Ammonia Decomposition Over Rare Oxides Support Ru And Ni Catalysts For The On-site Generation Of Hydrogen

Hydrogen had been considered as an ideal energy carrier and widely used in many industrial processes.However,the storage and transportation of hydrogen energy still are a great challenge due to the high flammability,explosive and low compression characteristics of hydrogen,and the use of chemical hydrogen storage method is expected to solve this problem.For on-situ hydrogen production for proton exchange membrane fuel cells,it is important to study highly active catalysts to catalyze ammonia decomposition to produce hydrogen without carboxyl compounds.In this paper,the effect of different methods,basic oxide and temperature on the preparation of lanthanum oxide was studied,and then the ammonia decomposition activity of Ru metal was studied.Furthermore,the specific surface area of La₂O₃carrier was improved by surfactant?CTAB?and the alkalinity of the carrier was regulated by adding other basic oxides to explore the decomposition performance of ammonia.Ammonia decomposition activity of Ni-Co bimetallic catalysts with different mass ratios on the solid solution support of Ce_0.6Zr_0.3Y_0.1O₂ was also studied.?1?Ammonia?NH₃?decomposition for hydrogen production is an excellent alternative to clean energy,but there is a need for more efficient and stable catalytic support to meet the increasing demand for mass production and transportation of hydrogen energy.Four kinds of La₂O₃ synthesized via the citric acid complex,KOH-K₂CO₃ co-precipitation,pyrolysis and urea method were used as supports of Ru-based catalysts by impregnation to investigate NH₃ decomposition.We herein prepared all catalysts for the production of CO_x-free hydrogen from ammonia decomposition at 300?550oC.Among the prepared formulations,the Ru/La₂O₃-700-i catalyst,prepared by a successive conversional impregnation method,showed the highest NH₃ conversion?90.7%?with the GHSV of 18000 mL/g_cat·h at 525oC,which was significantly superior to the Ru/La₂O₃-700-p synthesized via a one-step pyrolysis method.Through XRD and TEM studies,we identified a pure La₂O₃ phase formation that was responsible for the high catalytic activity of Ru/La₂O₃-700-i for ammonia decomposition.CO₂-TPD and XPS results indicated that Ru/La₂O₃-700-i catalyst had high suitable basic sites,high surface oxygen vacancy and high surface Ru atomic concentration?%?.Moreover,the reaction TOF over the Ru/La₂O₃-700-i catalyst(1537.6 h^-1)was higher than that of the Ru/La₂O₃-700-p catalyst(1364.1 h^-1).The activity of Ru/La₂O₃-700-i catalyst was found to be even further enhanced in the presence of KOH.?2?The decomposition of NH₃ for hydrogen production was studied using Ni supported on La₂O₃-T catalysts prepared by a surfactant-templated method to elucidate the influence of supports of calcination temperature on the activity of these catalysts.The catalytic performance for all synthesis samples were investigated for300?600oC at atmospheric pressure.It was found that Ni/La₂O₃-450 has the highest activity among the other catalysts and the decreasing order of NH₃ conversion as follow:Ni/La₂O₃-450>Ni/La₂O₃-550>Ni/La₂O₃-650?Ni/La₂O₃-750?Ni/La₂O₃-850.This is attributed to create high surface area,higher moderate basicity strength and surface oxygen species concentration(i.e.O^2-)evidenced the BET,CO₂-TPD and XPS characterization,respectively.In addition,5 wt%Ni catalysts supported on various XLa?MgLa,ZrLa,CeLa,NdLa and YLa?mixed oxide systems to elucidate the influence of supports composition on the activity of these catalysts.This results show that Ni/MgLa has the highest activity among the other catalysts and the decreasing order of NH₃ conversion as follows:Ni/MgLa>>Ni/NdLa?Ni/YLa>Ni/CeLa>>Ni/ZrLa.This is attributed to the fact that MgO has a moderate basic site,which can appropriately tailor the basic site of Ni/La₂O₃ catalyst and significantly increase the specific surface area of the carrier.Another series of mixed Mg-La oxide supports with different Mg/La molar ratios?Mg/La=1,3,5,7 and 9?were prepared to investigate the effect of Mg content in the MgLa mixed oxide for ammonia decomposition.This catalytic activity demonstrates that the 5 wt%Ni with 5Mg/La ratio catalyst was the most active.When the Ni loading amount was changed in the range of 10–40 wt%for Ni/5MgLa catalyst,the sample with 40 wt%Ni exhibited completely NH₃ conversion at 600oC and high GHSV=30000 mL h^-1 g^-1_cat.?3?Ammonia has become an attractive source for CO_x-free hydrogen production for fuel cell applications.The catalytic performance of Ce_0.6Zr_0.3Y_0.1O₂ solid solutions supported Ni,Co and Ni-Co bimetallic catalysts are evaluated in the temperature range of 300-600oC at atmospheric pressure.Due to the synergistic effect between Ni and Co,CZY supported Ni-Co bimetallic catalysts show higher ammonia decomposition activity compared to Ni or Co monometallic samples.The Ni-Co bimetallic catalyst with the Ni/Co mass ratio of 1/9 exhibits the highest NH₃conversion with the GHSV of 6000 mL h^-1 g^-1_cat,which reaches 100%conversion at600oC.Moreover,the Ni₁Co₉/CZY catalyst shows good thermal stability during the72 h reaction time.The Ni₁Co₉/CZY have the highest total H₂-uptake of 0.35mmol?g^-1 and the highest TOF_H2 value(40.57 min^-1)at 350oC among all the catalysts.Our characterization confirms the formation of Ni-Co alloy is responsible for the high activity of Ni₁Co₉/CZY catalyst for the ammonia decomposition.