In Situ XRD Study on Promotional Effect of Potassium on Carburization of Spray‐dried Precipitated Fe2O3 Catalysts. Issue 9 (28th March 2017)

• Record Type: Journal Article
• Authors: Niu, Liwei; Liu, Xingwu; Liu, Xi; Lv, Zhengang; Zhang, Chenghua; Wen, Xiaodong; Yang, Yong; Li, Yongwang; Xu, Jian
• Is Part Of: ChemCatChem. Volume 9:Issue 9(2017)
• Page Start: 1691
• Page End: 1700
• Publication Date: 2017-03-28
• Subjects: carburization -- Fischer–Tropsch synthesis -- iron -- potassium -- X-ray diffraction; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201601665
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: A study of the promotional effect of potassium on the carburization behavior of a series of spray‐dried precipitated Fe2 O3 catalysts (100 Fe, 100 Fe/0.52 K, 100 Fe/1.54 K, and 100 Fe/2.4 K) has been performed by using in situ XRD. The average crystallite size evolution for species such as α‐Fe2 O3, Fe3 O4, χ‐Fe5 C2, and θ‐Fe3 C were followed. The potassium promoter clearly inhibits the reduction of α‐Fe2 O3 to Fe3 O4, where the decreasing binding energy in the Fe 2p3/2, O 1s and K 2p3/2 spectra from X‐ray photoelectron spectroscopy (XPS) suggests an electron density increase in Fe and O upon potassium promotion, leading to the enhanced covalency in the Fe−O bond. In terms of crystallite size during carburization, an optimum potassium loading exists in catalyst 100 Fe/0.52 K, which shows the fastest reduction to Fe3 O4 with minimum crystallite sizes of around 7 to 15 nm. Potassium has no clear effect in determining the final crystallite size of χ‐Fe5 C2 . An arch‐shaped curve in the evolution of crystallite size of the Fe3 O4 intermediate was observed, which can be explained by the activation energy difference between the bidirectional steps of the outward oxygen diffusion and the inward carbon diffusion. Abstract : Promoting Potassium : The promotional effect of potassium on the carburization behavior of a series of spray‐dried precipitated Fe2 O3 catalysts is studied by using in situ XRD. The potassium promoter inhibits the reduction of α‐Fe2 O3 to Fe3 O4, in which X‐ray photoelectron spectra suggest an electron density increase in Fe and O upon potassium promotion, leading to enhanced covalency in the Fe−O bond. An optimum potassium loading exists in catalyst 100 Fe/0.52 K, which shows the fastest reduction to Fe3 O4 with minimum crystallite sizes of around 7 to 15 nm.