Highly active and selective Ni-based catalysts for partial oxidation of methane (POM) to syngas (CO/H,) have been studied and developed. Spectroscopic characterization by XRD, XPS, EPR, etc. demonstrated that under th...Highly active and selective Ni-based catalysts for partial oxidation of methane (POM) to syngas (CO/H,) have been studied and developed. Spectroscopic characterization by XRD, XPS, EPR, etc. demonstrated that under the POM reaction conditions, the Ni-components of the catalysts investigated were reduced and enriched on the surface to form metallic Ni0-phase. A comparative study of the first series of transition-metals showed that only Ni and Co have a high POM activity and selectivity, whereas the others (including Mn, Fe, Cu, etc. ) give mainly complete combustion products, Co, and H2O. The results favor the following viewpoints: the PoM activity is related with the rapidly changeable valence transitionmetal sites, M0/M2+ (e. g. Ni0/Ni2+ ), on the surface of the functioning catalysts;the transition-metal sites in zero-valence state seem to be responsible for the activation and dehydrogenation of methane by homolytic splitting of its C-H bonds on these sites. and the nature of rapidly changeable valence of the active sties is requisite for activation and rapid conversion of dioxygen.展开更多
The partial oxidation of methane to synthesis gas is studied in this paperover Ni/Al_2O_3 catalysts under atmospheric pressure. The effects of Ni loading on the activity andstability of catalysts with 5 mm α-Al_2O_3 ...The partial oxidation of methane to synthesis gas is studied in this paperover Ni/Al_2O_3 catalysts under atmospheric pressure. The effects of Ni loading on the activity andstability of catalysts with 5 mm α-Al_2O_3 and θ-Al_2O_3 pellets as supports were measured in acontinuous fixed bed reactor. It is found that the optimum Ni loading is 10%. And the effect ofreaction conditions on partial oxidation of methane is also studied. The methane conversion and COselectivity increase with the increase of the reaction temperature and the space velocity on10%Ni/α-Al_2O_3 catalysts. The best CH_4/O_2 mole ratio is 2 for CO selectivity, and the optimumspace velocity is 5.4x10^5 h^(1).展开更多
A nickel nanowire catalyst was prepared by a hard template method, and characterized by transmission electron microscopy （TEM）, N2 physical adsorption, X-ray photoelectron spectrometry （XPS）, X-ray diffraction （...A nickel nanowire catalyst was prepared by a hard template method, and characterized by transmission electron microscopy （TEM）, N2 physical adsorption, X-ray photoelectron spectrometry （XPS）, X-ray diffraction （XRD） and H2 temperature-programmed reduction （H2-TPR）. The catalytic properties of the nanowire catalyst in the partial oxidation of methane to syngas were compared with a metallic Ni catalyst which was prepared with nickel sponge. The characterization results showed that the nickel nanowire catalyst had high specific surface area and there was more NiO phase in the nickel nanowire catalyst than in the metallic Ni catalyst. The reaction results showed that the nickel nanowire catalyst had high CH4 conversion and selectivities for H2 and CO under low space velocity.展开更多
A metallic Ni catalyst was prepared with nickel sponge, followed by acid treatment. It was further promoted with yttria by an impregnation method. The catalysts were characterized by SEM, BET, XRD, TPR, XPS, etc., and...A metallic Ni catalyst was prepared with nickel sponge, followed by acid treatment. It was further promoted with yttria by an impregnation method. The catalysts were characterized by SEM, BET, XRD, TPR, XPS, etc., and studied in the partial oxidation of methane to syngas. The characterization results showed that the yttria promoted metallic Ni catalysts had high specific surface area and more NiO. The reaction results showed that the yttria promoter increased the CH4 conversion and the selectivity for H2 and CO.展开更多
Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a pr...Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a precursor containing Ni（～5‐μm diameter） and CeO2（～200‐nm diameter）powders were heated simultaneously using an RF plasma at a power level of ～52 kVA and a powder feeding rate of ～120 g/h. From the X‐ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles（ 50‐nm diameter） on their surfaces. The catalytic performance was evaluated under atmospheric pressure at 500 °C and a CH4：O2 molar ratio of 2：1 with Ar diluent. Although the Ni content was high（～50 mol%）, the experimental results reveal a methane conversion rate of 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on‐stream test at 550 °C for 24 h.However, at 750 °C, the on‐stream test revealed the formation of filament‐like carbons with an increased methane conversion rate over 90%.展开更多
The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not ...The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reactiorrconditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.展开更多
A new monolithic Ni/ CeO2-ZrO2/γ-Al2O3 catalyst for combined partial oxidation and CO2 reforming of methane was prepared. The result shows that the addition of O2 to the feed can improve the activity of the catalyst ...A new monolithic Ni/ CeO2-ZrO2/γ-Al2O3 catalyst for combined partial oxidation and CO2 reforming of methane was prepared. The result shows that the addition of O2 to the feed can improve the activity of the catalyst and adjust the H2/CO ratio of the productive gases.展开更多
The effects of MgO promoter on the physico-chemical properties and catalytic performance of Ni/Al_(2)O_(3) catalysts for the partial oxidation of methane to syngas were studied by means of BET,XRD,H2-TPR,TEM and perfo...The effects of MgO promoter on the physico-chemical properties and catalytic performance of Ni/Al_(2)O_(3) catalysts for the partial oxidation of methane to syngas were studied by means of BET,XRD,H2-TPR,TEM and perfor-mance evaluation.It was found that the MgO promoter bene-fited from the uniformity of nickel species in the catalysts,inhibited the formation of NiAl2O4 spinel and improved the interaction between nickel species and support.These results were related to the formation of NiO–MgO solid solution and MgAl_(2)O_(4) spinel.Moreover,for the catalysts with a proper amount of MgO promoter,the nickel dispersiveness was enhanced,therefore making their catalytic performance in methane partial oxidation improved.However,the excessive MgO promoter exerted a negative effect on the catalytic performance.Meanwhile,the basicity of MgO promoted the reversed water–gas shift reaction,which led to an increase in CO selectivity and a decrease in H2 selectivity.The suitable content of MgO promoter in Ni/Al_(2)O_(3) catalyst was∼7 wt-%.展开更多
Four perovskite-type complex oxides (LaNiO_3, La_2NiO_4, LaCoO_3 andLa_2CoO_4) were successfully prepared using two sol-gel methods, the Pechini method (PC) and thecitric acid complexing method (CC). The catalysts wer...Four perovskite-type complex oxides (LaNiO_3, La_2NiO_4, LaCoO_3 andLa_2CoO_4) were successfully prepared using two sol-gel methods, the Pechini method (PC) and thecitric acid complexing method (CC). The catalysts were characterized by XRD and TPR. Afterreduction, the activity of the catalysts in the CO_2 reforming of methane was tested. Ni-basedcatalysts from La_2NiO_4 precursors were the most active and stable catalyst after calcination above850 ℃, which gave a methane conversion of 0.025 mmol/(g·s) for those prepared by the PC methodand 0.020 mmol/(g·s) by the CC method. It was proposed that the well-defined structure and lowerreducibility is responsible for the unusual catalytic behavior observed over the pre-reducedLa2NiO_4 catalyst.展开更多
Auto-thermal reforming of methane, combining partial oxidation and reforming of methane with CO2 or steam, was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/CeO2 catalysts, in a temperature range of 300-900℃. The auto-th...Auto-thermal reforming of methane, combining partial oxidation and reforming of methane with CO2 or steam, was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/CeO2 catalysts, in a temperature range of 300-900℃. The auto-thermal reforming occurs in two simultaneous stages, namely, total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% starting from 450℃. For combination with CO2 reforming, the Pt/CeO2 catalyst showed the lowest initial activity at 800℃, and the highest stability over 40 h on-stream. This catalyst also presented the best performance for the reaction with steam at 800℃. The higher resistance to coke formation of the catalyst supported on ceria is due to the metal-support interactions and the higher mobility of oxygen in the oxide lattice.展开更多
文摘Highly active and selective Ni-based catalysts for partial oxidation of methane (POM) to syngas (CO/H,) have been studied and developed. Spectroscopic characterization by XRD, XPS, EPR, etc. demonstrated that under the POM reaction conditions, the Ni-components of the catalysts investigated were reduced and enriched on the surface to form metallic Ni0-phase. A comparative study of the first series of transition-metals showed that only Ni and Co have a high POM activity and selectivity, whereas the others (including Mn, Fe, Cu, etc. ) give mainly complete combustion products, Co, and H2O. The results favor the following viewpoints: the PoM activity is related with the rapidly changeable valence transitionmetal sites, M0/M2+ (e. g. Ni0/Ni2+ ), on the surface of the functioning catalysts;the transition-metal sites in zero-valence state seem to be responsible for the activation and dehydrogenation of methane by homolytic splitting of its C-H bonds on these sites. and the nature of rapidly changeable valence of the active sties is requisite for activation and rapid conversion of dioxygen.
基金This work was supported by National Science Foundation Committee of China (Grant number 20106013).
文摘The partial oxidation of methane to synthesis gas is studied in this paperover Ni/Al_2O_3 catalysts under atmospheric pressure. The effects of Ni loading on the activity andstability of catalysts with 5 mm α-Al_2O_3 and θ-Al_2O_3 pellets as supports were measured in acontinuous fixed bed reactor. It is found that the optimum Ni loading is 10%. And the effect ofreaction conditions on partial oxidation of methane is also studied. The methane conversion and COselectivity increase with the increase of the reaction temperature and the space velocity on10%Ni/α-Al_2O_3 catalysts. The best CH_4/O_2 mole ratio is 2 for CO selectivity, and the optimumspace velocity is 5.4x10^5 h^(1).
基金The financial supports by the National High Technology Research and Development Program of China (863 Program) under Grant No. 2007AA05Z104 and 2006AA05Z115key project of Tianjin Natural Science Foundation under Grant No. 07 JCZDJC00200 are gratefully acknowledged
文摘A nickel nanowire catalyst was prepared by a hard template method, and characterized by transmission electron microscopy （TEM）, N2 physical adsorption, X-ray photoelectron spectrometry （XPS）, X-ray diffraction （XRD） and H2 temperature-programmed reduction （H2-TPR）. The catalytic properties of the nanowire catalyst in the partial oxidation of methane to syngas were compared with a metallic Ni catalyst which was prepared with nickel sponge. The characterization results showed that the nickel nanowire catalyst had high specific surface area and there was more NiO phase in the nickel nanowire catalyst than in the metallic Ni catalyst. The reaction results showed that the nickel nanowire catalyst had high CH4 conversion and selectivities for H2 and CO under low space velocity.
基金supports by the Key Project of Tianjin Natural Science Foundation under Grant No.07 JCZDJC00200the National High Technology Research and Development Program of China(863 Program)under Grant No.2007AA05Z104 and 2006AA05Z115 are gratefully acknowledged
文摘A metallic Ni catalyst was prepared with nickel sponge, followed by acid treatment. It was further promoted with yttria by an impregnation method. The catalysts were characterized by SEM, BET, XRD, TPR, XPS, etc., and studied in the partial oxidation of methane to syngas. The characterization results showed that the yttria promoted metallic Ni catalysts had high specific surface area and more NiO. The reaction results showed that the yttria promoter increased the CH4 conversion and the selectivity for H2 and CO.
基金supported by Renewable Energy Technologies Development Program(No.2008NFC02J0200002009)Technology Innovation Program(No.10048910)funded by the Ministry of Trade,Industry and Energy(MI,Korea)
文摘Ni‐CeO2 catalysts with a nickel content of 50 mol% were prepared using RF thermal plasma, and their catalytic activities for methane partial oxidation were characterized. For the synthesis of Ni‐CeO2 catalysts, a precursor containing Ni（～5‐μm diameter） and CeO2（～200‐nm diameter）powders were heated simultaneously using an RF plasma at a power level of ～52 kVA and a powder feeding rate of ～120 g/h. From the X‐ray diffraction data and transmission electron microscopy images, the precursor formed into high crystalline CeO2 supports with nanosized Ni particles（ 50‐nm diameter） on their surfaces. The catalytic performance was evaluated under atmospheric pressure at 500 °C and a CH4：O2 molar ratio of 2：1 with Ar diluent. Although the Ni content was high（～50 mol%）, the experimental results reveal a methane conversion rate of 70%, selectivities of CO and H2 greater than 90% and slight carbon coking during an on‐stream test at 550 °C for 24 h.However, at 750 °C, the on‐stream test revealed the formation of filament‐like carbons with an increased methane conversion rate over 90%.
文摘The effect of CeO2 and CaO promoters on the ignition performance over Ni/MgO-Al2O3 catalyst for the partial oxidation of methane （POM） to synthesis gas was investigated. It was found that the POM reaction could not be ignited over lwt%Ni/MgO-Al2O3 catalyst without the promoters in the temperature range from 773 K to 1073 K. CeO2 and CaO promoters enhanced the ignition performance and the POM reactivity of lwt%Ni/MgO-Al2O3 catalyst remarkably. Moreover, the improving effect became greater with the increase of the promoter content under the investigated reactiorrconditions. The modification effects of CeO2 and CaO promoters were closely related to the concentration and reducibility of the surface and bulk oxygen species.
基金The authots would like to thank the National Natural Science Foundation of China(No:20273043)the National Key Basic Reseatch Project of China(G 1999022407)for providing financial support for this project.
文摘A new monolithic Ni/ CeO2-ZrO2/γ-Al2O3 catalyst for combined partial oxidation and CO2 reforming of methane was prepared. The result shows that the addition of O2 to the feed can improve the activity of the catalyst and adjust the H2/CO ratio of the productive gases.
文摘The effects of MgO promoter on the physico-chemical properties and catalytic performance of Ni/Al_(2)O_(3) catalysts for the partial oxidation of methane to syngas were studied by means of BET,XRD,H2-TPR,TEM and perfor-mance evaluation.It was found that the MgO promoter bene-fited from the uniformity of nickel species in the catalysts,inhibited the formation of NiAl2O4 spinel and improved the interaction between nickel species and support.These results were related to the formation of NiO–MgO solid solution and MgAl_(2)O_(4) spinel.Moreover,for the catalysts with a proper amount of MgO promoter,the nickel dispersiveness was enhanced,therefore making their catalytic performance in methane partial oxidation improved.However,the excessive MgO promoter exerted a negative effect on the catalytic performance.Meanwhile,the basicity of MgO promoted the reversed water–gas shift reaction,which led to an increase in CO selectivity and a decrease in H2 selectivity.The suitable content of MgO promoter in Ni/Al_(2)O_(3) catalyst was∼7 wt-%.
文摘Four perovskite-type complex oxides (LaNiO_3, La_2NiO_4, LaCoO_3 andLa_2CoO_4) were successfully prepared using two sol-gel methods, the Pechini method (PC) and thecitric acid complexing method (CC). The catalysts were characterized by XRD and TPR. Afterreduction, the activity of the catalysts in the CO_2 reforming of methane was tested. Ni-basedcatalysts from La_2NiO_4 precursors were the most active and stable catalyst after calcination above850 ℃, which gave a methane conversion of 0.025 mmol/(g·s) for those prepared by the PC methodand 0.020 mmol/(g·s) by the CC method. It was proposed that the well-defined structure and lowerreducibility is responsible for the unusual catalytic behavior observed over the pre-reducedLa2NiO_4 catalyst.
文摘Auto-thermal reforming of methane, combining partial oxidation and reforming of methane with CO2 or steam, was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/CeO2 catalysts, in a temperature range of 300-900℃. The auto-thermal reforming occurs in two simultaneous stages, namely, total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% starting from 450℃. For combination with CO2 reforming, the Pt/CeO2 catalyst showed the lowest initial activity at 800℃, and the highest stability over 40 h on-stream. This catalyst also presented the best performance for the reaction with steam at 800℃. The higher resistance to coke formation of the catalyst supported on ceria is due to the metal-support interactions and the higher mobility of oxygen in the oxide lattice.
