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Element selective oxidation on Rh-Pd bimetallic alloy surfaces
Kondoh, Hiroshi,Toyoshima, Ryo,Shirahata, Naoki,Hoda, Asami,Yoshida, Masaaki,Amemiya, Kenta,Mase, Kazuhiko,Mun, Bongjin Simon The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.45
<P>The interactions between oxygen and Rh-Pd bimetallic alloy surfaces were investigated using surface sensitive experimental techniques and density functional theory calculations. The alloy surfaces were oxidized under 10<SUP>−5</SUP> Torr and 100 mTorr oxygen upon heating above 250 °C. A thin Rh oxide layer was preferentially formed on a Rh1Pd9(100) surface, while a thin Pd oxide layer was formed on a Rh1Pd9(111) surface, though the Rh oxide is thermodynamically more stable irrespective of the surface orientation. Chemical analyses revealed that the initial Rh fraction for the (111) surface was significantly lower than that for the (100) surface, which suggests that the oxidized element on the surface is kinetically selected depending on the near surface initial composition.</P>
Toyoshima, Ryo,Yoshida, Masaaki,Monya, Yuji,Suzuki, Kazuma,Amemiya, Kenta,Mase, Kazuhiko,Mun, Bongjin Simon,Kondoh, Hiroshi The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.43
<P>We investigated the high-density CO adsorption phase formed on a Pt(111) surface when exposed to CO gas of pressure ranging from UHV to 100 mTorr using near-ambient-pressure (NAP)-XPS. Combined results from the NAP-XPS measurements and DFT calculations reveal the adsorption structure of CO molecules in the dense CO overlayer, which is stable under realistic conditions.</P> <P>Graphic Abstract</P><P>We investigated the high-density CO adsorption phase formed on a Pt(111) surface when exposed to CO gas of pressure ranging from UHV to 100 mTorr with near-ambient-pressure (NAP)-XPS. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp04318a'> </P>
Ueda, Kohei,Yoshida, Masaaki,Isegawa, Kazuhisa,Shirahata, Naoki,Amemiya, Kenta,Mase, Kazuhiko,Mun, Bongjin Simon,Kondoh, Hiroshi American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.3
<P>The nitric oxide (NO) reduction by carbon monoxide (CO) on Ir(111) surfaces under near ambient pressure conditions was studied by a combination of near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and mass spectrometry (MS), particularly paying attention to the dominant reaction pathway to formation of molecular nitrogen (N-2). Under a relatively low CO pressure condition (50 mTorr NO + 10 mTorr CO), two reaction pathways to form N-2 are clearly observed at different ignition temperatures (280 and 400 degrees C) and attributed to a reaction of NO adsorbed at atop site (NOatop) with atomic nitrogen (N-ad) and associative desorption of N-ad, respectively. Since the adsorption of NOatop is inhibited by CO adsorbed at atop site (COatop), the ignition of the NOatop + N-ad reaction strongly depends on the coverage of COatop; the ignition temperature shifts to higher temperature as increasing CO pressure. In contrast, for the Nad + Nad reaction the ignition temperature keeps almost constant (similar to 400 degrees C). The online MS results indicate that the latter reaction is the dominant pathway to N-2 formation and the, former one less contributes to N-2 formation with accompanying a small amount of nitrous oxide (N2O). No evidence for contribution of the isocyanate (NCO) species as an intermediate was observed in the operando NAP-XP spectra.</P>