Soft chemical transformation of α-MoO3 to β-MoO3 as a catalyst for vapor-phase oxidation of methanol

Monoclinic molybdenum trioxide, β-MoO3, was synthesized as an active catalyst for vapor-phase oxidation of methanol by a soft chemical transformation of α-MoO3. The addition of HNO3 to an aqueous solution of α-MoO3, followed by drying and calcination, resulted in the formation of yellow powders consisting of β-MoO3. The β-MoO3 content increased with the amount of HNO3, but the addition of excess HNO3 inhibited β-MoO3 formation. The maximum yield was obtained at a HNO3/Mo molar ratio of 0.37. Thermal analyses indicated that HNO3 controlled dehydration of the dried precursor to induce β-phase formation. The resulting β-MoO3 had a higher activity than α-MoO3 in the partial oxidation of methanol to formaldehyde at temperatures below 600 K.

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► β-MoO3 was synthesized by a soft chemical transformation of α-MoO3.
► The key to the synthesis was the addition of HNO3 to an aqueous solution of α-MoO3.
► HNO3 controlled dehydration of the dried precursor to crystallize β-MoO3.
► The resultant β-MoO3 was highly active in the low-temperature oxidation of methanol.