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R Imbihl - One of the best experts on this subject based on the ideXlab platform.
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tuning excitability by alloying the rh 111 ni h2 o2 system
Physical Chemistry Chemical Physics, 2016Co-Authors: Tim Smolinsky, Mathias Homann, R ImbihlAbstract:The dynamic behavior of the O2 + H2 reaction on a Rh(111) surface alloyed with Ni has been studied in the 10−5 mbar range using photoemission electron microscopy (PEEM) as a spatial resolving method. For T = 773 K and p(O2) = 5 × 10−5 mbar the bifurcation diagram has been mapped out as a function of the Ni coverage in a range of 0 ML ≤ ΘNi ≥ 1.3 ML. A critical Ni coverage of ΘNi,crit = 0.13 monolayers (ML) is required for excitability. In the excitable parameter range pulse trains and irregular Chemical Wave patterns are found. Whereas the propagation speed of the pulses exhibits no clear-cut dependence on the Ni coverage, the frequency of the local PEEM intensity oscillations increases linearly with Ni coverage in the range from ΘNi = 0.13 ML to ΘNi = 1.3 ML.
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Chemical Waves and rate oscillations in the h2 o2 reaction on a bimetallic rh 111 ni catalyst
Journal of Physical Chemistry C, 2012Co-Authors: Florian Lovis, Andrea Locatelli, Tim Smolinsky, Miguel Angel Nino, R ImbihlAbstract:Self-organization phenomena such as rate oscillations, Chemical Wave patterns, and precipitation of nanoparticles can be observed in the catalytic H2 + O2 reaction on a Rh(111) surface after alloying with Ni. The bimetallic Rh(111)/Ni surface has been studied in the 10–6–10–4 mbar range using PEEM (photoemission electron microscopy) and LEEM/SPELEEM (low energy electron microscopy and its spectroscopic variant) as the main analytical methods. The Rh(111)/Ni catalysts are prepared by thermal decomposition of Ni(CO)4 on Rh(111), resulting in an alloyed surface with about 25% Ni in the topmost layers. One finds rate oscillations and Chemical Wave patterns comprising target patterns, pulse trains, and rotating spiral Waves. The oscillatory behavior is attributed to periodic changes in the composition of the bimetallic surface alloy causing concomitant variations in catalytic activity. Under pattern-forming reaction conditions, three-dimensional NiO particles develop on top of the alloyed Rh/Ni surface, with d...
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square Chemical Waves in the catalytic reaction no h2 on a rhodium 110 surface
Nature, 1994Co-Authors: Florian Mertens, R ImbihlAbstract:IT WAS realized as early as 19061 that coupling between an autocatalytic reaction and the diffusion of the autocatalytic component can give rise to a propagating reaction front—a Chemical Wave. Chemical Waves have been studied intensively in fluid-phase reaction–diffusion systems2, but in recent years a variety of spatiotemporal patterns has also been observed for oscillatory reactions on single-crystal surfaces3,4. One important new aspect that has been introduced by these studies is that of anisotropic diffusion, as a consequence of the fixed surface geometry on which the diffusion of the adsorbed particles takes place. Here we report the observation of a transition from elliptical to square-shaped concentric Chemical Waves in the reaction of NO and H2 on a rhodium(HO) surface. The elliptical pattern is characteristic of simple anisotropic diffusion, but we attribute the origin of the square pattern to a state-dependent anisotropy—that is an anisotropy that varies along the Wave profile as changes in the adsorbate coverage generate different reconstructions of the substrate structure. This interplay between diffusional anisotropy and the state of the system can be expected to be quite general and to give rise to new varieties of oscillatory patterning.
Tim Smolinsky - One of the best experts on this subject based on the ideXlab platform.
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tuning excitability by alloying the rh 111 ni h2 o2 system
Physical Chemistry Chemical Physics, 2016Co-Authors: Tim Smolinsky, Mathias Homann, R ImbihlAbstract:The dynamic behavior of the O2 + H2 reaction on a Rh(111) surface alloyed with Ni has been studied in the 10−5 mbar range using photoemission electron microscopy (PEEM) as a spatial resolving method. For T = 773 K and p(O2) = 5 × 10−5 mbar the bifurcation diagram has been mapped out as a function of the Ni coverage in a range of 0 ML ≤ ΘNi ≥ 1.3 ML. A critical Ni coverage of ΘNi,crit = 0.13 monolayers (ML) is required for excitability. In the excitable parameter range pulse trains and irregular Chemical Wave patterns are found. Whereas the propagation speed of the pulses exhibits no clear-cut dependence on the Ni coverage, the frequency of the local PEEM intensity oscillations increases linearly with Ni coverage in the range from ΘNi = 0.13 ML to ΘNi = 1.3 ML.
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Chemical Waves and rate oscillations in the h2 o2 reaction on a bimetallic rh 111 ni catalyst
Journal of Physical Chemistry C, 2012Co-Authors: Florian Lovis, Andrea Locatelli, Tim Smolinsky, Miguel Angel Nino, R ImbihlAbstract:Self-organization phenomena such as rate oscillations, Chemical Wave patterns, and precipitation of nanoparticles can be observed in the catalytic H2 + O2 reaction on a Rh(111) surface after alloying with Ni. The bimetallic Rh(111)/Ni surface has been studied in the 10–6–10–4 mbar range using PEEM (photoemission electron microscopy) and LEEM/SPELEEM (low energy electron microscopy and its spectroscopic variant) as the main analytical methods. The Rh(111)/Ni catalysts are prepared by thermal decomposition of Ni(CO)4 on Rh(111), resulting in an alloyed surface with about 25% Ni in the topmost layers. One finds rate oscillations and Chemical Wave patterns comprising target patterns, pulse trains, and rotating spiral Waves. The oscillatory behavior is attributed to periodic changes in the composition of the bimetallic surface alloy causing concomitant variations in catalytic activity. Under pattern-forming reaction conditions, three-dimensional NiO particles develop on top of the alloyed Rh/Ni surface, with d...
Florian Lovis - One of the best experts on this subject based on the ideXlab platform.
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Chemical Waves and rate oscillations in the h2 o2 reaction on a bimetallic rh 111 ni catalyst
Journal of Physical Chemistry C, 2012Co-Authors: Florian Lovis, Andrea Locatelli, Tim Smolinsky, Miguel Angel Nino, R ImbihlAbstract:Self-organization phenomena such as rate oscillations, Chemical Wave patterns, and precipitation of nanoparticles can be observed in the catalytic H2 + O2 reaction on a Rh(111) surface after alloying with Ni. The bimetallic Rh(111)/Ni surface has been studied in the 10–6–10–4 mbar range using PEEM (photoemission electron microscopy) and LEEM/SPELEEM (low energy electron microscopy and its spectroscopic variant) as the main analytical methods. The Rh(111)/Ni catalysts are prepared by thermal decomposition of Ni(CO)4 on Rh(111), resulting in an alloyed surface with about 25% Ni in the topmost layers. One finds rate oscillations and Chemical Wave patterns comprising target patterns, pulse trains, and rotating spiral Waves. The oscillatory behavior is attributed to periodic changes in the composition of the bimetallic surface alloy causing concomitant variations in catalytic activity. Under pattern-forming reaction conditions, three-dimensional NiO particles develop on top of the alloyed Rh/Ni surface, with d...
Norbert Kruse - One of the best experts on this subject based on the ideXlab platform.
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Chemical Wave propagation and rate oscillations during the no2 h2 reaction over pt
Ultramicroscopy, 1998Co-Authors: Christian Voss, Norbert KruseAbstract:Abstract We have studied the catalytic reduction of NO 2 with hydrogen on Pt tips by means field ion microscopy (FIM) and have observed kinetic instabilities like explosive ignitions of the reaction as well as self-sustained rate oscillations under certain conditions of temperature and pressure. These phenomena were found to occur at the apex of a Pt tip that resembled a top- and edge-truncated pyramid rather than a hemisphere. The pacemakers of the oscillations were identified to be the “corner” {0 1 2} planes which were most likely reconstructed under reaction conditions. Clear evidence was obtained that the communication mechanism between successively igniting {0 1 2} planes is based on surface reaction/diffusion. One-dimensional Wavefronts were observed to move along the 〈2 1 1〉 zone lines. For increasing hydrogen pressures and decreasing temperatures rate oscillations took also place on Pt(0 0 1). Reaction Waves were triggered by defects or small Pt clusters atop of this plane. While the frequency of the oscillations ( f =1.1 Hz) was stable over hundreds of cycles, the amplitudes were found to vary quite strongly even on a short time scale.
Miguel Angel Nino - One of the best experts on this subject based on the ideXlab platform.
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Chemical Waves and rate oscillations in the h2 o2 reaction on a bimetallic rh 111 ni catalyst
Journal of Physical Chemistry C, 2012Co-Authors: Florian Lovis, Andrea Locatelli, Tim Smolinsky, Miguel Angel Nino, R ImbihlAbstract:Self-organization phenomena such as rate oscillations, Chemical Wave patterns, and precipitation of nanoparticles can be observed in the catalytic H2 + O2 reaction on a Rh(111) surface after alloying with Ni. The bimetallic Rh(111)/Ni surface has been studied in the 10–6–10–4 mbar range using PEEM (photoemission electron microscopy) and LEEM/SPELEEM (low energy electron microscopy and its spectroscopic variant) as the main analytical methods. The Rh(111)/Ni catalysts are prepared by thermal decomposition of Ni(CO)4 on Rh(111), resulting in an alloyed surface with about 25% Ni in the topmost layers. One finds rate oscillations and Chemical Wave patterns comprising target patterns, pulse trains, and rotating spiral Waves. The oscillatory behavior is attributed to periodic changes in the composition of the bimetallic surface alloy causing concomitant variations in catalytic activity. Under pattern-forming reaction conditions, three-dimensional NiO particles develop on top of the alloyed Rh/Ni surface, with d...