An FT–IR Study of the Chlorination of γ-Alumina Surfaces
1998
Abstract Surface chlorination of two aluminas (Degussa and Condea; S BET =100 m 2 g −1 ) has been realized either by reaction of CHCl 3 on an alumina pellet inside the IR cell or by flowing HCl (g) on alumina powder for one hour outside the IR cell. The FT–IR analysis of the chlorinated samples showed that the bands assigned to OH groups, specially in the range of higher wavenumbers (3800–3700 cm −1 ), are sensitive to the presence of chlorine on the surface taking the place of the more basic surface OH groups by substitution reaction. The nature of the additive products influenced the bands in the 1600–1200 cm −1 region. The evolution of surfaces rehydratation showed that the chlorinated aluminas are more stable than the raw ones with respect to the presence of H 2 O on the surface. The hydrolysis modified the surfaces of both raw Al 2 O 3 , whereas the surfaces of the chlorinated aluminas were restored after thermal treatment at 870 K. La chloration de surface de deux alumines (Degussa et Condea) de surface specifique de 100 m 2 g −1 a ete realisee soit par reaction de CHCl 3 avec la surface a l’interieur de la cellule infrarouge soit par passage de HCl (g) sur la poudre d’alumine durant une heure a l’exterieur de celle-ci. L’etude infrarouge des surfaces chlorees montre la presence de reactions de substitution entre les groupes OH de la surface et le chlore des deux agents chlorants. Ce sont les groupes OH les plus basiques qui reagissent. La nature des additifs modifie aussi le spectre dans la region 1600–1200 cm −1 . Une rehydratation a revele que les alumines ainsi chlorees sont plus stables que celles non traitees en ce qui concerne l’action de la molecule H 2 O sur la surface. En effet l’hydrolyse affecte la surface des deux alumines brutes, alors que celle des alumines chlorees est restauree apres chauffage a 870 K.
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