Kinetic-thermal processes of hydrogen sorption on Pd/WO3 and Pd/MoO3 bronze

Abstract

Kinetic-thermal investigations of the hydrogen sorption process in the temperature range from ambient to 720 K on powder samples of Pd/WO3 and Pd/MoO 3 show that it takes place according to the "hydrogen spillover" mechanism, during which the corresponding hydrogen bronzes are formed. Hydrogen sorption changes the structure of the Pd/WO3 bronze, while it breaks the structure of the Pd/MoO3 bronze producing the amorphous state on heating to 570 K. The hydrogen bronze Pd/HxWO 3, heated in oxygen, decomposes at around 830 K, resuming the original form of the yellow Pd/WO3 bronze. A repeated cyclic heating of Pd/HxMOO 3 bronze in hydrogen and oxygen in turn (thermogravimetric analysis and differential scanning calorimetry methods) shows that the sorbed hydrogen reacts violently with oxygen and to form water. In the opposite way, hydrogen sorption on the sample after heating in oxygen also proceeds violently, producing hydrogen bronze after the initial formation of water with oxygen. When heated in oxygen after hydrogen up to 720 K, the sample is oxidized to the maximum extent, returning to the original grey colour and the crystal state. Further heating in hydrogen produces a hydrogen bronze of dark blue colour, while the structure is decomposed. The kinetic processes were investigated and kinetic and thermal parameters were determined. The change in structure is also demonstrated by X-ray diffractometry and electron microscopy.