Composite Catalyst for NOx Conversion
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Solution Overview
Problem
Existing SCR catalysts face limitations in accessing catalytic sites, leading to incomplete conversion of nitrogen oxides (NOx) in exhaust gases, particularly in lean-burn and diesel engines, as species like NOx, NO2, N2O, and NH3 have restricted access to catalytic sites within the catalyst.
Innovation Solution
A composite material comprising a macroporous silicate-based material partially substituted with microporous zeolites functionalized with copper, iron, or both, which enhances mass transfer of gaseous species to catalytic sites, improving NOx conversion and selectivity for N2O.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional SCR catalysts are used, then the catalyst structure is simple, but access to catalytic sites is limited leading to incomplete NOx conversion
Solution Approach 1:
The patent employs a composite catalyst structure combining macroporous silicate-based material (providing open pore structure for mass transfer) with microporous zeolites functionalized with copper and/or iron (providing catalytic activity). This composite approach allows gaseous species to access catalytic sites effectively while maintaining high NOx conversion efficiency, resolving the contradiction between simple structure and high productivity.
Solution Approach 2:
The catalyst utilizes a hierarchical porous structure with macropores (from silicate-based material) and micropores (from zeolites). The macropores facilitate mass transfer of gaseous species to the catalytic sites within the microporous zeolite regions, ensuring complete access and high conversion efficiency without requiring overly complex structures.
2Reliability
If catalysts with dense structure are used, then mechanical strength is improved, but mass transfer of gaseous species to catalytic sites is restricted
Solution Approach 1:
The catalyst exhibits local quality differentiation: the macroporous silicate-based material provides open pore structures for efficient mass transfer in external regions, while the microporous zeolite domains provide dense catalytic sites for NOx conversion. This spatial differentiation of structural properties allows both high mass transfer efficiency and structural integrity to coexist.
Solution Approach 2:
The catalyst structure follows a nested architecture where microporous zeolite particles are embedded within or coated on the macroporous silicate-based material. The macropores serve as transport channels leading to the nested microporous catalytic regions, enabling efficient mass transfer while maintaining structural strength through the hierarchical arrangement.
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 composite material achieves high levels of NOx conversion and improved selectivity for N2O, with the combination of large pores from the silicate-based material and catalytic activity from the zeolites, resulting in enhanced mass transfer and catalytic performance compared to conventional SCR catalysts.
Implementation Method 1
The microporous zeolite is functionalised with either copper, iron or both copper and iron... the NOx is reduced as the gases pass through or over the catalysed substrate
Implementation Method 2
the access of species in the exhaust gas (e.g. NOx, NO2, N2O and NH3) to catalytic sites within the catalyst may be limited... enhances mass transfer of gaseous species to catalytic sites
Implementation Method 3
The reductant is absorbed onto the catalyst and the NOx is reduced as the gases pass through or over the catalysed substrate
Data Source
AI summary
A composite material comprises a macroporous silicate-based material at least partially substituted with at least one microporous zeolite, wherein the microporous zeolite is functionalised with either copper, iron or both copper and iron, and wherein the composite material is in the form of particles. The composite material can be obtained using a method comprising the steps of: (i) providing a mixture comprising a silicate-containing scaffold having a macroporous structure, an aluminium source and an organic template; (ii) hydrothermally treating the mixture to form a microporous zeolite-containing structure substantially retaining the macroporous structure of the silicate-containing scaffold; (iii) incorporating copper, iron or both copper and iron into the zeolite. The silicate-containing scaffold can be a diatomaceous earth.