| Hydrogen has been considered as an ideal energy carrier with the most development prospects in the future due to its high energy capacity and environmentally benign nature.However,the safe storage and tansportaion of hydrogen remains a bottleneck for large-scale application of hydrogen energy.Therefore,the search for safe and stable chemical hydrogen storage materials to conveniently store and release hydrogen under mild conditions is highly desired.Hydrous hydrazine?N2H4·H2O?has been considered as an ideal liquid-phase chemical hydrogen storage material due to its high hydrogen content?8.0 wt%?,low-toxicity,stable and easy transportation.The production from complete decomposition of N2H4·H2O is only hydrogen in addition to nitrogen,without any solid byproduct in the presence of suitable catalysts.Therefore,hydrogen production from N2H4·H2O has received considerable attention for researchers.Up to now,noble-metal-containing Ni-based catalysts have been developed as efficient catalysts for N2H4·H2O dehydrogenation reaction,but the limited storage and the high cost of noble metal still hinder their practical applications.However,most of the reported noble-metal-free catalysts failed to show satisfactory catalytic activity and their H2 selectivity remain to be further improved.Thus,the key and challenge of this thesis is to develop an excellent performance,100%H2 selectivity and high stability noble-metal-free catalyst for complete hydrogen generation from N2H4·H2O.In this thesis,the main results are divided into two parts as following:?1?We have demonstrated a facile one-step co-reduction method for the synthesis of a series of lower crystalline NiFe-La?OH?3 nanocatalysts without the help of surfactant or support.It was found that doping of La?OH?3 can effectively reduce the particle size and crystallinity of NiFe nanoparticles.The resultant Ni0.88Fe0.12-La?OH?3nanocatalyst exhibits an excellent catalytic activity,100%H2 selectivity,and satisfied recyclability for hydrogen production from N2H4·H2O under alkaline conditions at343 K.The excellent performances for the dehydrogenation of N2H4·H2O could be attributed to the synergistic electronic effect between NiFe nanoparticles and La?OH?3,as well as ultrafine and lower crystalline NiFe nanoparticles due to the addition of La?OH?3.In addition,the kinetics study shows that the reaction for dehydrogenation of N2H4·H2O follows a fist-order kinetics and zero-order kinetics with respect to the catalyst and initial N2H4 concentration,respectively.?2?In order to further stabilize NiFe nanoparticles and improve the catalytic performances of noble-metal-free catalysts,we designed and synthesized a nano CeZrO2 solid solutions,and used as the support for immobilizing the NiFe nanoparticles by impregnation-reduction method without the help of surfactant?denoted as NiFe/CeZrO2?.It was found that nano CeZrO2 solid solutions not only could act as the barrier to protect the NiFe nanoparticles from serious aggregation,but also can increase the electron density of the metal centers,resulting in a significantly improve catalytic performance.The resultant Ni0.8Fe0.2/Ce0.9Zr0.1O2 catalyst shows100%H2 selectivity for the dehydrogenation of N2H4·H2O under alkaline condition at343 K,and the turnover frequency?TOF?value is calculated to be 119.2 h-1,which is much higher than most of noble-metal-free catalysts ever reported.Moreover,the H2selectivity has no decline after five runs,indicating that the prepared NiFe/CeZrO2catalyst possesses high durability and stability under the current conditions. |
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