Synthesis of MFI Zeolite-encapsulated Metal Nanoparticles by the Dry-gel Conversion Method and Ethane Dehydroaromatization for the Production of Valuable Chemicals

A novel method for encapsulating Pt nanoparticles within MFI zeolites via dry-gel conversion (DGC) is proposed. First, an impregnation method was used to form a Pt-supported MFI zeolite (Pt/MFI), which was coated with an amorphous silica–alumina layer. This layer was transformed to the zeolite by DGC, resulting in the formation of a zeolite-encapsulated Pt nanoparticle (Pt@MFI) catalyst. TEM results confirmed that the Pt particle sizes in Pt@MFI and Pt/MFI were ∼4.0 nm and ∼4.5 nm, respectively. Pt/MFI showed activity for hydrogenation of toluene and 1,3,5-trimethylbenzene, forming methylcyclohexane and 1,3,5-trimethylcyclohexane, respectively. In contrast, Pt@MFI efficiently hydrogenated toluene to methylcyclohexane, with almost no hydrogenation of 1,3,5-trimethylbenzene. Furthermore, Pt nanoparticles in Pt@MFI exhibited higher thermal stability than in Pt/MFI. These findings indicate that the Pt metal nanoparticles in Pt@MFI were primarily present within the zeolite, forming an encapsulated structure. The catalytic activities of Pt@MFI and Pt/MFI for ethane dehydrogenation at 700 °C were assessed. Pt@MFI demonstrated higher dehydrogenation activity than Pt/MFI because of the high resistance of Pt particles to sintering resulting from the encapsulated structure.