SO_4^(2-)对铁基催化剂上费托合成反应的影响

Effect of SO_4^(2-) on Fischer-Tropsch Synthesis over Iron-Based Catalyst

以FeCuK/SiO2为母体催化剂,用不同浓度的NH4HSO4水溶液进行等体积浸渍,制备了不同SO42-含量的费托合成(FTS)铁基催化剂.采用原子发射光谱、低温N2吸附、X射线光电子能谱、程序升温还原和穆斯堡尔谱等技术对催化剂进行了表征,并在H2/CO摩尔比0.67,WHSV=2 000 h-1,压力1.5 MPa和温度250℃条件下进行了浆态床FTS反应.结果表明,少量SO42-能促进催化剂在H2中的还原;在合成气还原过程中,少量SO42-对催化剂的碳化程度影响不大,但大量SO42-严重抑制催化剂的碳化.在约500 h的运行实验中,各催化剂样品表现出的催化活性有所差异,但均呈现较好的稳定性.SO42-可抑制水煤气变换反应活性,且随着SO42-含量的增加,抑制作用愈加明显;同时,催化剂上浸渍少量SO42-可有效抑制CH4的生成,提高低碳烯烃的选择性.

A series of Fe-based catalyst samples with different amounts of SO4^2- for Fischer-Tropsch synthesis （FTS） were prepared by iso-volume impregnation of the FeCuK/SiO2 precursor with NH4HSO4 solution. The catalyst samples were characterized by atomic emission spectroscopy, N2 adsorption, X-ray photoelectron spectroscopy, temperature-programmed reduction, and M6ssbauer effect spectroscopy. The catalytic performance of the catalyst samples for the FTS reaction was measured in a continuous stirred tank slurry reactor under the reaction conditions of n （H2 ）/n （CO） = 0.67, WHSV = 2 000 h^-1, 1.5 MPa, and 250 ℃. The results showed that the addition of SO4^2- promoted the reduction of the catalyst in H2. A low level of SO4^2- slightly influenced the extent of carburization, and the excessive addition of SO4^2- restrained carburization apparently in syngas. The catalyst samples with different SO4^2- amounts displayed different FTS reactivity, but all the samples were stable during 500 h on stream. Moreover, the addition of SO4^2- could suppress the water-gas shift reaction. The low level of SO4^2- suppressed methane selectivity and promoted slightly alkene selectivity.