Oxygen chemisorption and oxide film growth on Ni{100}, {110}, and {111}: Sticking probabilities and microcalorimetric adsorption heats

Abstract

Using single-crystal adsorption calorimetry, heat data have been measured for the adsorption of oxygen on the three low-index planes of Ni at 300 K along with corresponding sticking probabilities. New data are presented with coadsorbed potassium on each plane, and temperature-dependent data for O2/Ni{100}. The initial heats of adsorption of oxygen on Ni{100}, {110}, and {111} are 550, 475, and 440 kJ (mol O2)−1, respectively, at 300 K, and the heat is found to drop rapidly with coverage in the chemisorption regime, indicating strong interadsorbate interactions. However, this rapid decline is not seen with coadsorbed potassium, a difference discussed both in terms of electron availability and coadsorbate attractions. The integral heats of adsorption for oxide film formation are 220, 290, and 320 kJ mol−1, respectively. Corresponding sticking probability measurements show initial values, all less than unity, of 0.63, 0.78, and just 0.23, again for the {100}, {110}, and {111} surfaces in that order. The coverage dependence of the sticking probability is consistent in each case with a passivating oxide film four layers thick. Comparable data for Ni{100} obtained using a pyroelectric detector gave good agreement with the conventional results at 300 K. At 410 K, however, the heat-coverage curve was flat up to 0.25 monolayers. Data were also obtained at 90 K. Analysis and Monte Carlo simulation of the temperature-dependent adsorption heat curves indicates that the large drop in adsorption heat with coverage seen at room temperature is consistent with a local second-nearest neighbor adatom–adatom repulsion rather than a long-range electronic effect.

Mathematical modelling of the unsteady-state oxidation of nickel gauze catalysts

“…5. This result is in agreement with the observations of Labohm et al (1983), Vreeburg et al (1992a, b), and Stuckless et al (1997) at similar temperatures on monocrystals.…”

“…The kinetics of nickel oxidation were described in several papers: (Labohm, Gijzeman, & Geus, 1983;Leclercq, Pietrzyk, Gengembre, & Leclercq, 1986;Hoang-Van, Kachaya, Teichner, Arnaud, & Dalmon, 1989;Vreeburg, vanKooten, Gijzeman, & Geus, 1992a;Vreeburg, Tongeren, Gijzeman, & Geus, 1992b;Stuckless, Wartnaby, Al-Sarraf, Dixon-Waren, Kovar, & King, 1997;Gellings & Bouwmeester, 2000). Most of these studies were carried out on mono-crystals in ultrahigh vacuum at temperatures under 600 K. The results obtained show that the surface coverage by oxygen species is higher than one indicating a multilayer oxygen adsorption.…”

“…The author concludes that at elevated temperatures the reaction proceeds in two consecutive steps: ÿrstly, the oxygen chemisorpts on the surface and dissociates, and then it di uses into the bulk. In addition (Stuckless et al, 1997) report that the heterogeneity of the surface can lead to an important decrease of the oxidation rate since the adsorption of oxygen decreases with the amount of oxide present at the surface (the oxygen sticking probability diminishes with the oxygen coverage).…”

“…Taking into account the subsurface di usion the value of 2:4 mol(O) kg −1 cat is in the range of those observed on monocrystals at lower temperatures (100 -500 K). Typical values reported for oxygen coverage at low temperatures vary in a range from 1 to 7 monolayer (ML) (Labohm et al, 1983;Leclercq et al, 1986;Hoang-Van et al, 1989;Vreeburg et al, 1992a, b;Stuckless et al, 1997;Gellings & Bouwmeester, 2000). 1 ML (monolayer) corresponds to approximately 1:9 × 10 15 atoms=cm 2 .…”

Theoretical Study of Hydrogen Adsorption on Ruthenium Clusters

“…Due to the small particles size of a well dispersed catalysts, most or almost all of its atom are surface atoms, so they exhibit structural and reaction properties different from those of the bulk, they are appropriate to surface reactions as the most process in catalysis are. Many previous researches showed that the catalytic properties of clusters are structure dependent, leading to different adsorption energies and sites for different structures of clusters [1][2][3][4][5][6]. Hydrogen is employed in many modern technologies [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], so surface reactions of hydrogen molecules in transition metals have been carried out over the adsorption and desorption of hydrogen and deuterium molecules on well-defined single crystal metals.…”