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J.M.G. Carballo et al. / Catalysis Today xxx (2012) xxx–xxx
9
Then 27 kPa of O was added to the IR cell and the temperature was
increased to 773 K. The spectra were recorded at room temperature,
the catalyst activity only slightly recovered after thermal treatment
in H2 and decreased further following treatment in static air. The
partial recovery of the catalytic activity is due to the thermal treat-
2
4
23, 473, 573, 673 and 773 K. The spectra of the surface species
and gas species detected after H /CO adsorption on the reactivated
ment in H , which does not completely remove the carbonaceous
2
2
catalyst are shown in Figs. 8 and 9, respectively.
After thermal treatment in H2 in the IR cell the intensity of
the band accounting to CO species adsorbed on Ru metal particles
deposits. In contrast, thermal treatment in air succeeds in removing
these deposits. However, thermal treatment in air results in severe
morphological change to the Ru/TiO , as shown by HAADF-STEM.
2
slightly recovers. Moreover, the position of the CO band shifts
from 1980 to 2025 cm (Fig. 9b and c). The band at 3016 cm in
The formation of volatile Ru–carbonyl species and the oxidation
Ru particles are not the primary causes of catalyst deactivation.
Sintering of Ru particles is also discarded as a deactivation mecha-
nism based on the HAADF-STEM micrographs, which reveal that Ru
dispersion does not change significantly during the FTS reaction.
ad
−1
−1
Fig. 10c indicates that CH evolves during the thermal treatment of
4
the spent catalyst in H . This feature indicates that the carbona-
2
ceous deposits are hydrogenated and that the Ru sites become
available for further CO adsorption. However, the extension of the
gasification process in H2 is moderate in view of the low intensity
of the COad bands in Fig. 9c as compared to those in Fig. 9a. These
observations are in very good agreement with the catalytic data
discussed above, which showed that the initial activity could not
be fully restored upon thermal treatment in H2 at 673 K (Fig. 2a,
Episode B), but the results are in contrast with results reported
by other authors [58] that indicated recovery of the activity of Ru
catalysts for the FTS after thermal treatment in H2.
Acknowledgements
J.M. González-Carballo acknowledges financial support of the
Ministerio de Educación of Spain through the Formación de Profe-
sorado program (FPU). Projects ENE2007-67533-C02-02/ALT from
Ministerio de ciencia en innovación and Project S2009ENE-1743
from Comunidad de Madrid. Programa de Actividades de I + D entre
Grupos de Investigación de Tecnologías for funding this work.
On the other hand, when the spent catalyst is treated first
with O2 at high temperature and then in H , only a weak band
2
−1
References
(
at 2044 cm ) corresponding to carbonyl species on the reduced
Ru (Fig. 9d) is detected after H /CO adsorption at room tempera-
2
[
1] S. Shetty, A.P.J. Jansen, R.A. van Santen, Journal of the American Chemical Soci-
ety 131 (2009) 12874–12875.
ture. The frequency of the carbonyl band is almost identical to that
recorded for the fresh sample (Fig. 9a), but the intensity is clearly
lower.
[2] S. Shetty, R.A. van Santen, Catalysis Today 171 (2011) 168–173.
[3] R.A. van Santen, M.M. Ghouri, S. Shetty, E.M.H. Hensen, Catalysis Science &
Technology 1 (2011) 891–911.
The spectra of the surface and gas phase species formed during
the thermal treatment in air of the spent catalyst and their evolution
with temperature are shown in Fig. 11. Fig. 11a and b correspond to
magnification of selected regions of the spectra. The growing band
[
4] M. Nurunnabi, K. Murata, K. Okabe, T. Hanaoka, T. Miyazawa, K. Sakanishi,
Journal of the Japan Petroleum Institute 53 (2010) 75–81.
[5] M. Nurunnabi, K. Murata, K. Okabe, M. Inaba, I. Takahara, Applied Catalysis
A-General 340 (2008) 203–211.
[
6] K. Okabe, K. Murata, M. Nakanishi, T. Ogi, M. Nurunnabi, Y. Liu, Catalysis Letters
28 (2009) 171–176.
−1
at approximately 2350 cm in Fig. 11a accounts for the production
of CO2 due to the combustion of hydrocarbon and carbonaceous
species, as indicated by the disappearance of the bands within the
1
[7] K. Okabe, K. Murata, M. Nurunnabi, Y. Liu, Journal of the Japan Petroleum Insti-
tute 52 (2009) 139–142.
[
8] J.M. González Carballo, E. Finocchio, S. Garcia, S. Rojas, M. Ojeda, G. Busca, J.L.G.
Fierro, Catalysis Science & Technology 1 (2011) 1013–1023.
−1
3
000–2800 cm region in Fig. 11b. At the same time, the increase
in the absorbance of the samples is dramatic and the transmittance
decreases to almost zero, which points to a strong electronic inter-
action between TiO2 and the supported Ru oxide phase (Fig. 11c).
[9] J.M. González Carballo, J. Yang, A. Holmen, S. García-Rodríguez, S. Rojas, M.
Ojeda, J.L.G. Fierro, Journal of Catalysis 284 (2011) 102–108.
10] J. Kang, S. Zhang, Q. Zhang, Y. Wang, Angewandte Chemie International Edition
[
48 (2009) 2565–2568.
RuxTi1 O rutile-type solid solutions may be produced, which also
[11] X.-Y. Quek, Y. Guan, R.A. van Santen, E.J.M. Hensen, ChemCatChem 3 (2011)
1735–1738.
−x
2
have significant electronic conductivity and light absorption prop-
erties [59]. It is possible that Ru oxide can also enter into the anatase
structure [60]. The reduction step prior to CO adsorption allowed
for the reduction of a portion of the Ru centers to metal particles,
which decreases the electronic interaction with TiO2 [61].
In summary, our complete characterization data derived from
in situ FTIR showed that the primary deactivation mechanism of
Ru/TiO2 catalysts during the Fischer–Tropsch synthesis is the for-
mation and deposition of carbonaceous species on the active sites.
In addition, other techniques (Raman spectroscopy and HAADF-
STEM) have revealed that the formation of volatile carbonyls of Ru,
sintering of the Ru particles, and the oxidation of the Ru metallic
particles can be rejected as potential causes of deactivation. The
carbonaceous species can be removed, at least partially, by severe
thermal treatments in air. However, the performance of the catalyst
in the FTS is not fully recovered.
[
[
12] C.N. Hamelink, A.P.C. Faaij, H. den Uil, Energy 29 (2004) 1743–1771.
13] J.P. Hindermann, G.J. Hutchings, A. Kiennemann, Catalysis Review Science and
Engineering 35 (1993) 1–127.
[14] G.P. van der Laan, A.A.C.M. Beenackers, Catalysis Review Science and Engineer-
ing 41 (1999) 255–318.
[
[
15] M. Claeys, M. van Steen, Catalysis Today 71 (2002) 419–427.
16] C.J. Kim, US Patent 5,227,407 (1993).
[17] E. Kikuchi, M. Matsumoto, T. Takahashi, A. Machino, Y. Morita, Applied Catalysis
0 (1984) 251–260.
1
[
[
18] M.A. Vannice, R.L. Garten, Journal of Catalysis 63 (1980) 255–260.
19] N.E. Tsakoumis, M. Rønning, Ø. Borg, E. Rytter, A. Holmen, Catalysis Today 154
(2010) 162–182.
[
[
20] C.H. Bartholomew, Applied Catalysis A-General 212 (2001) 17–60.
21] J.G. Goodwin Jr., D.O. Goa, S. Erdal, F.H. Rogan, Applied Catalysis 24 (1986)
199–209.
[22] M.R. Goldwasser, M.L. Cubeiro, M.C. Da Silva, M.J. Pérez Zurita, G.
Leclercq, L. Leclercq, M. Dufour, L. Gengembre, G.C. Bond, A.D. Hooper, in:
R.L.E.C.P.N.J.H.S.M. de Pontes, M.S. Scurrell (Eds.), Studies in Surface Science
and Catalysis, Elsevier, 1997, pp. 15–22.
[23] H. Abrevaya, M.J. Cohn, W.M. Targos, H.J. Robota, Catalysis Letters 7 (1990)
183–195.
[
24] M. Ojeda, R. Nabar, A.U. Nilekar, A. Ishikawa, M. Mavrikakis, E. Iglesia, Journal
of Catalysis 272 (2010) 287–297.
4
. Conclusions
[25] A.M. Saib, D.J. Moodley, I.M. Ciobîc a˘ , M.M. Hauman, B.H. Sigwebela, C.J. West-
strate, J.W. Niemantsverdriet, J. van de Loosdrecht, Catalysis Today 154 (2010)
2
71–282.
Ru/TiO2 is a very active catalyst for the production of hydro-
[
[
26] R.A.D. Betta, A.G. Piken, M. Shelef, Journal of Catalysis 35 (1974) 54–60.
27] R.A. Dalla Betta, A.G. Piken, M. Shelef, Journal of Catalysis 40 (1975) 173–183.
[28] K.R. Krishna, A.T. Bell, Journal of Catalysis 130 (1991) 597–610.
29] R.M. Bowman, C.H. Bartholomew, Applied Catalysis 7 (1983) 179–187.
30] S. Mukkavilli, C.V. Wittmann, L.L. Taviarides, Industrial & Engineering Chem-
istry Process Design and Development 25 (1986) 487–494.
carbons via the Fischer–Tropsch synthesis. However, the very high
initial catalyst activity decreases with time on stream. Raman
soning species by hindering the adsorption of the reactants. In fact,
[
[31] T.E. Hoost, J.G. Goodwin Jr., Journal of Catalysis 137 (1992) 22–35.
Please cite this article in press as: J.M.G. Carballo, et al., Insights into the deactivation and reactivation of Ru/TiO2 during Fischer–Tropsch synthesis,