Insight into the transformation path from fcc-Co to hcp-Co during H2-CO-H2 processing

In the Fischer-Tropsch synthesis reaction, hcp-Co has more excellent catalytic performance than fcc-Co, thus, many studies have focused on the transformation from fcc-Co to hcp-Co via H2-CO-H2 '' processing (reductioncarbonization-reduction). However, the existing form of CO during carbonization is still unclear, and it is difficult to determine whether the generated carbon via CO disproportionation participates in the carbonization reaction. In this study, the environments with CO without C and with C without CO were attempted to be constructed, respectively. The formation and evolution of Co2C were studied by in-situ Raman, XRD, TPH-MS and HRTEM. The results show that: (1) the transformation from fcc-Co to hcp-Co can be realized in the environment with C but no CO; (2) CO directly participate the transformation from fcc-Co to hcp-Co in the H2-CO-H2 '' processing, and CO concentration and carbonization temperature jointly affect the H2-CO-H2 '' processing; (3) carbon deposition is inevitable during the whole H2-CO-H2 '' processing; however, the generated carbon does not participate in the reaction of forming Co2C within the transformation temperature range of the H2-CO-H2 '' processing.

Automated summary

This study reveals the transformation mechanism from fcc-Co to hcp-Co through the investigation of the effects of CO and C in different environments. The results indicate that the transformation from fcc-Co to hcp-Co can only be achieved in the presence of C without CO. CO directly participates in the transformation during the H2-CO-H2'' processing, and the concentration of CO and carbonization temperature jointly affect this process.