CO methanation over the 20% nickel catalyst prepared by impregnation-precipitation method on different supports of commercial γ-Al2O3, TiO2, SiO2 and nano-γ-Al2O3* was investigated. The nano-γ-Al2O3* support was pu...CO methanation over the 20% nickel catalyst prepared by impregnation-precipitation method on different supports of commercial γ-Al2O3, TiO2, SiO2 and nano-γ-Al2O3* was investigated. The nano-γ-Al2O3* support was pulverized using a ball milling method. Catalyst characterization was done using the methods of BET, XRD, SEM, ICP-OES methods. Carbon monoxide methanation process was carried out at the temperature of 350°C in pressure of 3 bar of H2:CO syngas with the molar ratio of 3:1 and with the GHSV of 3000 h-1 in a fixed bed reactor. The initial temperature of methane formation increased according to the order of Ni/γ-Al2O3* 2 γ-TiO2 γ-Al2O3. The Ni/γ-Al2O3*, which was prepared on the surface of nano milled γ-Al2O3 support, produced methane from the lowest temperature of 178°C to 350°C in CO methanation. The Ni/γ-Al2O3* catalyst gave the highest amount of methane (0.1224 mmol/g-cat) for 1 h methanation among other catalysts. XRD and SEM analysis proved that NiO particles in the Ni/γ-Al2O3* were finely distributed, and their sizes were smaller compared to those in the traditional one. The pulverization of γ-Al2O3 improved the dispersion of catalytic active nickel species inside porosity of the support leading to the improvement of its catalytic performance for CO methanation.展开更多
Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion for- mation during aluminum deoxidation process was proposed in Fe-O-Al melt. Thermodynamic properties of metastable i...Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion for- mation during aluminum deoxidation process was proposed in Fe-O-Al melt. Thermodynamic properties of metastable intermediates including （Al2O3）n clusters for prenucleation and α-Al2O3 nanoparticle for growth process were calculated using density functional theory. Furthermore, Gibbs free energy change of forming the intermediate by reaction between the dissolved aluminum （Al） and oxygen （O） in the melt was calculated. The results indicated that the thermodynamics of （Al2O3）n at steelmaking temperature are dependent on their structures, while that of α-Al2O3 nanoparticle are dependent on their size. The nuclei of α-Al2O3 which was originated from （Al2O3）n aggregated under a high supersaturation ratio of Al and O（Rs） in the melt. There existing excess oxygen because of the low Rs, but the secondary inclusions will be formed during the cooling process due to the excess oxygen. The nuclei lager than 20 nm can grow up spontaneously and instantaneously into primary inclusions because of thermodynamic drive. It is difficult to control the size of α-Al2O3 to be less than 20 nm, in the aluminum deoxidation process of the current conditions of steelmaking.展开更多
文摘CO methanation over the 20% nickel catalyst prepared by impregnation-precipitation method on different supports of commercial γ-Al2O3, TiO2, SiO2 and nano-γ-Al2O3* was investigated. The nano-γ-Al2O3* support was pulverized using a ball milling method. Catalyst characterization was done using the methods of BET, XRD, SEM, ICP-OES methods. Carbon monoxide methanation process was carried out at the temperature of 350°C in pressure of 3 bar of H2:CO syngas with the molar ratio of 3:1 and with the GHSV of 3000 h-1 in a fixed bed reactor. The initial temperature of methane formation increased according to the order of Ni/γ-Al2O3* 2 γ-TiO2 γ-Al2O3. The Ni/γ-Al2O3*, which was prepared on the surface of nano milled γ-Al2O3 support, produced methane from the lowest temperature of 178°C to 350°C in CO methanation. The Ni/γ-Al2O3* catalyst gave the highest amount of methane (0.1224 mmol/g-cat) for 1 h methanation among other catalysts. XRD and SEM analysis proved that NiO particles in the Ni/γ-Al2O3* were finely distributed, and their sizes were smaller compared to those in the traditional one. The pulverization of γ-Al2O3 improved the dispersion of catalytic active nickel species inside porosity of the support leading to the improvement of its catalytic performance for CO methanation.
基金financially supported by the National Natural Science Foundation of China (No. 51004054)Foundation from the Liaoning Province Education Department (No. L2013127)
文摘Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion for- mation during aluminum deoxidation process was proposed in Fe-O-Al melt. Thermodynamic properties of metastable intermediates including （Al2O3）n clusters for prenucleation and α-Al2O3 nanoparticle for growth process were calculated using density functional theory. Furthermore, Gibbs free energy change of forming the intermediate by reaction between the dissolved aluminum （Al） and oxygen （O） in the melt was calculated. The results indicated that the thermodynamics of （Al2O3）n at steelmaking temperature are dependent on their structures, while that of α-Al2O3 nanoparticle are dependent on their size. The nuclei of α-Al2O3 which was originated from （Al2O3）n aggregated under a high supersaturation ratio of Al and O（Rs） in the melt. There existing excess oxygen because of the low Rs, but the secondary inclusions will be formed during the cooling process due to the excess oxygen. The nuclei lager than 20 nm can grow up spontaneously and instantaneously into primary inclusions because of thermodynamic drive. It is difficult to control the size of α-Al2O3 to be less than 20 nm, in the aluminum deoxidation process of the current conditions of steelmaking.
