Topics in Catalysis

, Volume 58, Issue 12–13, pp 769–775 | Cite as

Active Sites for Light Driven Proton Reduction in Y2Ti2O7 and CsTaWO6 Pyrochlore Catalysts Detected by In Situ EPR

  • Dirk HollmannEmail author
  • Oliver Merka
  • Larissa Schwertmann
  • Roland MarschallEmail author
  • Michael WarkEmail author
  • Angelika BrücknerEmail author
Original Paper


In situ EPR spectroscopy proved to be a versatile tool to identify active sites for photocatalytic hydrogen generation in modified Y2Ti2O7 and CsTaWO6 catalysts of pyrochlore structure, in which the metal cations are located in two different positions A and B. It was found that the B-sites exclusively occupied by titanium (Y2Ti2O7) and tantalum/tungsten (CsTaWO6) act as electron traps on the surface. From these sites, electron transfer to the co-catalysts proceeds. Thus, the B-sites are responsible for photocatalytic water reduction.

Graphical Abstract


EPR Mechanism Electron transfer Pyrochlore Photocatalysis 



This work has been supported by the German Science Foundation (DFG, WA 1116) and the Evonik Degussa GmbH (part-financed by the State of North Rhine-Westphalia and co-financed by the European Union Investing in our Future, European Regional Development Fund).


  1. 1.
    Takanabe K, Domen K (2012) Preparation of inorganic photocatalytic materials for overall water splitting. ChemCatChem 4(10):1485–1497CrossRefGoogle Scholar
  2. 2.
    Osterloh FE (2013) Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting. Chem Soc Rev 42(6):2294–2320CrossRefGoogle Scholar
  3. 3.
    Tachibana Y, Vayssieres L, Durrant JR (2012) Artificial photosynthesis for solar water-splitting. Nat Photonics 6(8):511–518CrossRefGoogle Scholar
  4. 4.
    Armaroli N, Balzani V (2011) Towards an electricity-powered world. Energy Environ Sci 4:3193–3222CrossRefGoogle Scholar
  5. 5.
    Lewis NS, Nocera DG (2006) Powering the planet: chemical challenges in solar energy utilization. Proc Natl Acad Sci USA 103(43):15729–15735CrossRefGoogle Scholar
  6. 6.
    Takanabe K, Domen K (2011) Toward visible light response: overall water splitting using heterogeneous photocatalysts. Green 1(5–6):313–322Google Scholar
  7. 7.
    Maeda K, Xiong A, Yoshinaga T, Ikeda T, Sakamoto N, Hisatomi T, Takashima M, Lu D, Kanehara M, Setoyama T, Teranishi T, Domen K (2010) Photocatalytic overall water splitting promoted by two different cocatalysts for hydrogen and oxygen evolution under visible light. Angew Chem Int Ed 49(24):4096–4099CrossRefGoogle Scholar
  8. 8.
    Merka O, Bahnemann DW, Wark M (2014) Photocatalytic hydrogen production with non-stoichiometric pyrochlore bismuth titanate. Catal Today 225:102–110CrossRefGoogle Scholar
  9. 9.
    Ikeda S, Fubuki M, Takahara YK, Matsumura M (2006) Photocatalytic activity of hydrothermally synthesized tantalate pyrochlores for overall water splitting. Appl Catal A 300(2):186–190CrossRefGoogle Scholar
  10. 10.
    Zou Z, Arakawa H (2003) Direct water splitting into H2 and O2 under visible light irradiation with a new series of mixed oxide semiconductor photocatalysts. J Photochem Photobiol A 158(2–3):145–162CrossRefGoogle Scholar
  11. 11.
    Ikeda S, Itani T, Nango K, Matsumura M (2004) Overall water splitting on tungsten-based photocatalysts with defect pyrochlore structure. Catal Lett 98(4):229–233CrossRefGoogle Scholar
  12. 12.
    Wang L, Cao B, Kang W, Hybertsen M, Maeda K, Domen K, Khalifah PG (2013) Design of medium band gap Ag–Bi–Nb–O and Ag–Bi–Ta–O semiconductors for driving direct water splitting with visible light. Inorg Chem 52(16):9192–9205CrossRefGoogle Scholar
  13. 13.
    Yang H, Liu X, Zhou Z, Guo L (2013) Preparation of a novel Cd2Ta2O7 photocatalyst and its photocatalytic activity in water splitting. Catal Commun 31:71–75CrossRefGoogle Scholar
  14. 14.
    Zou Z, Ye J, Arakawa H (2003) Photocatalytic water splitting into H2 and/or O2 under UV and visible light irradiation with a semiconductor photocatalyst. Int J Hydr Energy 28(6):663–669CrossRefGoogle Scholar
  15. 15.
    Abe R, Higashi M, Zou Z, Sayama K, Abe Y (2004) Photocatalytic water splitting into H2 and O2 over R2Ti2O7 (R = Y, rare earth) with pyrochlore structure. Chem Lett 33(8):954–955CrossRefGoogle Scholar
  16. 16.
    Merka O, Bahnemann DW, Wark M (2012) Improved photocatalytic hydrogen production by structure optimized nonstoichiometric Y2Ti2O7. ChemCatChem 4(11):1819–1827CrossRefGoogle Scholar
  17. 17.
    Higashi M, Abe R, Sayama K, Sugihara H, Abe Y (2005) Improvement of photocatalytic activity of titanate pyrochlore Y2Ti2O7 by addition of excess Y. Chem Lett 34(8):1122–1123CrossRefGoogle Scholar
  18. 18.
    Kessler M, Schüler S, Hollmann D, Klahn M, Beweries T, Spannenberg A, Brückner A, Rosenthal U (2012) Photoassisted Ti-O activation in a decamethyltitanocene dihydroxido complex: insights into the elemental steps of water splitting. Angew Chem Int Ed 51(25):6272–6275CrossRefGoogle Scholar
  19. 19.
    Hollmann D, Grabow K, Jiao H, Kessler M, Spannenberg A, Beweries T, Bentrup U, Brückner A (2013) Hydrogen generation by water reduction with [Cp*2Ti(OTf)]: identifying elemental mechanistic steps by combined in situ FTIR and in situ EPR spectroscopy supported by DFT calculations. Chem Eur J 19(41):13705–13713CrossRefGoogle Scholar
  20. 20.
    Priebe JB, Karnahl M, Junge H, Beller M, Hollmann D, Brückner A (2013) Water reduction with visible light: synergy between optical transitions and electron transfer in Au-TiO2 catalysts visualized by in situ EPR spectroscopy. Angew Chem Int Ed Engl 52(43):11420–11424CrossRefGoogle Scholar
  21. 21.
    Schwertmann L, Wark M, Marschall R (2013) Sol-gel synthesis of defect-pyrochlore structured CsTaWO6 and the tribochemical influences on photocatalytic activity. RSC Adv 3(41):18908–18915CrossRefGoogle Scholar
  22. 22.
    Che M, Tench AJ (1982) Characterization and reactivity of mononuclear oxygen species on oxide surfaces. In: D.D. Eley HP, Paul BW (eds) Advances in catalysis, vol. 31. Academic Press, San Diego, pp 77–133CrossRefGoogle Scholar
  23. 23.
    Hurum DC, Agrios AG, Gray KA, Rajh T, Thurnauer MC (2003) Explaining the enhanced photocatalytic activity of Degussa P25 mixed-phase TiO2 using EPR. J Phys Chem B 107(19):4545–4549CrossRefGoogle Scholar
  24. 24.
    O’Connor JR, Chen JH (1964) Energy levels of d1 electrons in CaF2: evidence of strong dynamic Jahn-Teller distortions. Appl Phys Lett 5(5):100–102CrossRefGoogle Scholar
  25. 25.
    Zheng W-C, Mei Y, Yang Y-G, Liu H-G (2012) Research on the optical spectra, g factors and defect structures for two tetragonal Y2+ centers in the irradiated CaF2: Y crystal. Spectrochim Acta Part A 97:648–651CrossRefGoogle Scholar
  26. 26.
    Solomonov VI, Spirina AV, Konev SF, Cholakh SO (2014) Trivalent zirconium and hafnium ions in yttrium oxide ceramics. Opt Spectrosc 116(5):793–797CrossRefGoogle Scholar
  27. 27.
    Mabbs FE, Collison D (1999) The use of matrix diagonalization in the simulation of the EPR powder spectra of d-transition metal compounds. Mol Phys Rep 26:39–59Google Scholar
  28. 28.
    Spalek T, Pietrzyk P, Sojka Z (2005) Application of the genetic algorithm joint with the Powell method to nonlinear least-squares fitting of powder EPR spectra. J Chem Inf Model 45(1):18–29CrossRefGoogle Scholar
  29. 29.
    Hollmann D, Karnahl M, Tschierlei S, Kailasam K, Schneider M, Radnik J, Grabow K, Bentrup U, Junge H, Beller M, Lochbrunner S, Thomas A, Brückner A (2014) Structure-activity relationships in bulk polymeric and sol–gel-derived carbon nitrides during photocatalytic hydrogen production. Chem Mater 26(4):1727–1733CrossRefGoogle Scholar
  30. 30.
    Che M, Tench AJ (1983) Characterization and reactivity of molecular oxygen species on oxide surfaces. In: D.D. Eley HP, Paul BW (eds) Advances in catalysis, vol. 32. Academic Press, San Diego, pp 1–148CrossRefGoogle Scholar
  31. 31.
    Howe RF, Grätzel M (1987) EPR study of hydrated anatase under UV irradiation. J Phys Chem 91(14):3906–3909CrossRefGoogle Scholar
  32. 32.
    Anpo M, Che M, Fubini B, Garrone E, Giamello E, Paganini M (1999) Generation of superoxide ions at oxide surfaces. Top Catal 8(3–4):189–198CrossRefGoogle Scholar
  33. 33.
    Peng X-J, Zhang Y, Feng W, Ai L-M, Chen J, Zhang F-J (2013) The characterization and photochromism of copolymer composite films containing phosphotungstic acid. J Mol Struct 1041:139–143CrossRefGoogle Scholar
  34. 34.
    Sweeney KL, Halliburton LE, Kappers LA (1986) Self-trapped electrons in lithium tantalate. Phys Lett A 116(2):81–84CrossRefGoogle Scholar
  35. 35.
    Allen LC (1989) Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms. J Am Chem Soc 111(25):9003–9014CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Leibniz-Institute for Catalysis e.V. at the University of RostockRostockGermany
  2. 2.Institute for ChemistryCarl-von-Ossietzky-University OldenburgOldenburgGermany
  3. 3.Laboratory for Industrial ChemistryRuhr-University BochumBochumGermany
  4. 4.Institute of Physical ChemistryJustus-Liebig-University GiessenGiessenGermany

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