Yoshiko Shigehara

The effect of metallic potassium addition on catalytic properties of nickel for hydrogenation of ethylene

Hydrogenation of ethylene on NiK catalyst has been studied and disclosed a nature different from simple nickel catalyst. Activity degradation with time and self-hydrogenation of ethylene was not found on the NiK catalyst. In order to monitor the behavior of hydrogen and ethylene on catalyst surfaces during the hydrogenation, the reaction of H2D2 mixture with ethylene, the reaction of H2 with a mixture of C2H4C2D4 and kinetic measurements were carried out. The rate of isotopic mixing in ethylene over the NiK catalyst is much slower either in the presence or in the absence of hydrogen. It is concluded that the dissociative adsorption of ethylene on nickel is effectively depressed by addition of potassium, resulting in a weaker inhibition of hydrogen chemisorption. In accordance with this conclusion, the reaction order in hydrogen is lower, H2D2 exchange reaction takes place even in the presence of ethylene.

Gas chromatographic determination of reversible adsorption of hydrogen: VII. The rate of reversible adsorption of hydrogen on a nickel catalyst

Abstract The rate of reversible adsorption of hydrogen was determined by means of plate height of a nickel catalyst column in gas Chromatographic elution of deuterium by hydrogen, adopting Gidding equation for the plate height. The activation energy of desorption is derived from the variation of the desorption rate with temperature to be about 1.5 kcal/mole at low temperature (−195 to −183 °C) and about 16 kcal/ mole at around 0 °C.

Gas chromatographic determination of reversible adsorption of hydrogen: VIII. Reversible adsorption of hydrogen over cobalt oxide

Abstract The rapid and reversible part of the stationary adsorption of hydrogen at low temperatures has been measured by means of a gas chromatographic technique utilizing deuterium as a tracer, in addition to the conventional static measurament of adsorption. The deuterium isotope effect was taken into account in estimating the amount of reversible adsorption assuming a Langmuir isotherm. The amount of reversible adsorption over the cobalt oxide sample at liquid nitrogen temperature and atmospheric pressure was 2–4 × 10 14 molecules/cm 2 increasing with the preevacuation temperature of the sample from 160 to 470 °C. A molecular adsorption is suggested for this temperature. The observed isotope effect in the adsorption constant, K D K H , was 1.4 to 1.9, increasing with the evacuation temperature of the sample. A small amount of irreversible adsorption was found at −195 °C in addition to the reversible adsorption. When the oxide was preevacuated at 470 °C, the irreversible adsorption was considerable above −75 °C and seemed to be a reaction with the oxide surface rather than adsorption.

Gas chromatographic determination of reversible adsorption of hydrogen: VI. The H2D2 exchange reaction on a copper catalyst in relation to the reversible adsorption of hydrogen

Abstract The H 2 -D 2 exchange reaction on a copper catalyst was examined by means of a pulse flow technique in relation to the reversible adsorption of hydrogen. The Arrhenius plots of the exchange activity showed a break around 20 °C at which the reversible adsorption of hydrogen reached a maximum. This result suggests that the exchange reaction at lower temperatures takes place on special sites of higher activity but of smaller number and other than those for the reversible adsorption at lower temperatures, and another type of site of lower activity but of larger number operates at temperatures higher than about 20 °C, which are responsible for the reversible adsorption above 20 °C.

Gas chromatographic determination of reversible adsorption of hydrogen: II. The properties of reversibly adsorbed hydrogen on a nickel catalyst

Abstract The nature of the reversible adsorption of hydrogen on nickel, the determination of which was reported for the first time in a preceding paper, has been investigated in terms of heat of adsorption and by the effect of catalyst reduction and the effect of water vapor as a carrier gas impurity. The heat of adsorption was found to be about 2 kcal/mole at low temperature (−195–−100 °C) and about 13 kcal/mole at around 0 °C (−30–60 °C), which indicates two different types of adsorption. The adsorption sites for them appeared to be developed in the early stage of reduction. Adsorbed water is likely to activate another type of hydrogen adsorption.