Hydroxyls nests in defective silicalites and strained structures derived upon dehydroxylation: vibrational properties and theoretical modelling

Defective silicalite, an efficient and selective catalyst in the gas phase Beckmann rearrangement reaction, has been characterised by infrared spectro scopy and by molecular modelling techniques. We report a detailed TR study on the effect of outgassing treatments at increasing temperature on silanol s bands and on framework modes. The effect of a temperature decrease up to 100 K (during the IR measurement) on the H-bonding interactions has also be en investigated. The interaction of silanols with mesitylene, a probe molec ule which cannot penetrate the channels, has been studied in order to disti nguish between internal and external OH groups. Molecular mechanics and nb initio methods have also been used to model the structure and the vibration al features of a properly designed nest in order to support the assignments of the LR spectrum.