Segmented SCR and Ammonia Oxidation Catalyst for Emissions Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current ammonia selective catalytic reduction (SCR) systems face challenges in effectively converting ammonia at a wide range of temperatures and producing minimal nitrogen oxide byproducts, particularly during temperature increases where ammonia adsorption capacity decreases, leading to ammonia slip and potential corrosive mixtures in exhaust systems.
Innovation Solution
A catalyst system comprising copper or iron on a small pore molecular sieve material, physically mixed with platinum and rhodium on a refractory metal oxide support, including alumina, silica, and zirconia, is used to oxidize ammonia, with specific configurations and dopants to enhance performance across varying temperatures and minimize nitrogen oxide emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ammonia SCR catalyst is used to convert NOx, then NOx conversion efficiency is improved, but ammonia slip occurs at high temperatures
Solution Approach 1:
The catalyst system is segmented into two distinct functional zones: an SCR catalyst zone for NOx conversion and an AMOx catalyst zone for ammonia oxidation. This segmentation allows each zone to perform its specific function optimally without interfering with the other, resolving the contradiction between NOx conversion efficiency and ammonia slip prevention.
Solution Approach 2:
The AMOx catalyst acts as an intermediary component between the SCR catalyst and the exhaust outlet. It receives excess ammonia from the SCR zone and converts it to N2, preventing ammonia slip while maintaining the high NOx conversion efficiency of the SCR catalyst.
2Productivity
If ammonia dosing is increased to improve NOx conversion rate, then NOx conversion efficiency is improved, but ammonia slip increases
Solution Approach 1:
The AMOx catalyst converts the harmful effect of excess ammonia (ammonia slip) into a beneficial outcome by oxidizing it to N2. This allows the system to use higher ammonia dosing rates to improve NOx conversion while the AMOx zone prevents the corresponding increase in ammonia slip.
3Productivity
If ammonia is converted at high temperatures, then NOx conversion is maintained, but ammonia adsorption capacity decreases
Solution Approach 1:
The system changes the operational parameters by introducing a second catalyst zone with different catalytic properties. The AMOx catalyst is specifically designed to operate effectively at high temperatures where the SCR catalyst's ammonia adsorption capacity decreases, maintaining overall system reliability across the full temperature range.
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 system achieves effective ammonia oxidation with low N2O and NH3 emissions, maintaining good NOx conversion efficiency across a wide temperature range, thereby reducing ammonia slip and associated corrosion risks.
Implementation Method 1
A catalyst system comprising copper or iron on a small pore molecular sieve material, physically mixed with platinum and rhodium on a refractory metal oxide support, including alumina, silica, and zirconia, is used to oxidize ammonia
Implementation Method 2
copper or iron on a small pore molecular sieve material having a maximum ring size of eight tetrahedral atoms
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
Described is a catalyst comprising a washcoat including copper or iron on a small pore molecular sieve material having a maximum ring size of eight tetrahedral atoms physically mixed with platinum and rhodium on a refractory metal oxide support including alumina, silica, zirconia, titania, and physical mixtures or chemical combinations thereof, including atomically doped combinations. Also described is a catalyst comprising a first washcoat zone including copper or iron on a small pore molecular sieve material having a maximum ring size of eight tetrahedral atoms, the first washcoat zone being substantially free of platinum group metal; and a second washcoat zone including copper or iron on a small pore molecular sieve material having a maximum ring size of eight tetrahedral atoms physically mixed with platinum or platinum and rhodium on a refractory metal oxide support including alumina, silica, zirconia, titania, and physical mixtures or chemical combinations thereof, including atomically doped combinations. Methods and systems for treating emissions are also described.