Direct Conversion of Syngas to Light Olefins through Fischer–Tropsch Synthesis over Fe–Zr Catalysts Modified with Sodium
Zhunzhun Ma, Hongfang Ma, Haitao Zhang, Xian Wu, Weixin Qian, Qiwen Sun, Weiyong Ying
Abstract
temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mössbauer 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%.