Cu-Fe Molecular Sieve SCR Catalyst Preparation
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Solution Overview
Problem
Traditional V-based SCR catalysts deactivate at high temperatures and produce excessive N2O during NOx purification in diesel vehicle exhaust, limiting their application in diesel vehicle post-processing systems, while low-cost Cu-Fe composite molecular sieve catalysts also generate high N2O levels, restricting their industrial use.
Innovation Solution
A method involving the preparation of a molecular sieve SCR catalyst using a mixture of Beta and Si-Al zeolites, modified with transition or rare-earth metals, loaded with Fe by equivalent-volume impregnation and Cu by ion exchange, which reduces N2O production while maintaining a wide activity temperature window and high hydrothermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional V-based catalyst is used, then catalytic activity is maintained, but catalyst deactivates at high temperature (650-750°C) due to TiO2 crystalline phase transformation and VOx volatilization
Solution Approach 1:
The patent changes the chemical composition parameters of the catalyst by replacing V-based active components with Cu and Fe, and replacing TiO2 support with molecular sieve structures. This parameter change enables the catalyst to maintain stability at high temperatures (650-750°C) where traditional V-based catalysts deactivate due to phase transformation and volatilization.
Solution Approach 2:
The patent employs composite material design by combining Cu and Fe as dual active components on a molecular sieve support structure. This composite approach creates a catalyst system that leverages the synergistic effects of different materials to achieve both high-temperature stability and catalytic activity, overcoming the limitations of single-material catalysts.
2Ease of manufacture
If low-cost Cu-Fe composite molecular sieve catalyst is used, then cost is reduced, but large amount of N2O by-product is produced during SCR reaction
Solution Approach 1:
The patent optimizes the Cu/Fe ratio parameter and adjusts the preparation conditions (ion exchange time, temperature, concentration) to control the distribution and oxidation state of Cu and Fe species. This parameter optimization enables the catalyst to maintain low-cost composition while suppressing N2O formation pathways and promoting N2 selectivity.
Solution Approach 2:
The patent creates local quality differences by controlling the spatial distribution of Cu and Fe species within the molecular sieve structure. Through ion exchange and impregnation methods, Cu and Fe are selectively positioned in specific sites of the molecular sieve, creating local active sites with optimized electronic and geometric properties that favor N2 production over N2O.
3Ease of manufacture
If Cu and Fe are used as active components instead of precious metal or VOx, then catalyst cost is reduced and toxicity is eliminated, but N2O yield increases
Solution Approach 1:
The patent uses composite material design by combining Cu and Fe in specific ratios and configurations on the molecular sieve support. This composite structure creates synergistic effects where Cu and Fe work together to promote the desired SCR reaction pathway to N2 while suppressing the alternative pathway to N2O, thereby reducing harmful emissions despite using low-cost, non-toxic materials.
Solution Approach 2:
The patent utilizes the porous molecular sieve structure to control the interaction between reactants and active sites. The porous structure provides controlled access to Cu and Fe active sites, optimizing reactant distribution and residence time to favor complete reduction to N2 rather than partial reduction to N2O, thereby reducing harmful by-products.
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 method effectively reduces N2O yield and enhances catalyst stability, ensuring compliance with stringent emission standards and extending the catalyst's operational temperature range, thus overcoming the limitations of traditional and low-cost catalysts.
Implementation Method 1
Cu by ion exchange
Implementation Method 2
Fe loading by equivalent-volume impregnation
Implementation Method 3
NH3-SCR reaction with NOx on the surface of the catalyst to generate N2 and H2O
Implementation Method 4
ammonia gas hydrolyzed by urea performs NH3—SCR reaction
Data Source
AI summary
A method for preparing a molecular sieve SCR (selective catalytic reduction) catalyst and a prepared catalyst therethrough. In the method, several molecular sieves are mixed and modified by transition metal or rare-earth metal via ion exchange, then loaded Fe by equivalent-volume impregnation, and loaded Cu by one or more liquid ion exchange. This present invention, combined with several techniques, such as modification of stable molecular sieve by transition and rare-earth metal, Fe loading by equivalent-volume impregnation and Cu loading by one or more liquid ion exchange, and after through stable and effective modification and loading control, the obtained catalyst material is coated on a carrier substrate via size mixing and coating process to be prepared into an integral catalyst.