Low and high-temperature in situ X-ray absorption study of the local order in orthorhombic α-MoO₃ upon hydrogen reduction

In-situ x-ray absorption spectroscopy has been applied to the study of the modifications of the short range order in orthorhombic α-MoO₃ under low and high-temperature hydrogen reduction. It was observed that at low-temperature (T ≈ 110°C) reduction, a formation of molybdenum bronzes H_xMoO₃ (x ≤ 2) occurs while at high-temperature (T ≥ 400°C) reduction, α-MoO₃ transforms into MoO₂. Both processes have great applied importance since they are related to electrochromic and catalytic properties of α-MoO₃. The information on the local atomic and electronic structure, obtained from the Mo K-edge XAFS and XANES analyses, allowed us to follow all steps of the reduction process and to formulate a mechanism of hydrogen interaction with the layered-type structure of α-MoO₃.