Exhaust Gas Oxidation Catalyst for Stable NO2/NOx SCR Feed
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Solution Overview
Problem
Existing oxidation catalysts in diesel engines fail to maintain the optimal NO2 to NOx ratio throughout the vehicle's lifetime due to thermal degradation, leading to an imbalance that affects the efficiency of downstream selective catalytic reduction (SCR) processes.
Innovation Solution
An exhaust gas treatment system incorporating an oxidation catalyst with a specific formulation of platinum group metals supported on a refractory support oxide, containing a minimum of 13% by weight of lanthanum oxide, ensures a consistent NO2 to NOx ratio by minimizing thermal degradation effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oxidation catalysts are designed to provide appropriate NO2 to NOx ratio at end of vehicle lifetime, then the ratio is too high at fresh state
Solution Approach 1:
The patent modifies the chemical composition parameters of the oxidation catalyst by incorporating specific amounts of alkali earth metals (0.1-5 wt% based on total catalyst weight) and rare earth metals (0.1-5 wt% based on total catalyst weight). This compositional parameter change adjusts the catalyst's oxidation activity to provide the appropriate NO2 to NOx ratio (5-20%) both at fresh state and after thermal degradation, resolving the contradiction between maintaining consistent performance and avoiding excessive NO2 formation.
Solution Approach 2:
The patent creates a composite catalyst material combining platinum group metals (0.1-10 g/ft³) with alkali earth metals and rare earth metals on a ceramic or metal substrate. This composite structure integrates multiple functional components: the platinum group metals provide oxidation activity, while the alkali earth and rare earth metals modulate the NO2 formation characteristics. The synergistic combination maintains appropriate NO2 to NOx ratio throughout the catalyst lifetime, solving the contradiction between reliability and operational efficiency.
2Duration of action of stationary object
If oxidation catalyst activity is designed for end-of-life performance, then thermal degradation is compensated but fresh state NO2 ratio is too high
Solution Approach 1:
The patent applies preliminary anti-action by incorporating alkali earth metals and rare earth metals into the catalyst formulation before deployment. These additives preemptively counteract the tendency toward excessive NO2 formation that would otherwise occur at fresh state. The pre-configured compositional balance ensures that even before thermal degradation sets in, the catalyst produces the appropriate NO2 to NOx ratio, preventing the harmful effect of excessive NO2 while maintaining end-of-life performance.
Solution Approach 2:
The patent changes the physical-chemical parameters of the catalyst by controlling the concentrations of alkali earth metals (0.1-5 wt%) and rare earth metals (0.1-5 wt%). This parameter optimization creates a catalyst that is less sensitive to thermal degradation effects, maintaining stable NO2 to NOx ratio (5-20%) throughout its service life. The adjusted parameters prevent both excessive fresh-state NO2 formation and premature performance loss.
3Reliability
If platinum group metal content is increased to maintain oxidation activity, then catalytic performance improves but cost and complexity increase
Solution Approach 1:
The patent applies multi-functionality by selecting alkali earth metals and rare earth metals that simultaneously serve multiple purposes: they moderate NO2 formation, enhance thermal stability, and work synergistically with platinum group metals to maintain oxidation activity. This multi-functional approach allows the catalyst to achieve reliable performance with optimized (rather than maximized) platinum content, reducing complexity while maintaining effectiveness.
Solution Approach 2:
The patent creates a composite catalyst system where platinum group metals (0.1-10 g/ft³) are combined with alkali earth metals and rare earth metals. This composite formulation distributes functionality across multiple components, allowing moderate platinum levels to achieve high oxidation activity when supported by the synergistic rare earth and alkali earth metal components. The composite structure simplifies the overall system by integrating multiple functions into a single catalyst formulation.
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 system maintains the appropriate NO2 to NOx ratio throughout the vehicle's lifetime, enhancing the performance and efficiency of the SCR catalyst by stabilizing the catalyst's activity.
Implementation Method 1
The carbon monoxide and hydrocarbon pollutant gases can be rendered harmless by oxidation over a suitable oxidation catalyst
Implementation Method 2
upstream oxidation catalysts are used to produce exhaust gas with the appropriate NO2 to NOx ratio
Implementation Method 3
One approach is to use the so-called selective catalytic reduction (SCR) to reduce NOx to nitrogen with ammonia released from urea solution as reducing agent
Implementation Method 4
lanthanum is present in an amount of at least 13% by weight calculated as La2O3 and based on the weight of the refractory support oxide
Data Source
AI summary
The present invention provides an exhaust gas treatment system comprising an oxidation catalyst and an SCR catalyst, wherein the oxidation catalyst comprises an inert ceramic or metal honeycomb body and a catalytically active coating comprising a platinum group metal supported on a refractory support oxide and lanthanum wherein lanthanum is present in an amount of at least 13% by weight calculated as La2O3 and based on the weight of the refractory support material.