Ethylene hydrogenation catalysis on Pt(111) single-crystal surfaces studied by using mass spectrometry and in situ infrared absorption spectroscopy

Tillekaratne, Aashani; Simonovis, Juan Pablo; Zaera, Francisco

doi:10.1016/j.susc.2015.11.005

Cited by 25 publications

(21 citation statements)

References 87 publications

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“…A long-travel manipulator is used to transfer the sample between this main analytical tier of the UHV chamber and a second level set up to carry out RAIRS experiments. The arrangement used for this technique is similar to that of another instrument available in our laboratory for catalytic studies. ,, The IR beam from a Bruker Tensor 27 Fourier-transform infrared (FTIR) spectrometer is directed through a polarizer and a NaCl window into the UHV environment and focused at grazing incidence (∼85° from the surface normal) onto the sample by using a spherical mirror (ϕ = 3 in., f = 6 in.). The reflected beam is then collected by a second spherical mirror (after going through a second NaCl window) and focused onto a narrow-band mercury–cadmium–telluride (MCT) detector.…”

Section: Methodsmentioning

confidence: 99%

Chemistry of Ruthenium Diketonate Atomic Layer Deposition (ALD) Precursors on Metal Surfaces

Qin

Zaera

2018

J. Phys. Chem. C

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The thermal chemistry of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd) 3 ), a potential precursor for the chemical deposition of ruthenium -containing films, on Ni(110) single-crystal surfaces was characterized by using a combination of temperatureprogrammed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and reflection−absorption infrared spectroscopy (RAIRS). Additional characterization of the surface chemistry of the protonated ligand, Htmhd, was evaluated as well for reference. It was found that the molecularly adsorbed ruthenium compound reacts readily by approximately 310 K, loosing its ligands to both the gas phase and the surface as the central ion is reduced to its Ru 0 metallic state. The diketonate ligand, now bonded to the nickel surface, starts to decompose at around 400 K, and generates gas-phase carbon monoxide and molecular hydrogen in TPD peaks at 435 K. More extensive decomposition is seen at 535 K, yielding 2,2-dimethyl-3oxopentanal, isobutene, ketene, and carbon monoxide, and also carbon dioxide and molecular hydrogen at slightly higher temperatures. The XPS data corroborate the early reduction of the metal center and the losses of carbon-and oxygen-containing adsorbates to the gas phase, and the RAIRS traces show similar chemistry followed by the Ru complex and the free ligand, both converting via an initial decarbonylation step and a subsequent loss of the terminal tert-butyl groups. The early decomposition of the ligand on the metal surface points to potential problems with the clean deposition of metal films using diketonate complexes, but the ease with which those ligands are displaced from the central ion suggests that there is a potential for low-temperature film deposition chemistry under specific circumstances.

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Section: Methodsmentioning

confidence: 99%

Chemistry of Ruthenium Diketonate Atomic Layer Deposition (ALD) Precursors on Metal Surfaces

Qin

Zaera

2018

J. Phys. Chem. C

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“…The experiments reported here were all carried out in a UHV chamber equipped with several techniques for the cleaning and characterization of the surface as well as with a catalytic reactor where kinetic measurements can be carried out. The details of this instrumentation and the procedures used for the experiments are discussed in detail in previous publications. , Briefly, a platinum single crystal cut in the (111) orientation was mounted on a manipulator used for sample transfer between the two stages of the instrument and for surface alignment, and also for controlled cooling or heating to any temperature between approximately 100 and 1100 K (as measured using a chromel–alumel thermocouple spotwelded to the side). Most of the initial surface cleaning and preparation of this crystal was carried out before each experiment in the main UHV chamber, which is equipped with an ion gun for surface sputtering, a mass spectrometer for the analysis of the gas composition, and a set of controlled leak valves for gas dosing.…”

Section: Methodsmentioning

confidence: 99%

The Role of Carbonaceous Deposits in Hydrogenation Catalysis Revisited

2017

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The effect of carbonaceous deposits on the performance of Pt(111) surfaces as catalysts for the hydrogenation of ethylene was tested by decoupling their preparation, which was done beforehand in an ultrahigh vacuum (UHV) environment, from the catalytic runs, which were carried out in an enclosed "high pressure" cell. The time evolution of the gas composition during reaction was followed continuously by mass spectrometry, and the nature of the surface species was determined by in situ reflection−absorption infrared absorption spectroscopy (RAIRS). Reaction rates were seen to vary by up to approximately 40% depending on the type of molecules preadsorbed at room temperature, with the maximum activity seen with a propylidyne layer, the result of propylene adsorption. The rate with ethylidyne-covered Pt( 111) is reduced by ∼20%, with butylidyne by ∼35%, and with benzyl moieties by ∼40%. These changes are reversible: the surface regains the activity expected when starting with the clean substrate after one or two catalytic runs to full conversion. RAIRS data show that this is because the initial species are slowly replaced by a new layer of the adsorbate that forms with the olefin in the reaction mixture (ethylidyne for ethylene hydrogenation). More significant changes are seen if the adsorbed layers are dehydrogenated at higher temperatures: the turnover frequencies for ethylene hydrogenation are reduced by more than an order of magnitude upon the conversion of propylidyne to C n H(ads) species, by annealing at temperatures between 500 and 650 K. Some activity is regained upon annealing to even higher temperatures, presumably because of the formation of graphitic layers, which have a smaller footprint on the surface. It was concluded that although the main role of carbonaceous deposits in catalytic hydrogenations is to block surface sites, their influence is also affected by the reversibility of their bonding to the surface in a hydrogenation atmosphere and by the structure of their carbon skeleton.

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“…Typical data from such experiments are reported in the left panel of Figure , in this case for a D 2 :C 2 D 4 40:1 ratio and a total flux of 8000 ML/s (top, red trace). A second mass spectrum (bottom, blue trace) is reported for comparison, from a more conventional experiment carried out by using a so-called high-pressure cell, which is used to isolate the Pt surface from the UHV environment and enclose it in a small volume that can be pressurized and used as a batch reactor. , The fact that both deuteration and H–D isotope scrambling take place in both of these experiments is immediately apparent by the detection of significant signal intensities all the way to 36 amu. On the other hand, the final product distributions are clearly different in each case.…”

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Direct Addition Mechanism during the Catalytic Hydrogenation of Olefins over Platinum Surfaces

Dong

Ebrahimi

Tillekaratne

et al. 2016

J. Phys. Chem. Lett.

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The mechanism of the hydrogenation of olefins catalyzed by metal surfaces was probed by using isotope labeling in conjunction with a high-flux effusive molecular beam setup capable of sustaining steady-state conversion under well-controlled ultrahigh vacuum (UHV). The unique conditions afforded by this instrument, namely, a single collision regime and impinging frequencies equivalent to pressures in the mTorr range, led to the clear identification of two competing pathways: a multiple H-D isotope exchange channel explained by the well-known Horiuti-Polanyi mechanism but with an unusually high probability for β-hydride elimination from the alkyl surface intermediate (versus its reductive elimination to the alkane), and a direct addition route that produces dideuterated alkanes selectively. The latter may follow an Eley-Rideal mechanism involving an adsorbate (either the olefin or the hydrogen/deuterium atoms resulting from dissociative adsorption of H2/D2) and a gas-phase molecule (the other reactant), or, alternatively, it could reflect the limited diffusion of the hydrogen atoms on the surface under catalytic conditions because of site blocking by the islands of strongly bonded carbonaceous (alkylidyne) layers present during catalysis. Regardless, our data clearly show that the distribution of alkane isotopologues obtained from the conversion of olefins with deuterium can deviate significantly from statistical expectations.

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Ethylene hydrogenation catalysis on Pt(111) single-crystal surfaces studied by using mass spectrometry and in situ infrared absorption spectroscopy

Cited by 25 publications

References 87 publications

Chemistry of Ruthenium Diketonate Atomic Layer Deposition (ALD) Precursors on Metal Surfaces

Chemistry of Ruthenium Diketonate Atomic Layer Deposition (ALD) Precursors on Metal Surfaces

The Role of Carbonaceous Deposits in Hydrogenation Catalysis Revisited

Direct Addition Mechanism during the Catalytic Hydrogenation of Olefins over Platinum Surfaces

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