摘要：

A novel method for encapsulating Pt nanoparticles witnin 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 hydroge-nation of toluene and 1,3,5-trimethylbenzene,forming methylcyclohexane and l,3,5-trimethylcyclohexane,respectively.In contrast,Pt@MFI efficiently hydrogenated toluene to methylcyclohexane,with almost no hydro-genation 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 witnin the zeolite,forming an encapsulated structure.The catalytic activities of Pt@MFI and Pt/MFI for ethane dehy-drogenation at 700 ℃ were assessed.Pt@MFI demonstrated higher dehydrogenation activity than Pt/MFI because of the high resistance of Pt particles to sintering resulting from the encaosulated structure.

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