Term | Definition |
What is a zeolite? | Inorganic crystalline solid with high surface area, attributed to small pores (1-100A in diameter) present throughout structure. A mineral with a honeycomb-type structure and a unique "open" microporous molecular structure. |
General structure of a zeolite | They are an aluminosilicate framework structure with corner sharing SiO4 and AlO4 tetrahedra alternating throughout, in a lattice-like configuration. |
Pore characteristics of a zeolite | Sharply defined and shape selective. Act like molecular sieves. |
Rules that dictate the build of zeolites | Two aluminium ions cannot be adjacent to one another. Si/Al ratio of 1 to infinity. |
Some properties of low Si/Al ratios | Alkaline when in water, hydrothermally unstable, hydrophilic. |
Some applications for natural zeolites | Pollution control. Mining. Crops/Pastures. Horticulture. Stockfeeds. Aquaculture. Turf. Vermaculture. |
Building of zeolites | Structure of fused 4 and 6 membered rings. |
How to control zeolite structure? | Pore size and shape can be controlled by growing zeolites around a template. |
Steps of zeolite synthesis | To autoclave: sodium silicate, sodium aluminate, template, H2SO4 at 100-150C. Gels. Crystals: Filtering, washing, drying, calcination. Ion-exchange, drying, calcination. Zeolite. |
Techniques for zeolite characterisation | XRD, FTIR, Raman, surface area, XPS. |
Shape-selective catalysis by zeolites | Certain zeolites can be used to catalyse reactions and be specific to what product(s) is formed. |
Reactant-selective | Only one type of reactant molecule can be allowed to pass through the catalyst pores, due to size and shape. |
Product-selective | Only one type of product molecule can be allowed to pass through the catalyst pores, due to size and shape. Therefore, only a certain product is formed. "Observed" product |
Applications of shape-selective catalysts | Undesirable impurities can be continuously converted to easily removable compounds or harmless substances, the selectivity of a desired product can be increased and coke formation can be reduced. |
What is Zeolite Y? | ZY is a synthetic zeolite with structural type FAU, with a high Si/Al ratio. Ultra-stable Y. |
Applications of Zeolite Y? | FCC - Fluid CAtalytic Cracking is the process to "crack" heavy gas oils from larger molecules into small molecules, by breaking carbon bonds.
Alkylation - Introduction of an alkyl group onto a molecule. |
Green chemistry and zeolites | Solid acid properties have been utilised extensively.
Catalysts for: Friedels-craft acylation, salt-free esterfication of amino acids, green caprolactam process. Used in methanol to gasoline production. |
Zeolite A | Largest volume zeolite produced.
Water softener in laundry detergents.
Replaced harmful tri-phosphates. |