铁基费托催化剂还原机理及动力学研究进展

Research advances in reduction mechanism and kinetics of iron-based Fisher-Tropsch catalyst

费托合成技术是煤间接液化工艺过程中的关键技术,开发高活性、高产品选择性和高稳定性的催化剂是费托合成技术成功的最关键因素之一。论述了铁基费托合成催化剂的还原机理及还原动力学的研究进展,讨论了催化剂焙烧温度、还原H_2/CO比、还原压力和水分压对还原机理及还原动力学的影响规律。随催化剂焙烧温度升高,催化剂物相中超顺磁态的Fe^(3+)组分向顺磁态的α-Fe_2O_3组分转变,较高的焙烧温度导致催化剂晶格缺陷减少,晶粒尺寸增加,反应活化能和指前因子增加,催化剂的还原能力减弱。随还原气氛中CO分压的增加,催化剂的还原和碳化程度提高,催化剂表面形成更多的活性中心,催化剂活性升高。还原压力的升高促进了催化剂的还原和碳化,但过高的还原压力会抑制催化剂的还原和碳化。水分压对催化剂的还原路径没有明显影响,但水分压的增加对催化剂各还原步骤均有抑制作用,还原活化能增加。根据费托合成技术对铁基催化剂的性能要求,未来催化剂还原工艺的研究重点在于开发中温还原、合成气气氛下的低压催化剂还原工艺,以降低固定资产投资,缩短还原时间,提高催化剂的活性和稳定性,降低生产成本,提高企业竞争力。

Fischer-Tropsch synthesis process,which has gradually entered the industrialization operation stage,is the key technology of indirect coal liquefaction process and an important direction of clean coal utilization technology.The development of catalyst with high activity,high selectivity and high stability is one of the key factors of the success of Fischer- Tropsch synthesis technology. Catalyst reduction process is an important process to obtain high performance catalysts,and the study of the reduction mechanism and reduction kinetics is the key issue to the process development. This paper introduced the research progress of reduction mechanism and reduction kinetics of Fischer-Tropsch synthesis catalysts,and discussed the effect of the calcination temperature,reducing atmosphere,reducing pressure and water partial pressure on the reduction mechanism and reduction kinetics.With the increase of calcination temperature of the catalyst,the superparamagnetic magnetic Fe^（3＋） phase transforms to paramagnetic magnetic α-Fe_2O_3 phase,the lattice defects decreases,grain size increases,the activation energy and pre-exponential factor increases and the reducing ability of the catalyst decreases. With the increase of the partial pressure of CO in the reducing atmosphere,the degree of reduction and carbonization of the catalyst increases,more active centers forms on the surface of the catalyst,and the reducing ability of the catalyst increases.The increase of the reduction pressure promotes the reduction and carbonization of the catalyst,but the higher reduction pressure can inhibit the reduction and carbonization of the catalyst.The water pressure has no obvious effect on the reduction path of the catalyst,but the increase of water pressure can prevent the reduction of the catalyst,and the activation energy increases.According to the performance requirements to iron-based catalysts for Fischer-Tropsch synthesis technology,the research on catalyst reduction process should focus on the development of reduction process with middle temperature,syngas atmosphere and low pressure.It will reduce the investment and costs,shorten the reduction time,improve the catalytic activity and stability and improve the competitiveness of enterprises.