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Glycerol as a probe molecule to uncover oxidation mechanism in photocatalysis

Paper ID Volume ID Publish Year Pages File Format Full-Text
46621 46443 2012 9 PDF Available
Title
Glycerol as a probe molecule to uncover oxidation mechanism in photocatalysis
Abstract

Glycerol is a good probe molecule to understand what type of photocatalytic mechanism could occur at the catalyst surface, as the analysis of the produced intermediates is able to discriminate between a direct electron transfer and a radical mediated oxidation mechanism. The mechanism of transformation of glycerol is explored by an extensive analysis of formed intermediates as a function of glycerol concentration on two different commercial TiO2 powders. Over TiO2 Degussa P25 the transformation rate of glycerol shows a sharp maximum as a function of the substrate concentration. The type of product detected at low glycerol concentration (glyceraldehyde and dihydroxyacetone) changes after the sharp maximum giving mainly formaldehyde and glycolaldehyde. On Merck TiO2, characterized by a lower density and more uniform population of hydroxyls at surface sites, mainly glyceraldehyde and dihydroxyacetone are observed. Because these products are formed through an OH-like mechanism, the products observed on P25 derive from a direct electron transfer. The results are rationalized invoking the surface complex of glycerol where an inner sphere electron transfer occurs, which leads to glycerol fragmentation, and where the substrate-mediated recombination plays the major role. A simplified kinetic approach confirms the observed rate dependence on concentration.The working hypothesis is also confirmed by addition of fluoride anions that compete for surface sites and impede glycerol complexation. Without the possibility of inner sphere electron transfer, on P25 only glyceraldehyde and dihydroxyacetone are observed. Thus different catalysts differ for the possibility of surface complexation.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Glycerol is a probe to assess different aspect of photocatalytic reaction rates. ► Single site photocatalysis is ruled out. ► Reactivity in the chemisorbed state leads to CC bond cleavage. ► Reactivity in the physisorbed state leads to H-abstraction. ► Photocatalytic reaction mechanism and back reactions depend on surface chemistry.

Keywords
Glycerol; Photocatalysis; Fluorination; Shallow traps; OH radical
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis B: Environmental - Volume 128, 30 November 2012, Pages 135–143
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