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Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature

Paper ID Volume ID Publish Year Pages File Format Full-Text
40426 45853 2013 8 PDF Available
Title
Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature
Abstract

•The sol–gel and hydrothermal treatment let to obtain Cr3+ incorporated to SiO2 support.•The Cr3+ ions are stable and resistant to segregation in air up to 350 °C.•These Cr3+ ions produce Lewis acid sites that catalyze the 2-propanol dehydration.•The Cr6+ ions formed after in air calcination (450 °C) develops weak Brönsted sites.•2,6-Lutidine adsorption lets to quantify the Lewis and Brönsted sites by FTIR.

Cr/SiO2 catalysts (4–8% Cr, w/w), obtained from Cr(III) salts and tetraethylortosilicate (TEOS), were prepared by the sol–gel method. After TEOS hydrolysis in ammoniacal solution (pH: 9.5), the gel was treated under hydrothermal conditions at 120–220 °C. The solids were characterized by N2 sorptometry, TG–DTA, DRUV–vis, XRD, and FTIR. In vacuum or N2 atmosphere, Cr3+ ions were stable up to 450 °C. However, calcination in air promotes the partial oxidation of Cr3+ to Cr6+ as the temperature increases from 200 to 450 °C. The amount of Cr6+ formed depends on the temperature of the hydrothermal treatment. 2,6-Lutidine adsorption allows to determine the evolution, with respect to calcination temperature, of both Lewis and Brönsted acid centers. Cr3+ ions were related to the presence of Lewis sites, and Cr6+ ions to the development of weak Brönsted acid sites. Accordingly, the 2-propanol dehydration reaction rate shows an increase when the catalysts are treated in N2 at 450 °C, while catalysts calcined in air develop a lower acidity. The dehydration reaction is attributed to the presence of Lewis acid centers.

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Keywords
Cr/SiO2; Sol–gel; DRUV–vis; 2,6-Lutidine; 2-Propanol
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Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 457, 24 April 2013, Pages 26–33
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
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Full-text PDF Download
Online Support
Any Questions? feel free to contact us