Pt supported on hierarchical zeolite: selective impregnation of pt nanoparticles in micro-/mesopores of hierarchical zeolite

Abstract

The work presented in this thesis demonstrates the selective impregnation of Pt nanoparticles into the micro-/mesopores of hierarchical MFI zeolite. Zeolite is crystalline aluminosilicate material possessing uniform micropore (diameter < 2nm) structure which is widely used in various applications, such as adsorbents, catalysts, and ion-exchange materials. Also, it is possible to impregnate Pt nanoparticles into the zeolite framework and create highly active catalyst in hydrogenation, isomerization, hydrocracking of alkanes, and hydrolysis of alkyl compounds. Pt nanoparticles supported zeolite can act as bi-functional catalysts in various reactions, e.g. hydroisomerization. However, for example in the case of hydroisomerization, the isomer yield could not exceed the maximum of hydrocracking yield by using Pt nanoparticles supported bulk MFI zeolite. To enhance the hydroisomerization yield, the catalysts should increase the external surface area to the reaction and decrease in the diffusion path length, such as creation of mesopores and nanocrystallinity, to increase the isomer yield. Due to the large external surface area and reduced diffusion path length of mesoporous(MP) MFI zeolite, usage of MP MFI zeolite with tunable mesoporosity as a support for Pt nanoparticles is expected to greatly enhance the hydroisomerization yield. For these reasons, it is possible to create bi-functional catalysts with enhanced activity with MP MFI zeolite, and the catalytic activity could be varied by using selectively impregnated Pt nanoparticles in micro-/mesopores of MP MFI zeolite. Therefore, it is essential to discuss the various methods to selectively situate Pt nanoparticles in micro-/mesopores of MP MFI zeolite. For Pt nanoparticles situated in the micropores of MP MFI zeolite, the ion-exchange method of Pt cations, $([Pt(NH_3)_4]^{2+})$, was used. The careful pretreatment in fast flowing oxygen ambient with very slow heating rate of Pt cation-exchanged MP MFI zeol...