Abstract
The general objectives of this research were to investigate the effect of the support and the gas atmosphere on the decomposition and reduction of cobalt nitrate hexahydrate supported on silica and alumina to gain a greater understanding of the calcination and reduction procedures used in catalyst manufacturing processes. The decomposition was followed by TGA-DSC-MS. The observed breakdown on the unsupported complex is similar but not identical to previous reports with NO detected as an evolved gas. In an oxygen/argon atmosphere the decomposition is generally simplified for the supported samples with a fewer number of weight loss events. When supported on alumina, cobalt nitrate is stabilised with decomposition events shifting to higher temperatures, whereas when supported on silica, cobalt nitrate is destabilised with only one significant decomposition event, which occurs at a lower temperature than that of the unsupported complex. In a hydrogen/nitrogen atmosphere partial decomposition of cobalt nitrate occurs before reduction is initiated with both supported samples. When supported on alumina, cobalt nitrate reduction is catalysed with the two events that occur below 350 °C happening at lower temperatures, while reduction above 350 °C is moved to higher temperatures. The silica-supported complex in contrast exhibits reduction events that are all reduced in temperature relative to the unsupported salt. However, there is evidence of the formation of cobalt silicate with a high temperature reduction. The study has shown that the calcination and direct reduction of supported cobalt nitrate is significantly affected by the support and that different conditions are required to achieve the same state.
Highlights
Research into cobalt catalysts is an area of importance to industry due to their extensive application in a range of industrial processes, most notably Fischer-Tropsch synthesis [1, 2]
The general objectives of this research were to investigate the effect of the support and the gas atmosphere on the decomposition and reduction of cobalt nitrate hexahydrate supported on silica and alumina to gain a greater understanding of the calcination and reduction procedures used in catalyst manufacturing processes
Cobalt nitrate is stabilised with decomposition events shifting to higher temperatures, whereas when supported on silica, cobalt nitrate is destabilised with only one significant decomposition event, which occurs at a lower temperature than that of the unsupported complex
Summary
Research into cobalt catalysts is an area of importance to industry due to their extensive application in a range of industrial processes, most notably Fischer-Tropsch synthesis [1, 2]. On occasion direct reduction from the salt to the metal is employed. During these processes the metal salt and the support can interact modifying the behaviour of the material to any subsequent process. There have been many studies examining the structural, chemical as well as electronic properties of these catalysts. These results have been obtained using a combination of different methods, the majority of which make use of techniques such as temperature-programmed reduction and oxidation (TPO/TPR), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermo gravimetric analysis and differential scanning calorimetry (TGA-DSC) [3,4,5,6,7]. It has been well documented that the different preparation variables influence the structure and
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