Zeólitas hierarquicamente estruturadas: um estudo da inserção de Mesoporosidade via Mecanoquímica

Abstract

Structurally, zeolites basically consist of a three-dimensional network formed from silicon and aluminum tetrahedra that are interconnected by means of oxygen atoms. Due to their various properties and characteristics, it can be said that zeolites are one of the most used catalysts in the industry; however, the intrinsic microporosity of these materials has limited their application aimed at processing larger molecules. In this work, the influence of mechanochemical methods in obtaining zeolitic materials with hierarchical pore structure was studied, through the insertion of mesoporosity via dry grinding in a ball mill, seeking to obtain zeolites with greater accessibility of active sites for subsequent application in the cumene cracking reaction. The zeolitic materials used in this process were Mordenite, LTX and USY. In the application of the mechanochemical method, the variables rotation speed (200, 400 and 600 rpm) and rotation time (20, 40 and 60 min) were evaluated. Subsequent mechanochemical studies at higher rotation times (2 and 4 hours) were also performed. The materials obtained were characterized by means of XRD, 27Al NMR, XRF, N2 Adsorption/Desorption and SEM. For the mordenite zeolite, the acid materials previously submitted to a rotation speed of 200 rpm and higher rotation times showed more acceptable structural and textural maintenance compared to other milling studies and, in addition, exhibited a more relevant increase in the volume of mesopores. For LTX zeolite, the low Si/Al ratio presented by the material ended up causing a structural collapse; which in turn hampered the possibility of application of this material. For USY Commercial zeolite samples, the modification in zeolitic accessibility was only possible at intermediate grinding speeds (400 rpm). By linking the structural, morphological and textural results with the results obtained through the cumene cracking reaction, it was possible to prove that, in Mordenite zeolite samples, the control of mechanochemical parameters can promote an increase in accessibility, reflecting in higher rates of conversion of the cumene molecule in the first 60 minutes of reaction. As for the USY Commercial zeolite materials, the mechanochemical modifications reflected significant changes in the conversion and selectivity of cumene compared to the starting USY Commercial zeolite, reaching a conversion of approximately 90%.