N-Heptane hydroisomerization over Pt/MFI zeolite nanosheets: Effects of zeolite crystal thickness and platinum location

摘要

Platinum was supported on MFI-type (ZSM-5) zeolites with various crystal thicknesses ranging from 300 to 2 nm (i.e., from bulk crystal to nanosheet). Two series of Pt/MFI were prepared by the ion exchange of Pt(NH_3)42+ and the impregnation of colloidal Pt nanoparticles. The ion exchange yielded Pt nanoparticles that were supported inside zeolite pores, whereas the impregnation yielded Pt nanoparticles supported exclusively on the external crystal surfaces. The two series of Pt/MFI were used as catalysts for the hydroisomerization of n-heptane to investigate the effects of zeolite crystal thickness and Pt location. This research showed that the product selectivity to branched isomers could be significantly improved by decreasing zeolite crystal thickness to nanosheets. The selectivity improvement was attributed to short diffusion path lengths for branched products to escape before cracking.