Effect of In_(2)O_(3)particle size on CO_(2) hydrogenation to lower olefins over bifunctional catalysts

A reaction-coupling strategy is often employed for CO_(2)hydrogenation to produce fuels and chemicals using oxide/zeolite bifunctional catalysts.Because the oxide components are responsible for CO_(2)activation,understanding the structural effects of these oxides is crucial,however,these effects still remain unclear.In this study,we combined In_(2)O_(3),with varying particle sizes,and SAPO‐34 as bifunctional catalysts for CO_(2)hydrogenation.The CO_(2)conversion and selectivity of the lower olefins increased as the average In_(2)O_(3)crystallite size decreased from 29 to 19 nm;this trend mainly due to the increasing number of oxygen vacancies responsible for CO_(2) and H_(2) activation.However,In_(2)O_(3)particles smaller than 19 nm are more prone to sintering than those with other sizes.The results suggest that 19 nm is the optimal size of In_(2)O_(3)for CO_(2)hydrogenation to lower olefins and that the oxide particle size is crucial for designing catalysts with high activity,high selectivity,and high stability.

Fabrication of K-promoted iron/carbon nanotubes composite catalysts for the Fischer–Tropsch synthesis of lower olefins

K-promoted iron/carbon nanotubes composite（i.e., Fe K-OX） was prepared by a redox reaction between carbon nanotubes and K2FeO4followed by thermal treatments on a purpose as the Fischer–Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and Fe K-IM catalysts prepared by impregnation method followed by thermal treatments. The novel Fe K-OX composite catalyst is found to exhibit higher hydrocarbon selectivity,lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the Fe K-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active,selective and stable iron-based composite catalysts for the FTO reaction.

Conversion of syngas into lower olefins over a hybrid catalyst system

Lower olefins,produced from syngas through Fischer-Tropsch synthesis,has been gaining worldwide attention as a non-petroleum route.However,the process demonstrates limited selectivity for target products.Herein,a hybrid catalyst system utilizing Fe-based catalyst and SAPO-34 was shown to enhance the selectivity toward lower olefins.A comprehensive study was conducted to examine the impact of various operating conditions on catalytic performance,such as space velocity,pressure,and temperature,as well as catalyst combinations,including loading pattern,and mass ratio of metal and zeolite.The findings indicated that the addition of SAPO-34 was beneficial for enhancing catalytic activity.Furthermore,compared with AlPO-34 zeolite,the strong-acid site on SAPO-34 was identified to crack the long-chain hydrocarbons,thus contributing to the lower olefin formation.Nevertheless,an excess of strong-acid sites was found to detrimentally impact the selectivity of lower olefins,attributed to the increased aromatization and polymerization of lower olefins.The detailed analysis of a hybrid catalyst in Fischer-Tropsch synthesis provides a practical strategy for improving lower olefins selectivity,and has broader implications for the application of hybrid catalyst in diverse catalytic systems.