Evolution of Co Species in CO<sub>2</sub>-Assisted Ethane Dehydrogenation: Competing Cleavage of C–H and C–C Bonds
Yingbin Zheng, Junjie Li, Xinbao Zhang, Shaoguo Li, Jie An, Fucun Chen, Xiujie Li, Xiangxue Zhu
Abstract
Integrating CO 2 into alkane dehydrogenation reactions provides an effective strategy to improve the metal catalyst stability. The structural evolution of supported metal species, particularly in a mild oxidation atmosphere, plays an important role in catalytic performance. Here, the influence of the introduction of CO 2 on the state of Co species and the corresponding dehydrogenation performance over Co/Silicalite-1 was investigated in detail. The manipulation of the CO 2 /C 2 H 6 feeding ratios dictated the selective bond breakage of either C–H or C–C in ethane, which was derived from the differentiated nanostructuring of Co species during reactions through a series of designed control-reaction tests and characterization results. At a CO 2 /C 2 H 6 feeding ratio of 4.0, Co nanoparticles underwent a transformation into active metallic Co species, which facilitated dry-reforming reaction with an ethene selectivity below 2%. When the CO 2 /C 2 H 6 feeding ratio was below 2.0, the generation of active metallic Co species was suppressed and the dehydrogenation reaction dominated over the Co 2+ sites. The effective suppression of reduction and sintering of active Co 2+ species led to a stable dehydrogenation performance lasting over 120 h, with ethene selectivity consistently exceeding 95% during this period. The elucidation of the state changes of Co species holds significant implications for the design of dehydrogenation catalysts.