Characterisation of defective silicalites

The structure and the adsorptive properties of internal defects in two chem ically very pure silicalite samples, characterised by a high and low concen tration of defects (internal SiOH nests generated by Si vacancies), are inv estigated by means of several physical methods (neutron diffraction, IR spe ctroscopy of adsorbed NH3, microcalorimetry of NH3 adsorption and quantum c hemical computation). The role of cooperative effects in hydrogen bonded ch ains and rings of silanols covering the internal defective nanocavities in influencing the absorptive properties of the material is elucidated. This s tudy provides an explanation of the less hydrophobic character of defective silicalite relative to perfect silicalite and sheds light on the reason wh y defective silicalite acts as an efficient and selective catalyst for the gas phase Beckman rearrangement reaction where cyclohexanone oxime is conve rted into caprolactam.