Fluidized-bed OCM reaction: A promising Mn₂O₃-Na₂WO₄/TiO₂ catalyst and a numerical study

The fluidized-bed reactor with excellent heat and mass transfer features has great appeal for application in the oxidative coupling of methane (FB-OCM), whereas qualified fluid catalysts represent a grand challenge. Herein, we report a high-performance Mn₂O₃-Na₂WO₄/TiO₂ fluid catalyst (5.4 wt% Mn₂O₃ and 2 wt% Na₂WO₄), which was obtained by the incipient-wetness impregnation method and examined in the OCM reaction in an electric-heating quartz fluidized-bed reactor (i.d., 2 cm). The standard normalization method on the basis of carbon atom was used for calculating the CH₄ conversion and C_2-C₃ selectivity. This catalyst achieves 35.5 % CH₄ conversion, 66 % C₂-C₃ selectivity and particularly 15.1 % single-pass yield of C₂H₄ for a feed of CH₄/O₂/H₂O=3/1/1 with a catalyst dosage of 20 mL at 700 °C and a total GHSV of 7200 h⁻¹. Such catalyst is stable for at least 50 h without signs of deactivation and agglomeration/defluidization. The catalyst particle size is crucial for the FB-OCM reaction with respect to the reaction light-off and catalyst fluidization. The catalyst with preferable particle size of 450–600 μm can not only trigger the OCM reaction at a relatively low temperature of 630 °C but also warrant active bubbling fluidization. Furthermore, thanks to the low amount of Na₂WO₄ and interpenetrating structure of TiO₂-nanorod, such catalyst achieves good anti-aggregation and robust mechanical strength (with a low attrition index of 1.9 %). The effects of water-adding amount in feedstock and catalyst particle size distribution on the hydrodynamics behaviour were investigated in a laboratory-scale fluidized-bed OCM reactor by using numerical simulation method.