Preparation and Performance Study of Highly Efficient Ni-Pt/CeO2 Catalyst for Hydrogen Generation from Decomposition of Hydrous Hydrazine

Author:Dai Hao

Supervisor:wang ping


Degree Year:2019





Hydrogen is an attractive renewable energy carrier,but its widespread use is severely restricted by the lack of viable means for efficient and safe storage of hydrogen.Hydrous hydrazine(N2H4 H2O)has received considerable attention as a promising candidate for chemical hydrogen storage.This is a result of its many favorable attributes,such as high hydrogen density(8 wt%),relatively low cost,satisfactory stability under ambient conditions,and free of solid.In this thesis,series of efficient Ni-Pt/CeO2 catalysts for hydrogen production by N2H4 H2O decomposition were prepared,and the key issues for the development and application of N2H4 H2O hydrogen production system were explored,including the kinetic study of catalytic reaction,the study of catalyst degradation,the preparation of monolithic catalyst and the development of low-cost catalyst.Firstly,the kinetics of the catalytic decomposition of alkaline N2H4·H2O solutions is investigated over bimetallic Ni-Pt nanocatalysts supported ceria(CeO2),which is prepared by a one-pot co-precipitation method.The resultant Ni-Pt/CeO2 catalyst exhibits high activity and 100%H2 selectivity for the N2H4 H2O decomposition.The effects of reaction temperature,N2H4 H2O concentration,NaOH concentration and catalyst concentration on the reaction rate are studied systematically.The kinetic rate equation can be expressed as:r=-d[N2H4·H2Oydt=-K[N2H4·H2O]0.52/0.043[NaOH]0.57/0[catalyst]1.03,where k=4.64 ×108 exp(-6591.29/T).Particularly,the catalytic decomposition of N2H4· H2O with respect to N2H4·H2O concentration follows a near-zero order kinetics at the initial reaction stage with high N2H4·H2O concentrations and the fraction-order kinetics at low N2H4·H2O concentrations.Our results provide valuable insights into the catalytic decomposition kinetics of N2H4·H2O.Secondly,we report an experimental study of the performance degradation of Ni-Pt/CeO2 catalyst using TPD-MS,FTIR,HRTEM techniques.Our study on the post-used Ni-Pt/CeO2 catalyst found that a predominant N2 species and various reaction intermediates over-strongly bound on the catalyst surface.Furthermore,the amount of the bound N2 species at Ni sites is approximately linearly correlated with the activity decay degree.These results provide a straightforward explanation of the performance degradation phenomenon and highlight the critical role of adsorbate/catalyst interaction in determination of the catalytic performanceThirdly,we report the synthesis of a monolithic catalyst composed of Ni-Pt/CeO2 nanoparticles and granular activated carbon using a simple impregnation-reduction method.It was found that the activity and H2 selectivity of the resulting catalyst can be readily regulated by changing the annealing temperature and atmosphere.The optimal Ni-Pt/CeO2/GAC catalyst enabled complete and rapid decomposition of N2H4 H2O to generate H2 with a 100%selectivity at moderate temperature in the presence of 1 M NaOH.Importantly,by using this monolithic catalyst,we constituted a N2H4·H2O-based HG system with a material-based hydrogen capacity as high as 6.54 wt%.This finding represents a promising step toward the development of N2H4 H2O as a viable hydrogen storage carrierFinally,we synthesize a highly dispersed Pt on NiO/CeO2 surface by strong electrostatic adsorption method.After heat treatment under H2 atmosphere,the fine grain size and/or amorphous Ni-Pt bimetal alloy nanoparticles are formed in the Ni-Pt/CeO2-SEA catalyst Compared with the other catalysts prepared by the common methods,such as impregnation,galvanic replacement and deposition-precipitation method,the Ni-Pt/CeO2-SEA catalyst showed the optimal catalytic activity and 100%H2 selectivity.This superior performance should be due to the more active sites and the promoted intrinsic catalytic activity is obtained simultaneously in the Ni-Pt/CeO2-SEA catalyst.