Efficient epoxidation over dinuclear sites in titanium silicalite-1

Abstract

Titanium silicalite-1 (TS-1) is a zeolitic material with MFI framework structure, in which 1 to 2 per cent of the silicon atoms are substituted for titanium atoms. It is widely used in industry owing to its ability to catalytically epoxidize olefins with hydrogen peroxide (H2O2), leaving only water as a byproduct1,2; around one million tonnes of propylene oxide are produced each year using this process3. The catalytic properties of TS-1 are generally attributed to the presence of isolated Ti(iv) sites within the zeolite framework1. However, despite almost 40 years of experimental and computational investigation4,5,6,7,8,9,10, the structure of these active Ti(iv) sites is unconfirmed, owing to the challenges of fully characterizing TS-1. Here, using a combination of spectroscopy and microscopy, we characterize in detail a series of highly active and selective TS-1 propylene epoxidation catalysts with well dispersed titanium atoms. We find that, on contact with H217O2, all samples exhibit a characteristic solid-state 17O nuclear magnetic resonance signature that is indicative of the formation of bridging peroxo species on dinuclear titanium sites. Further, density functional theory calculations indicate that cooperativity between two titanium atoms enables propylene epoxidation via a low-energy reaction pathway with a key oxygen-transfer transition state similar to that of olefin epoxidation by peracids. We therefore propose that dinuclear titanium sites, rather than isolated titanium atoms in the framework, explain the high efficiency of TS-1 in propylene epoxidation with H2O2. This revised view of the active-site structure may enable further optimization of TS-1 and the industrial epoxidation process.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: The TS-1 epoxidation catalyst.
Fig. 2: Experimental and calculated solid-state 17O NMR spectra.
Fig. 3: Complementary characterization of TS-1 materials.
Fig. 4: Mechanistic investigations.

Data availability

All data that led us to the conclusions presented here are available with the paper or from the corresponding author on reasonable request. Source data are provided with this paper.

References

  1. 1.

    Notari, B. in Studies in Surface Science and Catalysis Vol. 60 (eds Inui, T., Namba, S. & Tatsumi T.) 343–352 (Elsevier, 1991).

  2. 2.

    Teles, J. H., Hermans, I., Franz, G. & Sheldon, R. A. Oxidation in Ullmann’s Encyclopedia of Industrial Chemistry 1–103 (Wiley-VCH, 2015).

  3. 3.

    Lin, M., Xia, C., Zhu, B., Li, H. & Shu, X. Green and efficient epoxidation of propylene with hydrogen peroxide (HPPO process) catalyzed by hollow TS-1 zeolite: a 1.0 kt/a pilot-scale study. Chem. Eng. J. 295, 370–375 (2016).

    CAS  Google Scholar 

  4. 4.

    Sankar, G. et al. The three-dimensional structure of the titanium-centered active site during steady-state catalytic epoxidation of alkenes. J. Phys. Chem. B 105, 9028–9030 (2001).

    CAS  Google Scholar 

  5. 5.

    Thomas, J. M., Catlow, C. R. A. & Sankar, G. Determining the structure of active sites, transition states and intermediates in heterogeneously catalysed reactions. Chem. Commun. 24, 2921–2925 (2002).

  6. 6.

    Gamba, A., Tabacchi, G. & Fois, E. TS-1 from first principles. J. Phys. Chem. A 113, 15006–15015 (2009).

    CAS  PubMed  Google Scholar 

  7. 7.

    Solans-Monfort, X., Copéret, C. & Eisenstein, O. Theoretical Modeling: An Access to Molecular Understanding of Single-Site Silica Based Heterogeneous Catalysts (American Scientific Publishers, 2009).

  8. 8.

    Bordiga, S., Lamberti, C., Bonino, F., Travert, A. & Thibault-Starzyk, F. Probing zeolites by vibrational spectroscopies. Chem. Soc. Rev. 44, 7262–7341 (2015).

    CAS  PubMed  Google Scholar 

  9. 9.

    Signorile, M. et al. Effect of Ti speciation on catalytic performance of TS-1 in the hydrogen peroxide to propylene oxide reaction. J. Phys. Chem. C 122, 9021–9034 (2018).

    CAS  Google Scholar 

  10. 10.

    Signorile, M. et al. Computational assessment of relative sites stabilities and site-specific adsorptive properties of titanium silicalite-1. J. Phys. Chem. C 122, 1612–1621 (2018).

    CAS  Google Scholar 

  11. 11.

    Bordiga, S. et al. The structure of the peroxo species in the TS-1 catalyst as investigated by resonant Raman spectroscopy. Angew. Chem. Int. Ed. 41, 4734–4737 (2002).

    CAS  Google Scholar 

  12. 12.

    Lin, W. & Frei, H. Photochemical and FT-IR probing of the active site of hydrogen peroxide in Ti silicalite sieve. J. Am. Chem. Soc. 124, 9292–9298 (2002).

    CAS  PubMed  Google Scholar 

  13. 13.

    Matsumoto, K., Sawada, Y., Saito, B., Sakai, K. & Katsuki, T. Construction of pseudo-heterochiral and homochiral di-μ-oxotitanium(Schiff base) dimers and enantioselective epoxidation using aqueous hydrogen peroxide. Angew. Chem. Int. Ed. 44, 4935–4939 (2005).

    CAS  Google Scholar 

  14. 14.

    Sawada, Y., Matsumoto, K. & Katsuki, T. Titanium-catalyzed asymmetric epoxidation of non-activated olefins with hydrogen peroxide. Angew. Chem. Int. Ed. 46, 4559–4561 (2007).

    CAS  Google Scholar 

  15. 15.

    Berkessel, A., Günther, T., Wang, Q. & Neudörfl, J.-M. Titanium salalen catalysts based on cis-1,2-diaminocyclohexane: enantioselective epoxidation of terminal non-conjugated olefins with H2O2. Angew. Chem. Int. Ed. 52, 8467–8471 (2013).

    CAS  Google Scholar 

  16. 16.

    Lansing, M., Engler, H., Leuther, T. M., Neudörfl, J.-M. & Berkessel, A. Titanium cis-1,2-diaminocyclohexane salalen catalysts of outstanding activity and enantioselectivity for the asymmetric epoxidation of nonconjugated terminal olefins with hydrogen peroxide. ChemCatChem 8, 3706–3709 (2016).

    CAS  Google Scholar 

  17. 17.

    Lane, B. S. & Burgess, K. Metal-catalyzed epoxidations of alkenes with hydrogen peroxide. Chem. Rev. 103, 2457–2474 (2003).

    CAS  PubMed  Google Scholar 

  18. 18.

    Kholdeeva, O. A. Hydrogen peroxide activation over TiIV: what have we learned from studies on Ti-containing polyoxometalates? Eur. J. Inorg. Chem. 1011, 1595–1605 (2013).

  19. 19.

    Takahashi, E. et al. Synthesis and oxidation catalysis of a Ti-substituted phosphotungstate, and identification of the active oxygen species. Catal. Sci. Technol. 5, 4778–4789 (2015).

    CAS  Google Scholar 

  20. 20.

    Ehinger, C., Gordon, C. P. & Copéret, C. Oxygen transfer in electrophilic epoxidation probed by 17O NMR: differentiating between oxidants and role of spectator metal oxo. Chem. Sci. 10, 1786–1795 (2019).

    CAS  PubMed  Google Scholar 

  21. 21.

    Müller, U., Rudolf, P., Krug, G. & Senk, R. Process for the preparation of a titanium zeolite catalyst. WO patent WO2011064191 (2011).

  22. 22.

    Parvulescu, A.-N. et al. Molding for a hydrophobic zeolitic material and process for its production. WO patent WO2015059171A1 (2015).

  23. 23.

    Yamamoto, K. et al. Activation of O2 by organosilicon reagents yields quantitative amounts of H2O2 or (Me3Si)2O2 for efficient O-transfer reactions. Helv. Chim. Acta 101, e1800156 (2018).

    Google Scholar 

  24. 24.

    Caughlan, C. N., Smith, H. S., Katz, W., Hodgson, W. & Crowe, R. W. Organic compounds of titanium. II. Association of organic titanates in benzene solution. J. Am. Chem. Soc. 73, 5652–5654 (1951).

    CAS  Google Scholar 

  25. 25.

    Lamberti, C. et al. Ti location in the MFI framework of Ti−silicalite-1: a neutron powder diffraction study. J. Am. Chem. Soc. 123, 2204–2212 (2001).

    CAS  PubMed  Google Scholar 

  26. 26.

    Langhendries, G., De Vos, D. E., Baron, G. V. & Jacobs, P. A. Quantitative sorption experiments on Ti-zeolites and relation with α-olefin oxidation by H2O2. J. Catal. 187, 453–463 (1999).

    CAS  Google Scholar 

  27. 27.

    Shin, S. B. & Chadwick, D. Kinetics of heterogeneous catalytic epoxidation of propene with hydrogen peroxide over titanium silicalite (TS-1). Ind. Eng. Chem. Res. 49, 8125–8134 (2010).

    CAS  Google Scholar 

  28. 28.

    Wells, D. H., Delgass, W. N. & Thomson, K. T. Evidence of defect-promoted reactivity for epoxidation of propylene in titanosilicate (TS-1) catalysts: a DFT study. J. Am. Chem. Soc. 126, 2956–2962 (2004).

    CAS  PubMed  Google Scholar 

  29. 29.

    Prileschajew, N. Oxydation ungesättigter Verbindungen mittels organischer Superoxyde. Ber. Dtsch. Chem. Ges. 42, 4811–4815 (1909).

    CAS  Google Scholar 

  30. 30.

    Snyder, B. E. R., Bols, M. L., Schoonheydt, R. A., Sels, B. F. & Solomon, E. I. Iron and copper active sites in zeolites and their correlation to metalloenzymes. Chem. Rev. 118, 2718–2768 (2018).

    CAS  PubMed  Google Scholar 

  31. 31.

    O’Dell, L. A. & Schurko, R. W. QCPMG using adiabatic pulses for faster acquisition of ultra-wideline NMR spectra. Chem. Phys. Lett. 464, 97–102 (2008).

    ADS  Google Scholar 

  32. 32.

    Perras, F. A., Widdifield, C. M. & Bryce, D. V. QUEST quadrupolar exact software: a fast graphical program for the exact simulation of NMR and NQR spectra for quadrupolar nuclei. Solid State Nucl. Magn. Reson. 45-46, 36–44 (2012).

    CAS  PubMed  Google Scholar 

  33. 33.

    Kresse, G. & Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B 47, 558–561 (1993).

    CAS  ADS  Google Scholar 

  34. 34.

    Kresse, G. & Hafner, J. Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Phys. Rev. B 49, 14251–14269 (1994).

    CAS  ADS  Google Scholar 

  35. 35.

    Kresse, G. & Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6, 15–50 (1996).

    CAS  Google Scholar 

  36. 36.

    Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

    ADS  Google Scholar 

  37. 37.

    Hammer, B., Hansen, L. B. & Nørskov, J. K. Improved adsorption energetics within density-functional theory using revised Perdew-Burke-Ernzerhof functionals. Phys. Rev. B 59, 7413–7421 (1999).

    ADS  Google Scholar 

  38. 38.

    Grimme, S., Antony, J., Ehrlich, S. & Krieg, S. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 132, 154104 (2010).

    PubMed  ADS  Google Scholar 

  39. 39.

    Pereira, M. M. et al. Biomass-mediated ZSM-5 zeolite synthesis: when self-assembly allows to cross the Si/Al lower limit. Chem. Sci. 9, 6532–6539 (2018).

    CAS  PubMed  PubMed Central  Google Scholar 

  40. 40.

    Gutierrez-Acebo, E., Rey, J., Bouchy, C., Schuurman, Y. & Chizallet, C. Location of the active sites for ethylcyclohexane hydroisomerization by ring contraction and expansion in the EUO zeolitic framework. ACS Catal. 9, 1692–1704 (2019).

    CAS  Google Scholar 

  41. 41.

    Goncalves, T. J., Plessow, P. N. & Studt, F. On the accuracy of density functional theory in zeolite catalysis. ChemCatChem 11, 4368–4376 (2019).

    CAS  Google Scholar 

  42. 42.

    Henkelman, G. & Jónsson, H. A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives. J. Chem. Phys. 111, 7010–7022 (1999).

    CAS  ADS  Google Scholar 

  43. 43.

    te Velde, G. et al. Chemistry with ADF. J. Comput. Chem. 22, 931–967 (2001).

    Google Scholar 

  44. 44.

    Adamo, C. & Barone, V. Toward reliable density functional methods without adjustable parameters: the PBE0 model. J. Chem. Phys. 110, 6158–6170 (1999).

    CAS  ADS  Google Scholar 

  45. 45.

    van Lenthe, E., Baerends, E. J. & Snijders, J. G. Relativistic regular two-component Hamiltonians. J. Chem. Phys. 99, 4597–4610 (1993).

    ADS  Google Scholar 

  46. 46.

    van Lenthe, E., Baerends, E. J. & Snijders, J. G. Relativistic total energy using regular approximations. J. Chem. Phys. 101, 9783–9792 (1994).

    ADS  Google Scholar 

  47. 47.

    van Lenthe, E., Baerends, E. J. & Snijders, J. G. Geometry optimizations in the zero order regular approximation for relativistic effects. J. Chem. Phys. 110, 8943–8953 (1999).

    ADS  Google Scholar 

  48. 48.

    van Lenthe, E., Baerends, E. J. & Snijders, J. G. The zero-order regular approximation for relativistic effects: the effect of spin-orbit coupling in closed shell molecules. J. Chem. Phys. 105, 6505–6516 (1996).

    ADS  Google Scholar 

  49. 49.

    van Lenthe, E., van Leeuwen, R., Baerends, E. J. & Snijders, J. G. Relativistic regular two-component Hamiltonians. Int. J. Quantum Chem. 57, 281–293 (1996).

    Google Scholar 

  50. 50.

    Frisch, M. J. et al. Gaussian 09, revision D.01 (Gaussian, 2009).

  51. 51.

    Dunning, T. H. & Hay, P. J. in Methods of Electronic Structure Theory (ed. Schaefer, H. F.) 1–18 (Springer, 1977).

  52. 52.

    Weigend, F. & Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: design and assessment of accuracy. Phys. Chem. Chem. Phys. 7, 3297–3305 (2005).

    CAS  PubMed  Google Scholar 

Download references

Acknowledgements

C.P.G. thanks the Scholarship Fund of the Swiss Chemical Industry (SSCI) for funding. H.E. thanks the Fonds der Chemischen Industrie for a Kekulé doctoral fellowship. We thank F. Gaida for recording the UV–vis spectra of compounds 1, 1-O2 and the salalen ligand. We acknowledge B. Hinrichsen and P. Müller from BASF for the XRD and TEM measurements, and S. S. Lee from ScopeM at ETH Zürich for assistance with Raman measurements. We acknowledge J. Sauer, A. Comas-Vives, W.-C. Liao, K. Yamamoto, D. Mance, G. Noh, C. Ehinger, E. Lam, L. Lätsch and J. Meyet for discussions.

Author information

Affiliations

Authors

Contributions

C.P.G. performed the NMR measurements and DFT calculations and led the writing process. H.E. prepared the salalen ligand and the Berkessel–Katsuki catalyst 1. A.-N.P. prepared the TS-1 sample. A.S.T. performed Raman measurements; M.P. did STEM-EDX measurements. T.L. was involved in STEM-EDX and Raman measurements. All authors contributed to the design of the project, data interpretation and writing.

Corresponding author

Correspondence to Christophe Copéret.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Richard Catlow, Bert Weckhuysen and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Solid-state 17O NMR spectra of all TS-1 samples and H217O.

ae, Solid-state 17O NMR spectra of the five TS-1 samples: 1.9 wt% Ti (sample 1; a), 1.9 wt% Ti (sample 2; b), 1.5 wt% Ti (c), 1.0 wt% Ti (d) and 0.5 wt% Ti (e). f, Solid-state 17O NMR spectrum of H217O (red line, DFT-calculated spectrum).

Extended Data Fig. 2 STEM-EDX images.

ae, STEM-EDX images of the five TS-1 samples: 1.9 wt% Ti (sample 1; a), 1.9 wt% Ti (sample 2; b), 1.5 wt% Ti (c), 1.0 wt% Ti (d) and 0.5 wt% Ti (e).

Extended Data Fig. 3 SEM and HR-TEM images.

a, b, SEM image (left) and HR-TEM image (right) of the TS-1 samples with 1.9 wt% Ti (a, sample 1; b, sample 2). c, d, HR-TEM images of the TS-1 samples with 1.0 wt% Ti (c) and 1.5 wt% Ti (d).

Extended Data Fig. 4 Powder XRD patterns.

ae, Powder XRD of the five TS-1 samples (after calcination): 1.9 wt% Ti (sample 1; a), 1.9 wt% Ti (sample 2) with signs of an anatase phase marked by arrows (b), 1.5 wt% Ti (c), 1.0 wt% Ti (d) and 0.5 wt% Ti (e).

Extended Data Fig. 5 Additional Raman spectra.

The Raman spectra were measured at a wavelength of 266 nm. At this wavelength, the signals associated with TiOx clusters are not resonance-enhanced, so similar features are observed in all spectra.

Extended Data Fig. 6 FT-IR spectra.

The spectra are shifted in steps of 20% on the vertical axis to enable direct comparison.

Extended Data Fig. 7 Additional mechanisms.

a, Calculated potential-energy surface for propylene epoxidation on a mononuclear Ti site, via a bis-hydroperoxo species. b, Analogous mechanism via a hydroperoxo species. c, Potential-energy surface for propylene epoxidation from a hydroperoxo species on an isolated Ti site with an adjacent vacancy. Relative electronic energies (E) are given in kcal mol−1.

Extended Data Fig. 8 Models used to calculate NMR spectra.

a, Cluster models used to calculate the NMR signatures shown in Fig. 2. b, Structure and simulated spectrum (red) of a mononuclear peroxo species with adjacent vacant site; the experimental spectrum of TS-1 impregnated with H217O2 is shown in blue. c, Structure and simulated spectrum (red and purple) of a mononuclear hydroperoxo species with an adjacent vacant site; the experimental spectrum is shown in blue. d, Structure and simulated spectrum (red and purple) of mononuclear hydroperoxo species, in which the hydroperoxo ligand is oriented differently compared to the structure used to calculate the spectrum shown in Fig. 2; the experimental spectrum is shown in blue.

Extended Data Fig. 9 Additional 17O NMR spectra.

a, Solid-state 17O NMR spectrum of TS-1 (1.9 wt%, sample 1) contacted with H217O. b, Solid-state 17O NMR spectrum of Ti-free MFI contacted with H217O2.

Extended Data Fig. 10 UV–vis spectra related to the Berkessel–Katsuki catalyst.

UV–vis spectra of the Berkessel ligand (blue), the Berkessel–Katsuki catalyst 1 (red) and the corresponding peroxo species 1-O2 (green) are shown. The spectra were acquired in dichloromethane solution, with concentrations of 0.049 mmol l−1, 0.022 mmol l−1 and 0.022 mmol l−1, respectively.

Source data

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Gordon, C.P., Engler, H., Tragl, A.S. et al. Efficient epoxidation over dinuclear sites in titanium silicalite-1. Nature 586, 708–713 (2020). https://doi.org/10.1038/s41586-020-2826-3

Download citation

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing