Small Pore Molecular Sieve Catalyst for Ammonia Oxidation
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Solution Overview
Problem
Current catalyst systems fail to effectively reduce ammonia (NH3) emissions from rich-burn engine exhausts while meeting stringent regulations for NOx, HC, and CO emissions, especially at high temperatures, due to inadequate selectivity and excessive oxidation of NH3 to NOx.
Innovation Solution
Employing a small pore molecular sieve supported transition metal catalyst as an ammonia oxidation catalyst (AOC) in a system with a three-way catalyst and an oxygen-containing gas input to selectively oxidize NH3 to N2, utilizing a Cu-supported CHA Framework Type molecular sieve like Cu/SAPO-34, and optionally incorporating a platinum group metal layer to minimize NOx production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional precious-metal based oxidation catalysts are used to remove NH3, then NH3 removal efficiency is improved above 225°C, but considerable N2O and NOx are produced as undesired side products
Solution Approach 1:
The patent employs a small pore molecular sieve (such as SAPO-34 with 8-membered ring channels) as the catalyst support. The restricted pore geometry confines the oxidation reaction pathways, allowing NH3 to be oxidized to N2 rather than N2O or NOx. The molecular sieve's pore structure acts as a shape-selective catalyst that favors the formation of nitrogen gas over other oxidation products.
Solution Approach 2:
The invention uses a composite catalyst system combining a small pore molecular sieve support with transition metal active sites (such as Cu, Fe, or Co). This composite structure integrates the shape-selective properties of the molecular sieve with the catalytic activity of the transition metal, achieving high NH3 conversion to N2 with minimal side product formation.
2Productivity
If SCR catalysts are used for lean-burn applications, then NOx conversion is improved, but excessive oxidation of NH3 to NOx occurs at temperatures above 400°C
Solution Approach 1:
The small pore molecular sieve structure provides temperature-stable shape selectivity that prevents NH3 over-oxidation even at temperatures above 400°C. The restricted pore geometry maintains reaction pathway control under high-temperature conditions where conventional SCR catalysts fail, ensuring NH3 is converted to N2 rather than oxidized to NOx.
Solution Approach 2:
The invention changes the fundamental catalytic parameters by using a molecular sieve-based catalyst with different pore size, acidity, and metal dispersion characteristics compared to conventional SCR catalysts. These parameter changes result in superior temperature stability and selectivity for N2 formation across a wide temperature range.
3Object-generated harmful factors
If sub-stoichiometric quantity of NH3 is injected to avoid slippage, then NH3 slip is reduced, but NOx conversion decreases
Solution Approach 1:
The small pore molecular sieve catalyst acts as an intermediary that enables complete NH3 conversion to N2 without requiring excess NH3 injection. The catalyst's unique properties allow stoichiometric or near-stoichiometric NH3 dosing to achieve both complete NOx reduction and complete NH3 conversion, eliminating the need for the traditional compromise between NH3 slip control and NOx conversion efficiency.
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 system achieves high selectivity in oxidizing NH3 to N2, reducing emissions below 10 ppm, while maintaining low NOx and CO emissions, and demonstrating durability and thermal stability at high temperatures.
Implementation Method 1
small pore molecular sieve supported transition metal catalysts for the reduction of ammonia (NH3) from rich-burn exhaust
Implementation Method 2
ammonia oxidation catalyst (AOC) in a system with a three-way catalyst and an oxygen-containing gas input to selectively oxidize NH3 to N2
Implementation Method 3
small pore molecular sieve supported transition metal catalysts
Implementation Method 4
Cu-supported CHA Framework Type molecular sieve like Cu/SAPO-34
Data Source
AI summary
Provided is a system for reducing ammonia (NH3) emissions comprising a substrate and an ammonia oxidation catalyst disposed thereon, wherein the ammonia oxidation catalyst comprises a small pore molecular sieve supporting a transition metal selected from Cu, Fe, Ce, Mn, Ni, Zn, Ga, Mo, and Cr, provided that the ammonia oxidation catalyst is effective at oxidizing ammonia in an exhaust gas stream; and provided that the ammonia oxidation catalyst composition and the substrate are free of Platinum Group Metals.