高效MFe_(2)O_(4)(M=Zn、Mg、Cu和Mn)尖晶石催化剂应用于费托合成

Highly effective MFe_(2)O_(4)(M=Zn,Mg,Cu and Mn)spinel catalysts for Fischer-Tropsch synthesis

一系列尖晶石催化剂,包括ZnFe_(2)O_(4)、MgFe_(2)O_(4)、CuFe_(2)O_(4)和MnFe_(2)O_(4)被用于费托合成反应(Fischer-Tropsch synthesis,FTS)。Zn、Mg、Cu和Mn很容易与Fe形成尖晶石。其中,在前处理和反应过程中,Zn和Mg能够显著维持尖晶石结构,使得CO转化率较低。在反应过程中,Cu和Mn有利于碳化铁的生成,导致CuFe_(2)O_(4)和MnFe_(2)O_(4)对FTS性能影响显著。C_(2)^(=)-C_(4)^(=)ZnFe_(2)O_(4)对烃分布和C_(2)−C_(4)烯/烷比影响很小。MgFe_(2)O_(4)的C_(5+)选择性较低,同时由于Mg的碱性作用,从而提高了选择性和C_(2)−C_(4)烯/烷比。Cu可以促进催化剂的碳化,从而使CuFe_(2)O_(4)具有较高的活性。同时,CuFe_(2)O_(4)可以显著提高C_(5+)选C_(2)^(=)-C_(4)^(=)择性。此外,Cu可以促进H_(2)的解离和活化,从而有利于烯烃的二次加氢,降低选择性和C_(2)−C_(4)烯/烷比。虽然Mn在反应过程中会促进催化剂的碳化,但MnFe_(2)O_(4)对碳链的长短影响很小。然而,Mn能促进少量ε-Fe_(2)C的生成,这是导C_(2)^(=)-C_(4)^(=)致MnFe_(2)O_(4)具有较高选择性和C_(2)−C_(4)烯/烷比的原因。同时,所有尖晶石催化剂都具有较低的二氧化碳选择性,符合当前的绿色环保发展要求。

A series of spinel catalysts,including ZnFe_(2)O_(4),MgFe_(2)O_(4),CuFe_(2)O_(4),and MnFe_(2)O_(4),were prepared and applied to the Fischer-Tropsch synthesis(FTS).Zn,Mg,Cu and Mn easily form spinels with Fe.Among them,Zn and Mg can significantly maintain the spinel structure during the pretreatment and reaction,resulting in a low CO conversion.Cu and Mn are beneficial to the formation of iron carbide during the reaction,resulting in an apparent influence on FTS performance.ZnFe_(2)O_(4) has little effect on the hydrocarbon distribution and the olefin/paraffin(O/P)ratio of C_(2)−C_(4).MgFe_(2)O_(4) exhibits low selectivity for C_(5+)C_(2)^(=)-C_(4)^(=)hydrocarbons,and the selectivity of and the O/P ratio of C_(2)−C_(4) in the product are increased due to the alkaline effect of Mg.Cu can promote the carbonization of the catalyst,so that CuFe_(2)O_(4) has higher activity.Meanwhile,CuFe_(2)O_(4) can significantly improve the selectivity of C_(5+)hydrocarbons.Moreover,Cu can promote the dissociation and activation of H_(2),C_(2)^(=)-C_(4)^(=)which is beneficial to the secondary hydrogenation of olefins,thereby reducing the selectivity of and the O/P ratio of C_(2)−C_(4).Mn promotes carbonization during the reaction,but MnFe_(2)O_(4) has little effect on the chain growth of hydrocarbon.However,Mn can promote the generation of a certain amount of ε-Fe_(2)C,which may explain the higher selectivity of C_(2)^(=)-C_(4)^(=) and the O/P ratio of C_(2)−C_(4) for MnFe_(2)O_(4).All spinel catalysts exhibit low CO_(2) selectivity,which meets the current green environmental protection requirements.