1. 1 H. Topsøe, B. S. Clausen, and F. E Massoth, in“Hydrotreating Catalysis, Science and Technology”, Springer-Verlag, Berlin (1996).
2. 2 J. C. Elliot in“Structure and Chemistry of the Apatites and Other Calcium Orthophosphates”, Elsevier, Amsterdam, (1994).
3. 3 M. V. Twigg, in“Catalyst Handbook”, Manson Publishing, London (1996).
4. 4 A. El Ouassouli, A. Ezzemouri, A. Ezzamarty, M. Lakhdar, and J. Leglise, J. Chim. Phys., 1999 (in press).
5. 5 J. B. Peri, Discuss Farad. Soc., 52, 55 (1971).