engleski

Preparation of embryonic zeolite units-mesoporous matrix composites by nano casting

Zeolites are crystalline aluminosilicates materials with well defined micropores with numerous applications in catalysis, separations and ion exchange. However, they are scarcely used directly as powders since this can cause problems such as pressure drop and difficulties in separation and operation. In order to overcome these difficulties different methods are applied, mostly shaping them to desired macroscopic forms employing different binders. Hereby, we report the zeolitization of amorphous aluminosiliate matrix under hydrothermal conditions and extensive physicochemical characterization of prepared composites. The preparation of composites includes nano casting of embryonic MFI units followed by hydrothermal treatment. The embryonic germs were prepared at room temperature and then electrostatically anchored to the matrix by means of a cationic polymer. The modified matrices were subjected to hydrothermal treatment as the conditions were optimized to obtain very small zeolite units with open structure and high catalytic activity. Obtained composites were characterized by various techniques such as XRD, NMR, hyperpolarized 129Xe NMR, N2 adsorption and desorption, SEM, TGA/DTG, DLS and acidity measurements by in situ IR. Collected data show that the prepared materials are X-ray amorphous with bimodal pore systems containing micropores (zeolite) and mesopores (matrix). Number and strength of BrØnsted acid sites is significantly higher in the composites than in the parent matrix. The new materials exhibit high catalytic activity in cracking of bulky molecules that cannot be processed on conventional zeolite catalysts.

composite, amorphous matrix, embryionic zeolites, acidity, catalytic cracking

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