A titanosilicate molecular sieve with adjustable pores for size-selective adsorption of molecules

Abstract

Zeolites and related crystalline microporous oxides-tetrahedrally coordinated atoms covalently linked into a porous framework-are of interest for applications ranging from catalysis to adsorption and ion-exchange. In some of these materials (such as zeolite rho) adsorbates, ion-exchange, and dehydration and cation relocation can induce strong framework deformations. Similar framework flexibility has to date not been seen in mixed octahedral/tetrahedral microporous framework materials, a newer and rapidly expanding class of molecular sieves. Here we show that the framework of the titanium silicate ETS-4, the first member of this class of materials, can be systematically contracted through dehydration at elevated temperatures to 'tune' the effective size of the pores giving access to the interior of the crystal. We show that this so-called 'molecular gate' effect can be used to tailor the adsorption properties of the materials to give size-selective adsorbents suitable for commercially important separations of gas mixtures of molecules with similar size in the 4.0 to 3.0 A range, such as that of N2/CH4, Ar/O2 and N2/O2.

Advances in Pressure Swing Adsorption for Gas Separation

“…A special kind of titanosilicates, ETS-4, cation exchanged with alkaliearth metals can be used for kinetic separations [35,41,174,175]. In these materials, the pore size can be tuned with a very high accuracy by thermal treatment of the sample.…”

Synthesis and Fabrication of Inorganic Porous Materials: From Nanometer to Millimeter Sizes

“…In particular, the titanosilicate whose ETS-4 (Engelhard titanosilicate-4) counter cations have been replaced by strontium is stable under heat treatment and can reversibly and precisely adjust its pore size between 0.427 and 0.394 nm. [17] Further, recent environmental problems underlie frequent reports including those on the synthesis of zeolite from wastes, and there are expectations for increasing research advances in the field of zeolite synthesis.…”

Super-adsorbent material based on functional polymer particles with a multilevel porous structure

“…1 Owing to their superior physical and chemical features, including a large specific surface area, unique pore structure and tunable pore surface property, adsorbent materials have found utility in multiple applications, such as separation/purification, 2 as catalyst supports, 3 adsorption, 4 drug delivery, 5 gas separation/ storage, 6 electrode materials for electrochemical double layer capacitors and fuel cells 7,8 and so on.…”