水分压对铁基费托合成催化剂还原动力学的影响

Effect of H_2O Partial Pressure on Reduction Kinetics of Iron-Based Fischer-Tropsch Catalyst

利用恒温还原和程序升温还原技术研究了水分压对铁基费托合成催化剂还原路径、还原机理和表观活化能的影响.程序升温还原结果表明,水分压对催化剂的还原路径没有明显的影响,催化剂均首先由α-Fe2O3还原为Fe3O4,然后超顺磁态Fe3O4先还原为FeO,再还原为α-Fe,而顺磁态Fe3O4则直接还原为α-Fe.恒温还原结果表明,催化剂在2.5%H2O-97.5%H2气氛中还原时,还原过程达到平衡时的还原程度随还原温度的升高而增加.利用Hancock-Sharp方法分析了恒温还原过程的动力学模型.结果表明,还原温度较低时,催化剂在2.5%H2O-97.5%H2气氛中还原时受内扩散模型控制;还原温度较高时则受晶相形成与生长模型控制.利用Kissinger方法计算了还原过程的活化能,发现随着水分压的增加,表观活化能呈增大的趋势.水分压对Fe3O4还原为α-Fe过程的影响大于其对α-Fe2O3还原为Fe3O4过程的影响.

The effect of H20 partial pressure on the reduction pathway, mechanism, and apparent activation energy of an iron-based Fischer-Tropsch catalyst was investigated by isothermal and temperature-programmed reduction （TPR）. The TPR results indicated that the H2O partial pressure had no obvious influence on the reduction pathway of the catalyst in H2. a-Fe2O3 in the catalyst was first reduced to Fe3O4. The formed superparamagnetic Fe3O4 was reduced to a-Fe via FeO as an intermediate, while the formed paramagnetic Fe3O4 was reduced to a-Fe directly. The isothermal reduction of the catalyst showed that the reduction degree of the catalyst increased with the increase of reduction temperature when the reaction approached to equilibrium. The reduction mechanism analyzed based on the Hancock-Sharp method indicated that the reduction of the catalyst in 2.5%H2O-97.5%H2 at lower temperature was controlled by the inner diffusion model. However, at higher temperature the reduction process was controlled by the formation and growth of nuclei model. The apparent activation energy calculated based on the Kissinger method was increased with increasing H2O partial pressure in Ha. The H2O partial pressure had stronger influence on the reduction of Fe3O4 to a-Fe than that on the reduction of a-Fe2O3 to Fe3O4.