A time resolved in situ investigation into the formation of bismuth molybdate catalysts prepared by spray-dried methods

The formation of the catalytically active forms of bismuth molybdate with the formula Bi2O3⋅nMoO3 (where n=3, 2 or 1) from the corresponding precursors prepared by spray dry methods, have been studied using combined in situ XRD/QEXAFS and IR spectroscopy. This multi-technique approach yielded a great deal of information making it possible to identify a number of intermediate and contaminant species formed during the reaction. Attempts were also made to quantify the proportion and nature of the Mo(VI) containing species using a principle component analysis and least squares fitting approach of the XANES data. The results from this analysis were in good agreement with the observations made by the other techniques and suggested that in order to synthesise pure phases of the active catalysts it was often necessary to ensure that calcination was carried out at temperatures in excess of 400 °C.