A new supported Fe-MnO catalyst for the production of light olefins from syngas. I. Effect of support on the catalytic performance

CO-TPD and H₂-TPD and CO/H₂-TPSR were used to study the effect of the support on the performance of Fe-MnO catalysts in CO hydrogenation for the production of light olefins. It was found that a Fe-MnO/MgO catalyst (based on a basic support) is capable of strongly adsorbing CO and H₂ favorable for the production of light olefins and CO conversion. A Fe-MnO/ Al₂O₃ catalyst (based on an acidic support) only showed strong adsorption of H₂, but weaker adsorption of CO, and so, it was a poor catalyst for light olefins from syngas.     

Promotion effect of K2O and MnO additives on the selective production of light alkenes via syngas over Fe/silicalite-2 catalysts

The addition of K₂O and MnO promoters enhances catalyst activity and selectivity to light alkenes during CO hydrogenation over silicate-2 (Si-2) supported Fe catalysts. The results of CO hydrogenation and CO-TPD, CO/H₂-TPSR, C₂H₄/H₂-TPSR and C₂H₄/H₂ pulse reaction over Fe/Si-2 catalysts with and without promoters clearly show that the MnO promoter mainly prohibits the hydrogenation of C₂H₄ and C₃H₆. Therefore, it enhances the selectivity to C₂H₄ and C₃H₄ products. Meanwhile further incorporating the K₂O additive into the FeMn/ Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO adspecies. These produce much more [C_ad] via their dissociation and disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins. Moreover, the K₂O additive modifies the hydrogenating reactivity of [C_ad] and suppresses the disproportionation of C₂H₄ that occurs as a side-reaction. Both K₂O and MnO promoters play key roles for enhancing the selective production of light alkenes from CO hydrogenation over Fe/Si-2 catalyst.     

A new supported Fe-MnO catalyst for the production of light olefins from syngas. II. Effect of support on the secondary reactions of C2H4

The TPSR technique was used to investigate the effect of the support on the secondary reactions of ethylene formed during CO hydrogenation. Based on the results of CO hydrogenation and CO/H₂-TPSR characterization, it was found that different supports induced different secondary reactions, and thus affected the selectivity to light olefins directly. The Fe-MnO/MgO catalyst (based on basic support) causes disproportionation of C₂H₄, and thus, leads to the formation of C₃H₆. The Fe-MnO/Al₂O₃ catalyst (based on acidic support) showed obvious hydrogenation of C₃H₆. The disproportionation of C₂H₄ was also promoted by the Fe-MnO/Al₂O₃ catalyst, but because of its activity for C₃H₆ hydrogenation, a large amount of C₃H₈ was produced. The different C₂H₄ secondary reactions are relevant to different CO/H₂ reaction pathways over the catalyst surface, so the Fe-MnO/MgO catalyst is a desirable catalyst for the production of light olefins from CO/H₂ while the Fe-MnO / Al₂O₃ catalyst was not so.