Surface/interface structure and catalytic mechanism are of great scientific significance in many practical catalytic reactions.
Porous single crystals which combine an ordered lattice structure and disordered inter-connected pore provide an alternative to create twisted surfaces with clear active sites in porous microstructures. Due to the fact that porous single crystals present the advantages of clear lattice structure, precise chemical composition and clear termination surface, there is a huge potential to build continuously twisted active surface structure.
In a study published in Angew. Chem. Int. Ed., a group led by Prof. XIE Kui from Fujian Institute of Research on the Structure of Matter, Chinese Academy of sciences has grown transition metal nitrides Nb4N5 and MoN single crystals at 2 cm scale to create well-defined active structures at twisted surfaces, presenting high catalytic activity and stability toward non-oxidative dehydrogenation of ethane to ethylene.
The researchers first grew the parent single crystals of potassium niobate and sodium niobate, then removed the periodic target atomic layer including Li/Na/O in ammonia atmosphere at 850-950 °C, and simultaneously nitrified and reconstructed the framework structure of metastable Nb-O single crystal into the mesoporous Nb4N5 single crystal.
In the same way, they obtained porous MoN single crystals from zinc molybdate at 875-925 °C.
Besides, the researchers found that the unsaturated metal-nitrogen coordination structures including Nb-N1/5, Nb-N2/5, Mo-N1/3 and Mo-N1/6 at twisted surfaces mainly accounted for the C-H activation with chemisorption of H in molecular ethane.
The porous single crystals with clear twisted surface structures not only improve dehydrogenation performance but also avoid the deep cracking of ethane to enhance coking resistance, demonstrating ~11-25% ethane conversion and ~98-99% ethylene selectivity without degradation being observed even after the operation of 50 hours.
This study is of important reference for the study of the surface structure and catalytic mechanism in actual catalytic reactions.
