Effect Of Mineral Matters On The Coal-based Activated Carbons And Catalytic Methane Decomposition To Hydrogen

Catalytic methane decomposition to hydrogen posses many advantages,including simple technology process,no CO_x formation and easy separatation of products.Moreover,water-gas shift reaction and separation process in traditional hydrogen production can be avoided.Therefore,the key of large-scale application is to develop a low-cost catalyst with excellent catalytic performance.Coal-based activated carbon?AC?attracts special attention due to its low cost,wide carbon source and high temperature resistance.Mineral matters is an important component of coal,but its effect on the pore formation of AC is not clear.In this paper,four coals with different mineral compositions and contents are used as the carbon source to investigate the influence of mineral matters on preparation of AC,and the relationship between the texture properties of AC and its catalytic performance in methane decomposition to hydrogen.Four kinds of coal samples including Sihe?SH?,Fenghuang?FH?,Fujian anthracite?FJ?and Piliqing?PLQ?are used as carbon sources to prepare ACs by KOH activation at 850 ^oC.The effects of KOH/carbon ratio,activation temperature and activation time on the pore structure of ACs and its catalytic performance in methane decomposition are investigated.The results show that the impact of KOH/carbon ratio,activation temperature and activation time are different for the coals with different mineral content.The ACs prepared from the coal with higher mineral content under higher KOH/carbon ratio,activation temperature and longer activation time have the better developed pore structure,thus better catalytic activity and stability in methane decomposition to hydrogen.When a certain amount of Fe?NO₃?₃ is added to the SH coal,the BET specific surface area of resultant ACs increases and so does the mesoporisity.As a result,the catalytic stability of resultant ACs is improved.It is concluded that the addition of Fe in coal benefits the development of pore structure of resultant ACs and its catalytic performance in methane decomposition to hydrogen.The coals and ACs are demineralized by washing with different solvents to explore the effect of mineral composition in coal on the pore structure and catalytic performance of resultant ACs in methane decomposition.It is found that mineral matter in coal can react with activating agent and/or other mineral matter,and act as the template during the preparation of ACs,which can be removed by the washing treatment after activation and promotes the formation and development of porous structure.The catalytic activity and stability of ACs in methane decomposition are also improved.The mineral matters containing Ca,Fe and Mg play a positive role on the formation and development of pore in the preparation of AC,which enhance the specific surface area,especially the external surface area and mesoporisity,and thus improve the catalytic performance of ACs.The washing method of carbon materials after activation affects the pore structure and catalytic performance of resultant ACs,which is mainly related with the removal of mineral matters.For three high-ash coals,SH,FH and FJ,the specific surface area of resultant ACs is up to 1633 m²·g^-1,1657 m²·g^-1and 1281 m²·g^-1 after washing with HCl,repectively,much higher than those after washing with H₂O.The catalytic activity and stability of ACs are obviously enhanced by washing with HCl.For PLQ coal with low ash and high calcium content,water washing after KOH activation can prepare the AC with high sepecific surface area(1725 m²·g^-1)and better catalytic performance of the activated carbon can be obtained after only washing with water.The specific surface area and mesoporisity can be further increased by complete demineralization of ACs with HF,which also demonstrates the templete roles of mineral matters in coal during the development of pore sturcture.