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Titanosilicate

A titanosilicate, also called titanium silicate or silicotitanate, is a silicate mineral where some portion of the silicon atoms have been replaced by titanium(IV) atoms. The term most commonly refers to the zeolitic polymorph, also called titanium silicalite, which is a heterogeneous catalyst in industrial chemistry.

Applications

Titanosilicate catalysts are commonly used in oxidation reactions that employ hydrogen peroxide as an oxidant. The production of propylene oxide by epoxidation of propylene is a major industrial application.[1] Epoxidation by H2O2 is considered a greener alternative to epoxidation via propylene chlorohydrin, but this reaction of H2O2 and propylene competes with many side reactions. The formation of titanium coordination complexes in the zeolite structure improves selectivity for the epoxide.[2]

Synthesis

Titanosilicates can be prepared via crystallisation of silica and titanium dioxide with quaternary ammonium cations as a structure-directing agent. The silica and titanium dioxide are provided by hydrolysis of tetraethyl orthosilicate and tetrabutyl orthotitanate.[3]

Structure

TS-1, the major industrial titanosilicate, has the MFI crystal structure seen in ZSM-5, another significant synthetic zeolite. The titanium atoms are tetrahedrally coordinated, unlike the octahedral coordination found in the main polymorphs of titanium(IV) oxide. Because of the relatively small amount of titanium in the relatively large structure, it is difficult to determine the exact locations of active sites; this is a major obstacle in understanding the reaction mechanism of titanosilicate catalysis.[4]

Other titanosilicates have been produced in other zeolite structures, as well as related mesoporous materials such as Ti-MCM-41.[5]

History

The first synthetic titanosilicate zeolite, TS-1, was patented by Taramasso et al. in 1983.[6] TS-1 was first used industrially by EniChem in 1986, for the hydroxylation of phenol. They would later expand its usage into the production of cyclohexanone oxime. TS-1 as a catalyst for epoxidation of propylene was first deployed at industrial scale by Dow Chemical and BASF in 2008.[7]

References

  1. ^ Smeets, Valentin; Gaigneaux, Eric M.; Debecker, Damien P. (2022). "Titanosilicate Epoxidation Catalysts: A Review of Challenges and Opportunities". ChemCatChem. 14. doi:10.1002/cctc.202101132. hdl:2078.1/257495.
  2. ^ Yang, Jimei; Liu, Shuling; Liu, Yanyan; Zhou, Limin; Wen, Hao; Wei, Huijuan; Shen, Ruofan; Wu, Xianli; Jiang, Jianchun; Li, Baojun (2024). "Review and perspectives on TS-1 catalyzed propylene epoxidation". iScience. 27 (3). Bibcode:2024iSci...27j9064Y. doi:10.1016/j.isci.2024.109064. PMC 10875142. PMID 38375219.
  3. ^ Bai, Risheng; Navarro, M. Teresa; Song, Yue; Zhang, Tianjun; Zou, Yongcun; Feng, Zhaochi; Zhang, Peng; Corma, Avelino; Yu, Jihong (2020). "Titanosilicate zeolite precursors for highly efficient oxidation reactions". Chemical Science. 11 (45): 12341–12349. doi:10.1039/d0sc04603e. PMC 8162463. PMID 34094443.
  4. ^ Rzepka, Przemyslaw; Signorile, Matteo; Huthwelker, Thomas; Checchia, Stefano; Rosso, Francesca; Bordiga, Silvia; Van Bokhoven, Jeroen A. (2024). "Quantitative localisation of titanium in the framework of titanium silicalite-1 using anomalous X-ray powder diffraction". Nature Communications. 15 (1): 7757. Bibcode:2024NatCo..15.7757R. doi:10.1038/s41467-024-51788-7. PMC 11377426. PMID 39237487.
  5. ^ Peng, Rui; Zhao, Dan; Dimitrijevic, Nada M.; Rajh, Tijana; Koodali, Ranjit T. (2012). "Room Temperature Synthesis of Ti–MCM-48 and Ti–MCM-41 Mesoporous Materials and Their Performance on Photocatalytic Splitting of Water". The Journal of Physical Chemistry C. 116: 1605–1613. doi:10.1021/jp210448v.
  6. ^ US patent 4410501, Marco Taramasso, Giovanni Perego, Bruno Notari, "Preparation of porous crystalline synthetic material comprised of silicon and titanium oxides", issued 1983-10-10, assigned to SnamProgetti SpA 
  7. ^ Millini, Roberto; Bellussi, Giuseppe; Pollesel, Paolo; Rizzo, Caterina; Perego, Carlo (2022). "Beyond TS-1: Background and recent advances in the synthesis of Ti-containing zeolites". Microporous and Mesoporous Materials. 346. Bibcode:2022MicMM.34612286M. doi:10.1016/j.micromeso.2022.112286.

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