The density functional theory was used to investigate the adsorption of CH_4 and H_2O on different rank coal surfaces.The coal rank is the dominant factor in affecting the adsorption capacity of coal.In order to better understand gas and water interaction with coal of different maturity,we developed fourteen coal models to represent the different rank coal.The interactions of CH_4 and H_2O with coal surfaces were studied and characterized by their adsorption energies,Mulliken charges and electrostatic potential surfaces.The results revealed that the interaction between coal and CH_4 was weak physical adsorption,and that the interaction between coal and H_2 O consisted of physical and chemical adsorption.Adsorption energy of coal–H_2O system was larger than that of coal–CH_4 on all rank coals,suggesting that the adsorption priority in the coal models is H_2 O > CH_4.Consequently,the injection of H_2 O into the different rank coal could effectively enhance the coal bed methane(CBM) recovery.
The Co Mg O and Co Mn Mg O catalysts are prepared by a co-precipitation method and used as the catalysts for the synthesis of carbon nanotubes(CNTs) through the catalytic chemical vapor deposition(CCVD). The effects of Mn addition on the carbon yield and structure are investigated. The catalysts are characterized by temperature programmed reduction(TPR) and X-ray diffraction(XRD) techniques, and the synthesized carbon materials are characterized by transmission electron microscopy(TEM) and thermo gravimetric analysis(TG). TEM measurement indicates that the catalyst Co Mg O enclosed completely in the produced graphite layer results in the deactivation of the catalyst. TG results suggest that the Co Mn Mg O catalyst has a higher selectivity for CNTs than Co Mg O. Meanwhile, different diameters of CNTs are synthesized by Co Mn Mg O catalysts with various amounts of Co content, and the results show that the addition of Mn avoids forming the enclosed catalyst, prevents the formation of amorphous carbon, subsequently promotes the growth of CNTs, and the catalyst with decreased Co content is favorable for the synthesis of CNTs with a narrow diameter distribution.The Co Mn Mg O catalyst with 40% Co content has superior catalytic activity for the growth of carbon nanotubes.
