Preparation And Catalytic Performance Of Pt-based Catalysts For Decalin Dehydrogenation To Hydrogen

Hydrogen storage is one of the key issues for the hydrogen fuel cell application.Liquid-phase organic compounds,such as decalin,cyclohexane,or methylcyclohexane,are considered as potential candidates for high-density hydrogen storage.Among them,decalin can offer a hydrogen storage capacity of 7.3%.The current dehydrogenation catalysts suffer from coking and carbon deposition at high temperatures,which hinder the reversible cycle of hydrogen storage and release from organic hydrides.Pt-based catalysts are the common catalysts for decalin dehydrogenation and the support properties have a significant impact on the activity of Pt-based catalysts.Spinel Mg Al₂O₄ and layered double metal hydroxides（LDHs）materials have the characteristics of adjustable composition elements,desired thermal stability and acid-base double active centers.The structure and composition of supports can significantly improve the catalytic activity of corresponding catalysts.In this paper,different morphologies of MgAl₂O₄ were synthesized by alcohol heating method,sol-gel method,co-precipitation method and solid reaction method separately.The results show that catalysts using Mg Al₂O₄ synthesized by the alcohol heating method as catalyst support material generates large specific surface area and suitable acidity,which exhibites excellent decalin dehydrogenation performance.The Mg/Al molar ratio used in Mg Al₂O₄ synthesis was further adjusted to modify the the support structure.The experimental results showed that the catalysts with the Mg/Al molar ratio of 0.5 yields the best dehydrogenation activity performance.This study shows that maximum hydrogen yield can be obtrained at 3%of Pt loading and synergistic effect was found in Pt-Pd bimetallic catalyst for posiotive effect on H₂ yield.MgAl-LDH,another catalyst support used in this study,were synthesized by the hydrothermal method,urea hydrolysis method and co-precipitation method.The results indicate that the support prepared by hydrothermal method produces the largest specific surface area,the highest dispersion,the minimum Pt particle size and the best decalin dehydrogenation performance.Mg Al-LDH supports with different Mg/Al molar ratios were further prepared by the hydrothermal method.The results showed that the catalyst possesses the largest specific surface area,the smallest Pt particles and the best dehydrogenation performance when the Mg/Al molar ratio of 4 was used in syntheisis.Effect of different metals,such as Mg,Ni,Zn or Co on MAl-LDH catalyst performance were the investigated to find that the hydrogen yield as high as 18 mmol from 1 m L decalin for 2.5 h at 260°C over 1 wt%Pt/Mg₄Al-LDH.The results obtained from this study are helpful for designing and developping efficient decalin dehydrogenation catalysts,which are of great significance for the application of liquid organic hydride to hydrogen storage technology.