Nickel Foam Used For Methane Decomposition And Recycling The Carbon Deposited Spent Catalyst

Catalytic methane decomposition（CMD）is a promising hydrogen production process for co-production of CO_x-free hydrogen and carbon by-products with commercial value.In particular,under the pressure of environmental protection and after the large-scale commercial development of unconventional natural gas such as shale gas,the methane decomposition process has attracted widespread attention at home and abroad.However,CMD cannot be regarded as a mature process in the industry.The main obstacle is that the catalyst is easy to deactivate due to sintering at high temperatures and carbon deposits,and how to recycle the spent catalyst efficiently.In this work,we provide a simple strategy for preparation and development of robust unsupported nickel catalysts from commercial nickel foam（NF）.Several mild pre-treatment methods（acid treatment,thermal treatment,acid-thermal treatment）of NF were explored on the NF morphology,structure and used to promote the CMD reactivity.Effects of the pre-treatment conditions（thermal treatment temperature and time,and hydrogen reduction temperature and time）and reaction temperature（700 ^oC-850 ^oC）were also explored on CMD reactivity in a fixed-bed reactor.The morphology and structure of carbon deposits produced after CMD on nickel-based catalysts were characterized and analyzed.It is found that catalytic performance of the NF-based catalyst is highly dependent on the pre-treatment and reaction temperature.When the reaction temperature of CMD is 850 ^oC,the NF-based catalyst exhibits the best catalytic activity.The thermal and acid-thermal treatments could more greatly promote its catalytic activity（with methane conversion up to 74.6%and 91.8%after the initial unsteady state,respectively）of NF by affecting the surface morphology of NF and the size of nickel particles.In addition to high-purity hydrogen production,Ni-encapsulated carbon nano onions with a quasi-spherical shape（the particle size of about 26-82 nm）and filamentous carbons can be observed.To fully release potential abilities of the catalyst,this work proposes and explores the recycling of the spent catalyst as a new catalyst in the CMD test and evaluation as a supercapacitor electrode material.High and stable CH₄ conversion rate（up to around 90%-93%）can be achieved in a fixed bed reactor by simulating the operation mode in a fluidized-bed reactor for a continuous CMD process（carbon deposits or/and new catalysts were regularly and quantitatively removed or/and added,respectively）.Although the carbon-deposited catalyst was used as a supercapacitor electrode material and exhibited poor electrochemical performance,the carbon-nickel composite electrode material prepared by acid treatment（5 mol/L HCl）solution exhibited excellent specific capacitance performance.The WS-6 electrode shows excellent capacitance,with specific capacitance of up to 232.9 F/g at scan rate of 1 m V/s,and specific capacitance of up to 104.3 F/g at current density of 0.5 A/g.In this paper,the preparation method of high-activity unsupported catalyst for CMD using commercial NF preparation provides guidance for the design and preparation of new high-efficiency catalysts.The strategy of reusing the carbon deposited spent catalyst provides ideas and technical support for the reuse of the spent catalyst after CMD.