Unusual Nitrogen-Oxygen Adsorption Properties of Large Pore Titanium Silicate (ETS-10)

ETS-10 contains structural titanium atoms cross-linked by silica tetrahedral.  Almost straight-linear (like rods) octahedrally coordinated titania chains extend in two different crystallographic directions displaced by ½ u.c.  Each titanium imparts negative two charge to the structure which are balanced by exchangeable cations typically as Na+ and K+ during synthesis.  The structure results in a 3D channel system prescribed by 10- and 12-membered oxygen rings in two directions, therefore ETS-10 can be classified as a large-pore molecular sieve zeolite.  Unlike its cousin ETS-4, ETS-10 structure is very robust and can withstand high temperatures up to 450 C and a wide range of pH.  Although ETS-4 was heavily studied and even resulted in some applications (i.e. Molecular Gates) due to fine tunable pore size within 0.1 A, information about ETS-10 adsorption almost does not exist in literature.  In this work, we have looked at the oxygen and nitrogen adsorption properties of ETS-10 as pure and binary isotherms.  The data show several unexpected phenomena quite different than other zeolites with respect to pure component heat of adsorption, dependency of nitrogen selectivity on coverage, and impact of ion exchange.  This presentation will attempt to explain these unusual observations based on structure information and try to postulate if and how these behavior can be exploited in PSA applications.