Nickel hydrogen adsorption

S g of ethyl glycinate hydrochloride were dissolved in 400 cc of ethanol and 33.5 g of salicylic aldehyde were added. It is refluxed for half an hour and cooled. 38 cc of triethylamlne and 25 g of Raney nickel are then added whereafter hydrogenation is carried out at room temperature and under atmospheric pressure. After hydrogen adsorption was complete, the mixture was filtered and the alcohol evaporated off. The residue was taken up with acidified water, extracted with ether to eliminate part of the by-products, consisting mainly of o-cresol, then made alkaline with ammonia and extracted with ethyl acetate. The solvent was removed in vacuo and the residue crystallized from ether/petroleum ether. 36.7 g of o-hydroxybenzyl-aminoacetlc acid ethyl ester melting at 47°C are obtained. 

The effect of other surface impurities may be more severe than that of oxygen. For instance, adsorbed sulfur strongly inhibits hydrogen adsorption on nickel 58), while chlorine adsorbed on nickel is also likely to be a tenaciously held surface contaminant. 

Evidence for a marked difference between the surface and bulk compositions of dilute copper-nickel alloys has been reported recently by a number of investigators (82, 87-90). Much of the experimental evidence comes from hydrogen adsorption data (74, 82, 87, 90). The conclusions of van der Plank and Sachtler were based on the premise that nickel chemisorbs hydrogen while copper does not (82, 87). The total adsorption of hydrogen at room temperature was taken as a measure of the amount of nickel in the surface. However, in hydrogen adsorption studies on the catalysts used to obtain the catalytic results in Fig. 6, the amount of adsorption on the copper catalyst, while small compared to the adsorption on nickel, is not negligible (74) However, the amount of strongly adsorbed... 

In the first example (46), hydrogen adsorption on different sites of a nickel crystal was studied by considering the interaction of a hydrogen atom with a limited number of metal atoms. The nickel crystal was truncated to obtain the clusters shown in Fig. 31, containing 13,10, 9 and 8 nickel atoms, and representing models for the bulk crystal and for the (111), (100) and (110) surfaces respectively. The nearest-neighbour distance in all clusters was... 

Fig. X. Hydrogen adsorption at 78° and 300°K as a function of preadsorbed amount of oxygen on nickel.

Figure 5 shows data for catalytic activity, CO adsorption at 23°, surface area by the B.E.T. method using krypton at —196°, and the fast hydrogen adsorption at —196° plotted against the temperature at which the various films were sintered. All quantities were taken as unity for films sintered at 23°C. These experiments clearly indicate that the previously observed slow adsorption of hydrogen on nickel catalysts is not adsorption but is sorption consisting of adsorption and... 

Before leaving the nickel experiments, it may be well to refer to the experiments on hydrogen adsorption variously reported in the literature. As an example, the work of Maxted and Hassid (13) had as its main objective the measurement of the slow activated adsorption of hydrogen on reduced nickel oxide catalysts. It has been proved by the foregoing that the slow adsorption is actually absorption. When plotting their data as isobars, as was done in Fig. 9, the similarity between these isobars and those obtained with sintered nickel films is evident. 

Nickel films completely covered with oxygen will not adsorb hydrogen when exposed to this gas immediately after oxidation, but will regain their ability to adsorb hydrogen after several hours. Hydrogen thus adsorbed is not able to hydrogenate ethylene. Heats of adsorption measurements of this type of hydrogen adsorption have not been made. 

A radiotracer method was elaborated for the study of the adsorption phenomena on nickel electrodes formed by electrodeposition of nickel ( nicke-lized nickel electrode). Adsorption studies were carried out with labeled HCl, Fi2S04, H3PO4, thiourea, phenylacetic, and acetic acids in 0.1 mol dm HCIO4 supporting electrolyte. The potential dependence of the adsorption of these species was determined in the potential range —200 to +200 mV vs. relative hydrogen electrode (RHE). It was found... 

Mechanism (B) was postulated to explain an order of unity observed with palladium and nickel, where hydrogen adsorption was irreversible and p was low. The relevant steps for mechanism (B) are (1), (3), (4), (7)... 

In measuring dipole moments of an adsorption bond various methods have been reported in literature (19-22), and wide discrepancies exist in the results. For the nickel-hydrogen system we chose the photoelectric... 

Results of previous investigations 23,110, 111, 113, 141, 157-165) show that hydrogen adsorption on nickel at room temperature is lowered by preadsorbed sulfur. Moreover, the fraction by which hydrogen adsorption is reduced in polycrystalline and supported nickel catalysts is generally proportional to the mean fractional coverage of sulfur. This is illustrated by data in Fig. 16 from Bartholomew and co-workers 112, 113, 141, 157-162). 

Results pointing in the same direction were obtained recently by Schuit and De Boer (17), who found that activated adsorption of hydrogen occurs only on a partially oxidized surface of nickel supported on silica (3 1) but not on a thoroughly reduced surface. According to Schuit and De Boer, very prolonged evacuation or heating of a reduced nickel catalyst in an inert atmosphere leads to a slow activated hydrogen adsorption. This effect, however, disappears on renewed careful reduction... 

This view is supported by the statistical-mechanical interpretation of the adsorption isotherm at such low coverages that the differential heat of adsorption of hydrogen is nearly constant at 26 kcal./mole. From the agreement between the surface fraction calculated by means of equation (18) with n = 2, and the experimentally found value 0ob., for the hydrogen adsorption on nickel, Kwan et al. concluded that the surface of reduced nickel is homogeneous, or that every surface element is equally available for the chemisorption of hydrogen. 

As revealed by electron-diffraction patterns, Beeck and Ritchie obtained (llO)-oriented nickel films parallel to their support in an atmosphere of inert gas at a pressure of 1 mm. Hg, and non-oriented films in a high vacuum. From the B.E.T. area of these films available to hydrogen adsorption and from the number of chemisorbed atoms at — 195°C. and 0.1 mm. Hg pressure, which they consider to represent the saturation value of adsojption, these authors conclude that only (110) planes are present on the accessible surfaces of the oriented films (93). A similar investigation with a non-oriented film of nickel led to the conclusion that the area occupied by chemisorbed hydrogen atoms is compatible with the assumption that the non-oriented film exposes on its surface approximately p(iual fractions of the (100), (110), and (111) planes. There... 

Fig. 12.9. Relative extent of hydrogen adsorption on copper-nickel...

Fig 1 shows the correlatiofi of hydrogen adsorption and sulfur capacity on a series of nickel catalysts The slope, i e the atomic ratio S/H is determined to 0.74. This result was confirmed by Oliphant et al. It implies an apparent discrepancy when assuming a H/Ni - 1.0 as usually done Apparently more knowledge is required for the H /Ni system ... 

---