Preparation of the surface Ti, Al rich ETS-10 and modification of its pore structure and acidity by desilication and realumination

Abstract

The surface titanium (Ti) and aluminium (Al) rich ETS-10 was obtained by sequential processes of desilication and realumination. Combined X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) analysis confirmed that a part of silicon (Si) atoms in the framework of ETS-10 were removed via desilication which resulted in the enrichment of Ti atoms in ETS-10. The bulk Si/Ti atom ratio was decreased from 4.6 to 4.2, and the surface Si/Ti atom ratio was decreased from 9.1 to 5.5. Nitrogen adsorption–desorption analysis showed that the porosity of ETS-10 was improved along with the desilication process, and the most remarkable improvement was that the mesoporous volume was increased from 0.022 cm 3/g to 0.085 cm 3/g. The improved porosity facilitated the incorporation of Al atoms by supplying additional space, and with the processing of realumination to ETS-10, the bulk phase Al/Ti atom ratio reached to 0.4 and the surface phase Al/Ti atom ratio reached to 1.9. The results of 27Al MAS NMR pointed out that the majority of the Al atoms introduced to ETS-10 were tetrahedrally coordinated and thus generating bridging hydroxyl groups of Si–(OH)–Al sites for zeolite-type acidity. The acidity of ETS-10 was improved after realumination, which was concluded by the combined ammonia temperature-programmed desorption (NH 3-TPD) and pyridine (Py) adsorption performed via FT-IR analysis. The strong Brönsted and Lewis acid sites were increased together. Cumene cracking reaction was employed to test the acidity properties of Al-containing ETS-10, and the cumene conversion increased by 18% at 673 K compared with the as-synthesized ETS-10.