Mixed Zeolite SCR Catalyst Balancing NOx Conversion and Ammonia Storage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing SCR catalysts face challenges in maintaining catalytic efficiency and ammonia storage capacity at high and low operating temperatures, particularly under harsh hydrothermal conditions, leading to ammonia slip and reduced activity.
Innovation Solution
A catalyst composition comprising two zeolites with different framework structures, one containing a promoter metal, is prepared by mixing and aging the zeolites at temperatures below 650°C, distributing the promoter metal between the zeolites to enhance NOx conversion and ammonia storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If metal-promoted zeolite catalysts are used for SCR of nitrogen oxides, then catalytic activity is improved, but ammonia storage capacity decreases at high temperatures
Solution Approach 1:
The catalyst is segmented into two distinct zeolite components: a first zeolite (e.g., CHA structure) containing promoter metal for high-temperature NOx conversion, and a second zeolite (e.g., FAU structure) without promoter metal for ammonia storage. This segmentation allows each component to specialize in its optimal function, resolving the contradiction between catalytic activity and ammonia storage capacity.
Solution Approach 2:
The invention uses a composite catalyst system combining two different zeolite materials with complementary properties. The first zeolite provides catalytic activity through promoter metal sites, while the second zeolite provides ammonia storage capacity through its framework structure. The composite nature allows simultaneous optimization of both functions that cannot be achieved with a single zeolite type.
2Productivity
If promoter metal is added to zeolite to enhance NOx conversion, then catalytic efficiency is improved, but hydrothermal stability deteriorates
Solution Approach 1:
The promoter metal is segmented and placed only in the first zeolite component, separating the function of catalytic promotion from the function of structural stability. The second zeolite component serves as a stable structural backbone that does not undergo dealumination, thereby protecting the overall catalyst hydrothermal stability while still allowing the first zeolite to provide high catalytic efficiency.
3Quantity of substance
If high ammonia storage capacity is achieved, then low-temperature NOx conversion is improved, but ammonia slip increases at high temperatures
Solution Approach 1:
Different regions of the catalyst have different properties: the first zeolite with promoter metal has high catalytic activity for NOx conversion at high temperatures, while the second zeolite without promoter metal has high ammonia storage capacity. This local differentiation of properties allows the catalyst to store ammonia effectively at low temperatures and convert it efficiently at high temperatures, preventing ammonia slip.
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 catalyst composition exhibits improved NOx conversion and ammonia storage capacity across a wide temperature range, outperforming single-framework zeolite compositions, with enhanced performance even after high temperature exposure.
Implementation Method 1
Metal-promoted zeolite catalysts, also often referred to as ion-exchanged zeolite catalysts (e.g., iron-promoted and copper-promoted zeolite catalysts) for the selective catalytic reduction of nitrogen oxides with ammonia are known.
Implementation Method 2
In general, every SCR catalyst is able to store ammonia at low temperatures, which is often introduced into the engine exhaust gas stream to promote NOx conversion of the SCR catalyst.
Implementation Method 3
This decline has been attributed to dealumination of the zeolite and the consequent loss of metal-containing active centers within the zeolite.
Implementation Method 4
The SCR process selectively reduces nitrogen oxides with a reductant (e.g., ammonia) in the presence of a high level of oxygen, resulting in the formation predominantly of nitrogen and water
Data Source
AI summary
The present disclosure generally provides selective catalytic reduction (SCR) catalyst compositions, catalyst articles and catalyst systems including such catalyst articles for treating engine exhaust gas. In particular, the SCR catalyst composition includes a first zeolite and a second zeolite and has not been subjected to temperatures above 650° C. The first zeolite includes a promoter metal and has a first framework structure and at least a portion of the second zeolite is in a form selected from H+ form, NH4+ form, alkali metal form, alkaline earth metal form, and combinations thereof and has a second framework structure. The first framework structure and the second framework structure are different.