Following the structural changes in iron phosphate catalysts by in situ combined XRD/QuEXAFS technique

The structure of iron phosphate catalysts prepared by three different synthetic methods has been studied using in situ combined XRD/QuEXAFS. Two of the synthesis procedures have previously been employed to produce these catalysts whilst the third is a new method employing hydrothermal techniques. The combined XRD/QuEXAFS approach supported by ex situ measurements carried out using XRD, TGA and surface area measurements, showed that all three methods produced a catalyst precursor material, having the chemical composition of FePO4.2H(2)O. The in situ study clearly shows the loss of two water molecules during the initial stages of heating and a transformation to FePO4 having tridymite type structure takes place at temperatures above ca. 100degreesC. The crystallinity of the tridymite phase appeared to improve upon heating to ca. 500degreesC and above which a further transformation to a quartz phase takes place. Of the three catalysts, the material produced by hydrothermal methods was found to be the most phase pure and to possess a higher surface area than the materials prepared by the other two methods.