Low-Ammonia-Storage Slip Catalyst for Reduced N2O Formation
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Solution Overview
Problem
Existing ammonia slip catalysts fail to effectively convert ammonia to nitrogen over a wide range of temperatures in vehicle driving cycles while minimizing nitrogen oxide and nitrous oxide byproducts.
Innovation Solution
A catalyst comprising a combination of platinum on a siliceous support with low ammonia storage, combined with a first SCR catalyst, such as Cu-SCR or Fe-SCR, and optionally a second or third SCR catalyst, arranged in specific configurations to enhance ammonia conversion to nitrogen and reduce nitrogen oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional ammonia slip catalysts are used to convert ammonia to nitrogen, then ammonia removal is achieved, but nitrogen oxide and nitrous oxide byproducts are formed and ammonia conversion is not effective over a wide temperature range
Solution Approach 1:
The patent employs a composite catalyst formulation combining platinum on a siliceous support (with silica-to-alumina ratio ≥500) with Cu-SCR or Fe-SCR catalysts. This composite structure leverages the complementary properties of each component: platinum provides ammonia oxidation activity while the Cu-SCR or Fe-SCR catalysts facilitate selective catalytic reduction, together achieving wide-temperature-range ammonia conversion with minimal nitrogen oxide and nitrous oxide byproduct formation
Solution Approach 2:
The patent modifies the support parameters by using a siliceous support with a high silica-to-alumina ratio (≥500). This parameter change in the support composition reduces ammonia storage capacity while maintaining structural stability, which prevents ammonia from being stored and subsequently released as harmful byproducts, thereby improving both conversion efficiency and reducing harmful emissions
2Productivity
If more ammonia is added to maximize NOx conversion in SCR process, then NOx removal efficiency is improved, but excess ammonia is released into the atmosphere causing health and environmental issues
Solution Approach 1:
The patent extracts and addresses the harmful side effect of excess ammonia release by incorporating a dedicated ammonia slip catalyst section downstream of the SCR catalyst. This separate functional zone specifically targets and converts residual ammonia that escaped the SCR process, removing the harmful component without affecting the primary NOx conversion function
Solution Approach 2:
The ammonia slip catalyst acts as an intermediary between the SCR process and the atmosphere. It provides a controlled conversion pathway for excess ammonia, transforming it into harmless nitrogen and water vapor before atmospheric release, thereby mediating between the need for high ammonia dosing in SCR and the need to prevent ammonia pollution
3Reliability
If ammonia is not completely converted in SCR process, then ammonia can be released causing corrosion and health issues, but increasing ammonia dosage to ensure complete conversion leads to excess ammonia release
Solution Approach 1:
The patent segments the catalytic treatment into two distinct functional zones: the first zone (SCR catalyst) handles primary NOx reduction with ammonia, and the second zone (ammonia slip catalyst) handles residual ammonia conversion. This segmentation allows each zone to be optimized for its specific function, ensuring complete ammonia utilization for NOx reduction while providing a safety net to convert any slip ammonia, thereby achieving reliable complete conversion without systematic excess ammonia release
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
Improves nitrogen yield from ammonia at temperatures between 250°C to 350°C and reduces nitrogen oxide formation compared to conventional catalyst formulations.
Implementation Method 1
A catalyst comprising a combination of platinum on a support with low ammonia storage and a first SCR catalyst... improves nitrogen yield from ammonia at a temperature from about 250 °C to about 350 °C
Implementation Method 2
NOx needs to be reduced selectively with a catalyst and a reductant in a process known as selective catalytic reduction (SCR) that converts NOx into elemental nitrogen (N2) and water
Implementation Method 3
The reductant is absorbed onto the catalyst and the NOx is reduced as the gases pass through or over the catalyzed substrate
Data Source
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AI summary
Catalysts having a blend of platinum on a support with low ammonia storage with an SCR catalyst are disclosed. The catalysts can also contain one or two additional SCR catalysts. The catalysts can be present in one of various configurations. Catalytic articles containing these catalysts are disclosed. The catalytic articles are useful for selective catalytic reduction (SCR) of NOx in exhaust gases and in reducing the amount of ammonia slip. Methods for producing such articles are described. Methods of using the catalytic articles in an SCR process, where the amount of ammonia slip is reduced, are also described.