期刊
TOPICS IN CATALYSIS
卷 56, 期 15-17, 页码 1299-1313出版社
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s11244-013-0140-0
关键词
Palladium; Rhodium; Platinum; CO oxidation; Active surface; Surface oxide; Chemisorbed oxygen; In situ characterization
资金
- National Basic Research Program of China (973 Program) [2010CB732303, 2013CB933102]
- Major Project of Chinese Ministry of Education [309019]
- National Natural Science Foundation of China [20923004, 21033006, 21073149, 21273178]
- Program for Changjiang Scholars and Innovative Research Team in University [IRT1036]
- PhD Programs Foundation of Chinese Ministry of Education [20110121110010]
This mini review summaries recent works on identifying the active surfaces for CO oxidation on Pd, Pt, and Rh under oxygen rich conditions. A significantly high reaction rate for CO oxidation under oxygen rich conditions has been observed. Results using in situ characterization methods of ambient scanning tunneling microscope, surface X-ray diffraction, ambient pressure X-ray photoemission spectroscopy, X-ray absorption spectroscopy, and infrared reflection adsorption spectroscopy (IRAS), were included. Most X-ray related methods reveal that the achievements of the high reaction rates for CO oxidation on Pd, Pt, and Rh under oxygen rich conditions are accompanied with the appearance of oxides on the surface, leading to that the oxide phase is considered to be the active surface. In contrast, recent in situ IRAS results conclude that a chemisorbed oxygen covered metallic surface is the active surface. Kinetic data support that the reaction on the metallic surfaces can reach the high rate, e.g. a mass-transfer limit turnover frequency, without the necessity of the presence of oxide. Therefore, we point out that the appearance of oxides on Pt-group metals during CO oxidation is possibly due to the transfer-limit of CO gas, resulting in exposing the catalyst surface to an ambient atmosphere much richer in oxygen and thus building-up the oxide. Moreover, photons in X-ray related experiments may aid to overcome the formation barrier of oxide on a chemisorbed oxygen covered metallic surface. The formation of oxide is also affected by the mass-transfer properties of the in situ reaction cells. If the amount of incoming CO molecules under the mass-transfer limit of CO is high enough, the build-up of oxide may be precluded being consumed by reacting with CO.
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