Adsorption of acetylene and ethylene on a clean Ir(111) surface

Marinova, Ts.; Kostov, Konstantin

doi:10.1016/0039-6028(87)90206-8

Cited by 116 publications

(74 citation statements)

References 27 publications

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“…6, the experimental data can be fitted well using three sets of iridium components. Taking the 4f 7/2 spectra as an example, the component with the lowest binding energy of 60.9 eV (blue) is determined to be Ir, 53 consistent with the existence of Ir impurity in the XRD pattern (see Fig. S1 in Supplemental Material).…”

Section: 49mentioning

confidence: 79%

Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridateY2Ir2O7

et al. 2014

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Pyrochlore iridates have recently attracted growing interest in condensed matter physics because of their potential for realizing new topological states. In order to achieve such quantum states, it is essential to understand the magnetic properties of these compounds, as their electronic structures are strongly coupled with their magnetic ground states. In this work, we report a systematic study of the magnetic properties of pyrochlore Y 2 Ir 2 O 7 and its hole-doped compounds by performing magnetic, electron spin resonance (ESR), electrical transport and x-ray photoelectron spectroscopy (XPS) measurements. We demonstrate the existence of weak ferromagnetism on top of a large antiferromagnetic background in the undoped compound. Hole-doping by calcium was found to enhance both the ferromagnetism and the electrical conductivity. The XPS characterization shows the coexistence of Ir 4+ and Ir 5+ in the undoped compound, and the amount of Ir 5+ increases with Ca-doping, which highlights the possible origins of the weak ferromagnetism associated with the formation of Ir 5+ . We also observe a vertical shift in the M -H curves after field cooling, which may arise from a strong coupling between the ferromagnetic phase and the antiferromagnetic background.

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Section: 49mentioning

confidence: 79%

Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridateY2Ir2O7

et al. 2014

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“…[16], showing that the adsorptive species on Ir (111) can be well detected by high resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy. Interestingly, the researchers also found that at T [ 180°C (450 K) the saturated coverage after C 2 H 4 exposure was higher than that at 27°C (300 K); the proposed mechanism was the formations of new polymer species from ethylene on the catalyst surface at high temperatures ([180°C), which were absent in C 2 H 4 adsorption at ambient temperature (27°C) [16]. This previous result indicated that oligomers of ethylene and aromatic structures can be formed before ethylene desorption from the catalyst surface under relatively high temperatures.…”

Section: Drifts Analysis Of Ethanol Adsorption and Dehydrationmentioning

confidence: 98%

“…The weak bands observed at 905 cm -1 (terminal alkene) and 951 cm -1 are related to the twist and bend modes of the ethylene structure, respectively, and the band at 1850 cm -1 can be attributed to the overtone frequency of the out-of-plane bend of ethylene structure [14]. [16], showing that the adsorptive species on Ir (111) can be well detected by high resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy. Interestingly, the researchers also found that at T [ 180°C (450 K) the saturated coverage after C 2 H 4 exposure was higher than that at 27°C (300 K); the proposed mechanism was the formations of new polymer species from ethylene on the catalyst surface at high temperatures ([180°C), which were absent in C 2 H 4 adsorption at ambient temperature (27°C) [16].…”

Section: Drifts Analysis Of Ethanol Adsorption and Dehydrationmentioning

confidence: 99%

A DRIFTS Study of Catalyzed Dehydration of Alcohols by Alumina-supported Heteropoly Acid

Cheng

2009

Catal Lett

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Selectively catalyzed dehydration of ethanol, 1,2-propylene glycol, and glycerol on supported heteropoly acid (HPA) was studied using transient diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). Tungstosilicic acid (H 4 [SiW 12 O 40 ] denoted as H 4 SiW), supported on neutral mesoporous alumina as a catalyst, was studied to investigate the formation of intermediate products and desired dehydration products on the catalyst surface. Both ethylene-containing species and surfacebound carboxyl species were detected for all three alcohols. The formation of ethylene was promoted at lower temperatures while an increased reaction temperature facilitated the formation of acetate products when ethanol was used. When 1,2-propylene glycol was used, surfacebound carboxyl species were found as major intermediate products; these might have formed from propanal produced from the hydration reaction catalyzed by acid sites on HPA. Intermediate species from more complicated reactions were detected on the catalyst surface when glycerol was used, including aldehyde, surface-bound carboxyl species, and alkene species. The results indicated that acid dehydration might be facilitated either by the addition of water or lowering the reaction temperature. The work provides insight into reaction pathways for bio-polyols, and therefore is informative for designing cost-effective and efficient chemical catalysis systems for the conversion of bio-renewables.

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“…TPD spectra for desorption of H 2 from hydrogen-dosed Ir(210), and desorption of H 2 from acetylene-dosed Ir(210) exhibit differences that indicate clearly that desorption of H 2 from C 2 H 2 -dosed Ir is reaction-rate limited (W.C., I.E., Q.W., and T.E.M., unpublished data). This reactivity is almost certainly caused by formation of intermediate fragments (30,31) that may dissociate in a stepwise fashion on heating (ϪCCH? ϪCCH 3 ?…”

Section: Synchrotron Radiation Studies Of Metals On Wmentioning

confidence: 99%

Nanoscale surface chemistry

Madey

Pelhos

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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We report evidence in several experiments for nanometer-size effects in surface chemistry. The evidence concerns bimetallic systems, monolayer films of Pt or Pd on W(111) surfaces. Pyramidal facets with {211} faces are formed on annealing on physical monolayer of Pt, Pd on a W(111) substrate, and facet sizes increase with annealing temperature. We used synchrotron radiation-based soft x-ray photoemission to show that monolayer films of Pt, Pd, on W ''float'' on the outer surface, whereas multilayer films form alloys on annealing. Acetylene reactions over bimetallic planar and faceted Pd͞W surfaces exhibit size effects on the nanometer scale, that is, thermal desorption spectra of reactively formed benzene and ethylene (after acetylene adsorption) change systematically with facet size. In the second case, the decomposition of C 2H2 over planar and faceted Ir(210) surfaces also exhibits structure sensitivity; temperature programmed desorption of H 2 from C2H2 dissociation depends on the nanoscale surface structure. Finally, we have characterized interactions of Cu with the highly ordered S(4 ؋ 4)͞W(111) surface. The substrate is a sulfur-induced nanoscale reconstruction of W(111) with (4 ؋ 4) periodicity, having broad planar terraces (Ϸ30 nm in width). Fractional monolayers of vapordeposited Cu grow as threedimensional clusters on the S(4 ؋ 4) surface over a wide coverage range. At low Cu coverage (< 0.1 ML), Cu nanoclusters nucleate preferentially at characteristic 3-fold hollow sites; we find a clear energetic preference for one type of site over others, and evidence for self-limiting growth of nanoclusters.A n important issue in surface chemistry and catalysis is how surface structures and features with nanometer dimensions affect reactivity in heterogeneous systems (1-3). The focus of our work has been on several aspects of nanoscale phenomena that influence surface chemistry, including faceting of metallic and model bimetallic catalyst surfaces, and nucleation of subnanometer metallic clusters on sulfided surfaces. We study atomically rough substrates [bcc (111) surface of W, and fcc (210) surface of Ir] that are morphologically unstable, that is, the initially planar substrate becomes covered with nanoscale facets when covered with monolayer films of gases or other metals, and heated to elevated temperature. Major objectives of this work have been (i) to determine how the surface transition from planar to faceted affects the surface reactivity of metallic and bimetallic systems, and (ii) to characterize the nucleation and growth of metals on sulfided W surfaces. The three main components of this effort are surface structure, surface chemistry, and surface electronic properties.The importance of bimetallic catalysts based on Pt-group metals has been increasing in recent decades (4, 5). These catalysts display important advantages over classical reforming catalysts, including better stability, as well as improved activity and selectivity. In particular, refractory metals (W, Mo, Re, . . .) in combination with ...

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Adsorption of acetylene and ethylene on a clean Ir(111) surface

Cited by 116 publications

References 27 publications

Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridateY2Ir2O7

Enhanced weak ferromagnetism and conductivity in hole-doped pyrochlore iridateY2Ir2O7

A DRIFTS Study of Catalyzed Dehydration of Alcohols by Alumina-supported Heteropoly Acid

Nanoscale surface chemistry

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