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

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 cm3/g to 0.085 cm3/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 (NH3-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.

A surface Ti, Al rich ETS-10 was obtained by sequential desilication and realumination. The removing of Si atoms modulated the surface elemental composition and supplied additional space for Al incorporation. The pore structure and acidic property of ETS-10 was also improved.Figure optionsDownload as PowerPoint slideHighlights
► Desilication improved the pore structure of ETS-10 and made it rich of surface Ti atoms.
► Followed realumination formed tetrahedral coordinated Al in ETS-10.
► Realumination made ETS-10 rich of surface Al atoms.
► Both of B and L acidic site of Al-ETS-10 were enhanced.