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Low temperature water–gas shift: Differences in oxidation states observed with partially reduced Pt/MnOX and Pt/CeOX catalysts yield differences in OH group reactivity

Paper ID Volume ID Publish Year Pages File Format Full-Text
50621 46805 2010 7 PDF Available
Title
Low temperature water–gas shift: Differences in oxidation states observed with partially reduced Pt/MnOX and Pt/CeOX catalysts yield differences in OH group reactivity
Abstract

The Pt–ceria synergy may be described as the dehydrogenation of formate formed on the surface of the partially reducible oxide (PRO), ceria, by Pt across the interface, with H2O participating in the transition state. However, due to the rising costs of rare earth oxides like ceria, replacement by a less expensive partially reducible oxide, like manganese oxide, is desirable. In this contribution, a comparison between Pt/ceria and Pt/manganese oxide catalysts possessing comparable Pt dispersions reveals that there are significant differences and certain similarities in the nature of the two Pt/PRO catalysts. With ceria, partial reduction involves reduction of the oxide surface shell, with Ce3+ at the surface and Ce4+ in the bulk. In the case of manganese oxide, partial reduction results in a mixture of Mn3+ and Mn2+, with Mn2+ located at the surface. With Pt/CeOX, a high density of defect-associated bridging OH groups react with CO to yield a high density of the formate intermediate. With Pt/MnOX, the fraction of reactive OH groups is low and much lower formate band intensities result upon CO adsorption; moreover, there is a greater fraction of OH groups that are essentially unreactive. Thus, much lower CO conversion rates are observed with Pt/MnOX during low temperature water–gas shift. As with ceria, increasing the Pt loading facilitates partial reduction of MnOX to lower temperature, indicating metal–oxide interactions should be taken into account.

Graphical AbstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► Pt/CeOX and Pt/MnOX were prepared with comparable Pt particle sizes < 3 nm. ► Pt/CeOX displayed higher LTS activity over Pt/MnOX due to differences in oxide. ► Activated CeOX consists of Ce4+ in the core and Ce3+ in the surface shell. ► Activated MnOX contained subsurface Mn3+ and surface Mn2+. ► Bridging OH groups on ceria more reactive for formate formation during LTS.

Keywords
Water–gas shift; Pt/ceria; Manganese oxide; XANES; EELS; HR-TEM
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Low temperature water–gas shift: Differences in oxidation states observed with partially reduced Pt/MnOX and Pt/CeOX catalysts yield differences in OH group reactivity
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Communications - Volume 11, Issue 15, 25 September 2010, Pages 1193–1199
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