Precursor dependence of the nature and structure of non-stoichiometric magnesium aluminium vanadates

Abstract

Hydrotalcite-like compounds containing (a) MgII, AlIII and VIII in the layers and carbonate in the interlayers, or (b) MgII and AlIII in the layers and decavanadate in the interlayers, have been synthesized and characterized using powder X-ray diffraction, thermal analysis, FTIR spectroscopy. temperature-programmed reduction, and specific surface-area determination. The crystalline phases formed after calcination in air at 700 °C have been identified using these same experimental techniques. It has been found that the nature of the precursor determines the nature of the Mg–V–O phases formed; thus, when starting from (a), Mg3(VO4)2 containing isolated [VO4] units is formed, while when starting from (b), MgV2O6, containing pairs of edge-sharing [VO6] octahedra, is formed preferentially. Such a reactivity appears to depend on the nature of the support, and not on the stoichiometry (i.e., Mg/V atomic ratio) of the starting materials.