Layered Pd-Pt Diesel Oxidation Catalyst for Hydrothermal Durability
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Solution Overview
Problem
Conventional diesel oxidation catalysts face challenges in meeting stringent emission targets due to high costs associated with Platinum (Pt) and Palladium (Pd) content, requiring a more cost-effective solution that maintains performance and durability under diverse diesel exhaust conditions.
Innovation Solution
A layered and zoned diesel oxidation catalyst (DOC) system with a Pd-rich overcoat and a Pt-rich undercoat, designed to enhance hydrothermal durability and resist 'quenching' from transient pollutants, allowing for efficient CO and HC oxidation at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Pt and Pd content is used in conventional DOC, then catalytic activity and emission reduction performance are improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent applies local quality by creating a layered washcoat structure where the undercoat contains Pt and Pd for high-temperature oxidation, while the overcoat is Pd-rich for low-temperature oxidation. Each layer is optimized for its specific function and temperature range, allowing cost-effective PGM distribution throughout the catalyst structure while maintaining overall emission reduction performance.
2Ease of manufacture
If Pd content is increased to reduce cost, then manufacturing cost decreases, but hydrothermal durability and resistance to quenching deteriorate
Solution Approach 1:
The patent segments the catalyst into two distinct washcoat layers: an undercoat containing Pt and Pd that provides hydrothermal durability and resistance to quenching, and an overcoat enriched in Pd that provides cost-effectiveness and low-temperature oxidation activity. This segmentation allows each layer to specialize in its strength, resolving the contradiction between cost and durability.
3Reliability
If a layered structure with Pd-rich overcoat and Pt-rich undercoat is implemented, then hydrothermal durability and quenching resistance are improved, but device complexity increases
Solution Approach 1:
The patent changes the compositional parameter of the washcoat by creating a gradient structure where the Pd-to-Pt ratio varies through the layer depth. The undercoat has lower Pd content (higher Pt) for durability, while the overcoat has higher Pd content for cost-effectiveness. This parameter change approach achieves improved reliability with a systematic rather than arbitrary structure.
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 Pd-rich DOC system achieves high activity and durability, reducing costs by optimizing Pd and Pt usage, while maintaining effective NO and HC oxidation performance, thus meeting modern emission control requirements.
Implementation Method 1
a primary catalytic metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, alloys thereof, and mixtures thereof
Implementation Method 2
catalyse the oxidative conversion of the pollutants into more benign products (H2O and CO2)
Implementation Method 3
The introduction of the Zeolite in the DOC provides a mechanism for the low temperature condensative adsorption of a significant portion of the higher molecular weight unburnt HC species
Implementation Method 4
As the exhaust gas temperature increases the retained HC species are 'released' by evaporation and diffusion out of the porous structure of the Zeolite
Implementation Method 5
As the exhaust gas temperature increases the retained HC species are 'released' by evaporation and diffusion out of the porous structure of the Zeolite
Data Source
AI summary
There is described Pd enriched diesel oxidation catalysts and their application as catalysts for the oxidation of CO and HC emissions from a compression ignition/diesel engine. The catalysts are characterized by increased performance and hydrothermal durability these goals being achieved by employing a layered design to eliminate low temperature catalyst quenching by toxic HC species in the exhaust stream.