January 1995 Materials zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE Letters 22 (1995) 109-l 13 Al-0 infrared vibrational frequencies of y-alumina Jo& M. Saniger zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ Laboratorio de Qufmica de Materiales, Centro de Instrumentos. Universidad National Authoma de M&co, Apdo. Postal 70-186, Mhico D.F., 04510, Mexico Received 17 October 1994;accepted 27 October 1994 zyxwvutsrqponmlkjihgfedcbaZYXWVUT Abstract The yAl,03 structure was considered as a hydrogen spine1 and the complex Al-O infrared absorption band between 1100 and 350 cm- ’ was interpreted under the criteria for the band assignment of the spinels. Additionally, a deconvolution analysis of this band was made. The collection of virtual bands obtained suggests that a complement band assignment to the spine1 criteria may be done. 1. Introduction The gamma-alumina, ‘y-AlzOX, is an aluminum oxide form which belongs to the so-called transition alumi- nas. The transition aluminas are a family of materials obtained from the thermal treatment of aluminum hydroxides or oxohydroxides, such as gibbsite, bayer- ite, boehmite, etc. The pathway for the synthesis of these materials is complex, due to the fact that the specific transition alumina obtained is highly depend- ent on the precursor used and the sample thermal his- tory. A scheme of the transformation sequence from aluminum hydroxides to the final stable phase alpha- alumina, (Y-A1203, passing through the transition alu- mina metastable forms, may be consulted elsewhere [ 11. The chemical composition of the transition alu- minas is that of aluminum oxide, with a variable resid- ual content of hydroxyl groups depending on the specific dehydroxylation sequence of each sample. From a structural point of view, they all are formed by different tetrahedral and octahedral arrangements of aluminum atoms surrounded by oxygen atoms. Some tetrahedral and/or octahedral coordinated groups pos- sess aluminum vacancies in order to preserve the elec- 0167-577x/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSD10167-577x(94)00234-7 trical neutrality of the structure. The position of the remainder hydroxyl groups is related with the alumi- num vacancies. 1.1. The y-AIz03 structure Among the different transition aluminas, y-A1203 is perhaps the most widely used, mainly as support for a catalyst or as a catalyst itself, but also as ion exchanger or chromatographic media. It can be obtained by the thermal treatment of boehmite, AlOOH, and it is gen- erally accepted that it has a defect spinel-type structure [ 21 tetragonally deformed, comprising a face-centered cubic arrangement of 32 oxide ions and a random occu- pation of 214 of the 24 available cation sites ( 16 octahedral, 8 tetrahedral). The 3/-A1203 structure was studied by Lippens and de Boer [ 31, Saalfeld and Meh- rotra [4] and Wilson [5] and all of them concluded that its oxygen sub-lattice has a higher order than that of other transition aluminas, and the cation uacancies of the spine1 lattice seem to be confined to the tetra- hedral interstice [4,6]. In relation to the hydroxyl groups of y-A1,03, Soled [7] proposed that the OH- ions are a necessary component of the defective struc-