Evolution of Co Species in CO₂-Assisted Ethane Dehydrogenation: Competing Cleavage of C-H and C-C Bonds

Integrating CO2 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 CO2 on the state of Co species and the corresponding dehydrogenation performance over Co/Silicalite-1 was investigated in detail. The manipulation of the CO2/C2H6 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 CO2/C2H6 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 CO2/C2H6 feeding ratio was below 2.0, the generation of active metallic Co species was suppressed and the dehydrogenation reaction dominated over the Co2+ sites. The effective suppression of reduction and sintering of active Co2+ 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.