Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde

Tin-modified mesoporous silica MCM-48 with various Si/Sn ratios has been prepared by post synthesis modification in alkaline medium. Local rice husk ash (RHA) has been used as Si precursor in the synthesis of Si-MCM-48 samples while SnCl2 was used as the tin source in the modification. The tin-modif...

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Main Author:	Ka Lun, Wong
Format:	Thesis
Language:	English
Published:	2007
Subjects:	QD Chemistry
Online Access:	http://eprints.utm.my/id/eprint/13541/1/WongKaLunMFS2006.pdf
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spelling	my-utm-ep.135412018-07-25T08:01:15Z Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde 2007-12 Ka Lun, Wong QD Chemistry Tin-modified mesoporous silica MCM-48 with various Si/Sn ratios has been prepared by post synthesis modification in alkaline medium. Local rice husk ash (RHA) has been used as Si precursor in the synthesis of Si-MCM-48 samples while SnCl2 was used as the tin source in the modification. The tin-modified MCM-48 samples were characterized by using powder X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible diffuse reflectance (UV-Vis DR) spectroscopy, nitrogen physisorption measurement, field emission scanning electron microscopy (FESEM) and temperature-programmed reduction (TPR) analysis. Surface acidity of the prepared samples was determined by using pyridine adsorption-desorption measurement followed by FTIR spectroscopy. In addition, thermal and hydrothermal stability testing for the tin-modified samples were carried out. The FTIR, UV-Vis DR and XRD results show that tetrahedral tin species can be introduced into the mesoporous material without destroying the framework structure of the molecular sieves. Surface acidity studies confirm that Lewis acid sites had been generated on the mesoporous silica MCM-48 by post-synthesis modification. The generation of Lewis acid sites could be due to the introduction of tin species and/or because of defect sites that had been created during post-synthesis modification. Tin-modified sample SnM60 (Si/Sn = 60) possessed highest amount of Lewis acidity. In oxidation of benzyl alcohol, all the tinmodified samples gave 100% selectivity to benzaldehyde in reaction time under 22 hours. The catalytic activity can be correlated with the Lewis acid sites generated by post-synthesis modification. Purely siliceous MCM-48 and physically mixed tincontaining MCM-48 samples that possesses no Lewis acidity gave poor performance in the catalytic reaction. With the increase in the amount of oxidant in the reaction mixtures, the conversion of benzyl alcohol increased significantly but the selectivity for benzaldehyde was reduced. For reusability test, the catalytic performance of the re-used samples was maintained within 5-10% after two cycles of reuse without significant loss of activity. Comparison of the catalytic performance of SnM60 in the oxidation of unsaturated primary alcohols and saturated aliphatic primary alcohol towards the corresponding aldehydes showed higher % conversion of the unsaturated primary alcohols than that of the saturated aliphatic primary alcohol 2007-12 Thesis http://eprints.utm.my/id/eprint/13541/ http://eprints.utm.my/id/eprint/13541/1/WongKaLunMFS2006.pdf application/pdf en public masters Universiti Teknologi Malaysia, Faculty of Science Faculty of Science
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	QD Chemistry
spellingShingle	QD Chemistry Ka Lun, Wong Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
description	Tin-modified mesoporous silica MCM-48 with various Si/Sn ratios has been prepared by post synthesis modification in alkaline medium. Local rice husk ash (RHA) has been used as Si precursor in the synthesis of Si-MCM-48 samples while SnCl2 was used as the tin source in the modification. The tin-modified MCM-48 samples were characterized by using powder X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible diffuse reflectance (UV-Vis DR) spectroscopy, nitrogen physisorption measurement, field emission scanning electron microscopy (FESEM) and temperature-programmed reduction (TPR) analysis. Surface acidity of the prepared samples was determined by using pyridine adsorption-desorption measurement followed by FTIR spectroscopy. In addition, thermal and hydrothermal stability testing for the tin-modified samples were carried out. The FTIR, UV-Vis DR and XRD results show that tetrahedral tin species can be introduced into the mesoporous material without destroying the framework structure of the molecular sieves. Surface acidity studies confirm that Lewis acid sites had been generated on the mesoporous silica MCM-48 by post-synthesis modification. The generation of Lewis acid sites could be due to the introduction of tin species and/or because of defect sites that had been created during post-synthesis modification. Tin-modified sample SnM60 (Si/Sn = 60) possessed highest amount of Lewis acidity. In oxidation of benzyl alcohol, all the tinmodified samples gave 100% selectivity to benzaldehyde in reaction time under 22 hours. The catalytic activity can be correlated with the Lewis acid sites generated by post-synthesis modification. Purely siliceous MCM-48 and physically mixed tincontaining MCM-48 samples that possesses no Lewis acidity gave poor performance in the catalytic reaction. With the increase in the amount of oxidant in the reaction mixtures, the conversion of benzyl alcohol increased significantly but the selectivity for benzaldehyde was reduced. For reusability test, the catalytic performance of the re-used samples was maintained within 5-10% after two cycles of reuse without significant loss of activity. Comparison of the catalytic performance of SnM60 in the oxidation of unsaturated primary alcohols and saturated aliphatic primary alcohol towards the corresponding aldehydes showed higher % conversion of the unsaturated primary alcohols than that of the saturated aliphatic primary alcohol
format	Thesis
qualification_level	Master's degree
author	Ka Lun, Wong
author_facet	Ka Lun, Wong
author_sort	Ka Lun, Wong
title	Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
title_short	Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
title_full	Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
title_fullStr	Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
title_full_unstemmed	Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde
title_sort	synthesis and characterization of tin-modified mesoporous silica mcm-48 for selective oxidation of alcohol to aldehyde
granting_institution	Universiti Teknologi Malaysia, Faculty of Science
granting_department	Faculty of Science
publishDate	2007
url	http://eprints.utm.my/id/eprint/13541/1/WongKaLunMFS2006.pdf
_version_	1747814960510009344

Synthesis and characterization of tin-modified mesoporous silica MCM-48 for selective oxidation of alcohol to aldehyde

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