Exhaust Catalyst Laminate Structure for NOx Elimination
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Solution Overview
Problem
Exhaust gas purifying catalysts with supported noble metals on oxygen storage capacity (OSC) materials face rapid oxygen release, leading to inadequate NOx elimination performance due to rapid atmosphere switching and insufficient NOx discharge when the atmosphere reverts to a lean state.
Innovation Solution
A laminate structure catalyst with a noble metal-free OSC material layer and a separate noble metal layer, where the OSC material is cerium oxide or ceria-zirconia complex oxide, and the noble metal layer contains Rh and Pt, with a specific mass ratio and thickness to control oxygen storage and release rates, enhancing NOx elimination performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If noble metal is supported on OSC material to improve CO and HC elimination performance, then oxygen storage capacity is enhanced, but oxygen release rate becomes too fast causing insufficient NOx elimination
Solution Approach 1:
The catalyst coat layer is divided into multiple functional layers: a first layer containing OSC material (ceria-zirconia solid solution) for oxygen storage, and a second layer containing noble metals (Rh and Pt) for CO and HC elimination. This segmentation allows each layer to perform its specific function optimally without the noble metal accelerating oxygen release from the OSC material, thereby resolving the contradiction between CO/HC elimination performance and NOx elimination performance.
2Reliability
If OSC material stores oxygen to convert exhaust gas to reducing atmosphere for NOx elimination, then NOx elimination is improved, but when atmosphere reverts to lean state the catalyst is slow to revert causing insufficient NOx elimination
Solution Approach 1:
The first layer containing OSC material is positioned adjacent to the substrate surface, creating a localized oxygen storage reservoir close to the exhaust gas flow. This spatial arrangement allows the OSC material to rapidly buffer atmosphere changes at the catalyst inlet, enabling fast response to air/fuel ratio transitions and improving both NOx elimination during lean operation and the speed of atmosphere switching.
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 laminate structure design improves NOx elimination performance by slowing down oxygen storage and release rates, allowing for effective NOx elimination in both lean and rich atmospheres, achieving higher NOx removal efficiency compared to conventional catalysts.
Implementation Method 1
OSC materials that were inorganic materials having oxygen storage capacity (OSC) were used as carriers for noble metals. An OSC material stores oxygen present in an exhaust gas when the air/fuel ratio of the exhaust gas is lean and converts the exhaust gas into a reducing atmosphere. Meanwhile, when the air/fuel ratio of the exhaust gas becomes rich, oxygen stored by the OSC material is released and the exhaust gas is converted into an oxidizing atmosphere.
Implementation Method 2
the oxygen release rate of an OSC material becomes faster if the noble metal acts as an oxygen absorption and release intermediary
Implementation Method 3
the OSC material is a cerium oxide or a ceria-zirconia complex oxide
Data Source
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AI summary
The exhaust gas purifying catalyst disclosed here includes a substrate 10 and a catalyst coat layer 30 formed on the surface of the substrate 10. The catalyst coat layer 30 is formed in a laminate structure having two layers, with a first layer 34 being nearer to the surface of the substrate 10 and a second layer 32 being relatively further from this surface. The second layer 32 includes a carrier and a noble metal supported on the carrier. The first layer 34 is a noble metal-free layer that does not contain a noble metal but does contain an OSC material having oxygen storage capacity.