Hydrogen adsorption phase transitions

This article describes three research topics in the subsequent sections. Section 15.2 describes experimental and theoretical research pertinent to the exploration of hydrogen storage capacity, mostly at room temperature. Section 15.3 discusses the problem of quantum sieving, which is the separation of light isotopes, e.g., hydrogen from deuterium, by adsorption within nanotube bundles. Section 15.4 summarizes a variety of open questions concerning phase transition phenomena that have been proposed to occur for hydrogen within nanotube bundles. 

On palladium catalysts the main hydrogenating agent is hydrogen dissolved in the bulk of the metal. Specific adsorption of cations, the cadmium ion in particular, greatly increases the overpotential of the O phase transition [16]. The heat of the a transition in sulfuric acid and cadmium sulfate solutions (Table 2) was calculated from charging curves obtained at 20, 40, and 60°C in the region of the phase transition for the palladium — hydrogen system. 

In sulfuric acid the heat of sorption and desoiption of hydrogen in the region of the phase transition amoimts to 10 0 kcal/mole, which is in agreement with the published data [17]. Specific adsorption of cadmium cations on the palladium surface increases the heat of the jS O phase transition to 25 kcal/mole. The difference found in the heats of the direct and reverse transition is thermodynamically impossible, if the processes occur at the same centers, uniform in chemical composition. 

An analysis, made in 1 and 2 N solution of cadmium sxilfate, showed the absence of propionaldehyde and a practically quantitative yield of allyl alcohol. The change in the behavior of organic compounds when they are adsorbed on the modified palladium surface is xzndoubtedly due to an energetic hindrance to the /J — a phase transition. The preferential hydrogenation of acetylene derivatives before ethylene derivatives is determined by the greater exothermic nature of adsorption and hydrogenation in acetylene derivatives [3]. 

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