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Probing the product selectivity of Fischer–Tropsch catalysts is of prime scientific and industrial importancewith the aim to upgrade products and meet various end-use applications. In this work, the mechanisms for CH4 formation and C1–C1 coupling on a thermodynamically stable, terraced-like χ-Fe5C2 (510) surface were studied by DFT calculations. It was found that this surface exhibits high effective barriers of CH4 formation for the three cases (i.e., 3.66, 2.81, and 2.39 eV), indicating the unfavorable occurrence of CH4 formation under FTS conditions. The C + CH and CH + CH are the most likely coupling pathways, which follow the carbide mechanism. Subsequently, the effective barrier difference between CH4 formation and C1–C1 coupling was used as a descriptor to quantify FTS selectivity. A comparison of the selectivity between this surface and the reported FTS catalysts’ surfaces was discussed in detail. More interestingly, this surface shows unexpectedly high C2+ selectivity. This indicates that manipulating the crystal facet of χ-Fe5C2 catalyst can effectively tune the FTS selectivity, which will open a new avenue for highly selective Fe-based FTS catalysts.

Ethylene oxychlorination is the key technology in vinyl chloride (VCM, the monomer of PVC, polyvinyl chloride) production to close the chlorine loop by consuming the HCl released from the former cracking step. Due to the high demand for PVC, this leads to ethylene oxychlorination being one of the most important processes in the industry. This Review covers an indepth analysis of the dynamic nature of active sites for the main and side reactions involved in ethylene oxychlorination, featuring the findings and viewpoints from the dynamic kinetics study and analysis under industrial operating conditions. A unified picture of the mechanism of the surface reactions, and the effect of supports and promoters, has been presented based on the decoupled redoxcycle experiments, which leads to a significantly better understanding of the mechanism and provides valuable guidelines for effective catalyst design. Operando techniques and kinetic tools of the rate-diagram, as well as their application to the study of the redox-cycle in ethylene oxychlorination and kinetic models on both the main product and byproduct, are also reviewed. Perspectives on challenges and new process development and future research focus for better study of the VCM production chemistry are also proposed.

The mechanism of CH4 formation during Fischer–Tropsch synthesis on cobalt has been studied.

During the last years it has been an increasing focus on fundamental studies of the Fischer-Tropsch synthesis (FTS). Steady-state isotopic transient kinetic analysis and first principles investigation have proven to be important methods in studying the reaction mechanism of FTS. The present contribution deals with recent progresses in understanding of the F-T mechanism on Co catalysts based on combined DFT calculations, in situ characterization, steady-state isotopic transient kinetic analysis and microkinetics. A brief outlook into future perspectives of the FTS for converting synthesis gas from different carbon sources to fuels and chemicals is also provided.