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Effect of metal cations on zeolite acidity

Zeolites of faujasite type (FAU) are one of most widely used ones in the fuel industry. The tridimensional 12-member ring cages make them suitable as catalysts for fluid catalytic cracking (FCC) and support for platinum or palladium in a hydrocracking process. There are two subtypes of synthetics FAU type zeolites depending on their Si/Al ratio: the X type when the ratio is between 2 and 3 and Y type if ratio is 3 or higher. The high amount of aluminum in X type zeolite results in number of Brønsted’s acid sites much higher than in the Y type. While high number of active sites can speed up catalytic process significantly it can also lead to unwanted byproducts and formation of coke. These problems can be avoided with post synthetic modifications by wet impregnation with metal salts to tune in acidity of active sites. The synthesis gel of composition 4Na2O:Al2O3:10SiO2:158H2O was used for the preparation of FAU type zeolite. The reaction was conducted in teflon lined autoclaves for 48 h at 100°C.[1] One part of synthesized zeolite was modified during synthesis using cetrimonium bromide (CTAB) while the other part was post synthetically treated with aqueous solution of sodium hydroxide. This was done in order to create mesopores (Figure 1.) which can facilitate diffusion through crystal during catalysis.[2] The prepared parent materials were then wet impregnated using metal salts of magnesium(II), cobalt(II), nickel(II), or zinc(II).

Zeolite ; Faujasite ; wet impregnation ; acid sites

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