On the mechanism of the hydrogen–oxygen reaction on Pt(111)

Abstract The reaction between hydrogen and oxygen on Pt(111) is investigated with molecular beam relaxation spectroscopy in the temperature range between 300 and 1200 K. Three procedures were used for preparing the surface, resulting in different reactivities for the hydrogen–oxygen reaction. The observations are not compatible with a reaction mechanism which occurs homogeneously on the surface. Therefore we interpret them in terms of a non-homogeneous surface reaction model in which water formation is catalyzed by special reactive sites (reactive site model). Oxygen diffusion is found to be the rate-limiting process by which water is formed on Pt(111) at low oxygen coverages ( E a is 11.3±0.5 kcal mol −1 . Between 800 and 1200 K we find an effective activation energy for the reaction which is negative (−14.8 kcal mol −1 ). A consistent explanation of all our results can be given with the reactive site model when it is assumed that two O atoms take part in the formation of one water molecule. We estimate that the density of reactive sites is about 10 −5 on a well-prepared surface. Experimental results that have been reported previously are discussed. It is shown that the reactive site model can explain also those results quite well.

[1]  J. White,et al.  The decomposition of H2O on oxygen-covered pt(111): Thermal and vibrational excitation effects , 1984 .

[2]  R Gomer.  Diffusion of adsorbates on metal surfaces , 1990 .

[3]  M. Hugenschmidt,et al.  Hydrogen adsorption on oxygen covered Pt(111) , 1995 .

[4]  E. Fridell,et al.  An experimental study of the kinetics of OH and H2O formation on Pt in the H2 + O2 reaction , 1989 .

[5]  R. P. Merrill.  THE USE OF MOLECULAR BEAMS IN THE STUDY OF CATALYTIC SURFACES , 1971 .

[6]  A. Franken,et al.  The segregation and oxidation of silicon on Pt(111), or: The question of the “platinum oxide” , 1981 .

[7]  A. Luntz,et al.  Molecular beam studies of H2 and D2 dissociative chemisorption on Pt(111) , 1990 .

[8]  G. Fisher,et al.  Identification of an Adsorbed Hydroxyl Species on the Pt(111) Surface , 1980 .

[9]  E. Fridell,et al.  A laser‐induced fluorescence study of OH desorption from Pt(111) during oxidation of hydrogen in O2 and decomposition of water , 1995 .

[10]  G. Fisher,et al.  The hydrogen-oxygen reaction over the Pt(111) surface: Transient titration of adsorbed oxygen with hydrogen , 1982 .

[11]  B. Poelsema,et al.  A simple procedure for high precision orientation of single crystal surfaces , 1985 .

[12]  B. Poelsema,et al.  A molecular beam study of the interaction of CO molecules with a Pt(111) surface using pulse shape analysis , 1987 .

[13]  Vladimir P. Zhdanov,et al.  Kinetics of the hydrogen-oxygen reaction on platinum , 1991 .

[14]  S. T. Zwart,et al.  Adsorption study of hydrogen on a stepped Pt (997) surface using low energy recoil scattering , 1983 .

[15]  M. Hoffbauer,et al.  Dynamics of OH desorption from single crystal Pt(111) and polycrystalline Pt foil surfaces , 1987 .

[16]  J. White,et al.  The low temperature water formation reaction on Pt(111): A static SIMS and TDS study , 1984 .

[17]  Ertl,et al.  Existence of a 'Hot' Atom Mechanism for the Dissociation of O2 on Pt(111). , 1996, Physical review letters.

[18]  R. Gomer,et al.  Adsorption of hydrogen on platinum , 1969 .

[19]  A. B. Anton,et al.  THE MECHANISM AND KINETICS OF WATER FORMATION ON PT(111) , 1990 .

[20]  B. Poelsema,et al.  Surface science lettersLocal adlayer order and sticking probability: D2 adsorption on p(2 × 2)O/Pt(111) , 1991 .

[21]  B. Poelsema,et al.  The deuterium—oxygen reaction on Pt(111): Influence of atomic steps , 1990 .

[22]  L. Girifalco,et al.  MATHEMATICS OF DIFFUSION-CONTROLLED PRECIPITATION IN THE PRESENCE OF HOMOGENEOUSLY DISTRIBUTED SOURCES AND SINKS , 1961 .

[23]  G. Mitchell,et al.  Water formation on Pt(111): Reaction of an intermediate with H2(g) , 1986 .

[24]  B. Poelsema,et al.  A molecular beam study of the interaction between hydrogen and the Pt(111) surface , 1989 .

[25]  D. Bethune,et al.  The sticking of O2 on a Pt(111) surface , 1988 .

[26]  L. K. Verheij.  Kinetic modelling of the hydrogen-oxygen reaction on Pt(111) at low temperature (< 170 K) , 1997 .

[27]  B. Poelsema,et al.  Autocatalytic behavior and role of oxygen diffusion in the hydrogen-oxygen reaction on Pt(111) , 1992 .

[28]  G. Mitchell,et al.  Identification of the intermediate in the water formation reaction on Pt(111) , 1987 .

[29]  Patricia A. Thiel,et al.  The interaction of water with solid surfaces: Fundamental aspects , 1987 .

[30]  E. Fridell.  Kinetics of OH formation on Pt in H2O/O2 mixtures at high temperatures , 1992 .

[31]  B. Koel,et al.  Study of high coverages of atomic oxygen on the Pt(111) surface , 1989 .

[32]  B. Poelsema,et al.  Influence of a very low density of defects on the deuterium—oxygen reaction on Pt(111) , 1990 .

[33]  R. A. van Santen,et al.  Fundamental Aspects of Heterogeneous Catalysis Studied by Particle Beams , 1991 .

[34]  T. Germer,et al.  Direct characterization of the hydroxyl intermediate during reduction of oxygen on Pt(111) by time-resolved electron energy loss spectroscopy , 1989 .

[35]  G. Ertl,et al.  A molecular beam study of the adsorption and desorption of oxygen from a Pt(111) surface , 1981 .