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Trends in the CO oxidation and PROX performances of the platinum-group metals supported on ceria

Paper ID Volume ID Publish Year Pages File Format Full-Text
53429 46969 2015 9 PDF Available
Title
Trends in the CO oxidation and PROX performances of the platinum-group metals supported on ceria
Abstract

•Ceria loaded with Pt, Pd, Ir, Rh, or Ru was synthesized by solution combustion.•The H2-free CO oxidation activity order is: Rh > Pd > Pt > Ru > Ir.•H2 promotes CO oxidation and the PROX activity order is: Pt > Pd > Rh > Ir > Ru.•This order is consistent with published CO + O activation energy trends from DFT.•CO oxidation competes with CO methanation on Rh and Ru catalysts above 200 °C.

PGM–CeO2 (PGM = Pt, Pd, Ir, Rh, Ru) catalysts were prepared by one-step solution combustion synthesis (SCS) and characterized by elemental analysis, N2 volumetry, aberration-corrected HRTEM, X-ray diffraction, and CO-DRIFTS. The samples, consisting of 2–6 nm metal nanoparticles supported on mesoporous ceria, were tested in CO oxidation in absence and presence of hydrogen (PROX). To our knowledge, this work presents the first comparison of all the platinum-group metals (except Os) for these reactions in the same conditions. The as-prepared SCS catalysts are active in CO oxidation and a reducing treatment has no significant effect on their performances. While the best catalyst in H2-free CO oxidation is Rh–CeO2, the addition of a high hydrogen excess decreases the Rh catalyst activity but enhances the CO oxidation rate on all other systems, including alumina-supported metals employed as reference catalysts. The resulting PROX turnover frequencies (Pt > Pd > Rh > Ir > Ru) follow the trends predicted by published density-functional-theory calculations considering the COad + Oad elementary reaction as the rate-determining step. Pt–CeO2 is not only the most active but also the most selective catalyst, reaching near 100% CO2 at low temperature (ca. 100 °C). The alumina-supported catalysts appeared less active than their ceria-supported counterparts in both reactions. The effect of heating/cooling cycles on the reaction kinetics was also investigated. Whereas the Pt, Pd and Ir ceria-supported catalysts were stable throughout PROX cycles, Rh and Ru ones exhibited apparently chaotic behaviors above ca. 200 °C, which are proposed to be induced by favorable CO dissociation and methanation pathways and/or variable metal oxidation states.

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Keywords
CO oxidation; PROX; Methanation; Platinum-group metals; Ceria; Solution combustion synthesis
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Trends in the CO oxidation and PROX performances of the platinum-group metals supported on ceria
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 253, 15 September 2015, Pages 106–114
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