Hierarchical Mesoporous Beta Zeolite Synthesis
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Solution Overview
Problem
Conventional zeolites with micropore structures face diffusion limitations when dealing with larger chemical species, leading to inaccessible active sites and reduced catalytic efficiency, particularly in petrochemical and chemical conversion processes.
Innovation Solution
A method for producing hierarchical mesoporous beta zeolites involves mixing beta zeolites with an aqueous metal hydroxide solution, heating to desilicate, and then contacting with an ammonium salt solution followed by acidic treatment to increase the silicon-to-aluminum molar ratio, total pore volume, and average mesopore size, thereby enhancing access to catalytically active sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional micropore zeolite structures are used, then strong acidity and regular pore sizes are achieved, but diffusion limitations occur for larger chemical species
Solution Approach 1:
The zeolite structure is segmented into multiple pore size levels: micropores (original zeolite channels) and mesopores (larger secondary pores). This segmentation allows different pore sizes to serve different functions - micropores provide strong acidity for catalysis while mesopores facilitate diffusion of larger molecules, resolving the contradiction between catalytic activity and diffusion rate.
Solution Approach 2:
The invention introduces a new dimensional aspect to the pore structure by creating a hierarchical system with at least two distinct pore size dimensions. This hierarchical pore architecture adds a mesopore dimension to the traditional micropore structure, enabling simultaneous access for both small reactants and large products, thereby improving diffusion rate without sacrificing catalytic activity.
2Productivity
If desilication is performed to create mesopores, then diffusion limitations are reduced, but silicon-to-aluminum ratio decreases
Solution Approach 1:
The invention carefully controls the desilication process parameters (alkali concentration, treatment time, temperature) to achieve partial desilication that creates mesopores while minimizing silicon removal. By optimizing these parameters, the process creates the desired hierarchical pore structure with mesopores greater than 8 nm while maintaining the silicon-to-aluminum ratio above 12.5, thus preserving compositional stability.
Solution Approach 2:
The desilication process creates local modifications in the zeolite structure - mesopores are formed in specific regions while the overall framework composition is preserved. This local quality change allows mesopore formation for improved diffusion without significantly altering the bulk silicon-to-aluminum ratio, maintaining the material's inherent stability.
3Productivity
If hierarchical mesoporous structure is created, then access to active sites is improved, but manufacturing complexity increases
Solution Approach 1:
The invention performs preliminary desilication treatment on the zeolite before final catalyst formulation. This preliminary action creates the hierarchical pore structure in advance, simplifying subsequent processing steps. The mesopores are formed during the desilication stage, eliminating the need for additional complex pore-forming steps later in the manufacturing process.
Solution Approach 2:
The invention uses an ammonium salt solution as an intermediary to facilitate the desilication process and subsequent ion exchange. The ammonium ions serve as intermediaries that exchange with metal cations in the zeolite framework during desilication, and the ammonium salt solution acts as a mediator that enables controlled silicon removal while maintaining structural integrity. This intermediary approach simplifies the overall process compared to direct harsh chemical treatment.
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 hierarchical mesoporous beta zeolites with improved stability and catalytic performance by increasing the silicon-to-aluminum ratio and preserving pore volume and size, facilitating the use of larger hydrocarbon molecules in catalytic reactions without the need for expensive templating agents.
Implementation Method 1
heating the beta zeolite and the aqueous metal hydroxide mixture at a temperature of greater than or equal to 100° C., wherein the heating causes desilication of the beta zeolite
Implementation Method 2
contacting the desilicated beta zeolite with an ammonium salt solution to produce an intermediate hierarchical mesoporous beta zeolite... wherein the contacting causes ion exchange of sodium ions with ammonium ions
Implementation Method 3
treating the intermediate hierarchical mesoporous beta zeolite with an acidic solution to produce the hierarchical mesoporous beta zeolite that includes (e) a molar ratio of silicon to aluminum of greater than 12.5
Data Source
AI summary
A method for producing a hierarchical mesoporous beta includes mixing a beta zeolite with an aqueous metal hydroxide solution and heating the beta zeolite and the aqueous metal hydroxide mixture to produce a desilicated beta zeolite, contacting the desilicated beta zeolite with an ammonium salt solution to produce an intermediate hierarchical mesoporous beta zeolite, and treating the intermediate hierarchical mesoporous beta zeolite with an acidic solution to produce the hierarchical mesoporous beta zeolite. The hierarchical mesoporous beta zeolite includes a molar ratio of silicon to aluminum of greater than 12.5, a total pore volume of greater than or equal to the total pore volume of the intermediate hierarchical mesoporous beta zeolite, and an average mesopore size of greater than or equal to the average mesopore size of the hierarchical mesoporous beta zeolite. The method may also include calcining the intermediate hierarchical mesoporous beta zeolite.