The spectra were recorded before and after the

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Unformatted text preview: reduction steps to determine the changes in the catalysts caused by the reduction process. XRD spectra were also recorded at room temperature before and after the completed reduction to compare the effect of the reduction process without distortions of the 2Q values and the intensities caused by the temperature differences during the recording (Fig. 19 and 20). 90 3. Results and discussion - catalyst preparation and characterisation Ni Pt Pt Ni Pt 25°C Ni Ni Pt Pt Pt 900°C intensity [a.u.] Ni S S Pt Pt Ni S Pt 600°C D D,S Pt D SPt S Pt 300°C D,S D Pt D SPt S Pt 25°C 30 40 50 2q 60 70 Fig. 19 High temperature XRD spectra of the reduction process of Ni72C900C (D = NiO phase with periclase structure (bunsenite), Ni = metallic Ni phase, Pt = platinum (sample holder), S = NiAl2O4 spinel ) 91 3. Results and discussion - catalyst preparation and characterisation Pt D,S Pt Ni,S Pt D Ni D S 25°C Pt D,S Ni,S D Pt Pt D Ni S intensity [a.u.] 900°C Pt D D,S S Pt D Pt S 600°C Pt D D,S Pt S D Pt S 25°C 30 40 50 2Q 60 70 Fig. 20 High temperature XRD spectra the reduction process of Ni30C900 (D = divalent metal oxide phase with periclase structure, Ni = metallic Ni phase, Pt = platinum (sample holder), S = spinel phase) 3. Results and discussion - catalyst preparation and characterisation 92 All the spectra exhibited Pt reflections from the Pt ribbon on which the sample was placed and that will not be discussed in the following. Before the reduction process of Ni72C900 only reflections due the NiO and the NiAl2O4 were observed. At 600°C only the reflections corresponding to NiO disappeared completely. The reflection that was due to both, NiO and NiAl2O4, decreased drastically, whereas the reflection due to the NiAl2O4 alone seemed to be unchanged. Simultaneously two new reflections of metallic Ni were observed. At 900°C the spectrum exhibited only reflections due to metallic Ni. Although the spectra of Ni30C900 were less intensive a distinction of the different phases was still possible...
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