Integrated NOx Absorber and SCR Catalyst for Sulfur Poisoning
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Solution Overview
Problem
Current selective catalytic reduction (SCR) systems face inefficiencies at lower operating temperatures and are susceptible to sulfur poisoning, leading to premature NOx release and reduced catalyst lifetime due to the separate locations and operating temperature differences between SCR catalysts and NOx absorbers, as well as the interference of sulfur-containing impurities.
Innovation Solution
Integrating a NOx absorber composition with a SCR catalyst composition on the same substrate in a layered or zoned configuration, ensuring both components operate at similar temperatures and preventing sulfur poisoning by forming ammonium sulfates, thus minimizing premature NOx release and extending catalyst life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SCR catalyst and NOx absorber are located separately in the exhaust treatment system, then each component can be optimized for its specific function, but the temperature difference between them causes premature NOx release from the absorber before the catalyst reaches optimal operating temperature
Solution Approach 1:
The patent combines the SCR catalyst and NOx absorber into a single integrated component where the absorber is positioned upstream of the catalyst within the same housing. This merging eliminates the temperature differential issue by ensuring both functions operate at the same exhaust gas temperature, preventing premature NOx release while maintaining optimized performance of both absorption and catalytic conversion functions.
2Adaptability or versatility
If separate NOx absorber and SCR catalyst components are used, then the system can handle cold start conditions, but the system complexity increases and requires multiple maintenance interventions
Solution Approach 1:
By integrating the NOx absorber and SCR catalyst into a single component, the patent reduces system complexity while maintaining cold start capability. The absorber handles NOx storage during cold conditions, and the catalyst performs conversion when active, all within one unit that requires only single-point maintenance rather than separate servicing of multiple components.
3Quantity of substance
If alkaline earth metal oxide is used as NOx absorber material, then high NOx absorption capacity is achieved, but sulfur-containing impurities cause sulfate formation that poisons the catalyst and reduces lifetime
Solution Approach 1:
The patent introduces a sulfur trap material as an intermediary layer between the alkaline earth metal oxide absorber and the SCR catalyst. This intermediary layer captures sulfur-containing impurities through chemisorption, preventing them from reaching and poisoning the catalyst active sites. The sulfur trap acts as a protective barrier that allows the high-capacity absorber to function without suffering from sulfate formation issues.
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
This integrated approach enhances NOx conversion efficiency across a wider temperature range, reduces the need for separate NOx absorber components, and protects the catalyst from sulfur poisoning, leading to improved emission treatment system performance and extended component lifespan.
Implementation Method 1
NOx absorbers are used to trap NOx at temperatures below 200° C. and release NOx at temperatures exceeding 200° C. These materials typically comprise an alkaline earth metal (such as Ba, Ca, Sr, and Mg) oxide or cerium oxide and form an inorganic nitrate (for example, BaO or BaCO3 is converted to Ba(NO3)2) when adsorbing NOx gases at low temperatures.
Implementation Method 2
The SCR process uses catalytic reduction of nitrogen oxides with a reductant (e.g., ammonia (NH3) or ammonia precursor) in the presence of atmospheric oxygen, resulting in the formation predominantly of nitrogen (N2) and steam (H2O). Generally, catalysts employed in the SCR process have good catalytic activity at higher operating temperatures (i.e., from about 200° C. to 600° C.).
Implementation Method 3
At higher temperatures the inorganic nitrate decomposes to NO and/or NO2, releasing them back into the exhaust gas stream.
Implementation Method 4
Ammonia actually provides protection of the NOx absorber composition from minor sulfur-containing impurities present in the fuel against sulfur poisoning, by forming ammonium sulfates, thus preventing the sulfate species in the exhaust from reacting with the SCR catalyst composition or the NOx absorber composition.
Data Source
AI summary
The present invention is directed to selective catalytic reduction catalysts that combine SCR activity with NOx absorber activity. In particular, the disclosed catalytic article includes a substrate having a first and a second material disposed thereon, wherein the first material includes a selective catalytic reduction (SCR) catalyst composition and the second material includes a nitrogen oxides (NOx) absorber composition, wherein the NOx absorber composition does not substantially oxidize ammonia, and wherein the catalytic article is effective to abate NOx from an engine exhaust gas stream. Emission treatment systems for treating an exhaust gas including a catalytic article of the invention are provided, particularly systems that include an injector adapted for the addition of ammonia to the exhaust gas stream located upstream of the catalytic article.