Design of NiO–MgO materials with different properties

Abstract

Several NiO–MgO systems were prepared from commercial nickel nitrate hexahydrate and MgO by means of different preparative paths and with two NiO/MgO weight ratios. All the samples were structurally characterized by using BET, XRD, SEM and TPR techniques. These preparative paths lead to NiO–MgO samples with different NiO–MgO interaction degrees, which go from the formation of solid solution until the detection of clearly differentiated NiO and MgO phases by XRD. Samples with solid solution have surface areas in the range 35–51 m² g⁻¹ and did not show well-defined morphology. The use of an argon flow passing through the sample during the decomposition of the intermediate Ni₃(NO₃)₂(OH)₄ phase in the presence of magnesia avoids the solid solution formation and allows to obtain NiO/MgO systems with high surface area (80–90 m² g⁻¹) with defined octahedral morphology. Also, NiO/MgO systems of about 100 m² g⁻¹ and without solid solution were obtained by mixing high-area NiO and MgO in n-hexane. Low NiO–MgO interaction involves higher reduction degrees, high surface areas of the systems prepared, and the obtention of well-defined octahedral particles.