Hydrogen reversible

The lanthanides can form hydrides (qv) of any composition up to LnH. Lanthanide hydrides can desorb hydrogen reversibly with temperature. Therefore, the lanthanides and some of thek alloys ate good candidates for hydrogen (qv) storage, of which LaNi is probably the most promising (see... 

Zirconium monochloride reacts with sodium ethoxide to form additional adducts which hydrolyze in water. The monochloride does not react with benzene in a Friedel-Crafts reaction, and does not enter into intercalation reactions similar to those of zirconium disulfide. Both monohaUdes add hydrogen reversibly up to a limiting composition of ZrXH (131). 

Table 1 shows the summary of absorption and desorption kinetics and hydrogen reversible capacity of Mg hydrides with ceramic catalysts at 300°C. 

There are basically six methods in order to store hydrogen reversibly vith a high volumetric and gravimetric density. 

Intermetallics, which store hydrogen reversibly, can function as the negative... 

Hydrogens reverse orientation upon conformations) change of cyclohexane. 

The Ni/MH battery operates in a strongly oxidizing medium composed of a high concentration alkaline electrolyte. Because many chemical elements react to form hydrides in an alkaline electrolyte, it follows that if these elements are used as electrodes, they will oxidize and fail to store hydrogen reversibly. As already mentioned, the highest electrochemical capacity is observed only after 30 cycles and then the capacity remained constant for almost 100 cycles, as shown in Figure 4. This clearly indicates that degradation of the electrode material is very slow. 

Gross et al. (2002) NaAlHj Phase transformation, metal transport + + n.a. Liberation of hydrogen, reversible storage... 

Thus, there were several reports searching not only for new H-rich substances, but also for new hydrogen-poor, relatively unstable phases composed of light elements, which may appear for the first time as decomposition products, but later may turn out to store hydrogen reversibly. Different catalysts can be tested at this stage. Finally, the properties of the system can be improved, for example by using nanoengineering. 

A 0.5 wt. % Pt on silica catalyst gave the data listed below for the sorption of H2. Upon completion of Run 1, the system was evacuated and then Run 2 was performed. Find the dispersion and average particle size of the Pt particles. Hint. Run 1 measures the total sorption of hydrogen (reversible + irreversible) while Run 2 gives only the reversible hydrogen uptake. Calculate the dispersion based on the chemisorbed (irreversible) hydrogen. 

In this way it was found, amongst other cases, that a pressure of 18 atmospheres stops further evolution of hydrogen in 0 13 normal sulphuric acid in contact with zinc, and 1-3 normal in respect of zinc sulphate. And that a higher pressure of hydrogen reversed the reaction, causing precipitation of zinc, was shown hy leaving the apparatus to stand at the atmospheric temperature, after it had previously been warmed to inci eaae the pressure. 

Later studies by Garner and his co-workers showed that the fraction of carbon monoxide or hydrogen reversibly chemisorbed at room temperature varied from oxide to oxide. Zinc oxide was shown to be a case where the adsorption of carbon monoxide at room temperature was completely reversible. The heat of adsorption, determined both calorimetrically (5) and isosterically 6), was in the range 12-20 kcal./mole. For several other oxides, however, notably chromia, Mn20s and Mn20s Cr20s, the heat of adsorption of carbon monoxide was higher and the chemisorption was... 

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