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Open Access Thesis

Keywords

Porous materials--Surfaces; Benzaldehyde--Absorption and adsorption; Benzaldehyde--Reactivity; Catalysis; Academic theses;

Abstract

Benzaldehyde was dosed onto porous borosilicate glass in order to better understand the catalytic behavior of the surface of the porous glass. 18,000 L of benzaldehyde was dosed onto the porous glass at approximately 50 K and heated to a temperature of 470 K. The reactions that occurred were studied using FTIR spectroscopy and Temperature Programmed Desorption (TPD). The FTIR spectrum of the porous glass confirmed the presence of isolated surface hydroxyl groups (Si-OH), seen in the spectrum at 3750 cm1 , and the presence of isolated boron-OH groups, seen in the spectrum at 3700 cm1 . Neighboring surface hydroxyl groups were detected with the FTIR as well, as evidenced by the large absorption from 3100-3700 cm1 . Atomic force microscopy of the porous glass surface showed that the pores were at least 5 nm in depth and were approximately 40 nm in diameter. The piece of glass used was less than 0.2 mm thick. Benzaldehyde adsorbed on the porous glass surface produced peaks in the FTIR spectrum at 1692 cm-1 and 1658 cm-1 due to the C=O stretch and at 3070 cm-1 , 2925 cm-1 , and 2852 cm1 due to C-H stretches. The two C=O peaks were observed to disappear as the sample was heated through the range 205 K to 325 K, indicating hydrogen bonding to the surface hydroxyl groups from 205 K to approximately 315 K, followed by decomposition of the benzaldehyde and desorption of CO. New bands in the C-H stretching region appeared at 315 K to 325 K and then disappeared at temperatures above 325 K. The TPD of the desorption products from the porous glass surface confirmed that the benzaldehyde was decomposed, not desorbed. At no time when the sample was heated from 50 K to 470 K did benzaldehyde appear in the TPD. In fact, no mass above 44 was detected in the TPD, even though significant changes were seen in the FTIR spectrum from 205 K to 325 K. A large desorption of mass 28 was detected from 315 K to 340 K, which was mostly attributable to carbon monoxide. Desorption of mass 26 and mass 14 in the same temperature range were attributed to acetylene and ethylene, respectively. The proposed mechanism of carbon monoxide formation from benzaldehyde is the acid-catalyzed Gatterman-Koch mechanism, with the acidic surface hydroxyl groups acting as the source of catalyzing protons. It is proposed that the other product of the reaction, benzene, is partially decomposed to acetylene, which can be converted to ethylene by hydroboration.

Year of Submission

2003

Degree Name

Master of Science

Department

Department of Chemistry

First Advisor

Shoshanna Coon

Second Advisor

Paul Rider

Third Advisor

Laura Strauss

Comments

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Date Original

2003

Object Description

1 PDF file (93 leaves)

Language

en

File Format

application/pdf

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