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Thermal transformations of 2-chlorophenol on a surface of ZnO powder catalyst

Paper ID Volume ID Publish Year Pages File Format Full-Text
54546 47013 2014 7 PDF Available
Title
Thermal transformations of 2-chlorophenol on a surface of ZnO powder catalyst
Abstract

•Combination of in situ spectroscopies and of computational techniques was used to follow the reaction of 2-chlorophenol on ZnO catalyst.•Upon adsorption, C–Cl is competing with the O–H bond dissociation.•ZnO catalyst is selective towards the O–H dissociation of 2-chlorophenol.•Following thermal annealing of ZnO with preadsorbed 2-chlorophenol, chlorine is only released as chlorinated hydrocarbon fragments.

Catalytic transformation of multifunctional molecules requires understanding of the competing reactions on a surface of a heterogeneous catalyst. Here the reaction of 2-chlorophenol is investigated with ZnO powder that has a potential to be used in environmental remediation. Since it is important to follow every step of surface-catalyzed processes, adsorption and thermally induced transformations of 2-chlorophenol on ZnO powder catalyst were followed by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and supplemented by density functional theory (DFT) investigations. The room temperature adsorption FTIR results show that O–H dissociation is the primary reaction pathway. Room temperature adsorption studies followed by in situ thermal annealing to desired temperature and then quenching back to room temperature followed by XPS prove that C–Cl dissociation in 2-chlorophenol is competing with the O–H dissociation process on ZnO; however, the majority of chlorine is still bound to carbon and can only be removed by thermal annealing together with the phenyl group. DFT description helps to construct the reaction mechanism diagram and O–H dissociation is found to have a reaction barrier of only 62.4 kJ/mol, while C–Cl bond dissociation has a substantially higher barrier of 111.2 kJ/mol. Thus, this set of studies suggests that the reaction of 2-chlorophenol on ZnO powder proceeds selectively towards the O–H dissociation; however, the products released from its surface following thermal annealing contain chlorinated hydrocarbon fragments. This observation implies that it would be difficult to use unmodified ZnO as a catalyst for a direct utilization and mineralization of chlorophenols.

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Keywords
2-Chlorophenol; Adsorption; ZnO powder; FTIR; XPS; DFT
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 238, December 2014, Pages 111–117
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