Selective oxidation of propylene to acrolein by hydrothermally synthesized bismuth molybdates

• Bismuth molybdates with plate-like morphology were prepared by hydrothermal synthesis.
• Good catalytic activity and selectivity for propylene oxidation to acrolein.
• Thermal treatment decreased the propylene conversion resulting in lower acrolein yield.
• Addition of nitric acid or ammonia solution improved catalytic performance.
• Hydrothermal synthesis led to more active or selective catalysts than co-precipitation.

Hydrothermal synthesis has been used as a soft chemical method to prepare bismuth molybdate catalysts for the selective oxidation of propylene to acrolein. All obtained samples displayed a plate-like morphology, but their individual aspect ratios varied with the hydrothermal synthesis conditions. Application of a high Bi/Mo ratio during hydrothermal synthesis afforded γ-Bi2MoO6 as the main phase, whereas lower initial bismuth contents promoted the formation of α-Bi2Mo3O12. Synthesis with a Bi/Mo ratio of 1:1 led to a phase mixture of α- and γ-bismuth molybdate showing high catalytic activity. The use of nitric acid during hydrothermal synthesis enhanced both propylene conversion and acrolein yield, possibly due to a change in morphology. Formation of β-Bi2Mo2O9 was not observed under the applied conditions. In general, the catalytic performance of all samples decreased notably after calcination at 550 °C due to sintering.

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