Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe₂(SO₄)₃ as iron precursor. In addition, as for Fe₂(SO₄)₃, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO₃)₃·9H₂O due to the reduction in Fe₂(MoO₄)₃ phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO₃ and Fe₂(MoO₄) for FeCl₃·6H₂O and Fe₂(SO₄)₃ as precursors. Iron molybdate catalyst prepared with Fe(NO₃)₃·9H₂O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.