Collect. Czech. Chem. Commun. 1998, 63, 141-154

Adsorption Properties of ZSM-5 Zeolites

Pavol Hudeca, Agáta Smieškováa, Zdenek Žideka, Milan Zúbekb, Petr Schneiderc, Milan Kočiříkd and Jana Kozánkováe

a Department of Petroleum Technology and Petrochemistry, Slovak University of Technology, 812 37 Bratislava, Slovak Republic
b Research Institute for Petroleum and Hydrocarbon Gases, 824 12 Bratislava, Slovak Republic
c Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6-Suchdol, Czech Republic
d J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, 182 23 Prague 8, Czech Republic
e Department of Ceramics, Glass and Cement, Slovak University of Technology, 81 237 Bratislava, Slovak Republic


Adsorption properties determined by physical adsorption of nitrogen for a series of ZSM-5 zeolite samples with various Si/Al ratios and different crystal size were compared. In addition to the BET method, the t-plot method was used to determine the microporosity of samples. Very small crystals of ZSM-5 zeolites, generally below 1 μm, with Si/Al ratio between 14 and 21 exhibit adsorption isotherms typical for purely microporous solids. Samples with Si/Al ratios larger than (about) 95 show low-pressure steps and hysteresis loops and, depending on crystal morphology, also high-pressure hysteresis loops. The low-pressure steps were associated with steps on t-plots which showed two linear parts. Small increase of adsorption up to relative pressure 0.2 is characteristic for samples with Si/Al ratios between 25 and 50.

Keywords: ZSM-5 zeolites; Adsorption; t-Plot; Crystal size and morphology; Microporosity.