CHA-type Molecular Sieve Synthesis Using Amorphous Silica-Alumina
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Solution Overview
Problem
Current methods for preparing CHA-type molecular sieves are costly and time-consuming, particularly due to the use of expensive starting materials like zeolite Y and crystalline molecular sieves with stacking disorder, which are not suitable for producing pure or essentially pure CHA structures.
Innovation Solution
A method involving a synthesis mixture with non-molecular sieve sources of silicon and aluminum, an organic structure directing agent, water, and optionally an alkali or alkaline earth hydroxide, crystallized under specific molar ratios and conditions to produce a CHA-type molecular sieve with minimal stacking disorder, reducing costs and time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If zeolite Y is used as a starting material for CHA-type molecular sieve synthesis, then the crystallization process can be facilitated, but the production cost increases significantly
Solution Approach 1:
The patent replaces expensive zeolite Y starting material with inexpensive amorphous silica-alumina that can be discarded after serving as a template for CHA crystal formation. The amorphous material acts as a sacrificial template that guides crystallization but does not need to be recovered, significantly reducing production costs while maintaining crystallization efficiency
Solution Approach 2:
The patent changes the physical state parameter of the starting material from crystalline (zeolite Y) to amorphous (silica-alumina). This parameter change reduces material cost while the amorphous structure provides beneficial template effects for CHA-type crystal formation during hydrothermal synthesis
2Ease of manufacture
If crystalline molecular sieves with stacking disorder are used as starting material, then the synthesis process can be simplified, but the purity of the resulting CHA structure decreases
Solution Approach 1:
The patent uses amorphous silica-alumina as a disposable template that simplifies the synthesis process by eliminating the need for pre-formed crystalline starting materials. The amorphous material is consumed during crystallization to form pure CHA structures, avoiding the stacking disorder problems associated with recycling crystalline templates
Solution Approach 2:
The patent extracts and eliminates the stacking disorder problem by not using crystalline molecular sieves as starting materials. By starting with amorphous material, the harmful stacking disorder is prevented from occurring in the first place, allowing pure CHA structure formation
3Manufacturing precision
If conventional synthesis methods are used for CHA-type molecular sieves, then the crystal structure can be formed, but the production time is excessive
Solution Approach 1:
The patent performs preliminary action by preparing amorphous silica-alumina with the appropriate Si/Al ratio and surface characteristics before the hydrothermal synthesis step. This pre-prepared amorphous material is ready to immediately template CHA crystal formation upon contact with the synthesis gel, reducing the overall production time while ensuring proper crystal structure formation
Solution Approach 2:
The patent changes the temperature and time parameters of the hydrothermal synthesis by using amorphous silica-alumina as starting material. The amorphous nature of the template allows for faster nucleation and crystal growth rates compared to crystalline templates, reducing production time while maintaining crystal structure quality
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 enables the cost- and time-effective production of high-purity CHA-type molecular sieves with minimal stacking disorder, suitable for catalytic applications such as NOx removal from automotive exhaust gases, improving catalytic properties and reducing production costs.
Implementation Method 1
subjecting the mixture to conditions capable of crystallizing the molecular sieve of the CHA-type
Data Source
AI summary
The present invention relates to a method for the preparation of a molecular sieve of the CHA-type as well as catalytic applications thereof.