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Results and discussion catalyst preparation and

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Unformatted text preview: ation and characterisation 3.2.3. BET surface measurements The surface area of the calcined solids was determined by BET surface measurements for the catalysts Ni0C900, Ni10C900, Ni30C900, Ni50C900 and Ni72C900. The surface area decreased with increasing Ni/Mg ratio of the catalysts up to a ratio of 5/2 (Fig. 16). Basile et al. observed the same trend for very similar Ni/Mg/Al catalysts also derived from HT precursors calcined at 900°C for 16 hours [9, 123]. However, they observed generally a lower surface area (83-27 m2/g). Since no specific conditions of the calcination process were mentioned there, it is assumed that static conditions were applied. The remarkably higher surface area for the catalysts especially with a low Ni/Mg ratio indicate that the slow heating rate combined with the fast removal of the gases formed during the calcination using a flow of air is favourable for obtaining catalysts with a high surface area. 150 122.87 100 2 m /g 82.58 61.68 50 29.12 34.84 0 Ni0C900 Ni10C900 Ni30C900 catalyst Ni50C900 Ni72C900 Fig. 16 BET surface area of the catalysts Ni0C900, Ni10C900, Ni30C900, Ni50C900 and Ni72C900 3. Results and discussion - catalyst preparation and characterisation 86 3.2.4. Reducibility Since Ni catalysts used in the partial oxidation of C3H8 (as well as in the other related processes) are activated by reduction, the study of the reducibility of the catalysts was important in order to find a suitable reduction method and to investigate the state of the catalyst after reduction with respect to its composition and structure [124]. Temperature programmed reduction The TPR spectra of the catalysts calcined at 900°C are presented in Figure 17. In the case of Ni72C900, which does not contain magnesium, two reduction peaks were observed, a large one at 480°C and a smaller one at 820°C. The lower temperature reduction peak of Ni72C900 exhibited a shoulder at the lower temperature side. The TPR spectra of the other catalysts did not exhib...
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