Assessing molecular transport properties of nanoporous materials by interference microscopy: remarkable effects of composition and microstructure on diffusion in the silicoaluminophosphate zeotype STA-7.
The influence of the chemical composition and of the storage and activation protocol on the diffusion of methanol into strongly chemically zoned crystals of the silicoaluminophosphate zeotype STA-7 has been investigated by interference microscopy. Analysis of the evolution of transient intracrystalline concentration profiles reveals that just-calcined SAPO STA-7 crystals with lower Si content (Si/(Si + P) = 0.18) exhibit higher surface permeability and bulk diffusivity than those with higher Si content (S/(Si + P) = 0.37). Remarkably, crystals with the higher Si content which were stored in the calcined form crack during activation along planes of weakness already present in the as-prepared crystals, creating fresh surfaces through regions of lower Si that are much more easily penetrated by the adsorbing methanol than are the original surfaces.
Tzoulaki
Despina
D
Technische Chemie II, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany. despina.tzoulaki@tum.de
Heinke
Lars
L
Castro
Maria
M
Cubillas
Pablo
P
Anderson
Michael W
MW
Zhou
Wuzong
W
Wright
Paul A
PA
Kärger
Jörg
J