Ni-based Catalysts For Hydrogen Production From Hydrous Hydrazine And Hydrazine Borane

Hydrogen energy?H₂?has attracted much attention as a clean energy of high energy density.However,the safe and efficient hydrogen storage skill remains the key in the large scale applications.Hydrous hydrazine?N₂H₄·H₂O?has been considered to be a promising liquid chemical hydrogen storage material due to its high hydrogen content of 8.0 wt% and only N₂ as the by-product during hydrogen production process.Hydrazine borane?N₂H₄BH₃?,another hydrogen storage material,contains a large amount of hydrogen?15.4 wt%?.Especially,a promising approach for complete hydrogen production from N₂H₄BH₃ is by hydrolysis of the BH₃ group and selective decomposition of the N₂H₄ moiety of N₂H₄BH₃,corresponding to a theoretical gravimetric hydrogen storage capacity?GHSC?of 10.0 wt% for the system N₂H₄BH₃-3H₂ O.Therefore,the development of highly efficient and stable catalysts with a high H₂ selectivity is essential for the hydrogen production from hydrazine borane and hydrous hydrazine.This thesis aims at designing and synthesizing several Ni-based metal nanomaterials,and applying them as catalysts for dehydrogenation of hydrazine borane and hydrous hydrazine decomposition.The main contents are as follows:?1?Using an impregnation and co-reduction method,MOFs-immobilized NiFePd nanoparticles?NiFePd/MIL-101?have been successfully prepared and characterized by SEM,TEM,SAED,XRD,EDX,XPS and N₂ adsorption desorption analysis.NiFePd nanoparticles with particle size of about 3.2 nm are uniformly dispersed on the metal organic framework MIL-101.Ni_0.36Fe_0.24Pd_0.4/MIL-101 has been used as an efficient catalyst with a 100% hydrogen selectivity for dehydrogenation of N₂H₄BH₃ and N₂H₄·H₂O.Moreover the H₂ selectivity and activity almost have no obvious change after 5 runs,indicating the good stability of Ni_0.36Fe_0.24Pd_0.4/MIL-101 catalyst.?2?Mo-modified NiPd nanoparticles?NiPdMo NPs?have been facilely synthesized via a facile co-reduction method at room temperature.It was found that the synthesized NiPdMo NPs are well dispersed with an average size of about 4.0 nm.The introduction of Mo can improve the dispersion of catalyst,reduce the particle size as well as crystallinity of NiPd alloy,and transfer its electrons to Pd and Ni.These may enhance the catalytic performance of catalyst.Among all the synthesized catalysts,Ni_0.6Pd_0.4Mo_0.8 exhibits the highest catalytic activity for the hydrogen generation from N₂H₄BH₃ and N₂H₄·H₂O at 323 K,with the total turnover frequency?TOF?of 405.1 and 195.5 h-1.?3?A NaOH-assisted reduction method was applied to control the synthesis of ultrafine NiPt alloy nanoparticles supported by nano-sized La₂O₂CO₃.The assynthesized NiPt/La₂O₂CO₃ catalyst exerts excellent catalytic activity and 100% hydrogen selectivity for dehydrogenation of N₂H₄BH₃ at room temperature?298 K?,giving the highest TOF value of 1200.0 h-1 for N₂H₄BH₃ so far.In addition,NiPt/La₂O₂CO₃ catalyst also shows good activity and durability as well as a 100% hydrogen selectivity for decomposition of N₂H₄·H₂O at room temperature.Our synthesis is not limited to NiPt NPs alone,but can be easily extended to other bimetallic NPs,providing a general approach to metal nanocatalysts for the hydrogen generation from N₂H₄BH₃ and N₂H₄·H₂O.