Zoned Catalyst for CNG Ammonia Emission Control
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Solution Overview
Problem
Current ammonia slip catalysts designed for diesel engines are ineffective for stoichiometric CNG engines due to differences in fuel composition and operating conditions, leading to inadequate ammonia emission control, which fails to meet stringent China VI regulations.
Innovation Solution
A catalytic article for CNG engines featuring a substrate with a first zeolite catalytic region and a second region comprising a platinum group metal component, oxygen storage capacity material, and inorganic oxide, specifically designed to treat exhaust gases from stoichiometric CNG engines, effectively reducing ammonia emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a typical ammonia slip catalyst (ASC) design is used, then NOx reduction is achieved, but ammonia emission control is insufficient for stoichiometric CNG engines
Solution Approach 1:
The catalyst employs a zoned structure with different catalytic compositions in different regions: a first zone containing a Cu-ZSM-5 zeolite for ammonia oxidation, and a second zone containing Pt-Ba/CeO2-Al2O3 for NOx reduction and three-way catalysis. This spatial differentiation of catalytic functions allows simultaneous optimization of ammonia emission control and NOx reduction, resolving the contradiction between achieving NOx reduction and effectively controlling ammonia emissions in stoichiometric CNG engines.
2Object-generated harmful factors
If conventional three-way catalysts are applied, then CO and HC emissions are reduced, but ammonia is generated as a by-product
Solution Approach 1:
The catalyst converts the harmful ammonia by-product generated during NOx reduction into nitrogen gas through ammonia oxidation. The Cu-ZSM-5 zeolite in the first catalytic zone selectively oxidizes ammonia to N2, transforming this harmful emission into a benign substance. This approach maintains the high emission treatment efficiency of three-way catalysts while eliminating the ammonia by-product problem.
3Object-generated harmful factors
If ammonia emission limit is reduced to 10 ppm, then air quality degradation is prevented, but catalyst performance requirements increase
Solution Approach 1:
The catalyst is segmented into two distinct catalytic zones with specialized functions: the first zone uses Cu-ZSM-5 zeolite specifically optimized for ammonia oxidation to achieve the stringent 10 ppm emission limit, while the second zone uses Pt-Ba/CeO2-Al2O3 for comprehensive NOx reduction and three-way catalysis. This segmentation allows each zone to be optimized for its specific function, meeting the tight emission requirements without excessive overall system complexity.
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 catalytic article significantly improves ammonia emission control, meeting China VI regulations by simultaneously treating NOx, CO, and HC emissions, with enhanced performance compared to conventional three-way catalysts.
Implementation Method 1
a first catalytic region beginning at the outlet end and extending for less than the axial length L, wherein the first catalytic region comprises a first zeolite
Implementation Method 2
a second oxygen storage capacity (OSC) material
Implementation Method 3
a second catalytic region beginning at the inlet end, wherein the second catalytic region comprises a second platinum group metal (PGM) component
Data Source
AI summary
A three-way catalyst article, and its use in an exhaust system for compressed natural gas engines, is disclosed. The catalyst article for treating exhaust gas from compressed natural gas (CNG) engine comprising: a substrate comprising an inlet end, an outlet end with an axial length L; a first catalytic region beginning at the outlet end and extending for less than the axial length L, wherein the first catalytic region comprises a first zeolite; and a second catalytic region beginning at the inlet end, wherein the second catalytic region comprises a second platinum group metal (PGM) component, a second oxygen storage capacity (OSC) material, and a second inorganic oxide; wherein the second PGM component is selected from the group consisting of palladium, platinum, rhodium or a combination thereof.