Elucidating the Active-Phase Evolution of Fe-Based Catalysts during Isobutane Dehydrogenation with and without CO<sub>2</sub> in Feed Gas
Jiapei Wang, Min Liu, Junjie Li, Chuanfu Wang, Xinbao Zhang, Yingbin Zheng, Xiujie Li, Longya Xu, Xinwen Guo, Chunshan Song, Xiangxue Zhu
Abstract
Fe-based catalysts are promising as inexpensive and nontoxic dehydrogenation catalysts, but the active phase has not been elucidated in CO2-assisted dehydrogenation. In this study, the phase evolution of supported iron catalyst was studied with in situ XRD, ex situ XRD, XPS, TEM, TG-DTA, and experiments with reaction atmosphere switching. The results show that the original Fe2O3 phase is gradually reduced to α-Fe and then α-Fe is carburized to Fe3C in a low CO2/i-C4H10 ratio feed atmosphere. The Fe3C phase serves as an active phase for i-C4H10 dehydrogenation. When CO2 is introduced, the Fe3C phase also shows high activity for reforming and cracking, leading to higher CO2 conversion, lower butene selectivity, and a larger amount of coke deposition. With increasing CO2/i-C4H10 feed ratio, the iron species in the catalyst would stay at a higher valence state for a longer time. The Fe3O4 phase is maintained throughout the reactions with a CO2/i-C4H10 feed ratio of 1/2 or higher, which results in a relatively stable isobutane conversion. This work correlates active-phase evolution with catalytic performance and provides a fundamental insight into Fe-based catalysts for butane dehydrogenation.