TY - JOUR

T1 - Near-ambient pressure xps and ms study of co oxidation over model pd-au/hopg catalysts: The effect of the metal ratio

AU - Bukhtiyarov, Andrey V.

AU - Prosvirin, Igor P.

AU - Panafidin, Maxim A.

AU - Fedorov, Alexey Yu

AU - Klyushin, Alexander Yu

AU - Knop-Gericke, Axel

AU - Zubavichus, Yan V.

AU - Bukhtiyarov, Valery I.

N1 - Funding Information: Funding: This work was performed within the framework of the budget project of the Ministry of Science and Higher Education of the Russian Federation for the Synchrotron Radiation Facility SKIF, Boreskov Institute of Catalysis. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2021/12

Y1 - 2021/12

N2 - In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite (HOPG)-supported bimetallic Pd-Au catalysts towards the CO oxidation based on the Pd/Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd/Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu-2 sample with a lower Pd/Au surface ratio (~0.75) was already active at temperatures less than 150◦C, while the PdAu-1 sample with a higher Pd/Au surface ratio (~1.0) became active only at temperatures above 200◦C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near-surface regions of the two-component Pd-Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd/Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near-surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmosphere.

AB - In this study, the dependence of the catalytic activity of highly oriented pyrolytic graphite (HOPG)-supported bimetallic Pd-Au catalysts towards the CO oxidation based on the Pd/Au atomic ratio was investigated. The activities of two model catalysts differing from each other in the initial Pd/Au atomic ratios appeared as distinctly different in terms of their ignition temperatures. More specifically, the PdAu-2 sample with a lower Pd/Au surface ratio (~0.75) was already active at temperatures less than 150◦C, while the PdAu-1 sample with a higher Pd/Au surface ratio (~1.0) became active only at temperatures above 200◦C. NAP XPS revealed that the exposure of the catalysts to a reaction mixture at RT induces the palladium surface segregation accompanied by an enrichment of the near-surface regions of the two-component Pd-Au alloy nanoparticles with Pd due to adsorption of CO on palladium atoms. The segregation extent depends on the initial Pd/Au surface ratio. The difference in activity between these two catalysts is determined by the presence or higher concentration of specific active Pd sites on the surface of bimetallic particles, i.e., by the ensemble effect. Upon cooling the sample down to room temperature, the reverse redistribution of the atomic composition within near-surface regions occurs, which switches the catalyst back into inactive state. This observation strongly suggests that the optimum active sites emerge under reaction conditions exclusively, involving both high temperature and a reactive atmosphere.

KW - Adsorption-induced segregation

KW - Bimetallic Pd-Au nanoparticles

KW - CO oxidation

KW - NAP XPS

UR - http://www.scopus.com/inward/record.url?scp=85120640464&partnerID=8YFLogxK

U2 - 10.3390/nano11123292

DO - 10.3390/nano11123292

M3 - Article

C2 - 34947641

AN - SCOPUS:85120640464

VL - 11

JO - Nanomaterials

JF - Nanomaterials

SN - 2079-4991

IS - 12

M1 - 3292

ER -