Preparation Of ZSM-5 Supported Transition Metal Catalyst And Its Performance For Hydrogen Production By Ammonia Decomposition

The extensive use of fossil fuels and serious environmental pollution have promoted the rapid development of clean and renewable energy.Hydrogen has the advantages of high calorific value and non-polluting combustion products,and is considered to be one of the most promising new energy sources.In NH₃,H accounts for 17.8%（mass fraction）,which is an efficient hydrogen storage medium,and NH₃ is easy to liquefy,and there is no problem of H₂transportation and storage.Therefore,hydrogen production by ammonia decomposition is an effective way to promote the development of hydrogen energy.In this paper,de-ZSM support was obtained by dealumination of ZSM-5with HNO₃,and then a series of ammonia decomposition hydrogen production catalysts were prepared by impregnation method and subsequent heat treatment with Fe,Co and Ni as active components.The structure of the catalyst was characterized by XRD,TEM,XPS,H₂-TPR,CO₂-TPD,BET and other characterization methods,and the performance of the catalyst for hydrogen production from ammonia decomposition was evaluated by using a fixed bed.Among Ni/de-ZSM series catalysts,5%Ni/de-ZSM-600℃has better hydrogen production performance from ammonia decomposition.Its apparent activation energy is 74.16 k J mol^-1,the ammonia decomposition conversion rate is 89.11%at 650℃,and the hydrogen generation rate is 28.41 mmol min^-1 g^-1_cat.Further studies show that the active component is Ni⁰ rather than Ni O in the process of hydrogen production by ammonia decomposition;the high specific surface area and microporous structure of the ZSM-5 support can better disperse metal nanoparticles;the strength of the basic sites on the catalyst surface and The quantity is the main reason for the improvement of the hydrogen production performance of ammonia decomposition.Among La-5%Ni/de-ZSM series catalysts,0.03 La-5%Ni/de-ZSM-600℃has the better hydrogen production performance from ammonia decomposition.Its apparent activation energy is 50.38 k J mol^-1,the ammonia decomposition conversion rate is 95.04%at 650°C,the hydrogen generation rate is 30.21 mmol min^-1 g^-1_cat,and it can run stably for 60 h at 600°C.Structural analysis shows that the active component of La-5%Ni/de-ZSM series catalysts is still Ni⁰ after doping with La,and the content of Ni atoms is increased.The doping of La has little effect on the specific surface area of the catalysts.However,the doping of La increases the strength of the surface basic sites of the catalyst,which facilitates the desorption of H atoms on the active site Ni,and improves the hydrogen production performance of Ni/de-ZSM by ammonia decomposition.Among the Fe/de-ZSM series catalysts,15%Fe/de-ZSM-600℃has the better hydrogen production performance from ammonia decomposition.Its apparent activation energy is 49.80 k J mol^-1,the ammonia decomposition conversion rate is 91.06%at 600°C,and the hydrogen generation rate is 29.03mmol min^-1 g^-1_cat.Structural analysis shows that Fe⁰ is the active component in the Fe/de-ZSM series catalysts to catalyze the decomposition of ammonia for hydrogen production.High carrier specific surface area,suitable strength and quantity of surface basic sites are the main factors affecting the catalytic activity.Among Co/de-ZSM series catalysts,5%Co/de-ZSM-600℃has the better hydrogen production performance from ammonia decomposition.Its apparent activation energy is 61.93 k J mol^-1,the ammonia decomposition conversion rate is 91.79%at 650℃,and the hydrogen generation rate is 29.27 mmol min^-1 g^-1_cat.Structural characterization analysis found that Co⁰ was the active component in the Co/de-ZSM series catalysts to catalyze the decomposition of ammonia for hydrogen production.The high dispersion and small particle size of metal nanoparticles are the main factors to improve the hydrogen production performance of ammonia decomposition.