NOx Adsorber DOC Catalyst Segmentation for Low-Temperature Performance
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Solution Overview
Problem
Current NOx adsorber diesel oxidation catalysts face challenges in achieving improved NOx adsorption and desorption performance, especially at low temperatures, and stability during lean/rich desulfation processes.
Innovation Solution
A NOx adsorber diesel oxidation catalyst comprising a substrate with specific coatings: a first NOx adsorber coating with palladium on ceria, a second NOx adsorber coating with an alkaline earth metal and platinum group metal on a non-zeolitic oxidic material, and a diesel oxidation catalyst coating with platinum group metal on another non-zeolitic oxidic material, strategically positioned to enhance adsorption and desorption capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ceria- or barium-based materials are used for NOx adsorption, then NOx adsorption capacity and desorption temperature are improved, but performance at low temperatures deteriorates and thermal stability during lean/rich desulfation is reduced
Solution Approach 1:
The catalyst is divided into two distinct functional zones along the substrate: a first NOx adsorber coating zone (x% from outlet to inlet) containing Pd/Ceria for high-temperature adsorption, and a second NOx adsorber coating zone (y% from inlet to outlet) containing alkaline earth metal and Pt on non-zeolitic oxidic material for low-temperature adsorption. This segmentation allows each zone to specialize in different temperature ranges, resolving the contradiction between high adsorption capacity and low-temperature performance.
Solution Approach 2:
Different coating compositions are applied to different locations of the substrate. The first NA coating uses Pd/Ceria optimized for high-temperature operation, while the second NA coating uses alkaline earth metal/Pt on non-zeolitic oxidic material optimized for low-temperature operation. This local quality differentiation ensures optimal performance at each temperature regime without compromising the other.
2Quantity of substance
If traditional NOx adsorber coatings are used, then NOx adsorption is achieved, but irreversible sulfation damage occurs during lean/rich desulfation cycles
Solution Approach 1:
The patent converts the harmful sulfation effect into a beneficial desulfation mechanism. The alkaline earth metal in the second NA coating reacts with sulfur to form sulfates during lean operation, which are then reduced to H2S and eventually to elemental sulfur or metal sulfides during rich operation, preventing irreversible sulfation damage. This cyclic sulfation-desulfation process actually removes sulfur from the system over time.
Solution Approach 2:
The patent changes the chemical state of sulfur through controlled oxidation-reduction cycles. During lean operation, sulfur is oxidized to SO2 and then adsorbed as sulfate. During rich operation, the sulfate is reduced back to H2S and eventually to elemental sulfur or metal sulfides. This parameter change between oxidation states enables reversible sulfur management, improving reliability against permanent sulfation.
3Device complexity
If single-coating NOx adsorber catalysts are used, then device complexity is reduced, but performance across different temperature ranges and desulfation conditions deteriorates
Solution Approach 1:
The dual-coating structure provides multi-functionality: the first NA coating (Pd/Ceria) handles high-temperature NOx adsorption and contributes to desulfation, while the second NA coating (alkaline earth metal/Pt on non-zeolitic oxidic material) handles low-temperature NOx adsorption and facilitates reversible desulfation. Together, they create a universal catalyst that performs across the entire temperature range and under both lean and rich conditions, justifying the increased structural complexity.
Data Source
AI summary
A NOx adsorber diesel oxidation catalyst for the treatment of an exhaust gas, the catalyst comprising: a substrate comprising an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end and a plurality of passages defined by internal walls of the substrate extending therethrough; a first NOx adsorber (NA) coating, said coating comprising palladium supported on a first non-zeolitic oxidic material comprising ceria; a second NOx adsorber (NA) coating, said coating comprising one or more of an alkaline earth metal supported on a support material and a platinum group metal component supported on a second non-zeolitic oxidic material; and a diesel oxidation catalyst (DOC) coating, said coating comprising a platinum group metal component supported on a third non-zeolitic oxidic material.