硅对铁基费-托合成催化剂的影响

Effect of Silica Promoter on Iron-Based Catalyst for Fischer-Tropsch Synthesis

用共沉淀法制备了一系列不同硅含量的铁基催化剂,采用N2吸附和原位X射线衍射对催化剂进行了表征,在固定床反应器中考察了催化剂的费-托合成反应活性、选择性和稳定性.结果表明,含硅的催化剂具有较大的比表面积和较小的平均孔径,在CO还原及费-托合成反应中生成的碳化铁物种的稳定性比不含硅的催化剂高.在费-托合成反应中,不含硅的催化剂具有较高的初始活性,但易失活;含硅的催化剂具有较低的初始活性,但稳定性较高.Fe7C3是活性最高的碳化铁物种.随着硅含量的增加,催化剂的费-托合成反应更易生成低碳数产物.

A series of SiO2-incorporated precipitated Fe-Si-Cu-K （100Fe： ：xSi：3.0Cu：2.0K, x =0, 2.8, 6.4, 8.2, atomic ratio） catalysts were prepared using the co-precipitation method for the Fischer-Tropsch synthesis （FTS）. The in-situ X-ray diffraction （XRD） and N2 physisorption were used to characterize the catalysts. The catalytic properties for FTS were tested in a fixed-bed reactor under pressure of 1.0 MPa and temperature of 543 K. The SlOE incorporation increased the surface area and decreased the pore size of the precipitated iron catalysts, and the transition of different iron oxide and iron carbide phases （Fe2O3, Fe3O4, Fe3C, Fe5C2, and FeTC3） was detected by in-situ XRD during the catalyst reduction in CO and FTS reaction in syngas （H2/CO molar ratio= 0.7）. The activity of the catalyst without SiO2 increased sharply with time on stream during the FTS process, which was accompanied by the transition of Fe5C2 to Fe7C3. The catalyst without SiO2 deactivated rapidly when the highest CO conversion was achieved, whereas a persistent increase in the activity of catalysts with SiO2 was achieved with time on stream. These indicate that SiO2 can stabilize the activity of the precipitated iron catalyst. The observed effects of SiO2 on the catalytic performance of precipitated iron catalysts can be explained by the fact that SiO2 can improve the dispersity of iron oxides and iron carbides in the catalyst and restrain the conversion of different iron carbide phases during the catalyst reduction and FTS reaction.