Effective diffusivities of lighter hydrocarbons in Cu- and Co-MFI-type zeolite catalysts

Intracrystalline and effective diffusivities of ethane, propane, ethylene and propylene were measured for several kinds of MFI-type zeolite, such as silicalite-1, H-MFI, Cu- and Co-MFI-type zeolites at temperatures ranging from 323 to 823 K. The intracrystalline diffusivity represents the mobility of molecules within zeolite crystals, and was found to be reduced to 1/100 for paraffins and 1/1000 for olefins by the existence of active sites (proton, Cu and Co ions), as compared with silicalite-l. The effective diffusivity was evaluated by multiplying the intracrystalline diffusivity by a partition factor. Although the intracrystalline diffusivity of olefins was about 1/10 to 1/100 of that of paraffins, the effective diffusivity of olefins was almost equal to that of paraffins. The calculated effective diffusivity of ethylene within Cu-MFI was in good agreement with those evaluated by the kinetic analysis of the catalytic decomposition of NO with ethylene over Cu-MFI catalyst. (C) 2001 Elsevier Science Ltd. All rights reserved.