Operando investigation of the catalytic behavior of Wells–Dawson heteropolycompounds in the oxidation of propene

A complete characterization of the solid-state behavior of the Wells–Dawson heteropolycompounds in relevant conditions for a catalytic oxidation reaction in the gas phase was obtained by following the evolution of the Wells–Dawson salt under reducing and oxidizing model conditions by in situ X-ray diffraction analyses and in situ Raman spectroscopy. It was found that the oxido-reduction strength of the working condition is a tool to control the rearrangement of the Wells–Dawson compound into oxide species. Precisely, an oxidizing feed was shown to stabilize the Wells–Dawson compound, i.e. delay the irreversible transformation of the structure to a mixture of oxides, and thus may be used to modulate the catalytic behavior of the catalyst. Looking for the influence of the oxido-reduction atmosphere, an operando setup combining Raman spectroscopy with online analysis of gaseous products of the catalytic propene oxidation was then used to gain further information on the solid-state behavior of Wells–Dawson heteropolycompounds at work. Along a reaction temperature profile, a peak of propene conversion could be obtained. This was hypothesized to be due to the in situ formation of a propene-containing bronze Mo oxide looking phase. The formation of such phase seems to be facilitated when a more reductive atmosphere is applied on the Wells–Dawson during the reaction.