Design of the catalysts for direct conversion of syngas to light olefins and optimization of the reaction conditions

ZSM-5 catalysts with same particle size and different Si/Al molar ratio were synthesized successfully by hydrothermal synthesis method, and then, Fe-Cu-K-containing ZSM-5 samples were prepared via aqueous incipient wetness impregnation. The effect of Si/Al molar ratio on the FTO reaction was systematically investigated. The results indicated that the conversion of CO and selectivity to light olefins strongly depended on the reaction conditions and the acidic properties of the zeolite. The ZSM-5/FeCuK catalyst with a Si/Al molar ratio of 50 possessed the highest CO conversion (84.71%) and selectivity to light olefins (32.08%) compared with others. H₂-TPR results showed that the reduction of Fe phase in Z50/FeCuK was the highest. With the combination of DRIFTS, TG-DTA and XRD techniques, it was found that there were more carbonate and hydrocarbon species adsorbed on the surface of Z50/FeCuK and more FeC_x phases were formed after reaction compared with the other catalysts. Finally, the reaction conditions were optimized and the results showed that the catalyst had the best performance at 310 ℃, H₂/CO(volume ratio)=2 and 1.0 MPa.