Fe−Zr−Na catalysts synthesized by coprecipitation and impregnation methods were implemented to investigate the promoting effects of Na and Zr on the iron-based catalyst for hightemperature Fischer−Tropsch synthesis (HTFT). The catalysts were characterized by Ar adsorption− desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, CO temperature-programmed desorption, H 2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy (MES). The results indicated that Na changed the active sites on the catalyst surface for the CO and hydrogen adsorption, owing to the electron migration from Na to Fe atoms, which resulted in an enhanced CO dissociative adsorption and a decrease in hydrogen adsorption on the metallic Fe surface. The decreased H/C ratio on the catalyst surface accounted for the increased chain propagation and weakened hydrogenation of light olefins. Besides, Na could also facilitate the carbonization of catalysts and protect the iron carbide against oxidation, which provides more active sites for HTFT reaction and is beneficial to the C−C coupling. Zr could decrease the hematite crystallite size and stabilize the active phase to improve the HTFT activity. At an optimal Na loading of 1.0 wt %, the Fe−Zr−1.0Na catalyst exhibited the highest light olefin selectivity of 35.8% in the hydrocarbon distribution at a CO conversion of 95.2%.

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In a 5 m high turbulent fluidized bed with a 0.3 m inner diameter, local solids concentration in the dense region and axial pressure difference along the column were measured using an optical fibre probe (PC6M) and differential pressure sensors (PX653), respectively. The time-series signals of the solids concentration fluctuations are analyzed via statistical methods. The axial and radial profiles of solids concentration are non-uniform. In the developing dense region, the radial profiles of solids concentration are significantly influenced by operating conditions, and the fluctuation of solid concentration is considerably enhanced with the development of flow. In the fully developed dense region, the axial solids concentration decreases monotonously with height, and the radial profiles of solids concentration are exponential. The flow development in the dense region could be accelerated by the superficial gas velocity. Based on the analysis of the characteristics of the radial solids concentration distribution in the dense region, an empirical correlation of this distribution is proposed. The formulated correlation is found to be consistent with the experimental data reported in the literature.