Nanosized NiO,CeO_(2) and NiO-CeO_(2) mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method.All the samples were characterized by different techniques as to their chemical compositio...Nanosized NiO,CeO_(2) and NiO-CeO_(2) mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method.All the samples were characterized by different techniques as to their chemical composition,structure,morphology and texture.On the catalysts submitted to the same reduction pretreatment adopted for the activity tests the surface basic properties and specific metal surface area were also determined.NiO and CeO_(2) nanocrystals of about 4 nm in size were obtained,regardless of the Ni/Ce molar ratio.The Raman and X-ray photoelectron spectroscopy results proved the formation of defective sites at the NiO-CeO_(2) interface,where Ni species are in strong interaction with the support.The microcalorimetric and Fourier transform infrared analyses of the reduced samples highlighted that,unlike metallic nickel,CeO_(2) is able to effectively adsorb CO_(2),forming carbonates and hydrogen carbonates.After reduction in H2 at 400°C for 1 h,the catalytic performance was studied in the CO and CO_(2) co-methanation reaction.Catalytic tests were performed at atmospheric pressure and 300°C,using CO/CO_(2)/H_(2) molar compositions of 1/1/7 or 1/1/5,and space velocities equal to 72000 or 450000 cm^(3)∙h^(-1)∙gcat^(-1).Whereas CO was almost completely hydrogenated in any investigated experimental conditions,CO_(2) conversion was strongly affected by both the CO/CO_(2)/H_(2) ratio and the space velocity.The faster and definitely preferred CO hydrogenation was explained in the light of the different mechanisms of CO and CO_(2) methanation.On a selected sample,the influence of the reaction temperature and of a higher number of space velocity values,as well as the stability,were also studied.Provided that the Ni content is optimized,the NiCe system investigated was very promising,being highly active for the CO_(x) co-methanation reaction in a wide range of operating conditions and stable(up to 50 h)also when submitted to thermal stress.展开更多
Highly mesoporous Zn O and g-Al2O3nanowires（NWs） are both synthesized by a hydrothermal method using commercially available porous anodic aluminium oxide（AAO） as template. AAO membrane acts as template for Zn O NW...Highly mesoporous Zn O and g-Al2O3nanowires（NWs） are both synthesized by a hydrothermal method using commercially available porous anodic aluminium oxide（AAO） as template. AAO membrane acts as template for Zn O NWs and both as template and precursor for g-Al2O3 NWs. The formation of intermediate phases of porous Zn6Al2（OH）16CO3and boehmite（g-Al OOH） were observed, both occurring during the hydrothermal synthesis of porous Zn O and g-Al2O3 NWs, respectively, and disappearing after annealing at 600 C. This novel template-assisted hydrothermal process leads to the formation of porous Zn O and g-Al2O3NWs（specific surface area of 192 m2 g 1and 263 m2 g 1, respectively）, showing pore sizes around 4 nm in diameter. The influence of the reaction parameters on the nanostructure morphology was also investigated. A Zn O seed layer, deposited on the AAO channels prior to the hydrothermal synthesis, leads to more compact Zn O nanowires（99 m2 g-1） protecting the AAO host from the chemical attack of the precursor solution.展开更多
基金Open Access funding provided by Universita degli Studi di Cagliari.
文摘Nanosized NiO,CeO_(2) and NiO-CeO_(2) mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method.All the samples were characterized by different techniques as to their chemical composition,structure,morphology and texture.On the catalysts submitted to the same reduction pretreatment adopted for the activity tests the surface basic properties and specific metal surface area were also determined.NiO and CeO_(2) nanocrystals of about 4 nm in size were obtained,regardless of the Ni/Ce molar ratio.The Raman and X-ray photoelectron spectroscopy results proved the formation of defective sites at the NiO-CeO_(2) interface,where Ni species are in strong interaction with the support.The microcalorimetric and Fourier transform infrared analyses of the reduced samples highlighted that,unlike metallic nickel,CeO_(2) is able to effectively adsorb CO_(2),forming carbonates and hydrogen carbonates.After reduction in H2 at 400°C for 1 h,the catalytic performance was studied in the CO and CO_(2) co-methanation reaction.Catalytic tests were performed at atmospheric pressure and 300°C,using CO/CO_(2)/H_(2) molar compositions of 1/1/7 or 1/1/5,and space velocities equal to 72000 or 450000 cm^(3)∙h^(-1)∙gcat^(-1).Whereas CO was almost completely hydrogenated in any investigated experimental conditions,CO_(2) conversion was strongly affected by both the CO/CO_(2)/H_(2) ratio and the space velocity.The faster and definitely preferred CO hydrogenation was explained in the light of the different mechanisms of CO and CO_(2) methanation.On a selected sample,the influence of the reaction temperature and of a higher number of space velocity values,as well as the stability,were also studied.Provided that the Ni content is optimized,the NiCe system investigated was very promising,being highly active for the CO_(x) co-methanation reaction in a wide range of operating conditions and stable(up to 50 h)also when submitted to thermal stress.
文摘Highly mesoporous Zn O and g-Al2O3nanowires（NWs） are both synthesized by a hydrothermal method using commercially available porous anodic aluminium oxide（AAO） as template. AAO membrane acts as template for Zn O NWs and both as template and precursor for g-Al2O3 NWs. The formation of intermediate phases of porous Zn6Al2（OH）16CO3and boehmite（g-Al OOH） were observed, both occurring during the hydrothermal synthesis of porous Zn O and g-Al2O3 NWs, respectively, and disappearing after annealing at 600 C. This novel template-assisted hydrothermal process leads to the formation of porous Zn O and g-Al2O3NWs（specific surface area of 192 m2 g 1and 263 m2 g 1, respectively）, showing pore sizes around 4 nm in diameter. The influence of the reaction parameters on the nanostructure morphology was also investigated. A Zn O seed layer, deposited on the AAO channels prior to the hydrothermal synthesis, leads to more compact Zn O nanowires（99 m2 g-1） protecting the AAO host from the chemical attack of the precursor solution.
