Tetra-functional Catalyst for Diesel Exhaust NOx Reduction
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Solution Overview
Problem
Current exhaust gas treatment systems for heavy-duty diesel engines face challenges in reducing NOx emissions while minimizing the use of platinum group metals and avoiding the loss of NO2 for soot regeneration, particularly when ammonia is injected upstream of a catalyzed soot filter.
Innovation Solution
A tetra-functional catalyst comprising a washcoat with platinum group metals supported on a metal oxide support, combined with oxidic compounds of V and W, and a zeolitic material containing Cu and Fe, which performs NO oxidation, hydrocarbon oxidation, ammonia oxidation, and selective catalytic reduction of NOx, thereby generating a favorable temperature for soot filter regeneration and minimizing ammonia and hydrocarbon slips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diesel oxidation catalyst (DOC) is installed upstream of the catalyzed soot filter to catalytically burn diesel fuel and produce temperature for filter regeneration, then soot regeneration is enabled, but the system requires expensive platinum group metals and cannot reduce NOx emissions effectively
Solution Approach 1:
The patent applies multi-functionality by designing a single catalyst that simultaneously performs DOC functions (hydrocarbon oxidation, soot regeneration) and SCR functions (NOx reduction). The catalyst contains multiple active components including Pt, Pd, Rh, and base metals (Fe, Cu, Zn) that enable it to catalyze both oxidation and reduction reactions, eliminating the need for separate DOC and SCR devices while reducing overall system complexity and cost
Solution Approach 2:
The patent merges the DOC and SCR catalysts into a single integrated unit. The washcoat contains multiple catalytic components (Pt, Pd, Rh, Fe, Cu, Zn) that are distributed throughout the catalyst structure, allowing the device to combine the oxidation functions of a DOC with the reduction functions of an SCR catalyst, thereby reducing system complexity and eliminating redundant components
2Reliability
If ammonia is injected upstream of the catalyzed soot filter for DeNOx, then NOx reduction is achieved, but the selectivity towards N2O increases and NO2-make is lost for passive soot regeneration
Solution Approach 1:
The patent applies local quality by creating different functional zones within the catalyst washcoat. The washcoat contains specific metal combinations (Pt, Pd for oxidation; Rh, Fe, Cu for reduction) that are distributed throughout the structure, allowing different regions to optimize for specific functions. This enables simultaneous NOx reduction and preservation of NO2 for soot regeneration, while controlling N2O formation through the specific local composition of catalytic sites
Solution Approach 2:
The patent changes the chemical composition parameters of the catalyst by incorporating specific base metals (Fe, Cu, Zn) alongside precious metals (Pt, Pd, Rh). This compositional change modifies the catalytic properties to reduce N2O selectivity and maintain NO2 production, allowing the catalyst to perform DeNOx while preserving the necessary NO2-make for passive soot regeneration
3Reliability
If conventional DOC and SCR catalysts are used separately, then specific functions are optimized, but the overall system requires more platinum group metals and higher cost
Solution Approach 1:
The patent reduces PGM content by designing a multi-functional catalyst that performs both DOC and SCR functions. The catalyst uses lower amounts of Pt and Pd while incorporating base metals (Fe, Cu, Zn) to provide the necessary catalytic activity for both oxidation and reduction reactions, thereby reducing the overall quantity of expensive platinum group metals required
Solution Approach 2:
The patent replaces expensive PGM-based catalysts with a more cost-effective composition that includes base metals (Fe, Cu, Zn) alongside reduced amounts of precious metals. This substitution strategy reduces dependence on expensive PGMs while maintaining catalytic functionality, effectively using cheaper alternative materials to achieve the same environmental performance
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 reduces NOx emissions, produces NO2 for passive soot filter regeneration, and minimizes N2O formation, while reducing the need for platinum group metals and eliminating the requirement for a diesel oxidation catalyst upstream of the catalyzed soot filter.
Implementation Method 1
a platinum group metal supported on a metal oxide support material
Implementation Method 2
the oxidation of nitrogen monoxide (NO)
Implementation Method 3
the oxidation of a hydrocarbon (HC)
Implementation Method 4
the oxidation of a hydrocarbon (HC)
Implementation Method 5
By oxidation of a hydrocarbon, a favorable temperature (i.e. an exotherm) is generated
Implementation Method 6
the oxidation of ammonia (NH3)
Implementation Method 7
the selective catalytic reduction of nitrogen oxides (NOx)
Implementation Method 8
By oxidation of a hydrocarbon, a favorable temperature (i.e. an exotherm) is generated that may heat a catalyzed soot filter located downstream of the catalyst
Data Source
AI summary
The present invention relates to a catalyst, preferably for the selective catalytic reduction of NOx, for the oxidation of ammonia, for the oxidation of NO and for the oxidation of a hydrocarbon, the catalyst comprising a washcoat comprising one or more layers, the washcoat being disposed on a substrate, wherein the washcoat comprises a platinum group metal supported on a metal oxide support material, and one or more of an oxidic compound of V, an oxidic compound of W and a zeolitic material comprising one or more of Cu and Fe.