Integrated Catalyst System for Stoichiometric Natural Gas Vehicles
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Solution Overview
Problem
Stoichiometric-burn natural gas vehicles face challenges in meeting China VI emission standards due to excessive ammonia (NH3) production when using existing catalysts for tail gas treatment, as these catalysts struggle to control NH3 emissions within the stringent limits.
Innovation Solution
An integrated catalyst system combining a three-way catalyst with a molecular sieve catalyst, where the molecular sieve catalyst is used to convert the byproduct NH3 into ammonia and water with high conversion rates, utilizing a small pore molecular sieve with a CHA structure and active components like platinum, palladium, or copper, and being applied in various configurations on a base body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-way catalyst is used to purify CO, HC and NOx in stoichiometric-burn natural gas vehicles, then the purification efficiency of these three pollutants is improved, but the emission of ammonia (NH3) increases significantly, failing to meet the China VI emission standard
Solution Approach 1:
The catalyst system is divided into two distinct functional segments: a three-way catalyst layer for purifying CO, HC and NOx, and a molecular sieve catalyst layer for removing NH3. This segmentation allows each layer to specialize in its specific function, with the three-way catalyst focusing on pollutant conversion and the molecular sieve catalyst focusing on NH3 adsorption and decomposition, thereby resolving the contradiction between high pollutant purification efficiency and low NH3 emission.
Solution Approach 2:
The patent employs a composite catalyst system combining two different catalyst materials with complementary functions. The three-way catalyst (typically containing precious metals like Pt, Pd, Rh) works synergistically with the molecular sieve catalyst (containing zeolite structures with specific pore sizes). This composite structure enables simultaneous achievement of high conversion rates for CO, HC and NOx while effectively controlling NH3 emissions through the molecular sieve's selective adsorption and catalytic decomposition properties.
2Productivity
If the activity of the three-way catalyst is increased to improve purification efficiency, then the conversion rates of CO, HC and NOx are improved, but the production of ammonia (NH3) byproduct increases, making it difficult to meet the 10 ppm emission limit
Solution Approach 1:
The patent converts the harmful NH3 byproduct into a beneficial outcome by using the molecular sieve catalyst to decompose NH3 into nitrogen and water vapor. The molecular sieve structure provides active sites that facilitate NH3 decomposition reactions, transforming this harmful emission into harmless substances (N2 and H2O), thereby meeting the stringent 10 ppm emission limit while maintaining high conversion rates for the original pollutants.
3Device complexity
If a single-layer three-way catalyst is used, then the device structure is simple, but it cannot simultaneously achieve high purification efficiency for CO, HC, NOx and low NH3 emission
Solution Approach 1:
The patent merges two catalyst layers into a single integrated catalyst system that functions as one unified component. The three-way catalyst layer and molecular sieve catalyst layer are combined in a core-shell or layered structure, allowing both functions (pollutant purification and NH3 removal) to be achieved within a single catalyst assembly. This merging approach maintains relative structural simplicity while significantly improving emission control performance to meet China VI standards.
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 integrated system effectively treats CO, HC, NOx, and NH3 in the tail gas of natural gas vehicles, achieving high conversion rates and ensuring NH3 emissions are below the China VI phase standard limits, even in low-oxygen environments typical of stoichiometric-burn conditions.
Implementation Method 1
The reactions occurred on the three way catalyst mainly comprise: oxidation reactions of HC and CO: CO+O2→CO2, and HC+O2→CO2+H2O
Implementation Method 2
reduction reactions of NO: NO+CO→CO2+N2, NO+HC→CO2+N2+H2O, and NO+H2→N2+H2O
Implementation Method 3
the molecular sieve catalyst is used to convert the byproduct NH3 into ammonia and water with high conversion rates
Data Source
AI summary
Disclosed in the present invention is an integrated catalyst system for stoichiometric-burn natural gas vehicles, the catalyst system consisting of a three-way catalyst, a molecular sieve catalyst, and a base body, the three-way catalyst and the molecular sieve catalyst being coated on a surface of the base body. In the integrated three-way catalyst and molecular sieve catalyst system of the present invention, at the same time that pollutants such as CO, HC, and NOx in the exhaust of stoichiometric-burn natural gas vehicles are processed, the produced byproduct NH3 can also be processed, and the conversion rates of CO, HC, NOx, and NH3 are high.