Non-zeolite Base Metal SCR Catalyst Thermal Durability
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Solution Overview
Problem
Existing SCR catalysts, particularly those based on zeolites and vanadium, face issues with thermal durability, hydrocarbon adsorption, and coking, which affect their performance in reducing NOx emissions, especially in vehicular diesel applications.
Innovation Solution
A non-zeolite, non-vanadium base metal catalyst system using cerium and zirconium oxides with dispersed transition metals like iron and tungsten, which enhances low-temperature activity and sulfur tolerance, is developed, with specific compositions and heat activation processes to improve thermal stability and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If zeolite-based catalysts are used for SCR, then NOx conversion activity is achieved, but thermal durability deteriorates due to dealumination during high temperature hydrothermal ageing
Solution Approach 1:
The patent removes the zeolite framework from the catalyst system and replaces it with non-zeolite base metal catalysts comprising transition metals (Fe, Co, Ni, Cu, Mn) supported on oxides (Al2O3, SiO2, TiO2, ZrO2). This extraction of the problematic zeolite component eliminates dealumination while maintaining NOx conversion functionality through alternative metal-oxide active sites.
Solution Approach 2:
The patent employs composite catalyst systems combining transition metals with oxide supports (e.g., Fe/W on ZrO2, Co/Mn on Al2O3). These composite structures provide both the active metal sites for NOx reduction and the thermally stable oxide framework, achieving synergistic effects that improve both activity and thermal durability simultaneously.
2Productivity
If zeolite-based catalysts are used for SCR, then NOx conversion is achieved, but performance deteriorates due to hydrocarbon adsorption and coking at relatively low temperatures
Solution Approach 1:
The patent eliminates zeolite-based catalysts that are prone to hydrocarbon adsorption and replaces them with non-zeolite base metal catalysts. The metal-oxide combination inherently resists hydrocarbon adsorption and coking, maintaining NOx conversion activity even in the presence of hydrocarbons during cold-start conditions.
Solution Approach 2:
The patent converts the harmful effect of hydrocarbon presence into a beneficial outcome by using metal-oxide catalysts that do not adsorb hydrocarbons. Instead of being poisoned by hydrocarbon coking, the catalyst maintains stable active sites for NOx reduction, effectively turning the problematic hydrocarbon environment into a non-interfering condition.
3Productivity
If vanadium-based catalysts are used for SCR, then NOx reduction performance is achieved, but thermal durability deteriorates in certain applications
Solution Approach 1:
The patent removes vanadium from the catalyst composition and replaces it with transition metals (Fe, Co, Ni, Cu, Mn) supported on stable oxides. This substitution eliminates the thermal durability issues associated with vanadium volatilization and sintering while maintaining NOx reduction performance through alternative metal-oxide active sites.
Solution Approach 2:
The patent employs composite metal-oxide catalysts (e.g., Fe/W on ZrO2, Co/Mn on Al2O3) that combine the catalytic activity of transition metals with the thermal stability of oxide supports. This composite approach provides both NOx reduction performance and superior thermal durability, overcoming the limitations of vanadium-based systems.
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 demonstrates improved NOx conversion efficiency at low temperatures and maintains performance under high-temperature and sulfur-containing conditions, offering a more durable and effective alternative to traditional SCR catalysts.
Implementation Method 1
a method of selectively catalytically converting nitrogen oxides (NOx) present in a gas stream to nitrogen with a non-zeolite, non-vanadium base metal catalyst using a nitrogenous reductant such as ammonia (NH3)
Implementation Method 2
4NH3+5O2→4NO+6H2O
Data Source
AI summary
An article for treating a gas containing nitrogen oxides having a monolith substrate loaded with a catalytic composition containing at least one catalytic component consisting of (i) at least one transition metal dispersed on a mixed oxide or composite oxide or a mixture thereof as support material consisting of cerium and zirconium; or (ii) cerium oxide and zirconium oxide as single oxides or a composite oxide thereof or a mixture of the single oxides and the composite oxide dispersed on an inert oxide support material, wherein at least one transition metal is dispersed thereon, wherein the at least one transition metal is selected from the group consisting of a metal from Group VIB, IB, IVA, VB, VIIB, and VIII and mixtures of any two or more thereof, provided that at least one selected transition metal is tungsten, wherein the catalytic composition is disposed on said monolith substrate.