Segmented Pd-Pt Oxidation Catalyst for Diesel N2O Reduction
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Solution Overview
Problem
Current oxidation catalysts for diesel engines are ineffective in reducing nitrous oxide (N2O) emissions, which is a potent greenhouse gas, and often generate N2O during the oxidation of NOx, despite being used in conjunction with other emissions control devices that do not remove it.
Innovation Solution
An oxidation catalyst comprising a substrate with a first washcoat region of palladium (Pd) supported on cerium oxide and a second washcoat region of platinum (Pt) is used, which exhibits excellent CO oxidation activity at low temperatures, reduces N2O generation, and can act as a passive NOx adsorber to modulate NOx content for downstream emissions control devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If platinum-based oxidation catalysts are used to oxidize CO and HCs, then CO and HC oxidation activity is improved, but nitrous oxide (N2O) is generated by reduction of NOx
Solution Approach 1:
The catalyst is divided into two separate washcoat regions: a first region containing Pd on cerium oxide for CO and HC oxidation, and a second region containing Pt for NOx reduction. This segmentation prevents the Pt from generating N2O while the Pd-cerium oxide region maintains high oxidation activity for CO and HCs at low temperatures.
Solution Approach 2:
Different functional properties are assigned to different regions of the catalyst. The first washcoat region is optimized for oxidation activity (Pd on cerium oxide), while the second washcoat region is optimized for NOx reduction (Pt). This local differentiation allows each region to perform its specific function optimally without interfering with the other, preventing N2O generation while maintaining CO and HC oxidation efficiency.
2Ease of manufacture
If palladium is used instead of platinum, then cost is reduced and sulfur poisoning resistance is improved, but light-off temperature for CO and HCs increases
Solution Approach 1:
Palladium is combined with cerium oxide to form a composite material in the first washcoat region. The cerium oxide acts as a support and promoter that enhances the low-temperature oxidation activity of Pd, allowing the catalyst to achieve high CO and HC oxidation efficiency at lower temperatures while maintaining the cost and sulfur resistance advantages of Pd.
3Productivity
If oxidation catalyst is combined with other emissions control devices, then CO and HC treatment is improved, but nitrous oxide (N2O) generated by the oxidation catalyst is not removed
Solution Approach 1:
The second washcoat region containing Pt is designed to reduce NOx to nitrogen (N2) instead of allowing it to be reduced to N2O. By providing a controlled reduction environment in the second region, the catalyst converts the potential harm of NOx reduction into a beneficial outcome (N2 production), while the first region handles CO and HC oxidation without generating N2O.
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 effectively oxidizes CO and HCs at low temperatures without producing substantial N2O, and can store and release NOx at different temperature ranges, enhancing the efficiency of emissions control in diesel engines by reducing N2O emissions and optimizing NOx management.
Implementation Method 1
Palladium is generally cheaper than platinum, but is less active toward CO and HCs (e.g. Pd has a higher light-off temperature for CO and HCs than Pt). Palladium is also more susceptible to poisoning by sulfur in fuel compared to platinum.
Implementation Method 2
Some platinum group metals, particularly when supported on a refractory oxide, can also promote the oxidation of nitric oxide (NO) to nitrogen dioxide (NO2).
Implementation Method 3
The oxidation catalyst of the invention has excellent CO oxidation activity at low temperatures (i.e. a low light off temperature for CO (e.g. a low T50)). The oxidation catalyst of the invention may additionally or alternatively provide the following advantages: (i) it does not, in use, generate or produce a substantial amount of nitrous oxide (N2O); (ii) it can act as a passive NOx adsorber (PNA); and/or (iii) it can modulate the NOx content of an exhaust gas for a downstream emissions control device.
Data Source
AI summary
An oxidation catalyst for treating an exhaust gas from a compression ignition engine, which oxidation catalyst comprises: a substrate; a first washcoat region comprising palladium (Pd) and a first support material comprising cerium oxide; and a second washcoat region comprising platinum (Pt) and a second support material.