On the role of lattice distortion in the catalytic properties of substituted orthovanadates La1−xFexVO4 Original Research Article

A series of mixed orthovanadates with nominal compositions La1−xFexVO4 were synthesized and characterized using powder X-ray diffraction, Mössbauer spectroscopy and temperature-programmed reduction techniques. The substitution resulted in the co-presence of two distinct mixed metal compositions having either monoclinic LaVO4 or a triclinic FeVO4 structure. Both these constituent phases were however, found to be of distorted nature, with no measurable change in respective crystal symmetry. Furthermore, the extent of this distortion depended upon the value of x and is attributed to the partial substitutions at A-site, i.e. with a part of La by Fe in LaVO4 lattice and a part of Fe by La in the FeVO4 phase. The substitution-induced lattice distortion is found to result in the lowering of the reduction temperature in case of both the above mentioned phases, and also in the synergistic enhancement in catalytic activity for a model CO oxidation reaction.