Characterisation studies on the new microporous aluminium-containing ETS-10 molecular sieve used for processing larger molecules

Abstract

This study reports on the physico-chemical characterisation of an aluminium-containing microporous titanosilicate ETS-10 material in its protonic form in connection with catalytic testing. ²⁷Al MAS NMR spectra reveal the successful incorporation of aluminium into the lattice structure. XRD patterns indicate that the investigated ETAS-10 material in its protonic form is relatively stable thermally, an indispensable requirement for the application as an industrial catalyst material. Nevertheless, for all samples, except parent ETAS-10, XRD and ²⁹Si MAS NMR measurements indicate that an increasing amount of amorphous silica is present. Acidity investigations with combined FT-IR spectroscopy and temperature-programmed ammonia desorption and with ¹H MAS NMR revealed that dehydroxylation of bridging hydroxyl groups, which are assumed to be of the type Ti-(OH)-Si, occur between 350 and 550°C. An increase in both the number and strength of catalytically active bridging hydroxyl groups seems to be limited by a conventional protonic ion-exchange. The acid properties corroborate excellently with the catalytic activity and selectivity in n-hexadecane and 1,3,5-triisopropylbenzene cracking. The results show that electron acceptor sites, which may originate from titaniumoxide impurities or defect sites especially in titanium octahedra, could be involved in the catalytic reactions forming radical precursors.