The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces

The adsorption, desorption, exchange, and equilibration reactions of hydrogen and deuterium on a platinum filament have been investigated by thermal desorption mass spectrometry. A surface saturated with hydrogen at 120 °K has a coverage 4.2 × 1014 molecules cm−2 and gives desorption spectra with four distinct peaks: β1,(165 °K), β2(220 °K), β3(280 °K), and β4(350 °K). Apparent activation energies and pre-exponential factors were determined for the β2-, β3-, and β4-peaks. For both co-adsorption and sequential adsorption of H2 and D2 the mass 2, 3, and 4 desorption spectra have identical shapes and the gas desorbs at equilibrium throughout. It is concluded that hydrogen adsorbs dissociatively. Exchange and equilibration were studied at 120, 210, and 285 °K by determining the surface composition and isotope distribution after varying fractions of preadsorbed H had been replaced. Following exchange at 120 °K the desorption spectra show a higher D content and a lack of equilibrium in the desorbing gas at low temperature. In most other experiments the mass 2,3, and 4 desorption spectra had identical shapes and the gas desorbed at equilibrium. The results are interpreted by a model which requires that the polycrystalline platinum surface is intrinsically heterogeneous. It appears that different mechanisms are unnecessary to interpret the differences in kinetics observed for exchange and equilibration at low temperatures.

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ChemInform Abstract: THE ADSORPTION, DESORPTION AND EXCHANGE REACTIONS OF OXYGEN, HYDROGEN, AND WATER ON PLATINUM SURFACES PART 1, OXYGEN INTERACTION

Chemischer Informationsdienst ◽

10.1002/chin.197503041 ◽

1975 ◽

Vol 6 (3) ◽

pp. no-no

Author(s):

Y. K. PENG ◽

P. T. DAWSON

Keyword(s):

Exchange Reactions ◽

Platinum Surfaces ◽

Adsorption Desorption ◽

Oxygen Interaction

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The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces IV. field emission studies on the adsorption of water, hydrogen and the reaction between hydrogen and adsorbed oxygen

Surface Science Letters ◽

10.1016/0167-2584(80)90701-x ◽

1980 ◽

Vol 92 (1) ◽

pp. A45

Author(s):

P.T. Dawson ◽

Y.K. Peng

Keyword(s):

Field Emission ◽

Adsorbed Oxygen ◽

Exchange Reactions ◽

Platinum Surfaces ◽

Adsorption Of Water ◽

Adsorption Desorption ◽

Emission Studies ◽

Water Hydrogen

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Modelling stream water chemistry with snowmelt

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1984.0068 ◽

1984 ◽

Vol 305 (1124) ◽

pp. 427-439 ◽

Cited By ~ 50

Keyword(s):

Ion Exchange ◽

Water Chemistry ◽

Seasonal Variations ◽

Stream Water ◽

Acid Precipitation ◽

Exchange Reactions ◽

Stream Water Chemistry ◽

Reservoir Models ◽

Southern Norway ◽

Adsorption Desorption

Simple hydrochemical reservoir models based on the mobile anion concept are described for the Birkenes and Storgam a catchments in southern Norway with acidified stream water. Key processes modelled include water routing, sulphate adsorption-desorption, ion-exchange reactions, weathering and a gibbsite equilibrium condition. The models reproduce much of the daily and seasonal variations in stream water chemistry which have been observed over several years. Model considerations have been used in an attempt to explain the acidification of stream water in these two areas. It is hypothesized that soil acidification has occurred and that acid precipitation is at least partly responsible. The results are tentative largely because the models are derived from present-day stream water chemistry.

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The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces. III. Water adsorption and exchange with oxygen and hydrogen

Canadian Journal of Chemistry ◽

10.1139/v77-234 ◽

1977 ◽

Vol 55 (10) ◽

pp. 1658-1666 ◽

Cited By ~ 7

Author(s):

Y. K. Peng ◽

P. T. Dawson

Keyword(s):

Exchange Reaction ◽

Hydrogen Adsorption ◽

High Vacuum ◽

Adsorbed Water ◽

Ultra High Vacuum ◽

Exchange Reactions ◽

Adsorption Of Water ◽

Apparent Activation Energies ◽

Distribution Studies ◽

Adsorption Desorption

Ultra-high vacuum thermal desorption experiments have been carried out on the adsorption of water, and the D2O/H and D216O/18O exchange reactions on platinum previously characterized by oxygen and hydrogen adsorption studies. Water is weakly adsorbed and only at T < 150 K, an observation confirmed by using H2 adsorption as a chemical probe for the presence of adsorbed water. The thickness of the adsorbed D2O layers was determined by a novel method involving monitoring the power output of the temperature programmer. Exchange occurs between adsorbed H and a D2O overlayer and the extent of exchange increases with the thickness of the overlayer. Isotope distribution studies show that the surface is heterogeneous and the exchange reaction does not occur at uniform rate. Exchange occurs between adsorbed 18O and a D216O overlayer. The extent of exchange is constant up to T ∼ 300 K showing that D2O is more strongly bound on O-covered Pt presumably as a result of H bonding. Heterogeneity also is apparent in the O-exchange reaction. The apparent activation energies for exchange are 1.8 and 2.9 kcal mol−1 for the half- and fully-covered surfaces, respectively.

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The Adsorption, Desorption, and Exchange Reactions of Oxygen, Hydrogen, and Water on Platinum Surfaces. I. Oxygen Interaction

Canadian Journal of Chemistry ◽

10.1139/v74-521 ◽

1974 ◽

Vol 52 (20) ◽

pp. 3507-3517 ◽

Cited By ~ 26

Author(s):

Y. K. Peng ◽

P. T. Dawson

Keyword(s):

Oxygen Adsorption ◽

Sticking Probability ◽

Exchange Reactions ◽

Kinetics Of Adsorption ◽

First Order ◽

Extensive Coverage ◽

Temperature Programmed ◽

Isotopic Mixing ◽

Adsorption Desorption ◽

Initial Sticking

The kinetics of adsorption and desorption of oxygen on a platinum filament have been studied by temperature-programmed desorption mass spectrometry. Oxygen adsorption becomes significant only after any carbon contamination is removed from the surface. At 300 °K oxygen adsorbs dissociatively into an atomic β-state which contains four overlapping sub-states. The initial sticking probability is 0.16 but this falls off rapidly with increasing coverage. A kinetic analysis for desorption from the β2- and β4-states gave Edes≠(β2) = 39 kcal mol−1 and Edes≠(β4) = 54 kcal mol−1 The desorption was first order suggesting a lack of mobility of the adatoms at the desorption temperature (∼700°K). No oxygen atom desorption could be detected in a line-of-sight experiment. Adsorption of a mixture of 32O2 and 36O2 resulted in complete isotopic mixing on desorption. At 115 °K, the β-state still populates first with the same initial sticking probability indicating adsorption is nonactivated. Moreover, the sticking probability remains at its high initial value for a much more extensive coverage range, suggesting a precursor state to adsorption. After the β3- and β4-states are fully occupied, further adsorption into the β-state is competitive with occupation of an α-state which desorbs at low temperatures (∼150°K) with first order kinetics and Edes≠(α) ∼6 kcal mol−1 No isotope mixing occurred in the α-state which is undoubtedly molecular. Prior population of the β1- and β2-states at 300 °K reduced the α-state adsorption at 115 °K suggesting that α and β occupy the same sites. Each site can adsorb either an atom or molecule since each molecule added to the β-state excludes two molecules from the α-state.

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The response of a small stream in the Lesni potok forested catchment, central Czech Republic, to a short-term in-stream acidification

Hydrology and Earth System Sciences ◽

10.5194/hess-7-411-2003 ◽

2003 ◽

Vol 7 (3) ◽

pp. 411-422 ◽

Cited By ~ 11

Author(s):

T. Navrátil ◽

M. Vach ◽

S. A. Norton ◽

P. Skrivan ◽

J. Hruška ◽

...

Keyword(s):

Czech Republic ◽

Recovery Period ◽

Base Cations ◽

Exchange Reactions ◽

Small Stream ◽

Stream Acidification ◽

Adsorption Desorption ◽

Acid Neutralisation ◽

Stream Substrate

Abstract. Lesni Potok stream drains a forested headwater catchment in the central Czech Republic. It was artificially acidified with hydrochloric acid (HC1) for four hours to assess the role of stream substrate in acid-neutralisation and recovery. The pH was lowered from 4.7 to 3.2. Desorption of Ca and Mg and desorption or solution of Al dominated acid-neutralisation; Al mobilisation was more important later. The stream substrate released 4,542 meq Ca, 1,184 meq Mg, and 2,329 meq Al over a 45 m long and 1 m wide stream segment; smaller amounts of Be, Cd, Fe, and Mn were released. Adsorption of SO42- and desorption of F‾ occurred during the acidification phase of the experiment. The exchange reactions were rapidly reversible for Ca, Mg and SO42-; but not symmetric as the substrate resorbed 1083, 790 and 0 meq Ca, Mg, and Al, respectively, in a 4-hour recovery period. Desorption of SO42-; occurred during the resorption of Ca and Mg. These exchange and dissolution reactions delay acidification, diminish the pH depression and retard recovery from episodic acidification. The behaviour of the stream substrate-water interaction resembles that for soil–soil water interactions. A mathematical dynamic mass-balance based model, MASS (Modelling Acidification of Stream pediments), was developed which simulates the adsorption and desorption of base cations during the experiment and was successfully calibrated to the experimental data. Keywords: Al, Ca, Mg, base cations, acid-neutralisation, stream acidification, recovery, stream sediment, experiment, modelling, adsorption, desorption, adsorption, Czech Republic, Lesni Potok

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Ultrathin Platinum Crystal Surface Structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118849 ◽

1985 ◽

Vol 43 ◽

pp. 394-395

Author(s):

R. L. Hines

Keyword(s):

Crystal Surface ◽

Surface Structures ◽

Platinum Surface ◽

Platinum Surfaces ◽

Resolution Level ◽

Experimental Facilities ◽

Carbon Backing ◽

Mesh Grid ◽

Atom Layer

The importance of atom layer terraces or steps on platinum surfaces used for catalysis as discussed by Somorjai justifies an extensive investigation of the structure of platinum surfaces through electron microscopy at the atomic resolution level. Experimental and theoretical difficulties complicate the quantitative determination of platinum surface structures but qualitative observation of surface structures on platinum crystals is now possible with good experimental facilities.Ultrathin platinum crystals with nominal 111 orientation are prepared using the procedure reported by Hines without the application of a carbon backing layer. Platinum films with thicknesses of about ten atom layers are strong enough so that they can be mounted on grids to provide ultrathin platinum crystals for examination of surface structure. Crystals as thin as possible are desired to minimize the theoretical difficulties in analyzing image contrast to determine structure. With the current preparation procedures the crystals frequently cover complete openings on a 400 mesh grid.

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