Honeycomb Catalytic Converter with Graded Cerium Concentration
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Solution Overview
Problem
Existing honeycomb catalytic converters face challenges in achieving high exhaust gas conversion performance due to insufficient oxygen supply to the substrate and poor NOx reduction performance when conditions switch from lean to rich, as the ceria-zirconia coat layer hinders oxygen reach and oxidizes supported Pd catalysts.
Innovation Solution
A honeycomb catalytic converter design with a ceria-zirconia composite oxide and alumina structure where cerium concentration is lower on the surface than in the central portion of the partition walls, allowing better oxygen penetration and supporting noble metals like Pd and Rh for enhanced catalytic activity, along with an inorganic binder for mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a ceria-zirconia coat layer is formed on the porous substrate to provide oxygen storage capacity, then exhaust gas oxidation performance is improved, but oxygen supply to the deep inside of the porous substrate is insufficient
Solution Approach 1:
The patent applies local quality by creating a non-uniform cerium concentration distribution within the partition wall. The cerium concentration is higher in the central portion and lower on the surface, allowing different regions to serve different functions: the surface region allows oxygen penetration while the central region provides oxygen storage capacity. This spatial differentiation resolves the contradiction between providing sufficient oxygen storage and maintaining oxygen supply to the substrate.
Solution Approach 2:
The patent uses a composite structure combining ceria-zirconia composite oxide with alumina in the partition wall. This composite material approach allows optimization of both oxygen storage capacity (from ceria-zirconia) and mechanical strength/porosity (from alumina), while the non-uniform cerium distribution within this composite structure enables simultaneous achievement of good oxygen supply and sufficient oxygen storage.
2Productivity
If a first catalyst (Pd) is supported inside the porous substrate, then catalytic activity is provided, but Pd impregnated inside the porous substrate fails to exhibit exhaust gas oxidization capacity
Solution Approach 1:
The patent applies local quality by differentiating the functional zones within the partition wall. The surface region with lower cerium concentration serves as the active catalytic zone where Pd is most effective, while the central region with higher cerium concentration provides oxygen storage. This spatial separation ensures that Pd catalysts are positioned where they can effectively access oxygen for oxidation reactions, resolving the issue of inactive internally impregnated catalysts.
3Productivity
If the surface of the porous substrate is covered by a coat layer with oxygen storage capacity, then oxidation performance is enhanced, but when exhaust gas switches from lean to rich condition, supported Pd is oxidized by large amount of oxygen released from the coat layer, resulting in poor NOx reduction performance
Solution Approach 1:
The patent resolves this contradiction through local quality by creating a controlled gradient in cerium concentration. The surface region with lower cerium concentration limits the release of oxygen during lean conditions, preventing excessive oxidation of Pd catalysts. Meanwhile, the central region with higher cerium concentration maintains sufficient oxygen storage capacity for oxidation performance. This spatial differentiation prevents the harmful effect of excessive oxygen release while maintaining beneficial oxidation capability.
4Productivity
If the concentration of ceria-zirconia composite oxide is increased to improve oxygen storage capacity, then exhaust gas conversion performance is improved, but mechanical strength of the honeycomb structured body deteriorates
Solution Approach 1:
The patent employs composite materials by combining ceria-zirconia composite oxide with alumina in the partition wall. Alumina provides mechanical strength and structural stability, while ceria-zirconia provides oxygen storage capacity. This composite approach allows achieving good exhaust gas conversion performance without compromising mechanical strength.
Solution Approach 2:
The patent applies local quality by concentrating the ceria-zirconia composite oxide in the central portion of the partition wall while maintaining a lower concentration on the surface. This non-uniform distribution ensures that mechanical strength is maintained in the surface region where structural integrity is critical, while sufficient oxygen storage capacity is provided in the central region.
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
This design improves exhaust gas conversion performance by ensuring sufficient oxygen reach and balanced mechanical strength, maintaining high NOx reduction efficiency even under varying fuel conditions.
Implementation Method 1
a first catalyst (Pd) is supported inside the porous substrate... since the surface of the porous substrate is covered by the coat layer made of a ceria-zirconia solid solution having an oxygen storage capacity (OSC), oxygen is not sufficiently supplied to the deep inside of the porous substrate due to the coat layer
Implementation Method 2
A common three-way catalytic converter includes a catalyst layer that is formed by wash-coating the slurry containing noble metal particles having catalytic activity on a honeycomb monolithic substrate... a honeycomb catalytic converter including: a honeycomb structured body... and a noble metal supported on the honeycomb structured body
Implementation Method 3
cerium on a surface of each partition wall has a lower concentration than cerium in a central portion of the partition wall in a thickness direction... allows oxygen to easily reach the central portion of each partition wall
Data Source
AI summary
The present invention provides a honeycomb catalytic converter including: a honeycomb structured body in which multiple through-holes are arranged longitudinally in parallel with one another with a partition wall therebetween; and a noble metal supported on the honeycomb structured body, wherein the honeycomb structured body contains a ceria-zirconia composite oxide and alumina, and cerium on a surface of each partition wall has a lower concentration than cerium in a central portion of the partition wall in a thickness direction.