Raman spectroscopic studies of the effects of tin promotion on a rhenium/alumina dismutation catalyst

Abstract

Raman spectroscopic studies have been carried out on a rhenium/alumina catalyst, active in metathesis reactions. Raman data comparing the state of the rhenium on the fresh catlyst (freshly activated and following air exposure), and on catalyst promoted with tetramethyltin are presented.

The ammonium perrhenate impregnated alumina catalyst precursor contains a tetrahedral oxidic rhenium species in a hydrated state. When the precursor is activated, a reduction in the number of attached hydroxyl groups and a distortion of the tetrahedral rhenium moiety occurs. The extent of hydration of the rhenium phase is therefore an important parameter determining metathesis activity. There is no evidence for the presence of a surface rhenium heptoxide phase.

An extra Raman band at 777 cm^–1, observed following tetramethyltin promotion, is attributed to a Re–Sn vibration. This Re–Sn interaction may be responsible for the observed promotional effect.