Ammonia Slip Catalyst with Intermediate Barrier Layer
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Solution Overview
Problem
Conventional Al2O3-supported ammonia slip catalysts for oxidizing ammonia to nitrogen suffer from low selectivity and platinum poisoning due to copper diffusion, leading to decreased catalytic activity over time.
Innovation Solution
An ammonia slip catalyst design with a higher washcoat loading of dilution oxide in the AMOX layer, specifically using a combination of titanium oxide as the carrier oxide and aluminum oxide as the dilution oxide, reduces platinum poisoning and increases catalytic activity by maintaining more catalytic centers available.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin washcoat loading (25 g/l) is used to minimize diffusion inhibition, then mass transfer resistance is reduced, but copper diffusion into the AMOX layer increases causing platinum poisoning and decreased catalytic activity
Solution Approach 1:
An intermediate barrier layer comprising 60-90 wt% aluminum oxide and 10-40 wt% titanium oxide is introduced between the AMOX catalyst layer and the Cu-exchanged molecular sieve layer. This intermediate layer acts as a physical barrier that retards copper diffusion from the molecular sieve into the AMOX layer, thereby protecting the platinum catalyst from poisoning while maintaining adequate mass transfer.
2Object-affected harmful factors
If a thicker washcoat loading is used to reduce copper diffusion, then platinum poisoning is decreased, but diffusion inhibition increases reducing catalytic efficiency
Solution Approach 1:
The catalyst structure is segmented into three distinct layers: (1) an AMOX catalyst layer containing platinum on metal oxide with dilution oxide, (2) an intermediate barrier layer with specific aluminum oxide and titanium oxide composition, and (3) a Cu-exchanged molecular sieve layer. This segmentation allows the intermediate layer to specifically address copper diffusion without requiring a uniformly thick washcoat that would impede mass transfer.
3Productivity
If conventional Al2O3-supported AMOX catalyst is used, then ammonia oxidation activity is achieved, but selectivity to nitrogen is insufficient due to side reactions forming NOx and N2O
Solution Approach 1:
The catalyst employs a composite structure combining AMOX catalyst components (platinum on metal oxide with dilution oxide) with Cu-exchanged molecular sieve in a multi-layer configuration. The AMOX layer provides high ammonia oxidation activity while the molecular sieve layer enhances selectivity to nitrogen through SCR reactions, and the intermediate layer ensures long-term stability by preventing copper diffusion.
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 increased washcoat loading enhances the catalyst's aging stability and maintains higher catalytic activity for ammonia oxidation, even after aging, by reducing copper poisoning effects, thus improving the selectivity towards nitrogen production.
Implementation Method 1
the reduction of NOx to nitrogen is not. Either the use of NOx storage catalysts or the use of so-called SCR catalysts is required for selective catalytic reduction (SCR)
Implementation Method 2
At temperatures above 175° C., ammonia (NH3) and CO2 form by hydrolysis: (NH2)2CO+H2O→2NH3+CO2
Implementation Method 3
so-called ammonia slip catalysts (ASC) are used to convert unconverted ammonia via the SCR catalyst. The ammonia is oxidized to nitrogen: 4NH3+3O2→2N2+6H2O
Implementation Method 4
The ammonia is oxidized to nitrogen: 4NH3+3O2→2N2+6H2O
Implementation Method 5
a larger quantity of dilution oxide in the AMOX layer counteracts the aging of the catalyst
Implementation Method 6
the Cu diffuses partially into the AMOX catalyst over the service life of the ASC
Data Source
AI summary
The present invention relates to a catalyst comprising a carrier substrate of length L, coating A arranged as the first layer on the carrier and containing platinum on a metal oxide, and coating B applied as the second layer to coating A and containing a Cu-exchanged molecular sieve and no noble metal, wherein the total washcoat quantity of coating A is 40 g/l or more of washcoat in relation to the coated catalyst volume.