Hydrogen overlayers

Jachimowski TA, Meng B, Johnson DP, Weinherg WH. 1995. Thermal desorption studies of high-coverage hydrogen overlayers on Ru(OOl) created with gas-phase atomic hydrogen. J Vac Sci Technol A 13 1564. 

The stable ethylene or acetylene plus hydrogen overlayer on Rh(lll) can be decomposed to surface CH (CD) species above 420 K. 

FIGURE 10.4 In this molecular portrayal of the structure of a solution of ammonia in water at equilibrium, we see that NH, molecules are still present because only a small percentage of them have been protonated by transfer of hydrogen ions from water. In a typical solution, only about 1 in 100 NH, molecules is protonated. The overlay shows only the solute species. 

FIGURE 10.15 In a solution of a weak acid, only sonic of the acidic hydrogen atoms are present as hydronium ions (the red sphere), and the solution contains a high proportion of the original acid molecules (HA, gray spheres. The green sphere represents the conjugate base of the acid and the blue spheres are water molecules. The overlay shows only the solute species. 

Similar SSIMS and TDS results were obtained for rhodium on tltanla and fiir hydrogen chemisorption on both substrates. In a blank experiment Involving i o metal over layer, temperature programming while following the T1 and TIO SIMS signals (Fig. 4) shows that the tltanla thin film does not begin to change until the temperature reaches about 760 K, well beyond the 615 K where Tl was first noted to Increase on the systems with thin metal overlayers. ... 

HREELS and TFD have played a unique role In characterizing the surface chemistry of systems which contain hydrogen since many surface techniques are not sensitive to hydrogen. We have used these techniques to characterize H2S adsorption and decomposition on the clean and (2x2)-S covered Ft(111) surface (5). Complete dissociation of H,S was observed on the clean Ft(lll) surface even at IlOK to yield a mixed overlayer of H, S, SH and H2S. Decomposition Is primarily limited by the availability of hydrogen adsorption sites on the surface. However on the (2x2)-S modified Ft(lll) surface no complete dissociation occurs at IlOK, Instead a monolayer of adsorbed SH Intermediate Is formed (5) ... 

Figure 3.16 Volcano plot for the hydrogen evolution reaction (HER) for various pure metals and metal overlayers. Values are calculated at 1 barof H2 (298K) and at a surface hydrogen coverage of either 0.25 or 0.33 ML. The two curved lines correspond to the model (3.24), (3.25) transfer coefficients (not included in the indicated equations) of 0.5 and 1.0, respectively, have also been added to the model predictions in the figure. The current values for specific metals are taken from experimental data on polycrystalline pure metals, single-crystal pure metals, and single-crystal Pd overlayers on various substrates. Adapted from [Greeley et al., 2006a] see this reference for more details.

Roudgar A, Gross A. 2005. Hydrogen adsorption energies on himetaUic systems at the sohd-vacuum overlayer and the sohd-liquid interface. Surf Sci 597 42-50. 

Figure 4.4 A series of STM images recorded during the exposure of a Cu(l 10) surface to hydrogen chloride at 295 K resulting in the formation of domains accompanied by step movement (1-8). With time this surface at 295K relaxes to give a well-ordered c(2 x 2)0 overlayer (9).

The amount of hydrogen partial pressure reduction depends upon the materials and the relative thickness of the cladding/ weld overlay and the base metal—the thicker the stainless barrier is relative to the base metal the better.32 Archakov and Grebeshkova33 mathematically considered how stainless steel corrosion barrier layers increase resistance of carbon and low alloy steels to high temperature hydrogen attack. 

There have been a few instances of high temperature hydrogen attack of base metal which was clad or overlayed with austenitic stainless steel. All of the reported instances involved C-0.5Mo steel base metal. In one case,34 high tem-... 

Report on the Effect of Stainless Steel Weld Overlay or Cladding on Hydrogen Attack of Underlying Steel, Materials Properties Council, New York, September 1984. 

Johnson et al.67 studied CO hydrogenation on bimetallic catalysts consisting of cobalt overlayers on W (100) and (110) single crystals at 200°C, 1 bar at a H2/ CO ratio of 2. AES spectra showed the postreaction Co/W surfaces to have high coverages of both carbon and oxygen, with carbon line shapes characteristic of bulk carbidic carbon.67 The catalytic activity apparently could not be correlated with surface carbon level.67... 

Fig. 7. Overlay of the DNQX and ATPO-iGluR2-SlS2 complexes including isoenergy contours according to GRID-methyl probe (beige, -2.9 kcal/mol), water probe (cyan, -8.5 kcal/mol), and hydrogen phosphate anion probe (magenta, -14.4 kcal/mol).

Release of odorous compounds including hydrogen sulfide from the wastewater into the overlaying atmosphere is a fundamental process for evaluating odor problems. As long as an odorous compound remains in the water phase, odor problems do not exist. 

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