Preparation,Modification Of Coal-based Activated Carbon And Its Application In Catalytic Decomposition Of Methane

Catalytic methane decomposition?CMD?is a new and promising hydrogen production process,which is widely concerned due to easy separation of the products and no CO/CO₂emission.As the core of catalytic reaction,the selection and preparation of catalyst is the key concern.Coal-based activated carbon?AC?has many advantages,such as wide source,low price,high temperature resistance,no metal carbide formation,but the mechanism of minerals in coal during the pore formation process is unclear.Although AC has good high temperature resistance,its low activity limits the industrial application.In this paper,to solve the low activity and easy deactivation of carbon-based catalyst,coal-based activated carbon was prepared and modified by controlling the preparation method,adding metal additives and different carbon source to realize the structural regulation of catalyst and obtain higher performance.The Xiaoquan coal was floated and used as carbon source,and KOH as activation agent to study the effect of mineral content and composition in coal on preparation of AC for CMD.The results showed that mineral content and composition of coal have obvious influence on the structure and performance of AC.With the increase of mineral content of coal,the prepared AC shows a decreasing trend of surface area while the mesoporous surface increases.The washing method after carbonization/activation of coal samples seriously affects the textures of resultant AC.Water washing and acid washing gradually removed the formed salts,and the mineral salts dissolved in the acid solution play a positive role in the pore formation,especially for mesopores.The specific surface area and pore volume of AC increase with the degree of deashing,but excessive minerals in coal will lead to the decrease of the specific surface area and pore volume because the structure of AC can be destroyed after removal of bulk minerals.Si-,Fe-and Ca-containing species in minerals can act as templates in the activation process of KOH,which is conducive to the formation of mesopores,thus improving the mesoporosity of the obtained AC.In the CMD,the initial catalytic activity and stability of the prepared AC is enhanced with the increasing content of mineral in coal precursor,which is mainly ascribed to higher mesoporosity of AC prepared from coal with higher mineral content,enhancing the carbon deposition ability of the catalysts.To improve the catalytic activity,SMT coal as carbon source was blended with metal precursors?Ni,Co,Fe?and KOH as the activation agent to prepare single or bimetallic catalysts supported on AC by one-step using carbon reducibility at high temperature.The results showed that the specific surface area and pore volume of the catalyst decreased with the increase of metal loading,but the mesoporosity increased by doping Co or Fe in Ni/AC.In terms of reducing the deactivation rate of Ni based catalyst,the catalytic performance of Ni-Fe catalyst is better than that of Ni-Co catalyst.SEM showed that carbon fiber was formed over Ni-Fe/AC catalyst after the reaction,while spherical encapsulated carbon was produced on both Ni/AC and Ni-Co/AC catalysts,indicating that the addition of Fe changed the form of carbon deposition.For Ni-Fe catalyst,the effects of different Fe/Ni ratio and carbonization temperature on the catalyst structure and the performance were also investigated.It was found that 15Ni-15Fe/AC at the carbonization temperature of 850 ^oC showed good catalytic performance,and fiber carbon was formed during CMD.Porous carbon materials were prepared by KOH activation using the mixture of BLG coal and straw as the carbon source.The results showed the specific surface area and pore volume of the prepared AC first increased and then decreased with increasing the straw content in the coal,but the mesoporosity increased.The mixture ratio of BLG coal to straw and ratio of KOH to coal exerted a significant impact on the structure and catalytic performance of the AC.When the ratio of BLG coal to straw is 5/5 and the ratio of KOH to coal is 3/1,the prepared catalyst exhibited good catalytic performance in methane decomposition.