What is titanium silicate molecular sieve?

What is titanium silicate molecular sieve?

Titanium-silica molecular sieve is characterized in that the molecular sieve has a three-dimensional pore structure composed of two sets of ten-membered ring channels and a set of nine-membered ring channels. Its first set of substantially parallel channels is a ten-membered ring composed of four coordinated atoms. Composition; The second set of pores is also composed of a ten-membered ring composed of four-coordinated atoms, and is perpendicular to the first set of pores; the third set of pores is interlaced with the first and second sets of pores, and is composed of four-coordinated atoms It is composed of a nine-membered ring, and the molar composition of the anhydrous oxide is (0.001 to 0.2) TiO2: SiO2. The molecular sieve can be used as a catalytic oxidation catalyst.
TS-1 is formed by partially replacing aluminum atoms in silicon-aluminum molecular sieves with Ti atoms. It belongs to the ZSM-5 series of zeolite molecular sieves. It has an MFI topology and consists of primary structural units such as silicon-oxygen tetrahedra and titanium-oxygen tetrahedrons, connected by oxygen bridges. , Constitute the secondary structural unit of the five-membered ring, and further form a three-dimensional microporous framework. The MFI molecular sieve has a two-dimensional pore structure. The ten-membered ring parallel to the a-axis is S-shaped with a pore size of 0.51nm×0.55nm. The ten-membered ring parallel to the b-axis direction is linear, and the pore diameter is 0.54nm×0.56nm.
ETS-4 is a titanium silicate molecular sieve with a unique microporous structure, and its molecular formula is H2Ti4Si12O38(TiO)Na8·8.5H2O. It is a new type of titanium silicate molecular sieve (USpatent 4938939) developed in 1990 by Kuznicki, a researcher of Engelhard Corporation in the United States. Studies have shown that the framework of ETS-4 is composed of tetrahedral-coordinated silicon atoms and octahedral-coordinated titanium atoms. The structure of this molecular sieve contains two sets of titanium-oxygen octahedra that are perpendicular to each other through a common vertex. One-dimensional -Ti-O-Ti-O-chain, this long chain is wrapped in a pore structure composed of silicon-oxygen tetrahedrons. The framework of ETS-4 has six-membered, eight-membered and twelve-membered rings, but its pore diameter is only 0.3-0.4nm (Zeolites, 1996, 16, 98-107). Therefore, the structure of ETS-4 can be regarded as the long chain of titanium dioxide with semiconductor properties contained in the silica framework structure, which makes ETS-4 possess many unique properties.
The ETS-4 framework is negative, with sodium counter cations on the surface, and other metal cations can be introduced through ion exchange (USpatent 5989316). ETS-4 has good adsorption capacity for heavy metals and radioactive metal ions (RMZ-Materials and Geoenvironment, 2004, 51, 660-663; Journal of Radioanalytical and Nuclear Chemistry, 2006, 269, 155-160.). The most striking thing is that Kuznicki recently reported the "molecular gate effect" (Nature, 2001, 412, 720-724) produced by the treated ETS-4 by increasing the dehydration temperature to control the size of the molecular sieve pores. Separate mixed gases with important commercial values in the range of 0.3-0.4nm. Some common molecules such as nitrogen, methane, oxygen, argon, and water molecules are about 3 to 4 angstroms in size, which are almost the same in size. The molecular sieve made by ETS-4 can effectively separate them. For example, N2/CH4, Ar/O2, and N2/O2 (US patent 6068682; Industrial & Engineering Chemistry Research, 2004, 43, 5281-5290.), in which the application of nitrogen removal from natural gas has achieved preliminary industrialization in the United States. This opens up a new direction for the application of ETS-4, and also makes it a new type of molecular sieve material that has received extensive attention in recent years.
In 1989, Kwznichi et al. reported that a large pore size ETS-10 molecular sieve with a framework titanium coordination environment different from the tetrahedral coordination framework titanium environment in TS-1 was synthesized. The octahedral coordinated Ti4+ atoms in the framework were connected to the tetrahedron through oxygen bridges. Si4+ atoms are connected at a common angle, ETS-10 has a 12-membered ring pore structure and a 0.8nm pore size. Due to the large pore size framework structure and the special framework titanium coordination state, it can be expected that ETS-10 has great application potential in molecular adsorption, ion treatment and catalytic reactions.