The chemical states of Ni species were systematically investigated using an in situ XAFS technique for a series of SiO₂-supported Ni catalysts with different Ni particle sizes. The Ni particles were refined by varying the Ni loading in the range between 0.10 and 5 wt% and by adding citric acid into the precursor solution. An in situ observation cell for fluorescence-yield XAFS measurements was developed for the dilute Ni catalysts. The chemical state of the supported Ni species converted between Ni(0) and NiO, and no other stable species were formed during the temperature-programmed oxidation and reduction processes. Refinement of the Ni particles resulted in decreasing the oxidation temperature and increasing the reduction temperature. These shifts were explained by the affinity of NiO to SiO₂, and more effective stabilization was thus anticipated for flattened small NiO particles with an increased contact area. In addition, the inhomogeneous distribution of small Ni particles observed for dilute catalysts was explained in terms of the precursor solution volume when nuclei of the precursor compound precipitated on SiO₂ during the drying process.

使用原位XAFS技术对一系列具有不同Ni粒径的SiO ₂负载的Ni催化剂系统地研究了Ni物种的化学状态。通过在0.10和 5wt％之间的范围内改变Ni负载并且通过将柠檬酸添加到前体溶液中来精炼Ni颗粒。一种原位开发了用于稀镍催化剂的荧光产率XAFS测量的观察池。在程序化的氧化和还原过程中，负载的Ni物种在Ni（0）和NiO之间转换的化学状态，没有形成其他稳定的物种。Ni颗粒的细化导致氧化温度降低和还原温度升高。这些变化是由NiO对SiO ₂的亲和力来解释的，因此可以预料对于具有增大的接触面积的扁平NiO小颗粒，可以实现更有效的稳定化。此外，当前体化合物的原子核沉淀在SiO ₂上时，根据前体溶液的体积解释了稀催化剂中观察到的小Ni颗粒的不均匀分布。 在干燥过程中。