Effect of Reduction and Carburization Pretreatment on Iron Catalyst for Synthesis of Light Olefins from CO Hydrogenation  

作　　者：AN Tong DANG Dan CHENG Yi 

机构地区：[1]Department of Chemical Engineering, Tsinghua University, Beijing 100084, P. R. China

出　　处：《Chemical Research in Chinese Universities》2017年第4期672-677,共6页高等学校化学研究（英文版）

基　　金：Supported by the National Natural Science Foundation of China（No. 21576151）.

摘　　要：Effect of reduction and carburization pretreatment on iron catalyst for CO hydrogenation to light olefins was investigated. The bulk structure and surface composition of the catalysts during pretreatment were characterized by means of X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS） and high-resolution transmission elec- tron microscopy（HRTEM）. The results indicated that phase transformation of iron phases involved a-Fe203---~Fe304 --,a-Fe both in the bulk and on the surface layers in hydrogen atmosphere. However, a-Fe203 was firstly transformed to Fe3C and then to Fe5C2 in CO atmosphere, while in syngas atmosphere directly to Fe5C2. As carburization pretreatment time was prolonged, the degree of carburization on the surface increased, and the increase degree of iron catalyst carburization in CO pretreatment was stronger than that in syngas pretreatment. It inferred that surface carbon species was more easily formed in syngas pretreatment instead of iron carbide in CO pretreatment. After hydrogen pretreatment, when the catalyst was reduced to a mixture of magnetite and metallic iron, the selectivity to light olefins was relatively low. Under the joint effects of the active sites from surface iron carbide and surface carbon layers blocking the active sites, longer CO pretreatment time resulted in higher methane selectivity and less light olefins. The selectivity to methane on H2-pretreated catalyst was lower than that of CO-pretreated catalyst.Effect of reduction and carburization pretreatment on iron catalyst for CO hydrogenation to light olefins was investigated. The bulk structure and surface composition of the catalysts during pretreatment were characterized by means of X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS） and high-resolution transmission elec- tron microscopy（HRTEM）. The results indicated that phase transformation of iron phases involved a-Fe203---~Fe304 --,a-Fe both in the bulk and on the surface layers in hydrogen atmosphere. However, a-Fe203 was firstly transformed to Fe3C and then to Fe5C2 in CO atmosphere, while in syngas atmosphere directly to Fe5C2. As carburization pretreatment time was prolonged, the degree of carburization on the surface increased, and the increase degree of iron catalyst carburization in CO pretreatment was stronger than that in syngas pretreatment. It inferred that surface carbon species was more easily formed in syngas pretreatment instead of iron carbide in CO pretreatment. After hydrogen pretreatment, when the catalyst was reduced to a mixture of magnetite and metallic iron, the selectivity to light olefins was relatively low. Under the joint effects of the active sites from surface iron carbide and surface carbon layers blocking the active sites, longer CO pretreatment time resulted in higher methane selectivity and less light olefins. The selectivity to methane on H2-pretreated catalyst was lower than that of CO-pretreated catalyst.

关 键 词：Light olefin Fischer-Tropsch synthesis CO hydrogenation Iron catalyst PRETREATMENT 

分 类 号：TQ113.2[化学工程—无机化工] TQ426.81