Controllable Fabrication Of High-purity Mesoporous Alumina And Its Methanation Application

Mesoporous alumina has been widely used in many fields,such as adsorption and catalysis,because of its high mechanical strength,specific surface area and pore volume,narrow pore size distribution and suitable surface acidic property.Therefore,the research of mesoporous alumina has always been the attention of scientists.In this paper,precursors and ?-Al2O3 with high purity,single crystal type and controllable pore size distribution were prepared using aluminum isopropoxide as raw materials through the process of hydrolysis,gelling and drying.Low cost recovery of solvent and optimization of pore structure and macroscopic properties of alumina were achieved.In addition,we explored the methanation activity of the mesoporous alumina of different pore structure after loading the active components of Ni.XRD,SEM,TEM,TG,IR and N2 adsorption-desorption isotherms were used to characterize the samples.The main results can be briefly described as follows:(1)Research on process parameters of hydrolysis,gelling and drying.The effects of the ratio of water to isopropyl alcohol of solvent,gelling temperature,gelling time and solid content on the structure and properties of Al2O3 and its precursors were studied.The results show that the gelling temperature plays an important role on crystal type of the precursor,and more isopropanol in solvent,higher gelling temperature,longer gelling time is conducive to the formation of larger pore.The pore volume of product can be ranged from 0.39 m L/g to 0.74 mL/g by changing the gelling conditions.(2)Effects of inorganic ammonium pore forming materials on the structure and properties of mesoporous alumina and its precursors.The results indicates that the addition of NH4HCO3,(NH4)2CO3,NH3·H2O and CH3COONH4 can obtain pure boehmite precursor,the highest specific surface area of the samples is 276.1 m2/g by using CH3COONH4 as pore forming agent,the largest pore volume of the samples is 0.72 mL/g by using(NH4)2CO3 as pore forming agent.In addition,the product which is using NH4HCO3 as pore forming materials showes a bimodal mesoporous distribution and its pore size is concentrated in about 4.5 nm and 17.4 nm,and the SEM images showes the regular honeycomb-like pore about 1?m.Moreover,with the increase of NH4HCO3,the specific surface area and pore volume of Al2O3 increased,and the surface morphology became rougher,and finally formed a honeycomb-like shape.(3)The synthesized carrier with different channels was loaded with active component Ni to evaluate methanation reaction.The result reveals that the Al2O3 catalyst with bimodal mesoporous distribution showes best catalytic activity,and all of the catalytic activity of synthetic Al2O3 support is better than commercial support.