Selective oxidation of propylene to acrolein by hydrothermally synthesized bismuth molybdates

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-Bi$_2$MoO$_6$ as the main phase, whereas lower initial bismuth contents promoted the formation of α-Bi$_2$Mo$_3$O$_{12}$. 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-Bi$_2$Mo$_2$O$_9$ 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