熔铁催化剂活性相的调控及其费托反应性能

Regulation of active phase of fused iron catalyst and its catalytic performance of Fischer-Tropsch synthesis

采用水热合成法,在制备MIL-101(Fe)的过程中加入熔铁催化剂,使熔铁催化剂表面涂覆MIL-101(Fe),通过碳化温度和碳化气氛的调变,制备了具有不同活性相组成(θ-Fe_(3)C和χ-Fe_(5)C_(2))的熔铁催化剂,同时将其在340℃、1MPa和GHSV=12000h^(-1)反应条件下,进行费托合成反应性能评价,并运用XRD、SEM、CO-TPD、N_(2)-物理吸附等表征手段进行表征分析。结果表明,当催化剂中含有θ-Fe_(3)C时,具有更高的C_(5)+选择性;在不同碳化气氛下,催化剂产生的活性相不同,且随碳化温度的升高,2种气氛下产生的活性相都可相互转化,但催化剂的反应性能相差显著。CO气氛下,当θ-Fe_(3)C部分转化为χ-Fe_(5)C_(2),催化剂具有较高的活性,这是由于θ-Fe_(3)C和χ-Fe_(5)C_(2)的协同作用更利于CO的解离吸附,提高了催化剂的活性;混合气氛(H_(2)+CO)下,当χ-Fe_(5)C_(2)部分转化为θ-Fe_(3)C,转变过程中由于χ-Fe_(5)C_(2)发生晶格畸变,抑制了CO的解离吸附,导致催化剂活性大幅下降。在CO气氛下,700℃碳化温度下所制得的催化剂具有最佳的催化反应性能,其CO转化率为74.4%,同时具有较高的C_(5)+选择性,为65.6%。

MIL-101(Fe)was coated on the surface of fused iron catalyst by hydrothermal synthesis method.Fused iron catalysts with different active phase compositions(θ-Fe_(3)C andχ-Fe_(5)C_(2))were prepared by adjusting the carbonization temperature and atmosphere.The catalytic performance of Fischer-Tropsch synthesis was evaluated at 340℃,1MPa and GHSV=12000h^(-1),and the catalysts were characterized by XRD,SEM,CO-TPD,and N_(2)-physisorption.The results showed that the catalysts withθ-Fe_(3)C had higher C_(5)+selectivity.Active phases produced by the catalyst were different under different carbonization atmospheres.With the increase of carbonization temperature,the active phases produced by the two atmospheres could be converted to each other,but the difference in catalyst activity was significant.Whenθ-Fe_(3)C was partially converted toχ-Fe_(5)C_(2) in CO,the synergistic effect ofθ-Fe_(3)C andχ-Fe_(5)C_(2) was more conducive to the dissociation and adsorption of CO,which improves the activity of the catalyst.Whenχ-Fe_(5)C_(2) was partially converted toθ-Fe_(3)C in the syngas,the lattice distortion ofχ-Fe_(5)C_(2) occurs,which inhibits the dissociation adsorption of CO and leads to a significant decrease in the catalyst activity.The catalyst carbonized at 700℃in CO had the best catalytic activity,which provided an CO conversion of 74.4%,and a C_(5)+selectivity of 65.6%.