Multifunctional Catalyst Palladium SCR Coking
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Solution Overview
Problem
Existing exhaust gas treatment systems face challenges in maintaining the effectiveness of SCR catalysts due to coking from hydrocarbon slip and reduced NOx reduction efficiency over time, particularly in close-coupled positions with size constraints.
Innovation Solution
Incorporating a platinum group metal, specifically palladium, into the SCR catalyst as part of a multifunctional catalyst system, which includes a diesel oxidation catalyst and a selective catalytic reduction catalyst with a zeolitic material, to reduce hydrocarbon slip and coking, while maintaining high NOx reduction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a separate oxidation catalyst is placed upstream of the SCR catalyst to raise exhaust temperature for desulfation, then the SCR catalyst regeneration is enabled, but hydrocarbon slip onto the SCR catalyst causes coking and deactivation
Solution Approach 1:
The patent combines the oxidation catalyst and SCR catalyst into a single integrated multifunctional catalyst component. The oxidation function is provided by platinum group metals (Pd, Pt) while the SCR function is provided by zeolitic materials (Cu-CHA, Fe-CHA) within the same catalyst structure, eliminating the need for a separate upstream oxidation catalyst and preventing hydrocarbon slip-induced coking
Solution Approach 2:
The multifunctional catalyst performs multiple functions simultaneously: oxidation of hydrocarbons and CO, selective catalytic reduction of NOx, and resistance to coking. This is achieved by incorporating both oxidation-active platinum group metals and SCR-active zeolitic materials into a single catalyst formulation that can handle both functions without compromising either
2Reliability
If the oxidation catalyst generates exotherm to heat up the SCR catalyst when NOx abatement is insufficient, then SCR catalyst activity is restored, but hydrocarbon-slip and subsequent coking on the SCR component occurs
Solution Approach 1:
By merging the oxidation and SCR functions into a single multifunctional catalyst, the patent eliminates the interface between separate catalysts where hydrocarbon slip would occur. The oxidation function is performed in-situ within the same component that performs SCR, preventing hydrocarbon accumulation and coking while maintaining the ability to generate exotherm for catalyst heating when needed
3Volume of moving object
If a close-coupled SCR catalyst position is used to reduce system size, then space constraints are satisfied, but hydrocarbon slip and coking are exacerbated
Solution Approach 1:
The integrated multifunctional catalyst allows for close-coupled positioning while preventing coking by combining oxidation and SCR functions in one component. The oxidation function actively consumes hydrocarbons before they can accumulate and cause coking, enabling the system to be compact without sacrificing catalyst reliability
Solution Approach 2:
The patent modifies the catalyst composition parameters by incorporating specific ratios of platinum group metals (0.1-5 g/L) and zeolitic materials with specific copper or iron loadings (0.1-10 wt%), creating a formulation that is particularly effective at preventing coking in close-coupled applications while maintaining small system volume
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 solution effectively reduces hydrocarbon slip and coking, thereby maintaining the SCR catalyst's efficiency and extending its operational lifespan, especially in close-coupled positions, by utilizing palladium in the SCR catalyst within the multifunctional catalyst system.
Implementation Method 1
a means for injecting hydrocarbons into an exhaust gas stream... a diesel oxidation catalyst... comprising one or more platinum group metals... wherein the one or more platinum group metals comprise, preferably consist of, platinum, preferably platinum and palladium
Implementation Method 2
a selective catalytic reduction (SCR) catalyst for the selective catalytic reduction of NOx, wherein the MFC comprises a substrate and a catalyst coating provided on the substrate, wherein the catalyst coating comprises the oxidation catalyst and the SCR catalyst, wherein the SCR catalyst comprises a zeolitic material with copper or iron loading
Implementation Method 3
generating an exotherm over the oxidation catalyst in this fashion may also be used to heat up the SCR catalyst
Data Source
AI summary
The present invention relates to an exhaust gas treatment system for treating exhaust gas from a lean burn combustion engine, wherein said exhaust gas comprises hydrocarbons and NOx, the exhaust gas treatment system comprising: (i) a means for injecting hydrocarbons into an exhaust gas stream; (ii) a diesel oxidation catalyst (DOC) comprising a substrate and a catalyst coating provided on the substrate, wherein the catalyst coating comprises one or more platinum group metals, wherein the one or more platinum group metals comprise platinum; (iii) a means for injecting a nitrogenous reducing agent into an exhaust gas stream; and (iv) a multifunctional catalyst (MFC) comprising an oxidation catalyst, and a selective catalytic reduction (SCR) catalyst for the selective catalytic reduction of NOx, wherein the MFC comprises a substrate and a catalyst coating provided on the substrate, wherein the catalyst coating comprises the oxidation catalyst and the SCR catalyst, wherein the oxidation catalyst comprises one or more platinum group metals, wherein the one or more platinum group metals comprise palladium and/or platinum, and wherein the SCR catalyst comprises a zeolitic material loaded with copper and/or iron; wherein the means for injecting hydrocarbons, the DOC, the means for injecting a nitrogenous reducing agent, and the MFC are located in sequential order in a conduit for exhaust gas, wherein the means for injecting hydrocarbons into an exhaust gas stream is located upstream of the DOC, wherein the DOC is located upstream of the MFC, and wherein the means for injecting a nitrogenous reducing agent into the exhaust gas stream is located between the DOC and the MFC. Furthermore, the present invention relates to a method for the treatment of exhaust gas using the exhaust gas treatment system according to the present invention, and to a method for the preparation of an exhaust gas treatment system according to the present invention.