offered by the purely empirical approach to obtain
materials with uniform acidity. If this had been
achieved, this would have been claimed. A real pessimism
may be expressed that the sol±gel method
could produce amorphous silica±aluminas with uniform
acidity, unless different chemical methods and an
extensive chemical engineering approach pave the
way to a rigorous control of the hydrolysis conditions
at the nanometer scale, or completely new family of
starting reactants is discovered.
We hope that the present work could, together with
other ones like that of Monaco and Ko [17] cited
above, further encourage the development of
advanced methods, in the Æeld both of chemistry
and chemical engineering, which could allow the
obtention of materials with a really homogeneous
acidity.
5. Conclusion
We can conclude that the industrial technologies
and the laboratory methods based on sol±gel processing
at the beginning of the present decennia were still
far from being able to produce silica±aluminas with a
single type of acidic sites, homogeneously distributed
on the surface. The nanoscale chemical composition
inhomogeneities and the presence in many cases of
impurities inhomogeneously distributed in the material,
are mainly responsible for this lack of homogeneity.
The so-called sol±gel methods which were currently
in use in industry until 1991 and which, in
most cases, did not use alkoxides, seem slightly less
efficient than our old laboratory method in reaching a
higher degree of homogeneity.
Acknowledgements
One of the authors, Corneliu SaÃrbu, gratefully
acknowledges the Universite¬ Catholique de Louvain
(Louvain-la-Neuve) for the research grant which
made the present work possible. The contribution
of Mrs. Jocelyn de Kerkhove, who has performed
the test of composition homogeneity of the mineral
samples used for determination of the KAlSi parameter
of our spectrometer, is also gratefully acknowledged.
References
[1] P.O. Scokart, F.D. Declerck, R.E. Sempels, P.G. Rouxhet, J.
Chem. Soc., Faraday Trans. 1 73 (1977) 359.
[2] J.P. Damon, B. Delmon, J.M. Bonnier, J. Chem. Soc., Faraday
Trans. 1 73 (1977) 372.
[3] C. Defosse¬, P. Canesson, P.G. Rouxhet, B. Delmon, J. Catal.
51 (1978) 269.
[4] J.P. Damon, J.M. Bonnier, B. Delmon, Bull. Soc. chim. Fr.
449 (1975).
[5] J.P. Damon, J.M. Bonnier, B. Delmon, J. Colloid Interface
Sci. 55 (1976) 381.
[6] P.G. Rouxhet, P.O. Scokart, P. Canesson, C. Defosse¬, L.
Rodrique, F.D. Declerck, A.J. Leonard, B. Delmon, J.P.
Damon, in: M. Kerker (Ed.), Colloid and Interface Science,
vol. 3, Academic Press, New York, 1976, pp. 81±94.
[7] Y. Matsumoto, K. Mita, K. Hashimoto, T. Tokoroyama, Appl.
Catal. A 131 (1995) L1.
96 C. SaÃrbu, B. Delmon / Applied Catalysis A: General 185 (1999) 85±97
[8] P.G. Menon, B. Delmon, in: G. Ertl, H. Kno»zinger, J.
Weitkamp (Eds.), Handbook of Heterogeneous Catalysis, vol.
1, VCH, Weinheim, 1997, pp. 100±118.
[9] M.A. Aegerter, D.F. Bozano, in: L.L. Hench, J.K.West (Eds.),
Chemical Processing of Advanced Materials, Wiley, New
York, 1992, pp. 175±186.
[10] J.I. Goldstein, D.B. Williams, Quantitative X-ray analysis, in:
D.C. Joy, A.D. Romig, J.I. Goldstein (Eds.), Principles of
Analytical Electron Microscopy, Plenum Press, New York,
1986, pp. 155±217.
[11] J.K. Park, J. Ardell, J. Microscopy 165(2) (1992) 301.
[12] N. Zaluzec, Private communication.
[13] C. Sarbu, B. Delmon, Proceedings of the Eleventh European
Congress Electron Microscopy EUREM'96, 25±30 August
1996, Dublin, Ireland, vol. 1, s. M2 (CD-version edited by the
organizers).
[14] K.F.J. Heinrich, Electron Beam X-Ray Microanalysis, Van
Nostrand Reinhold Co., Princeton, 1981, p. 156.
[15] J.I. Goldstein, D.B. Williams, Quantitative X-ray Analysis,
in: D.C. Joy, A.D. Romig, J.I. Goldstein (Eds.), Principles of
Analytical Electron Microscopy, Plenum Press, New York,
1986, pp. 188±189.
[16] H.A. Liebhafsky, H.G. Pfeiffer, P.D. Zemany, Anal. Chem. 27
(1955) 1257.
[17] S.J. Monaco, E.I. Ko, Chemtech 28 (1998) 23.
C. SaÃrbu, B. Delmon / Applied Catalysis A: General 185 (1999) 85±97 97
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