The structure of Ni active sites supported on amorphous silica-alumina supports with different contents of Al_(2)O_(3)loadings in relation to their activities in ethylene oligomerization were investigated.Two kinds of...The structure of Ni active sites supported on amorphous silica-alumina supports with different contents of Al_(2)O_(3)loadings in relation to their activities in ethylene oligomerization were investigated.Two kinds of Ni sites were detected by in situ FTIR-CO and H_(2)-TPR experiments,that are Ni^(2+)cations as grafted on weak acidic silanols and Ni^(2+)cations at ion-exchange positions.The ethylene oligomerization activities of these Ni/ASA catalysts were found an ascending tendency as the Al_(2)O_(3)loading decreased,which could be attributed to the enriched concentration of Ni^(2+)species on acidic silanols with a weaker interaction with the amorphous silica-alumina support.These Ni^(2+)species were more easily to be evolved into Ni^(+)species,which has been identified to be the active sites of ethylene oligomerization.Thus,it seems reasonable to conclude that Ni^(2+)species grafted on acidic silanols were the precursors of active sites.展开更多
Five mixtures (M1 to M5) of silica-alumina geomaterials and two varieties of alumina (AP and AR) were used for the elaboration of mullite refractory materials between 1500℃ and 1600℃. An X-ray diffraction (XRD) anal...Five mixtures (M1 to M5) of silica-alumina geomaterials and two varieties of alumina (AP and AR) were used for the elaboration of mullite refractory materials between 1500℃ and 1600℃. An X-ray diffraction (XRD) analysis showed that the refractory samples are composed of mullite, corundum and silica. The length of the mullite crystals was measured by a method of image analysis of scanning electron microscopy (SEM). Chemical and mechanical properties of these materials were investigated and correlated with their microstructure. Resistance towards Acid Attack test showed that the refractory samples present good resistance, as well as, the alumina powder AR obtained from waste of silica-alumina bricks proves to be efficient for an eventual use.展开更多
Nano-sized silica-alumina particles were in-situ synthesized in supersolubilizing reverse micellae.Both the most probable pore diameters and the particle sizes were distributed in nano-scale SiO2-Al2O3 particulates.Th...Nano-sized silica-alumina particles were in-situ synthesized in supersolubilizing reverse micellae.Both the most probable pore diameters and the particle sizes were distributed in nano-scale SiO2-Al2O3 particulates.The influence of SiO2/Al2O3 mass ratio and the surfactant content on the particle size and morphology,pore structure,and acidity was characterized by the low temperature nitrogen adsorption/desorption (BET),SEM,TEM and NH3-TPD methods.The test results indicated that the most probable pore diameter of SiO2-Al2O3 nanoparticles was around 10 nm,the specific surface area was about 223-286 m2 /g,the pore volumes were about 0.48-0.63 cm 3 /g,and the particle sizes of porous SiO2-Al2O3 calcined at 550 ℃ were distributed always in the range between 10 nm to 50 nm.The calcined SiO2-Al2O3 nano-powders showed their acidity being stronger than the porous γ-Al2O3 support.展开更多
Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely o...Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely observed in conventionally prepared silica-alumina.Here,we show that high population and dispersion of Al~Ⅴ species on the surface of amorphous silica-alumina(ASA)can be achieved by means of flame spray pyrolysis.High resolution TEM/EDX,high magnetic-field NMR and DFT calculations are employed to characterize the structure of as-prepared ASAs.Solid-state ^(27)Al multi-quantum MAS NMR experiments show that most of the Al~Ⅴspecies are formed independently from the alumina phase and are accessible for vip molecules on the surface.Upon water adsorption,these Al~Ⅴ species are transformed to Al~Ⅵ species,structurally similar to surface Al~Ⅳ species,as confirmed by DFT calculations.The outstanding catalytic activity of as-synthesized ASA is demonstrated using the in situ H/D exchange reaction with deuterated benzene as an example.The Al~Ⅴ-rich ASA provides a much lower activation energy(～30 kJ/mol)than that reported for zeolite H-ZSM-5(～60 kJ/mol).The superior catalytic performance is attributed to the high Al~Ⅴcontent promoting the surface active sites in ASA.The knowledge gained on the synthesis of Al~Ⅴ-rich ASAs and the nature of aluminum coordination in these materials could pave the way to more efficient silica-alumina based catalysts.展开更多
Hollow silica-alumina composite spheres were prepared by a polystyrene(PS)template method using various amounts of PS suspension.Homogeneous hollow spheres prepared using 40 g were found to be with a diameter of about...Hollow silica-alumina composite spheres were prepared by a polystyrene(PS)template method using various amounts of PS suspension.Homogeneous hollow spheres prepared using 40 g were found to be with a diameter of about 300 nm in scanning electron microscopy,and transmission electron microscopy demonstrated their hollow sphere morphology.From the nitrogen adsorption isotherm results,the homogeneous hollow spheres prepared using 40 g of the PS suspension were found to be an ordered pore structure.The activities of the hollow spheres prepared using various amounts of the PS suspension for hydrolytic dehydrogenation of ammonia borane were compared.The results showed that 10,7,and 6 mL of hydrogen were evolved from the aqueous ammonia borane solution in about 40 min in the presence of the hollow spheres prepared using 40,80,and 120 g of PS suspension,respectively.The homogeneous hollow spheres with an ordered pore structure showed the highest activity among all the hollow spheres.The amount of acid sites and the coordination number of aluminum active species were characterized using neutralization titration and solid-state ^(27)Al magic angle spinning nuclear magnetic resonance spectroscopy.The homogeneous hollow spheres with an ordered pore structure had high amount of acid sites and 4-coordinated aluminum species.The relative proportion of 4-coordinated aluminum species was related to the dispersion of aluminum species.These results indicate that the homogeneous hollow spheres with an ordered pore structure showed the high activity because of high amount of acid sites induced by the highly dispersed aluminum species.展开更多
文摘The structure of Ni active sites supported on amorphous silica-alumina supports with different contents of Al_(2)O_(3)loadings in relation to their activities in ethylene oligomerization were investigated.Two kinds of Ni sites were detected by in situ FTIR-CO and H_(2)-TPR experiments,that are Ni^(2+)cations as grafted on weak acidic silanols and Ni^(2+)cations at ion-exchange positions.The ethylene oligomerization activities of these Ni/ASA catalysts were found an ascending tendency as the Al_(2)O_(3)loading decreased,which could be attributed to the enriched concentration of Ni^(2+)species on acidic silanols with a weaker interaction with the amorphous silica-alumina support.These Ni^(2+)species were more easily to be evolved into Ni^(+)species,which has been identified to be the active sites of ethylene oligomerization.Thus,it seems reasonable to conclude that Ni^(2+)species grafted on acidic silanols were the precursors of active sites.
文摘Five mixtures (M1 to M5) of silica-alumina geomaterials and two varieties of alumina (AP and AR) were used for the elaboration of mullite refractory materials between 1500℃ and 1600℃. An X-ray diffraction (XRD) analysis showed that the refractory samples are composed of mullite, corundum and silica. The length of the mullite crystals was measured by a method of image analysis of scanning electron microscopy (SEM). Chemical and mechanical properties of these materials were investigated and correlated with their microstructure. Resistance towards Acid Attack test showed that the refractory samples present good resistance, as well as, the alumina powder AR obtained from waste of silica-alumina bricks proves to be efficient for an eventual use.
基金the financial support of Liaoning Province National Science Fund (No.20072009)
文摘Nano-sized silica-alumina particles were in-situ synthesized in supersolubilizing reverse micellae.Both the most probable pore diameters and the particle sizes were distributed in nano-scale SiO2-Al2O3 particulates.The influence of SiO2/Al2O3 mass ratio and the surfactant content on the particle size and morphology,pore structure,and acidity was characterized by the low temperature nitrogen adsorption/desorption (BET),SEM,TEM and NH3-TPD methods.The test results indicated that the most probable pore diameter of SiO2-Al2O3 nanoparticles was around 10 nm,the specific surface area was about 223-286 m2 /g,the pore volumes were about 0.48-0.63 cm 3 /g,and the particle sizes of porous SiO2-Al2O3 calcined at 550 ℃ were distributed always in the range between 10 nm to 50 nm.The calcined SiO2-Al2O3 nano-powders showed their acidity being stronger than the porous γ-Al2O3 support.
基金the financial supports by Australian Research Council Discovery Projects (DP150103842)Discovery Earlier Career Research Project (DE190101618)+1 种基金the Faculty's MCR Scheme, Energy and Materials Clusters at the University of Sydneythe support by the National Natural Science Foundation of China (21522310, 21473244 and 21210005)
文摘Pentacoordinated Al(Al~Ⅴ)species in silica-alumina are promising to promote the formation of acid sites or act as surface defects for tailoring single-atom catalysts.However,pentahedral coordination(Al~Ⅴ)is rarely observed in conventionally prepared silica-alumina.Here,we show that high population and dispersion of Al~Ⅴ species on the surface of amorphous silica-alumina(ASA)can be achieved by means of flame spray pyrolysis.High resolution TEM/EDX,high magnetic-field NMR and DFT calculations are employed to characterize the structure of as-prepared ASAs.Solid-state ^(27)Al multi-quantum MAS NMR experiments show that most of the Al~Ⅴspecies are formed independently from the alumina phase and are accessible for vip molecules on the surface.Upon water adsorption,these Al~Ⅴ species are transformed to Al~Ⅵ species,structurally similar to surface Al~Ⅳ species,as confirmed by DFT calculations.The outstanding catalytic activity of as-synthesized ASA is demonstrated using the in situ H/D exchange reaction with deuterated benzene as an example.The Al~Ⅴ-rich ASA provides a much lower activation energy(～30 kJ/mol)than that reported for zeolite H-ZSM-5(～60 kJ/mol).The superior catalytic performance is attributed to the high Al~Ⅴcontent promoting the surface active sites in ASA.The knowledge gained on the synthesis of Al~Ⅴ-rich ASAs and the nature of aluminum coordination in these materials could pave the way to more efficient silica-alumina based catalysts.
基金supported by NIMS and University of Tokyo microstructural characterization platform as a program of“Nanotechnology Platform”of the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan.
文摘Hollow silica-alumina composite spheres were prepared by a polystyrene(PS)template method using various amounts of PS suspension.Homogeneous hollow spheres prepared using 40 g were found to be with a diameter of about 300 nm in scanning electron microscopy,and transmission electron microscopy demonstrated their hollow sphere morphology.From the nitrogen adsorption isotherm results,the homogeneous hollow spheres prepared using 40 g of the PS suspension were found to be an ordered pore structure.The activities of the hollow spheres prepared using various amounts of the PS suspension for hydrolytic dehydrogenation of ammonia borane were compared.The results showed that 10,7,and 6 mL of hydrogen were evolved from the aqueous ammonia borane solution in about 40 min in the presence of the hollow spheres prepared using 40,80,and 120 g of PS suspension,respectively.The homogeneous hollow spheres with an ordered pore structure showed the highest activity among all the hollow spheres.The amount of acid sites and the coordination number of aluminum active species were characterized using neutralization titration and solid-state ^(27)Al magic angle spinning nuclear magnetic resonance spectroscopy.The homogeneous hollow spheres with an ordered pore structure had high amount of acid sites and 4-coordinated aluminum species.The relative proportion of 4-coordinated aluminum species was related to the dispersion of aluminum species.These results indicate that the homogeneous hollow spheres with an ordered pore structure showed the high activity because of high amount of acid sites induced by the highly dispersed aluminum species.
