1 catalyst precursors 311 elemental analysis the

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Unformatted text preview: e temperature profiles. 73 3. Results and discussion - catalyst preparation and characterisation 3. Results and discussion - catalyst preparation and characterisation 3.1. Catalyst precursors 3.1.1. Elemental analysis The coprecipitated solids are labelled according to their Ni content (expressed as metal atom%) as Ni0, Ni5, Ni10, Ni15, Ni30, Ni50 and Ni72 (Tab. 8). The measured amount of CO32- and NO3- reflected the amount of anionic charge needed to compensate the additional charge due to the substitution of Mg2+ by Al3+. The theoretical value of the total weight loss was calculated taking into account the amount of intercalated water, the destruction of the intercalated anions and the dehydroxylation of the metal hydroxides. Tab. 8: Chemical composition of the coprecipitated solids (int. = intended, obs. = observed, cal. = calculated) CO32- Composition [metal atom%] Ni Mg NO3- Total weight [mol %] Sample [mol %] loss [%] Al cal. obs. int. obs. int. obs. int. obs. Ni0 72.0 72.0 28.0 28.0 0.09 0.13 45.47 45.46 Ni5 5.0 5.0 67.0 66.0 28.0 29.0 0.10 0.16 46.89 46.74 Ni10 10.0 9.4 62.0 61.6 28.0 29.1 0.08 0.16 44.47 43.03 Ni15 15.0 15.7 57.0 55.8 28.0 28.5 0.08 0.16 44.76 45.23 Ni30 30.0 30.1 42.0 41.8 28.0 28.1 0.10 0.12 40.16 42.04 Ni50 50.0 50.3 22.0 21.4 28.0 28.3 0.06 0.16 38.19 39.23 Ni72 72.0 73.2 28.0 26.8 0.08 0.13 33.80 36.43 3. Results and discussion - catalyst preparation and characterisation 74 3.1.2. Structural analysis The XRD spectra of the coprecipitated and dried solids are presented in Figure 10. The diffraction patterns were compared to the 3 strongest reflections of Mg, Ni and Al hydroxides, nitrates, carbonates and mixtures of them using a continuously upgraded JCPDS database. After this first screening the spectra of the coprecipitated solids were carefully compared to the complete diffraction patterns of the following, which exhibited the most similar XRD patterns compounds (the JCPDS catalogue numbers are given in squared brackets). Mg3(NO3)2(OH)4 [26-1221] Ni(NO3)2 [14-0593] Ni(NO3)2· 4H2O [22-0751] Ni3(NO3)2(OH)4 [22-0752] Ni2(NO3)2(OH)2· 2H2O [27-0952 and 27-0939] Mg6Al2(OH)16CO3· 4H2O (hydrotalcite) [41-1428] Ni6Al2(OH)16CO3· 4H2O (takovite) [15-0087] The comparison showed that w...
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This document was uploaded on 10/07/2013.

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