Highly coke-resisting ZrO2-decorated Ni/A1203 catalysts for CO methanation were prepared by a two-step process. The support was first loaded with NiO by impregnating method and then modified with ZrO2 by deposition-pr...Highly coke-resisting ZrO2-decorated Ni/A1203 catalysts for CO methanation were prepared by a two-step process. The support was first loaded with NiO by impregnating method and then modified with ZrO2 by deposition-precipitation method （IM-DP）. Nitrogen adsorption- desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetdc analysis, H2 temperature- programmed reduction and desorption, NH3 temperature-programmed desorption, and zeta potential analysis were employed to characterize the samples. The results revealed that, compared with the catalysts with the same composition prepared by co-impregnation （CI） and sequential impregnation （SI） methods, the Ni/A1203 catalyst prepared by IM-DP showed much enhanced catalytic performance for syngas methanation under the condition of atmospheric pressure and a high weight hourly space velocity of 120000 mL.g-1 .h-1. In a 80 h life time test under the condition of 300-600 ~C and 3.0 MPa, this catalyst showed high stability and resistance to coking, and the amount of deposited carbon was only 0.4 wt%. On the contrary, the deposited carbon over the catalyst without ZrO2 reached 1.5 wt% after a 60 h life time test. The improved catalytic performance was attributed to the selective deposition of ZrO2 nanoparticles on the surface of NiO rather than A1203, which could he well controlled via changing the electrostatic interaction in the DP procedure. This unique structure could enhance the dissociation of CO2 and generate surface oxygen intermediates, thus preventing carbon deposition on the Ni particles in syngas methanation.展开更多
In this work, atomic layer deposition （ALD） was employed to fabricate coaxial multi-interface hollow Ni-A12OB-ZnO nanowires. The morpholog34 microstructure, and ZnO shell thickness dependent electromagnetic and micr...In this work, atomic layer deposition （ALD） was employed to fabricate coaxial multi-interface hollow Ni-A12OB-ZnO nanowires. The morpholog34 microstructure, and ZnO shell thickness dependent electromagnetic and microwave absorbing properties of these Ni-A12OB-ZnO nanowires were characterized. Excellent microwave absorbing properties with a minimum reflection loss （RL） of approximately -50 dB at 9.44 GHz were found for the Ni-A12OB-100ZnO nanowires, which was 10 times of Ni-A1203 nanowires. The microwave absorption frequency could be effectively varied by simply adjusting the number of ZnO deposition cycles. The absorption peaks of Ni-A1203-100ZnO and Ni-A12OB-150ZnO nanowires shifted of 5.5 and 6.8 GHz towards lower frequencies, respectively, occupying one third of the investigated frequency band. The enhanced microwave absorption arose from multiple loss mechanisms caused by the unique coaxial multi-interface structure, such as multi-interfacial polarization relaxation, natural and exchange resonances, as well as multiple internal reflections and scattering. These results demonstrate that the ALD method can be used to realize tailored nanoscale structures, making it a highly promising method for obtaining high- efficiency microwave absorbers, and opening a potentially novel route for frecluencv adiustment and microwave ima^in~ fields.展开更多
The effect of rare earth oxides （RE=Ce, La, Gd, and Dy） doping of alumina support in NiO/7-A1203 system was investi- gated on its catalytic performance in oxidative dehydrogenation （ODH） of cyclohexane. The physic...The effect of rare earth oxides （RE=Ce, La, Gd, and Dy） doping of alumina support in NiO/7-A1203 system was investi- gated on its catalytic performance in oxidative dehydrogenation （ODH） of cyclohexane. The physicochemical properties of various samples were followed up through N2 physisorption, temperature programmed reduction （H2-TPR）, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and potentiometric acid-base titration techniques. In the parent NiO/y-A1203 catalyst, Ni species were found to be strongly interacted with alumina surface. Addition of rare earth dopants to ）＇-A1203 in the catalyst system affected the nickel-alumina interaction and resulted in significant modifications in the catalytic performances in the ODH reaction. The results re- vealed the beneficial role of both La203 and Gd2Os doping in enhancing the ODH catalytic activity and selectivity to cyclohexene. H2-TPR and XPS results indicated that majority of Ni species in NiO/La203 modified T-A1203 were more weakly interacted with La203 and alumina whereas both NiO like species and nickel aluminate were present on the surface. Doping with cerium or dyspro- sium increased the nickel-support interaction and led to a decrease in surface nickel concentration. In case of doping with Ce, surface concentration of cerium oxide was higher than those of the other RE oxides; the doped catalyst reached its steady state activity faster than the other catalysts. The acid-base results suggested that RE metals were interacted most likely with acidic surface hydroxyl groups. The degree of nickel-alumina interaction decreased in the following order： LaAI〉GdAI〉CeAI〉DyA1.展开更多
基金supported by the National Natural Science Foundation of China(No.21476238)the National Basic Research Program(No.2014CB744306)+1 种基金the National Key Technology R&D Program of China(No.2010BAC66B01)the"Strategic Priority Research Program"of Chinese Academy of Sciences(Nos.XDA07010100 and XDA07010200)
文摘Highly coke-resisting ZrO2-decorated Ni/A1203 catalysts for CO methanation were prepared by a two-step process. The support was first loaded with NiO by impregnating method and then modified with ZrO2 by deposition-precipitation method （IM-DP）. Nitrogen adsorption- desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetdc analysis, H2 temperature- programmed reduction and desorption, NH3 temperature-programmed desorption, and zeta potential analysis were employed to characterize the samples. The results revealed that, compared with the catalysts with the same composition prepared by co-impregnation （CI） and sequential impregnation （SI） methods, the Ni/A1203 catalyst prepared by IM-DP showed much enhanced catalytic performance for syngas methanation under the condition of atmospheric pressure and a high weight hourly space velocity of 120000 mL.g-1 .h-1. In a 80 h life time test under the condition of 300-600 ~C and 3.0 MPa, this catalyst showed high stability and resistance to coking, and the amount of deposited carbon was only 0.4 wt%. On the contrary, the deposited carbon over the catalyst without ZrO2 reached 1.5 wt% after a 60 h life time test. The improved catalytic performance was attributed to the selective deposition of ZrO2 nanoparticles on the surface of NiO rather than A1203, which could he well controlled via changing the electrostatic interaction in the DP procedure. This unique structure could enhance the dissociation of CO2 and generate surface oxygen intermediates, thus preventing carbon deposition on the Ni particles in syngas methanation.
文摘In this work, atomic layer deposition （ALD） was employed to fabricate coaxial multi-interface hollow Ni-A12OB-ZnO nanowires. The morpholog34 microstructure, and ZnO shell thickness dependent electromagnetic and microwave absorbing properties of these Ni-A12OB-ZnO nanowires were characterized. Excellent microwave absorbing properties with a minimum reflection loss （RL） of approximately -50 dB at 9.44 GHz were found for the Ni-A12OB-100ZnO nanowires, which was 10 times of Ni-A1203 nanowires. The microwave absorption frequency could be effectively varied by simply adjusting the number of ZnO deposition cycles. The absorption peaks of Ni-A1203-100ZnO and Ni-A12OB-150ZnO nanowires shifted of 5.5 and 6.8 GHz towards lower frequencies, respectively, occupying one third of the investigated frequency band. The enhanced microwave absorption arose from multiple loss mechanisms caused by the unique coaxial multi-interface structure, such as multi-interfacial polarization relaxation, natural and exchange resonances, as well as multiple internal reflections and scattering. These results demonstrate that the ALD method can be used to realize tailored nanoscale structures, making it a highly promising method for obtaining high- efficiency microwave absorbers, and opening a potentially novel route for frecluencv adiustment and microwave ima^in~ fields.
基金the Center of Research Excellence in Petroleum Refining & Petrochemicals (project: CoRE-PRP-06) established by the Ministry of Higher Education at the King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia for finical support of this work
文摘The effect of rare earth oxides （RE=Ce, La, Gd, and Dy） doping of alumina support in NiO/7-A1203 system was investi- gated on its catalytic performance in oxidative dehydrogenation （ODH） of cyclohexane. The physicochemical properties of various samples were followed up through N2 physisorption, temperature programmed reduction （H2-TPR）, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and potentiometric acid-base titration techniques. In the parent NiO/y-A1203 catalyst, Ni species were found to be strongly interacted with alumina surface. Addition of rare earth dopants to ）＇-A1203 in the catalyst system affected the nickel-alumina interaction and resulted in significant modifications in the catalytic performances in the ODH reaction. The results re- vealed the beneficial role of both La203 and Gd2Os doping in enhancing the ODH catalytic activity and selectivity to cyclohexene. H2-TPR and XPS results indicated that majority of Ni species in NiO/La203 modified T-A1203 were more weakly interacted with La203 and alumina whereas both NiO like species and nickel aluminate were present on the surface. Doping with cerium or dyspro- sium increased the nickel-support interaction and led to a decrease in surface nickel concentration. In case of doping with Ce, surface concentration of cerium oxide was higher than those of the other RE oxides; the doped catalyst reached its steady state activity faster than the other catalysts. The acid-base results suggested that RE metals were interacted most likely with acidic surface hydroxyl groups. The degree of nickel-alumina interaction decreased in the following order： LaAI〉GdAI〉CeAI〉DyA1.
