High-throughput preparation and testing of MoNbSbV mixed oxide catalysts for direct oxidation of propane to acrylic and acetic acids Original Research Article

An automated robotic method using a solution at pH=2 containing four precursor salts dissolved has been developed and validated for high-throughput preparation of Mo, Nb, Sb and V mixed metal oxide solids, which are known to be selective for propane oxidation to acrylic (AA) and acetic (AcA) acids. Spherical shaped silica beads of exceptionally narrow size distribution were synthesised using oil drop technique from a Brace™ instrument. Automated impregnation of the beads by the previous solution has been developed and validated. Catalytic studies were performed using a conventional micro-reactor system with an Ultra-Fast™ GC analysis (<2 min against >30 min). After calcination of the samples under either N2 or air at 873 K, a mixture of phases was obtained, such as VSbO4, MoxM1−xO2.8 (M=V and/or Nb), Sb4(2)Mo10O31, and other minor phases, such as MoO3 if activated in air. Mixed oxide samples calcined under N2 gave better catalytic activity and selectivity to AA/AcA compared to those calcined under air. Measures of catalytic performance of 16 supposedly identical materials fell within a ±5% range of the median values, showing that our experimental set-up is relevant to combinatorial studies. By preparing 15 samples of different chemical composition, optimum catalytic performance was found to correspond to Mo0.55 Nb0.09 Sb0.18V0.18 mixed oxide calcined at 773 K under N2, containing a mixture of phases, in particular MoxM1−xO2.8 and Sb2Mo10O31, similarly to the M1 and M2 phases observed for MoNbTeV mixed oxide catalysts.