Preparation Of Magnesium-Based Noble Metal Nanocatalyst And Their Catalytic Performance For Hydrogen Production

As an efficient and clean alternative energy carrier,hydrogen energy has broad prospects due to the depletion of fossil-fuel reserves and increase in environmental pollution.Thereinto,sodium borohydride,as a hydrogen storage material,has attracted a great concern for modern research attributed to its high theoretical hydrogen storage capacity（10.8 wt%）,high controllability and environmental friendliness.Although the hydrolysis of sodium borohydride is an effective way to produce hydrogen,there are still many problems in this study field.In present,the developed catalysts still have many shortcomings including the poor adhesion between the active center of catalyst and the support,weak stability of the catalyst,short service life,and so on.Therefore,it is very important to prepare an economic,efficient and stable catalyst for the development of the national economy.This project use a micro-arc oxidation technology to prepare the magnesium oxide support and ruthenium nanoparticle catalyst on magnesium,which is simple and easy for industrial production.Meanwhile,this method also could solve the defects of the general catalyst,such as weak stability.The optimal preparation process of micro-arc oxidation is as follows:constant voltage mode is adopted,and the electrical paremetersis are seted to 500Hz,60,and 180V which represent the pulse number,pulse width,and arcing voltage,respectively.The whole running time lasts 10s,and the electrolyte temperature is 10℃.The calcination is carried out for the prepared catalyst in an atmosphere of 95%Ar+5%H₂ at a holding temperature of 400℃ for 2 hours,which results in a highest activity for obtained sample.The SEM characteristic results demonstrate that the acquired magnesium oxide support is a three-dimensional porous structure and the ruthenium nanoparticles are dispersed on the support uniformly.The images of TEM show the average diameter of the ruthenium nanoparticles is 2.8±1.2nm.XPS analysis results show that Ru-O is completely reduced to Ru（0） when the hydrogen reduction temperature is elevated to 400℃.Meanwhile,the kinetics of hydrolysis reaction of sodium borohydride is also studied.The effects of the concentration of NaBH₄ and NaOH,catalyst amount and reaction temperature are evaluated.The experimental results show that the hydrogen generation rate increases followed by decreasing with increasing of NaBH₄ concentration.On the other hand,the increasing NaOH concentration can inhibit the hydrogen production.Furthermore,the hydrogen production rate increases linearly with the increase of catalyst amount and the apparent activation energy is 44.6 kJ·mol^-1.By using the Ru/MgO catalyst with a concentration of 3.0 wt%NaBH₄ and 0.02 wt%NaOH,the hydrogen generation rate as high as 83,409mL·min^-1·g^-1 is achieved at 30℃ ambient condition.In the cyclic performance test,the hydrogen generation rate decreases not exceeding 35%even through 10th circular reactions,and the hydrolysis reaction could last as long as 30 hours,indicating an excellent stability of catalyst.In addition,the catalyst also achieves an "on-off" control model that paves a way for on-board and on-demand hydrogen production.