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Acid site properties of thermally stable, silica-doped alumina as a function of silica/alumina ratio and calcination temperature

Paper ID Volume ID Publish Year Pages File Format Full-Text
39579 45828 2014 8 PDF Available
Title
Acid site properties of thermally stable, silica-doped alumina as a function of silica/alumina ratio and calcination temperature
Abstract

•We report the properties of acid site concentrations for Si doped aluminas.•Acid site concentrations Si dopant levels and annealing temperatures.•Acid sites are essentially completely removed by annealing at 1200 °C.

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 aluminum in 5, 15 and 27% silica-doped alumina samples. Therefore, the total acid site concentration (Brønsted and Lewis sites) decreases by increasing the calcination temperature. In addition, the data show that increasing the silica/alumina ratio increases both the Brønsted and Lewis acid site concentrations. Based on these results, the acid site concentrations can be controlled by altering the Si/Al ratio and calcination temperature while maintaining high surface areas, large pore volumes, and large pore diameters.

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Keywords
Silica-doped alumina; Brønsted and Lewis acid sites; Thermal stability; Acid site concentration
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Acid site properties of thermally stable, silica-doped alumina as a function of silica/alumina ratio and calcination temperature
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 482, 22 July 2014, Pages 16–23
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us