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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>
Jeong, Beomgyun,Jeon, Hongrae,Toyoshima, Ryo,Crumlin, Ethan J.,Kondoh, Hiroshi,Mun, Bongjin Simon,Lee, Jaeyoung American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.4
<P>While model studies of surface science under ultrahigh vacuum (UHV) have made significant contributions to understanding electrochemistry, many issues related to electrochemical phenomena still remain unanswered due to the extreme environmental differences between UHV and liquid conditions. Electrochemical formic acid (HCOOH) oxidation is one such example. While the dehydration step in the indirect oxidation pathway (HCOOH → H<SUB>2</SUB>O + CO<SUB>ad</SUB> → 2H<SUP>+</SUP> + 2e<SUP>–</SUP> + CO<SUB>2</SUB>) is observed in the electrochemical oxidation of formic acid on Pt(111) surface, the surface science studies conducted in UHV condition reported the complete HCOOH dissociation to H<SUB>2</SUB> and CO<SUB>2</SUB> on Pt(111) surface with no adsorbed CO at room temperature. A dehydration mechanism may also exist in gas-phase HCOOH dissociation in some conditions different from UHV, but it has not been demonstrated with a surface science method due to pressure limitations. Using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), we observed the dehydration mechanism of gas-phase HCOOH in unprecedented high pressure environment for the first time. This study is a demonstration of reconciling the disagreement between electrocatalysis and surface science by bridging the environment gap.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-4/acs.jpcc.7b07735/production/images/medium/jp-2017-077355_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b07735'>ACS Electronic Supporting Info</A></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>
Yu, Youngseok,Koh, Yoobin Esther,Lim, Hojoon,Jeong, Beomgyun,Isegawa, Kazuhisa,Kim, Daehyun,Ueda, Kohei,Kondoh, Hiroshi,Mase, Kazuhiko,Crumlin, Ethan J,Ross Jr, Philip N,Gallet, Jean-Jacques,Bournel, Institute of Physics 2017 Journal of Physics, Condensed Matter Vol.29 No.46
<P>The study of CO oxidation on Pt(1 1 0) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure conditions, both the <I>α</I>-phase of PtO<SUB>2</SUB> oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to the exothermic nature of CO oxidation, the temperature of the Pt surface increases as CO oxidation takes place. As the CO/O<SUB>2</SUB> ratio increases, the production of CO<SUB>2</SUB> increases continuously and the surface temperature also increases. Interestingly, within the diffusion limited regions, the amount of surface oxide changes little while the chemisorbed oxygen is reduced.</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>