Zeolites
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| 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.
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| 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.
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| Pore characteristics of a zeolite | Sharply defined and shape selective. Act like molecular sieves.
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| Rules that dictate the build of zeolites | Two aluminium ions cannot be adjacent to one another. Si/Al ratio of 1 to infinity.
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| Some properties of low Si/Al ratios | Alkaline when in water, hydrothermally unstable, hydrophilic.
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| Some applications for natural zeolites | Pollution control. Mining. Crops/Pastures. Horticulture. Stockfeeds. Aquaculture. Turf. Vermaculture.
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| Building of zeolites | Structure of fused 4 and 6 membered rings.
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| How to control zeolite structure? | Pore size and shape can be controlled by growing zeolites around a template.
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| 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.
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| Techniques for zeolite characterisation | XRD, FTIR, Raman, surface area, XPS.
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| Shape-selective catalysis by zeolites | Certain zeolites can be used to catalyse reactions and be specific to what product(s) is formed.
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| Reactant-selective | Only one type of reactant molecule can be allowed to pass through the catalyst pores, due to size and shape.
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| 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
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| 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.
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| What is Zeolite Y? | ZY is a synthetic zeolite with structural type FAU, with a high Si/Al ratio. Ultra-stable Y.
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| 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.
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| 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.
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| Zeolite A | Largest volume zeolite produced.
Water softener in laundry detergents.
Replaced harmful tri-phosphates.
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