In situ X‐ray analysis of MoO 3 reduction

The reduction of MoO 3 to MoO 2 under hydrogen/argon atmosphere (5 vol. % H 2 /95 vol. % Ar) in the temperature range 323 K…623 K was studied in situ by means of wide‐angle X‐ray scattering. It has been found that the starting material, MoO 3 , consists of two different orthorhombic MoO 3 phases A and B with nearly the same structure parameters. The phase A (fraction of 37.1 wt%) describes the larger crystallites whereas the phase B (fraction of 62.9 wt.%) describes the smaller crystallites. Under the reduction to monoclinic MoO 2 phase during the heating, the thermal evolution of the phase fractions is different. A conclusion is drawn that MoO 2 is formed preferably in big crystallites. About 10 wt. % of MoO 2 has been found to form at 623 K resulting in about 69 wt. % after cooling to room temperature followed by holding in Ar/H 2 atmosphere about 24 h. Additionally, about 4.4 wt. % of the Mo 4 O 11 oxide probably formed in large crystallites was detected in the reduced powder after the cooling. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)