Ammonia Slip Catalyst for Reducing NOx and N2O Emissions
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Solution Overview
Problem
Current catalyst systems for reducing nitrogen oxides (NOx) in diesel engines and gas turbines face challenges in efficiently converting ammonia slip to nitrogen while minimizing nitrogen oxide and nitrous oxide byproducts over a wide range of temperatures and reducing ammonia release, which can be corrosive and harmful.
Innovation Solution
A catalyst article comprising a substrate with a first zone of a first SCR catalyst and a second zone of an ammonia slip catalyst (ASC) that includes a blend of a second SCR catalyst and an oxidation catalyst, where the ASC has DOC functionality, utilizing a platinum and palladium mixture in a 2:1 ratio to enhance ammonia conversion and reduce NOx and N2O formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an ammonia slip catalyst is installed downstream of the SCR catalyst to remove ammonia from exhaust gas, then ammonia conversion to nitrogen is improved, but nitrogen oxide and nitrous oxide byproducts are formed
Solution Approach 1:
The invention changes the chemical composition parameters of the catalyst by incorporating a specific blend of platinum (0.5-2.0 g/ft³) and palladium (0.25-1.0 g/ft³) in a 2:1 weight ratio, along with copper-exchanged chabazite molecular sieve at 30-60 g/ft³. This parameter optimization enables the catalyst to achieve high ammonia conversion while suppressing nitrogen oxide and nitrous oxide byproduct formation through enhanced selectivity control.
Solution Approach 2:
The invention uses a composite catalyst material combining multiple active components: platinum group metals (platinum and palladium), copper-exchanged chabazite molecular sieve, and a silica-alumina support. This composite structure synergistically combines the oxidation activity of platinum and palladium with the ammonia adsorption and SCR activity of copper-chabazite, achieving both high ammonia conversion and low byproduct formation.
2Productivity
If more than a stoichiometric amount of ammonia is added to the gas stream to maximize NOx conversion, then NOx conversion is improved, but excess ammonia release into the atmosphere worsens
Solution Approach 1:
The invention converts the harmful excess ammonia that would normally be released into the atmosphere into beneficial nitrogen gas. The ammonia slip catalyst downstream of the SCR catalyst oxidizes and converts the excess ammonia through catalytic reactions, transforming this harmful byproduct of high NOx conversion into harmless nitrogen, thus allowing the system to maintain high NOx conversion efficiency without environmental penalty.
3Productivity
If ammonia and water condense in regions downstream of the exhaust catalysts, then ammonia removal is improved, but corrosive mixture formation damages the exhaust system
Solution Approach 1:
The invention converts the harmful corrosive mixture formation into a beneficial process by catalytically converting ammonia to nitrogen gas before condensation can occur. The ammonia slip catalyst performs the conversion reaction in the gas phase, preventing ammonia and water from condensing together to form corrosive ammonium hydroxide or ammonium sulfate deposits that would damage downstream exhaust components.
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 article achieves improved ammonia conversion, reduced NOx and N2O formation, and enhanced exothermic performance, providing effective NOx removal and ammonia conversion across a wide temperature range without generating harmful byproducts.
Implementation Method 1
a gaseous reductant, typically anhydrous ammonia, aqueous ammonia, or urea, is added to an exhaust gas stream prior to the exhaust gas contacting the catalyst. The reductant is absorbed onto the catalyst and the NOx is reduced as the gases pass through or over the catalyzed substrate
Implementation Method 2
an ammonia oxidation catalyst (also known as an ammonia slip catalyst or 'ASC') is installed downstream of the SCR catalyst to remove ammonia from the exhaust gas by converting it to nitrogen
Implementation Method 3
The reductant is absorbed onto the catalyst
Data Source
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AI summary
Catalyst articles having a first zone containing a first SCR catalyst and a second zone containing an ammonia slip catalyst (ASC), where the ammonia slip catalyst contains a second SCR catalyst and an oxidation catalyst, and the ASC has DOC functionality, where the first zone is located on the inlet sideof the substrate and the second zone is located in the outlet side of the substrate are disclosed. The catalytic articles are useful for selective catalytic reduction (SCR) of NOx in exhaust gases, in reducing the amount of ammonia slip and in oxidizing organic residues. Exhaust systems containing the catalyst articles and methods of using the catalytic articles in an SCR process, where the amount of ammonia slip is reduced and hydrocarbon are oxidized by the ASC catalyst, are also described.