费托合成制低碳烯烃中碱金属对CoMn催化剂催化性能的影响

Effects of alkalis on the catalytic performance of CoMn catalysts for Fischer-Tropsch to olefin reactions

碳化钴(Co2C)在费托合成制低碳烯烃(Fischer-Tropsch to Olefin, FTO)中起着重要的催化作用。通过X射线衍射(X-ray Diffraction, XRD)、X射线吸收精细结构(X-ray Absorption Fine Structure, XAFS)等表征与方法,对碱金属在CoMn催化FTO中形成碳化钴的影响进行了研究。在钠(Na)、钾(K)元素的影响下,CoMn催化剂在活性评测中,低碳非饱和烃与低碳饱和烃的比例高达17.4与9.4,且仅有较低的甲烷(CH4)产生,而锂(Li)对CoMn催化剂的选择性影响较弱。通过XRD表征,发现Na、K对CoMn催化剂形成Co2C有很好的促进效果。XAFS揭示了CoMn催化剂的电子结构,催化反应后形成碳化钴的配位结构,为研究CoMn催化剂微观结构提供了基础理论。

[Background] Cobalt carbide（Co2C） has recently been reported to catalyze the Fischer-Tropsch to olefin（FTO） conversion of syngas with high selectivity. However, electronic state and coordination structure of cobalt carbide is limited by its complex reaction. [Purpose] This study aims to clarify the effect of alkalis of CoMn catalysts for FTO and understanding the atomic structure of cobalt carbide nanoparticles in the CoMn catalyst. [Methods] X-ray absorption fine structure（XAFS） experimental on beamline（BL14W1） of XAFS spectroscopy at the Shanghai Synchrotron Radiation Facility（SSRF） is conducted to explore the electronic state and coordination structure of cobalt carbide with the effects of alkalis. [Results] X-ray absorption near-edge structures（XANES） spectra indicts that Na, K acted as electronic donors to cobalt than Li. EXAFS spectra clarified show that the atomic structure of cobalt carbide nanoparticles. [Conclusion] The Na, K promoter had benefited the formation of the cobalt carbide in the evolution of the FTO catalysts.