Synthesis of γ-Bi2MoO6 catalyst studied by combined high-resolution powder diffraction, XANES and Raman spectroscopy

The formation of crystalline γ-Bi2MoO6 during hydrothermal synthesis was followed by a combination of HRPD, XANES and Raman scattering in situ techniques. The environment of Mo species changes from isolated tetrahedral MoO42− in the initial gel to distorted octahedra in γ-Bi2MoO6 (Raman, XANES). In the initial stages, spherical (Bi,Mo)2O3 particles form with a fluorite structure, and the growth of anisotropic platelets of γ-Bi2MoO6 follows in a second step (HRPD). The presence of molybdenum specie in the intermediate (Bi,Mo)2O3 mixed oxide was ascertained by EDS during complementary ex situ experiments. These particles are assumed to be involved in the crystal growth process, their structure acting as a skeleton for the formation of γ-Bi2MoO6 koechlinite.