Studies of Some Catalytic Properties of Zeolites

Abstract

The use of Yetype zeolites as catalysts for the vapour phase Beckmann rearrangement of alicyclic oximes has been investigated, particularly for the conversion of cyclopentanone oxime to 2-piperidone. The rearrangements of cyclopentanone oxime and cyclohexanone oxime were studied spectroscopically, and the conversion of cyclopentanone oxime studied further using a flow system. The active sites for the Beckmann rearrangement have been identified as surface hydroxyl groups located at specific sites within the zeolitic lattice. The most efficient catalysts for the rearrangement, therefore, are the decationated or hydrogen zeolites. The interaction of cyclohexanone oxime with zeolites containing no surface hydroxyl groups has also been studied, and the nature of the interaction inferred. The formation of an alkene-nitrile on this catalyst is indicated by the infrared spectra obtained. Using a flow system, the rearrangement of cyclopentanone oxime to 2-piperidone was studied as a function of the catalyst, temperature, solvent and carrier, and the results of the spectroscopic studies were confirmed and extended. The formation of 2-piperidone has been shown to be a function of catalyst acidity, and the reaction on zeolites containing no surface hydroxyl groups was shown to result in the formation of an alkene-nitrile. The formation of the latter is a function of the electrostatic potential of the zeolitic cation. Cyclopentanone, which is formed in small amounts for all catalysts studied, probably results from hydrolysis of the oxime by residual zeolitic water. The reason for the short catalyst lifetimes for the rearrangement of cyclopentanone oxime to 2-piperidone is formation of carbon on the catalyst surface. This results from decomposition of the rearrangement product, which is strongly held on the surface. It is predicted that decationated zeolites should be efficient catalysts for the rearrangement of oximes which are stable, and which produce stable products.