Authors
Maryam Khosravi Mardkhe, Kamyar Keyvanloo, Calvin H Bartholomew, William C Hecker, Todd M Alam, Brian F Woodfield
Publication date
2014/7/22
Journal
Applied Catalysis A: General
Volume
482
Pages
16-23
Publisher
Elsevier
Description
Acid site properties of silica-doped aluminas prepared by a simple solvent deficient hydrolysis of the alkoxides was investigated. The total acid concentration (Brønsted and Lewis sites) of silica-doped aluminas (SDAs) calcined in the range of 700–1200 °C with Si/Al ratios of 5, 15, 27 wt% was determined using temperature-programmed desorption of ammonia (ammonia-TPD). 27Al solid state MAS NMR (Al SS MAS NMR) was used to measure the intrinsic Lewis acid site concentration, and FTIR was also used as a separate measure of the Brønsted and Lewis acid site concentration. Results indicate that removing hydroxyl groups in the form of water molecules through calcination result in a lower concentration of Brønsted acid sites. Calcination at higher temperature also results in the transformation of unsaturated 5-coordinated aluminum (a strong Lewis acid) to higher concentrations of 6 and 4-coordinated …
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