We studied by high resolution transmission electron microscopy (HRTEM) unsupported bismuth-molybdenum-oxide catalysts. The microscope utilized was a JEOL 4000 EX electron microscope with a resolution better than 0.19 nm (point to point). The image simulation were performed on a personal computer with the aid of a commercial program. With the aid of image simulation it is possible to identify γ-Bi2MoO6 and X-Mo4O11 phases, among several other possibilities that fit the interplanar spacings and angles.
A very important aspect, thermal instability, was proved indirectly in the microscope, by the changes of the particles under the electron beam irradiation at 400 kV. After several minutes of irradiation, the amorphous surface layer was totally reconstructed to crystalline phases.
The fact that we observe many phases in this sample, is certainly deleterious to the catalytic properties, since not all of them are active. Also the sensitivity to the beam indicates that minimum exposure microscopy has to be applied in order to prevent unecessary complications for phase identification.