Structural study of the MO–Nd2O3 system obtained by a sol–gel procedure

Abstract The aim of the present work was to prepare a binary MO–Nd 2 O 3 system by the sol–gel method and to characterise a series of mixed oxides belonging to the binary MO–Nd 2 O 3 system (M = alkaline earth metal = Mg, Ca, Sr) to obtain suitable materials with catalytic properties. The molar ratio between the two oxides was MO/Nd 2 O 3  = 95/5. Different precursors as alkaline earth metal oxide source (MO), various starting solution compositions expressed in various molar ratios between reactants and different synthesis parameters (pH, temperature and time of reaction) have been used. The structural study by X-ray diffraction analysis was accomplished based on the X-ray 5.0 program, which has established the presence of the mixtures of crystalline polyphases. The lattice constants, the average size of the crystallites, the average lattice strains and the mass of unit cell variation have been calculated. The program also allowed the calculus of the anisotropy factor, which can give the image of the structural disorder. The surface defects are a consequence of structural changes inside of the crystalline lattice of the solid solutions and are quite important for catalytic properties. Some catalytic activity measurements have established the potential of the prepared sol–gel mixed oxides to be used in the oxidative dehydrogenation process of light alkanes (C 1 C 4 ). Sample 3SrNd was shown to present the best catalytic activity and selectivity in olefins in propane conversion ( C 2 = & C 3 = ) compared with 4Ca-Nd and 1Mg-Nd samples, which was interpreted as due to a better solid solution formation of Nd 3+ in SrO, favoured by the close ionic radius of Sr 2+ and Nd 3+ , as well as by the high basicity of Sr and the presence of a greater number of point defects.