Iron-based Fischer–Tropsch synthesis (FTS) catalysts evolve in situ on exposure to synthesis gas (CO & H₂) forming a mixture of iron oxides, iron carbides and carbonaceous deposits. Recently, the application of inelastic neutron scattering has shown the progressive formation of a hydrocarbonaceous overlayer during this catalyst conditioning period. The evolving nature of the catalyst alters the proportion of phases present within the catalyst, which may influence the transport of hydrogen within the reaction system. Preliminary quasi-elastic neutron scattering (QENS) measurements are used to investigate hydrogen diffusion within an un-promoted iron FTS catalyst that has experienced varying levels of time-on-stream (0, 12 and 24 h) of ambient pressure CO hydrogenation at 623 K. Measurements on the catalyst samples in the absence of hydrogen show the unreacted sample (t = 0 h) to exhibit little increase in motion over the temperature range studied, whereas the t = 12 and 24 h samples exhibit a pronounced change in motion with temperature. The contrast is attributed to the presence of the afore-mentioned hydrocarbonaceous overlayer. Measurements on the samples in the presence of liquid hydrogen show hydrogen diffusional characteristics to be modified as a function of the catalyst conditioning process but, due to the complexity of the evolving catalyst matrix, the hydrogen motion cannot be attributed to a particular phase or component of the catalyst. Problems in the use of hydrogen as a probe molecule in this instance are briefly considered. Coincident neutron diffraction studies undertaken alongside the QENS measurements confirm the transition from hematite pre-catalyst to that of Hägg carbide during the course of extended times-on-stream.

铁基费-托合成（FTS）催化剂在暴露于合成气（CO＆H ₂）形成氧化铁，碳化铁和碳质沉积物的混合物。近来，非弹性中子散射的应用已经显示出在该催化剂调节期间逐步形成烃质覆盖层。催化剂的不断发展的性质改变了催化剂内存在的相的比例，这可能会影响反应系统中氢的传输。初步的准弹性中子散射（QENS）测量用于研究未促进的铁FTS催化剂内的氢扩散，该催化剂在623年的环境压力下CO加氢时间（0、12和24 h）变化了水平K.在没有氢气的情况下对催化剂样品进行的测量表明，未反应的样品（t = 0 h）在研究的温度范围内运动几乎没有增加，而t = 12和24 h样品则显示出运动随温度的明显变化。对比归因于上述烃质覆盖层的存在。在存在液态氢的情况下对样品进行的测量表明，氢扩散特性会根据催化剂的调节过程而改变，但由于不断发展的催化剂基质的复杂性，氢的运动不能归因于特定的相或组分催化剂。在这种情况下，简要考虑了使用氢作为探针分子的问题。与同时进行的QENS测量同时进行的中子衍射研究证实，在延长运行时间的过程中，从赤铁矿预催化剂过渡到了Hägg碳化物。