Synthesis of hierarchical mordenite and chabazite zeolites and their catalytic properties

Abstract

Utilization of zeolites has been a strategic focus in converting carbon dioxide (CO2) into industrial chemicals because CO2 is one of the main greenhouse gases and has high concentration in atmosphere. Zeolites are microporous crystalline aluminosilicates widely employed in several catalytic reactions due to their selectivity, well-defined microporous structure, high specific area, high thermal stability, and active acidic sites. The feasibility of modifying their physical and chemical properties by changing the synthesis parameters or using post-synthesis treatments may afford them unique features. In this regard, hierarchical zeolites have been prepared for improving the accessibility of active sites by increasing the micropore sizes, introducing mesopores, or reducing crystal sizes. These strategies allow fast diffusion of both reactants and products, improve the catalytic activity, and extend the catalyst lifetime. In this context, this project aims to thoroughly study the crystallization mechanisms of hierarchical SSZ-13 and MOR zeolites in order to achieve the optimized synthesis conditions and high catalytic activity. The hierarchical zeolites will be synthesized, and the effects of crystallization time, temperature, and aging time will be evaluated. In addition, the zeolites will be evaluated regarding the accessibility, activity, and stability of their acid sites. Advanced characterization techniques such as XRD, N2 physisorption, SEM, ICP-AES, in situ solid-state NMR, and NH3-TPD will be used to establish the precise correlations among synthesis-property-function to obtain hierarchical structures for the conversion of methane to methanol and from methanol to products. The outcome of the proposed research will be essential to understanding the crystallization mechanisms of hierarchical zeolites, improving their synthesis conditions, and ultimately boosting their catalytic activity, accessibility of acid sites, and thermal stability. (AU)