Studies On Porous Single Crystal Vanadium Nitride Materials And Their Catalytic Mechanism

Porous metal materials have been widely used in the field of catalysis.Porous transition metal nitrides such as vanadium nitride have unique advantages of noble metal electronic structure and better catalytic activity.If these porous materials can be in the form of single crystals with long-range structural coherence,taking full advantage of the properties of porous single crystals,it will significantly improve the catalytic activity and stability of vanadium nitride.In this paper,the precursor single crystals of NH₄V₄O₁₀,BiVO₄,FeVO₄ and CoV₂O₆were nitrided into porous single-crystal vanadium nitride by a temperature-programmed reaction method,and the superiority and stability of the combination of transition metal vanadium nitride and porous single-crystal materials in catalytic performance were tested.The main research contents are as follows:（1）The NH₄V₄O₁₀ precursor was synthesized by hydrothermal method,and vanadium nitride porous single crystal particles were prepared by temperature-programmed reaction method to control vacuum degree.The crystal structure and microscopic morphology of vanadium nitride porous single crystal particles were studied in detail by various characterization methods,and the porous single crystal particles were determined to be synthesized.The hydrogen evolution reaction performance of porous single-crystal vanadium nitride was tested under the conditions of1.0 M KOH and 0.5 M H₂SO₄,and compared with that of porous polycrystalline vanadium nitride catalysts.Vanadium nitride porous single crystal has good hydrogen evolution reaction performance,the performance of porous single crystal is obviously better than that of porous polycrystal.Under the condition of 1.0 M KOH,the overpotential of porous single-crystal vanadium nitride reaches 74.67 m V when the current density is 10 m A/cm².Under the same experimental conditions,the overpotential of irregular vanadium nitride porous polycrystalline is 150.66 m V,which reflects the uniqueness of porous single crystal octahedron materials.（2）The molten salt method is used to grow BiVO₄,FeVO₄,CoV₂O₆ single crystals,which are transformed into vanadium nitride porous single crystals,Fe_0.1V_0.9N and Co_0.1V_0.9N porous single crystals,respectively,through a temperature-programmed reaction method with controlled vacuum.And using STEM,BET,HS-LEISS and other characterization methods,the lattice,pore and surface structure were studied in detail,and it was confirmed that the large-scale vanadium nitride porous single crystal with clear surface structure was prepared.Their crystal structures and microstructures were studied in detail by means of XRD,SEM,XPS and other characterization methods.Using Py-IR and NH₃-TPD and other characterization methods,the acid neutrality type and acid center strength of the vanadium nitride porous single crystal were studied.Three kinds of porous single crystals were used as catalysts to test the catalytic activity and stability of ethane-free dehydrogenation to ethylene.Here we create the well-defined active surfaces with the quantitative high-density Lewis sites in porous single-crystalline vanadium nitride monoliths and show the enhanced performance with ethane conversion of 36%and ethylene selectivity of 99%at 660°C.The porous single-crystalline VN,Fe_0.1V_0.9N and Co_0.1V_0.9N monoliths demonstrate the composition of V,Feand Coat the top layer leading to an electron-deficient active surface composed of unsaturated V-N,Fe-N and Co-N coordination structures at surface.The high-density Lewis sites confined in lattice at surface contribute to the catalytic activity and stability without performance degradation being observed even after a continuous operation of 200 hours.In this paper,the possibility of forming porous vanadium nitride single crystals was investigated,that is single crystal as the precursor was transformed into vanadium nitride porous single crystal by the programmed temperature reaction method which controlled the vacuum degree.This process can be widely used to study the development and preparation of other porous single crystals.In addition,the vanadium nitride porous single crystals were successfully synthesized,which show excellent catalytic activity and good stability in the fields of electrocatalysis and heterogeneous catalysis,providing a new process idea for the preparation and application of vanadium nitride materials.