (Fe), CaSO4, Ca19Zn2(PO4)14, CaZn2(PO4)2, ash, and/or soot.