(5b) Propene Ammoxidation By Bismuth Molybdate Using Forced Dynamic Operation

Ammoxidation (AMO) of propene and ammonia over bismuth molybdate (BMO) based catalysts to produce acrylonitrile (ACN) has been used since the 1950s. Acrylonitrile is the precursor to polyacrylonitrile (PAN), which can in turn be manufactured into acrylic fiber or carbon fiber (CF). ACN also serves as one of the monomers from which acrylonitrile butadiene styrene (ABS) is produced. CF production is largely dependent on ACN feedstock and is a fast-growing sector due to its lightweight and high tensile strength nature. BMO-based catalysts are used due to their activity and selectivity, where reductants are oxidized by lattice oxygen and the reduced sites are subsequently oxidized by gaseous O₂. As a selective oxidation reaction, AMO performance relies on the oxidation state of the catalyst, as well as the mobility of surface and lattice oxygen, which here is termed dynamic oxygen storage capacity (DOSC).

Forced dynamic operation (FDO), exposing the catalyst to cycling between reductant and oxidant rich phases, provides an interesting strategy to achieve higher selectivities and to help us better understand the mechanism, in that it provides transient feedback from catalysts in different oxidation states. In this work, a silica supported α-type BMO was synthesized. A commercial multicomponent promoted BMO catalyst provided by INEOS was also evaluated for comparison. FDO schemes with changing compositions of gases (C₃H₆, NH₃ and O₂) and conditions (frequency, amplitude, duty) were tested to identify the best pathway in improving ACN yield. DOSC measurements were used to characterize the oxygen storage/release capability of the catalysts. Our results show that FDO can provide promising acrylonitrile production rates compared with steady-state operation, potentially contributing to the pursuit of economic modular ACN manufacturing.