Nickel/Chromium oxide/Zirconium oxide Catalysts for Hydrogen/Deuterium Isotopic Exchange

Catalysts composed of nickel and promoted with different metal oxides proved to be suitable for H/D isotropic exchange between hydrogen and water vapour. They loss their activity due to water condensation on their surfaces. Several nickel/chromium oxide/zirconium oxide catalysts of different composition were prepared by the coprecipitation technique. The liquid phase activity of these catalysts were followed using the hydrogen peroxide decomposition on their surfaces at different temperatures. The surface characteristics of the examined catalysts were followed by applying the BET method. The results were discussed and lead to the required catalyst composition which resists the water condensation on its surface during operation and has relatively high activity in the vapour phase H/D isotopic exchange reaction between hydrogen and water.     

Supported Nickel-Cobalt Oxide Catalysts for the Isotopic Exchange of Deuterium between Hydrogen and Water Vapour

The specific catalytic activity of supported nickel-cobalt (II) oxide catalysts for the isotopic exchange of deuterium between hydrogen and water in the vapour phase was tested. The specific surface area of the catalysts was evaluated by nitrogen adsorption at ?195.8 °C and application of the BET-equation. The specific metallic surface area for these catalysts was carried out at liquid nitrogen temperature by hydrogen adsorption. Comparison between the specific activity of the catalysts and the specific surface area and specific metallic surface area teas made. The results of this study indicated that nickel catalysis supported with 15 – 20 mole% CoO exhibit a relatively high catalytic activity for the isotopic exchange reaction between hydrogen and water vapour, high specific surface area and high specific metallic surface area.     

Reactivation of Promoted Nickel Catalysts for Deuterium Exchange between Hydrogen and Water in the Vapour Phase

Binary promoted nickel – chromium oxide and ternary promoted nickel – chromium oxide – aluminium oxide mixed catalysts were prepared for use in the present study. The catalysts were prepared by co-precipitation of the corresponding metal nitrates as carbonates followed by calcination in nitrogen atmosphere at 350 °C and reduction in hydrogen atmosphere at 320 °C. To prevent spontaneous oxidation of the catalysts, bidistilled water was added followed by heating of the catalyst mixtures at about 110 °C in hydrogen atmosphere for few hours. Deactivation of catalysts was studied by measurements of the variation of their activities with the time of contact of the reacting gas mixtures with the catalyst surface in the reaction chamber. It was found that while the catalytic activity of ternary catalysts for the isotopic exchange of deuterium between hydrogen and water vapour was higher than that of the binary one, the loss in activity of the former teas faster than the latter. Reactivation of the catalysts were carried out at different temperatures between 110–160°C in hydrogen atmosphere. Catalytic activity measurements indicated that higher temperatures are better for the reactivation process.     

Separation of Deuterium Isotope by Chemical Exchange between Hydrogen and Water Vapour

The separation factor of deuterium (α) for the exchange reaction between hydrogen and water vapour at 100 °C has been measured and was found to be equals to 2.52 and 2.50, depending on the used experimental technique.

An empirical equation relating the variation of the separation factor with temperature for such isotopic exchange reaction has been deduced. The values of α were calculated from 0–800 °C and indicated close agreement with those calculated from spectroscopic data.

Comparison of the deduced empirical equation with the general equation relating the separation factor with temperature for such reaction, allowed the calculation of the zero point energy, as well as the free energy as a function of temperature.     

Hydrophobic Bimetallic Catalysts for H/D Exchange Reaction between Hydrogen and Water

Hydrophobic bimetallic catalysts of Pt-M on styrenedivinylbenzene were prepared, where M represents successively: Ir, Rh, Pd, Cu and Ag. The total metal loading was 0.5 wt% and the weight fractions of the metal M were: 0.0,0.05,0.1,0.25,0.5,0.75 and 1.0. For each sample, the catalytic activity for H/D exchange between hydrogen and water vapor was measured. In case of monometallic catalysts, no activity was detected for M = Cu and M = Ag, and the order of the activity values for the other metals was: Pt < Ir < Rh < Pd. For each bimetallic catalyst, the activity measurements indicated a clear interaction between the platinum and the second metal, thus the activity was significantly increased for M = Ir, increased for M = Rh, decreased for M = Pd, drastically decreased for M = Cu and M = Ag.     

Liquid Phase Kinetic and Thermodynamic Studies on Promoted Nickel Catalysts used for H/D Exchange

Successful choice of the suitable catalyst composition for hydrogen/deuterium exchange reaction between hydrogen and water requires understanding of chemical kinetics as well as surface properties and activity in both liquid- and vapour phases. The present study deals with the thermodynamic and kinetic behaviour of a simple liquid phase reaction on the surface of nickel catalyst promoted with zirconium oxide used for the H/D exchange. This study helps understand the condensation of water on the catalyst surface during operation which leads to its poisoning. In this specific case water molecules are responsible for selective poisoning of this type of catalysts. The reaction rate constant, the increase in Gibb,s free energy, the enthalpy, the entropy of activation and the energy of activation were calculated.     

Hochwirksame ternäre Ni-Cr2O3-Al2O3-Mischkatalysatoren für den Deuteriumaustausch zwischen Wasserstoff und Wasserdampf

Die vorliegenden Untersuchungen basieren auf der Hypothese, daβ die spezifische Aktivität eines binären Ni-Cr₂O₃-Mischkatalysators für den Deuteriumaustausch in System Wasserstoff/Wasserdampf durch Zusatz einer geeeigeneten Drittkomponente durch Synergese gesteigert werden kann. Entsprechend den Anforderungen, die an die Drittkomponente zu stellen sind, erweist sich Al₂O₃ als besonders geeingent. Die gemessenen spezifischen Aktivitälen der untersuchten ternären Mischkatalysatoren zeigen, daβ entsprechend der angenommenen Hypothese ein bemerkenswerter synergetischer Effekt durch Zusatz von Al₂O₃ als Drittkomponente zu dem binären Ni-Cr₂O₃-Mischkatalysator innerhalb bestimmter Konzentrationsverhältnisse (80–85 Mol.% Ni, 5–15 Mol-% Cr₂O₃ und 5–15 Mol-% Al₂O₃) auftritt.