Adsorption of hydrogen on tungsten

Figure 18 shows the heat of adsorption of hydrogen on tungsten at 23° in its dependence on surface coverage. The data plotted are those from five different experiments using small increments in each case. Figure 19 shows the same values as represented by the solid... 

After his immigration he continued his connection with the I. G. Farben-industrie A.G. as consultant for the General Aniline and Film Corporation and worked for about two years in the Department of Chemical Engineering of the Johns Hopkins University. The result of this period was an important paper published in the Journal of the American Chemical Society, Vol. 66, entitled The Adsorption of Hydrogen on Tungsten. ... 

Pig. 1. Adsorption of hydrogen on tungsten disulfide. I. Catalyst degassed at 300°C. II. Catalyst H2 treated and degassed at 300°C. 

Halsey, G., and Taylor, H. S. The adsorption of hydrogen on tungsten powder. Jour. Chem. Physics 15, 624-630 (1947). 

The displacement reaction Although it is believed that the key reason for selectivity is the activated adsorption of hydrogen on tungsten there is obviously no tungsten available in the beginning of the deposition (in a contact to silicon). The first reaction which will occur is that between silicon and WF6, the so called displacement reaction [Broadbent et al.44] ... 

R. Gomer, R. Wortman, R. Lundy (1957). J. Chem. Phys., 26, 1147-64. Mobility and adsorption of hydrogen on tungsten. 

A paper by 0. Beeck (33d) has only recently come to the author s notice. Working with evaporated films of metal of area of the order of 10,000 cm. Beeck has confirmed all Roberts results on the speed, extent, and heat of adsorption as a function of surface covered, for the adsorption of hydrogen on tungsten. Nickel shows a similar behavior. This makes extremely likely the view that adsorption on tungsten powder is complicated in some fashion, if not by solution, as suggested above, then by some kind of physical or chemical heterogeneity of the surface, as in the Halsey and Taylor picture. 

Figure 9.2. Variation in the heat of adsorption of hydrogen on tungsten with coverage and surface structure. Data from Ref. 166.

In this section a method for the direct calorimetric determination of heats of adsorption on evaporated metal films is described and results for the heals of adsorption of hydrogen on nickel, iron, and tungsten are reported. In all cases the heats of adsorption decrease with the fraction of surface covered in a mode that can satisfactorily be explained by interaction of adsorbed atoms. A criterion for mobility of the adsorbed atoms is developed... 

Mention has been made variously that the rate of adsorption of hydrogen on nickel and iron is very fast at room temperature. In fact, the rate is so fast that the limiting factor appears to be the rate at which gases enter the reaction chamber through the stopcock from the reservoir. This essentially instantaneous adsorption has been observed for many other metals, including platinum, rhodium, palladium, tungsten, tanta-... 

Fig. 18. Heats of adsorption of hydrogen on evaporated tungsten films at 23°C. as a function of surface covered.

The heat of adsorption of nitrogen on tungsten at room temperature was found to be 95,000 calories per mole and constant over the whole fraction of the surface which it will cover—that is, about 60%. The adsorption is instantaneous. In Fig. 21 is [shown the heat of adsorption of hydrogen on a tungsten surface covered 60% with nitrogen. 

The data of Rideal and Trapnell (7) for the adsorption of hydrogen on an evaporated tungsten film are fitted by (18), or rather by a limiting form of (18). When (1 — 8)Ax/kT is large, equation (18) becomes... 

In the room next to ours. Dr. J. K. Roberts was studying the adsorption of hydrogen on very pure tungsten wires using original techniques developed by him. Little did we know that a few years later he would question the validity of the Bonhoeffer Farkas mechanism of the catalytic para-hydrogen conversion. 

Jayasooriya, U.A., Chesters, M.A., Howard, M.W. et al. (1980) Vibrational spectroscopic characterization of hydrogen bridged between metal atoms - a model for the adsorption of hydrogen on low-index faces of tungsten. Surface Science, 93, 526-534. 

This has been applied to the adsorption of hydrogen on metallic tungsten [19]. 

Equation (89) shows that the allowance for the variation of the charge of the adsorbed atom in the activation-deactivation process in the Anderson model leads to the appearance of a new parameter 2EJ U in the theory. If U — 2Er, the dependence of amn on AFnm becomes very weak as compared to that for the basic model [see Eq. (79)]. In the first papers on chemisorption theory, a U value of 13eV was usually accepted for the process of hydrogen adsorption on tungsten. However, a more refined theory gave values of 6 eV.57 For the adsorption of hydrogen from solution we may expect even smaller values for this quantity due to screening by the dielectric medium. 

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