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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>
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>
Adsorption and Reaction of CO and NO on Ir(111) Under Near Ambient Pressure Conditions
Ueda, K.,Suzuki, K.,Toyoshima, R.,Monya, Y.,Yoshida, M.,Isegawa, K.,Amemiya, K.,Mase, K.,Mun, B. S.,Arman, M. A. Springer Science + Business Media 2016 Topics in catalysis Vol.59 No.5
<P>The adsorption and reaction of CO and NO on Ir(111) have been studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) together with low-energy electron diffraction, scanning tunneling microscopy, and mass spectroscopy (MS). Under both ultrahigh vacuum (UHV) and NAP conditions CO molecules occupy on-top sites of the Ir(111) surface at room temperature (RT) by forming two-dimensional clusters. Exposure to NO under UHV conditions at RT induces partially dissociative adsorption, while NAP NO exposure leads to a Ir(111) surface that is covered by molecular NO. We conducted in-operando NAP-XPS/MS observation of the NO + (CO)-C-13 reaction under a NAP condition as a function of temperature. Below 210 degrees C adsorption of NO is inhibited by CO, while above 210 degrees C the CO inhibition is released due to partial desorption of CO and dissociative adsorption of NO starts to occur leading to associative formation of N-2. Under the most active condition studied here the Ir surface is covered by a dense co-adsorption layer consisting of on-top CO, atomic N and O, which suggests that this reaction is not a NO-dissociation-limited process but a N-2/CO2 formation-limited process.</P>