Abstract
The thermal decomposition of cobalt, nickel, manganese, zinc, and copper nitrates supported on nanometric alumina was investigated and compared with decomposition of corresponding bulk nitrates. TG, DTA, and MS measurements in air were performed. The supported nitrates decompose in lower temperatures than the bulk ones and their decomposition proceeds in fewer stages which are better separated. Synthesized materials and bulk nitrates before degradation of nitrates groups undergo dehydration. For decomposition of manganese and copper nitrates, the last step of water vapour releasing is combined with degradation of nitrate groups thus formation of anhydrous metal nitrate during decomposition is not achievable. Thermal decomposition of bulk nitrates leads to oxides—Co3O4, NiO, MnO2, ZnO, and CuO—respectively, as the solid residue. The nickel, zinc, copper, and manganese nitrates while supported on alumina decompose to corresponding oxides (NiO, ZnO, CuO, MnO2) as well. For decomposition of cobalt nitrate while supported on Al2O3 as the solid residue CoAl2O4 were identified. The correlation between dehydration and degradation of nitrates groups temperatures for bulk and supported nitrates was analysed in terms of atomic properties of d-metals.
Highlights
Metal oxide submicrometer particles have received widespread interest recently because of their envisioned applications in electronics, optics, and magnetic storage devices as well as materials for catalytic applications [1, 2]
The samples of supported nitrates were prepared by impregnation the Al2O3 (\500 nm, analytical grade, Aldrich) with an aqueous solution of respective nitrate using the necessary amount of solution for the filling of the support pores
Small amount of nitrogen oxides are evolved below 175 °C what suggests that during dehydration decomposition of nitrate groups proceeds probably on the material surface, which is highly probable for nitrates
Summary
Metal oxide submicrometer particles have received widespread interest recently because of their envisioned applications in electronics, optics, and magnetic storage devices as well as materials for catalytic applications [1, 2]. The properties of metal oxide catalysts, such as specific surface area, phase composition, particle size, porosity, and activity are greatly affected by the conditions chosen for their preparation [3]. Metal nitrates hydrates are very often used as the precursors of metal oxides because they give materials of well-defined chemical composition and high specific surface area [4,5,6,7,8,9]. The advantage of nitrates compared to chlorides or sulphates is that they can be fully converted to corresponding oxides. Conditions for the synthesis of metal oxides having appropriate properties usually have to be found experimentally [10]
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