Preparation,characterization And Properties Of The Catalysts For The Dehydrogenation Of Hydrogen Carrier Methylcyclohexane

As a clean energy carrier,hydrogen is able to avoid the environmental pollution caused by fossil fuels.Future hydrogen economy mainly relies on the safety and low cost of the development of hydrogen storage technology.In recent decades,people put forward the high pressure compression,cryogenic liquid,metal hydrides,carbon materials and liquid organic hydrides such as hydrogen storage?naphthenic?of hydrogen storage methods.Over the past few decades,different hydrogen storage methods have been intended,such as hydrogen compression in pressurized vessels,hydrogen liquefaction,hydrogen adsorption in metal hydrides,cryogenic storage with hydrogen-adsorbing materials,and hydrogen storage in liquid organic hydrides?i.e.,cycloalkane?.The comparison between the different storage systems indicates that storing hydrogen in liquid organic hydrides has environmental,economical,technical,and social advantages.The system maintains a closed carbon cycle,which drastically reduces chemical and thermal pollutions caused by toxic gas emission.And the system does not require heavy capital investment because the existing energy infrastructure is very compatible.All of the previously mentioned reasons makes liquid organic hydrides in hydrogen storage become the best choice of the hydrogen storage technology in the near future.Liquid organic hydrides in hydrogen storage based on reversible catalytic hydrogenation dehydrogenation and hydrogen can be stored in organic carrier through catalytic hydrogenation reaction.When the demand of energy exists,the hydrogen is extracted from the organic carrier by a catalytic dehydrogenation reaction and fed into fuel cells to generate electricity.At present,the hydrogenation reaction has been applied to industrial process,the difficulty of hydrogen storage is the dehydrogenation of hydrogen carrier reaction process.Literature reports about the process often should be carried out under high temperature,and use of noble metal catalyst,which seriously hindered the application of organic liquid hydrides hydrogen storage technology.In this paper,the variety of non-noble metal catalysts or a small amount of noble metal was added in it have been designed and prepared and their catalytic activities were tested using methylcyclohexane?MCH?.The support used in the dehydrogenation catalysts is focused on activated carbon,La₂O₃,ACC?activated carbon cloth?,TiO₂,Al₂O₃,etc.And the activity components is focused on Ti,Cr,Co,Ta,Fe,Mo,W,Ru,Rh,Ir,Ni,Pd and Pt.There is a greatconcern about noble metal catalysts especially Pt and Pt-M?M is the second metal element?catalysts because its have high selectivity in the process of naphthene dehydrogenation.The reports concerned nano-alumina or coated carbon alumina?CCA?support was very few.Therefore,nano-alumina or coated carbon alumina?CCA?support was prepared by ultrasound-assisted precipitation method.The the specific surface area,the average pore diameter and pore volume of the composite support were high to 360 m²/g,12.68 nm,and 2.30cc/g,respectively.In the dehydrogenation of MCH,single metal catalysts of Ni,Cu and Pt have good dehydrogenation activity.When Ni-based catalysts used in MCH dehydrogenation,its economy is much better than noble metals Pt catalysts.but the reaction process is an exothermic,raise the temperature is advantageous to the dehydrogenation process,while Ni easy to reunite,so,high temperature will reduce the stability of the catalyst.In view of this,the design is mainly discussed in Ni catalyst added,Pt and Cu as the second activity component,so that more conducive to hydrogenolysis and keep the Ni in reduction state.In the dehydrogenation of MCH over the Ni-Pt bimetallic catalysts under the conditions of 350 ?and mixed sample airspeed 252 h-1,the MCH conversion rate and toluene selectivity were high to 96.99% and 100% respectively.Otherwise,the alumina carrier?CCA?was prepared through high temperature pyrolysis using glucose as carbon source which covering on the surface of alumina.The catalysts with different supports but having the same active component such as Ni-Cu/?-Al₂O₃ and Ni-Cu/CCA by impregnation method.To investigate the reaction performance of the catalysts by the MCH dehydrogenation.At the same time,the experiment optimized the reaction conditions of the MCH dehydrogenation reaction by making use of the Ni-Cu/CCA catalyst,and the results show that: the carrier by carbon amount is 10%?wt.?,the Ni:Cu is 10:1,the reaction temperature is 650 K,MCH feeding speed is 0.015 m L/min,the carrier gas flow rate is 8m L/min,the reaction pressure is 0.4MPa,the MCH dehydrogenation conversion rate reached95.27%,the selectivity of toluene is close to 100%.This article also tested the the stability of Ni-Cu/CCA catalyst and found that CCA as the carrier of catalyst stability performance is better than ?-Al₂O₃.This may be form an active component-carbon structure after coated carbon on catalyst surface,it can delay the decline of the active so as to ensure the activity of catalyst maintained at a higher level.Although this mentioned in the design of the various catalyst performancecompared with the present reports of precious metal catalyst is higher,but for use in the on board hydrogen storage system dehydrogenation process,requirements of hydrogen release rate is very high,this design to improve the response speed this aspect has not yet made the corresponding work,for on-board hydrogen storage system in the process of dehydrogenation catalyst still need to continuously explore.