employing mixtures of 10 20 and 30 he in n2 the

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Unformatted text preview: lcined samples was calculated from 3 point N2 adsorption isotherm measured using Ankersmit Quantasorb Jr., employing mixtures of 10, 20 and 30% He in N2. The response factor for each mixture was calibrated for each measurement. Each sample was dried at 347°C for 2 hours in a flow of 10% He in N2 prior to the measurement. The correlation coefficient for the N2 adsorption isotherm was in all measurements between 0.99985 and 1.00000. 2.4. Temperature programmed reduction and oxidation The reduction, oxidation and the Ni dispersion was studied by temperature programmed reduction (TPR) and temperature programmed oxidation (TPOx). The Ni dispersion was expressed as the amount of reducible Ni after passivation to the total 57 2. Experimental ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffifffffffffffffffffffffffffffffffffffff amount of reducible Ni2+ ions. In order to investigate all properties for one sample, first the calcined catalyst was reduced, then passivated, reduced again and finally oxidised. The set up used for the TPR experiments consisted of the reactant feed system, the reactor and the analytical unit. In the reactant feed system two mass flow controllers (Brooks, USA) were used to control the gas flows. One mass flow controller was used for inert gases, the other one for reactive gases, in these studies 5 vol% H2/Ar (Linde) and 5 vol% O2/He (Linde) mixtures. Each individual gas supply line could be opened and closed by toggle valves placed before the mass flow controllers. Only stainless  7KH reactor was heated steel or copper tubing was used outer diameter 3.2 mm (1/8Ž by an electrical furnace, controlled by a temperature controller (Chinotherm, Hungary, model LP-849). The reactor itself consisted of a quartz tube, inner diameter 4 mm, outer diameter 6 mm, in which the catalyst was placed on a quartz wool bed. The actual temperature of the catalyst was measured by a type-K thermocouple placed in a quartz capillary, which was positioned in the middle of the catalyst bed. The second thermocouple (type-K) necessary for...
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