Insight into the transformation path from fcc-Co to hcp-Co during H2CO 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 "H2COH2″ processing (reduction-carbonization-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 "H2COH2″ processing, and CO concentration and carbonization temperature jointly affect the "H2COH2″ processing; (3) carbon deposition is inevitable during the whole "H2COH2″ processing; however, the generated carbon does not participate in the reaction of forming Co2C within the transformation temperature range of the "H2COH2″ processing.