Inorganic Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.
Phys Chem Chem Phys. 2010 Jan 21;12(3):667-80. doi: 10.1039/b920256k. Epub 2009 Nov 19.
The effect of Cu on the reduction behavior and surface properties of supported and unsupported Fe-based Fischer-Tropsch synthesis (FTS) catalysts was investigated using in situ X-ray photoelectron spectroscopy (XPS) and in situ X-ray absorption spectroscopy (XAS) in combination with ex situ bulk characterization. During exposure to 0.4 mbar CO-H(2) above 180 degrees C, the reduction of CuO to Cu(0) marked the onset of the reduction of Fe(3)O(4) to alpha-Fe. The promotion effects of Cu are explained by a combination of spillover of H(2) and/or CO molecules from metallic Cu(0) nuclei to closely associated iron oxide species and textural promotion. XAS showed that in the supported catalyst, Cu(+) and Fe(2+) species were stabilized by SiO(2) and, as a result, Fe species were not reduced significantly beyond Fe(3)O(4) and Fe(2+), even after treatment at 350 degrees C. After the reduction treatment, XPS showed that the concentration of oxygen and carbon surface species was higher in the presence of Cu. Furthermore, it was observed that the unsupported, Cu-containing catalyst showed higher CO(2) concentration in the product gas stream during and after reduction and Fe surface species were slightly oxidized after prolonged exposure to CO-H(2). These observations suggest that, in addition to facilitating the reduction of the iron oxide phase, Cu also plays a direct role in altering the surface chemistry of Fe-based FTS catalysts.
采用原位 X 射线光电子能谱（XPS）和原位 X 射线吸收光谱（XAS）与非原位体相表征相结合的方法，研究了 Cu 对负载型和非负载型 Fe 基费托合成（FTS）催化剂还原行为和表面性质的影响。在 180°C 以上、0.4 mbar CO-H2 气氛中，CuO 还原为 Cu(0)标志着 Fe3O4 还原为α-Fe 的开始。Cu 的促进作用可通过从金属 Cu(0)核向紧密相关的氧化铁物种和结构促进作用的 H2 和/或 CO 分子的溢流来解释。XAS 表明，在负载型催化剂中，Cu(+)和 Fe(2+)物种被 SiO2 稳定，因此，即使在 350°C 下处理后，Fe 物种也没有明显还原到 Fe3O4 和 Fe2+以下。还原处理后，XPS 表明，在存在 Cu 的情况下，表面氧和碳物种的浓度更高。此外，还观察到，在还原期间和之后，不含 Cu 的负载型催化剂在产物气流中表现出更高的 CO2 浓度，并且在长时间暴露于 CO-H2 后，Fe 表面物种略微氧化。这些观察结果表明，Cu 除了促进氧化铁相的还原外，还直接影响 Fe 基 FTS 催化剂的表面化学性质。
