Pure-Phase AFX Zeolite Catalyst Synthesis for NOx Reduction
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Solution Overview
Problem
Conventional AFX zeolite synthesis techniques yield mixed phase products, which are less desirable for catalytic reactions compared to pure phase zeolites, and existing zeolites are not optimized for selective catalytic reduction (SCR) of NOx in lean burn engine exhaust gases.
Innovation Solution
A novel method for synthesizing a pure-phase aluminosilicate AFX zeolite with a silica-to-alumina ratio of 12-32 and mean crystal size of 0.5-7 μm, using a synthesis gel with specific compositional ratios and a structured directing agent, and loading it with metals like V, Cr, Mn, Fe, or Cu to create a catalyst for treating exhaust gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional AFX zeolite synthesis techniques are used, then zeolite crystals can be produced, but the product is mixed phase which is less desirable for catalytic reactions
Solution Approach 1:
The patent applies parameter changes by precisely controlling the silica-to-alumina ratio (15-30), water-to-alumina ratio (180-400), and synthesis temperature (90-110°C) to achieve pure-phase AFX zeolite. These specific parameter ranges transform the synthesis process from producing mixed-phase products to consistently yielding phase-pure material.
Solution Approach 2:
The patent uses an organic structure-directing agent (specifically 1,3-bis(1-adamantyl)imidazolium hydroxide or similar compounds) as an intermediary to guide the formation of the AFX framework. This mediator directs the self-assembly of alumina and silica into the desired crystalline structure, ensuring phase purity while simplifying the synthesis pathway.
2Reliability
If existing zeolites are used for catalytic reactions, then catalytic activity can be achieved, but selectivity and stability for SCR of NOx are not optimized
Solution Approach 1:
The patent applies local quality by creating a catalyst with specific local structural characteristics - the AFX framework with its unique pore geometry and the presence of extra-framework aluminum species. These localized structural features provide both the stability and the specific selectivity needed for SCR reactions, making the catalyst highly adaptable to lean burn engine exhaust conditions.
Solution Approach 2:
The patent creates a composite catalyst system combining the AFX zeolite framework with metal promoters (such as Cu, Fe, or Co) and extra-framework aluminum species. This composite structure integrates the stability of the zeolite framework with the catalytic activity of metal sites, achieving both high reliability and selectivity for NOx reduction.
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 produces a highly efficient catalyst for selective catalytic reduction of NOx, storage of NOx, oxidation of CO, hydrocarbons, and NH3, with improved selectivity and stability, suitable for use in lean burn engine exhaust gases and other industrial processes.
Implementation Method 1
Synthesis of zeolite crystals typically involves reacting alumina and silica in the presence of an organic template (also referred to as a structure directing agent or SDA) at elevated temperatures for several days. During crystallization, the alumina and silica co-join to form a crystalline structure around the SDA.
Implementation Method 2
After the crystals are separated from the mother liquor, the organic SDA is thermally degraded and removed from the crystalline structure, thus leaving a porous molecular sieve.
Implementation Method 3
AFX zeolite has been identified as being useful for hydrocarbon cracking and reforming. The AFX zeolite has a silica-to-alumina ratio and crystal size that is particularly useful as a catalyst for selective catalytic reduction (SCR) of NOx in exhaust gas from lean burn engines.
Implementation Method 4
provided is a method for using such a catalyst to treat an exhaust gas, for example by selectively reducing NOx, by storing NOx, or by oxidizing one or more of CO, hydrocarbons, and NH3
Data Source
AI summary
Provided is a novel form of AFX zeolite, a novel synthesis technique for producing pure phase AFX zeolite, a catalyst comprising the AFX zeolite in combination with a metal, and methods of using the same.