Fischer-Tropsch synthesis: An XAS/XRPD combined in situ study from catalyst activation to deactivation

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• 作者：Nikolaos E. Tsakoumis^a ; Alexey Voronov^a ; Magnus R&oslash ; nning^a ; Wouter van Beek^b ; ^c ; &Oslash ; yvind Borg^d ; Erling Rytter^a ; ^d ; Anders Holmen^a ; ^{holmen@chemeng.ntnu.no}
• 关键词：Fischer&ndash ; Tropsch synthesis ; Cobalt ; In situ ; XAS/XRPD ; Deactivation ; Aluminate formation
• 刊名：Journal of Catalysis
• 出版年：2012
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：July, 2012
• 卷：291
• 期：Complete
• 页码：138-148
• 文件大小：1019 K

摘要

A rhenium promoted (1 wt.%Re/20 wt.%Co/纬-Al₂O₃) and an un-promoted (20 wt.%Co/纬-Al₂O₃) Fischer-Tropsch catalyst were studied in situ throughout the common steps of laboratory catalyst testing, that is, reduction, pressurization, the initial period before reaching pseudo-steady state, deactivation, and post-mortem analysis. High-resolution X-ray powder diffraction (HR-XRPD) was combined with X-ray absorption spectroscopy (XAS) in order to reveal the changes occurring during the experimental procedure. A mass spectrometer (MS) connected to the reactor outlet allow monitoring of the gas phase and accordingly the catalyst performance with respect to activity. Fischer-Tropsch synthesis was performed at 493 K, 18 bar, H₂/CO = 2.1, and >50%CO conversion. The reduction at 673 K confirmed the transition from Co₃O₄ to CoO and eventually a mixture of face-centered cubic (fcc) metallic cobalt, hexagonal close packed (hcp) metallic cobalt and a fraction of unreduced cobalt. The promoted catalyst exhibits a transformation during the initial stages of the Fischer-Tropsch synthesis possibly associated with minor re-oxidation of cobalt to Co²⁺ tetrahedrally coordinated, part of a CoAl₂O₄ surface structure. Throughout Fischer-Tropsch synthesis, HR-XRPD and XAS signals are unaffected, suggesting the absence of bulk cobalt transformations occurring at the initial Fischer-Tropsch deactivation period. No significant gradients in the concentration of cobalt species or the size of the crystallites have been found as a function of the length of the catalytic bed.