A DFT Insight into the Tuning Effect of Potassium Promoter on the Formation of Carbon Atoms via Carburization Gases Dissociation on Iron-Based Catalysts

The research of the formation mechanism of iron carbides is significant to design the high-performance catalysts for the Fischer-Tropsch synthesis (FTS) process. In this paper, the effect of potassium promoter on the formation of atomic carbon via carburization gases dissociation on the iron-based catalyst, the C2H4, C2H2 and CO/H-2 adsorption energies and dissociation paths as well as the rate constants of the corresponding elementary steps are investigated by DFT on the Fe(110), Fe(110)-K2O, Fe(211) and Fe(211)-K2O surfaces. The calculation results demonstrated that the K2O promoter can modify the capabilities of surface C formation via the thermodynamic method as well as the kinetical method. The K2O promoter can increase the CO adsorption energy while decreasing the C2H4 adsorption energy both on Fe(110) and Fe(211) surfaces. Kinetically, via tuning the catalyst surfaces from Fe(110) to Fe(211), the K2O promoter can inhibit the ability of C2H4/C2H2 dissociation to atomic carbon, while enhancing the ability of CO/H-2 decomposition to atomic carbon. The C2H4/C2H2 dissociation rate constants on Fe(211) and Fe(211)-K2O are about 10(7) times slower than that on Fe(110) and Fe(110)-K2O, whereas the dissociation rate constants of CO/H-2 on Fe(211) are about 10(6) times faster than that on Fe(110), and about 10(7) times faster on Fe(211)-K2O than on Fe(110)-K2O.