Study On Iron-based FTS Catalyst Supported On CNTs

Direct conversion of synthesis gas to light olefins has been considered as a possible solution to meet the growing demand of C2H4 and C3H6.Improving the content of light olefins was one of the most important research directions of Fischer-Tropsch synthesis?FTS?.As a new carrier,CNTs was regarded as an ideal with appropriate specific surface area,low resistance and high stability.This paper was to discuss the preparation of catalysts in incipient wetness impregnation method which chose Fe as the active center,CNTs as the carrier and the investigation of the impact of the content of promoter on catalyst performance in fixed bed reactor.This paper was also to discuss the optimization of the composition of catalyst and the influence of process conditions such as temperature,pressure and space velocity.This paper was to use catalyst characterization techniques such as BET,XRD,H₂-TPR,CO2-TPD,XPS,Raman,TEM and Mossbauer to discuss the influence of different promoter on the structure and FTS performance of catalysts.The results indicated that the addition of moderate amount of Mn promoter could promote the reduction and increased the surface basicity of catalysts,therefore enhanced the CO dissociation adsorption and suppressed H₂ adsorption.Catalytic results showed that under the condition of 300 ??1MPa?3000h^-1 and H₂/CO=1,CO conversion was 11.24%and selectivity of light olefins was 32.13%with 3%Mn adiition.The further addition of Mn was unfavorable to the reduction and surface basicity of catalysts.Li promoter was introduced as the second promoter on the basis of FeMn/CNTs,which could further enhance CO conversion and light olefins selectivity.The addition of Li promoter would suppress the reduction of catalysts and result in aggregation of iron particles to some extent.The proper introduction of Li promoter on FeMn/CNTs increased the surface basicity of catalysts and promoted the transformation of Fe3+ specious and the formation of active phase,?-Fe5C2,which was favorable to light olefins selectivity.Catalytic results showed that under the condition of 300 ??1MPa?3000h^-1 and H₂/CO=1,CO conversion was 14.18%and selectivity of light olefins was 48.42%with 1.5%Li addition.Too much additive Li could reduce the surface basicity of catalysts and restrained the formation of the active phase of reaction,?-Fe₅C₂.