LaAl12O19 hexaaluminate was prepared by reverse microemulsion method in the water/TritonX-100/n-butoanol/cyclohexane. LaMAl11O19 were prepared using transition-metal M(M=Fe,Co) to substitute Al in the hexaaluminate la...LaAl12O19 hexaaluminate was prepared by reverse microemulsion method in the water/TritonX-100/n-butoanol/cyclohexane. LaMAl11O19 were prepared using transition-metal M(M=Fe,Co) to substitute Al in the hexaaluminate lattice with same method. The LaAl12O19 hexaaluminate and effects of M on phase composition, specific surface area and activities evaluation for methane combustions were investigated by means of XRD, BET, H2-TPR and eatalytic reaction of methane combustion. Reverse microemulsion method is beneficial to maintain high surface area. The specific surface areas of prepared catalysts have about 11.6～16.3 m2·g-1. XRD spectrum analysis of Co-doping and no-doping catalyst indicated that hexaaluminate phase catalysts were dominated and companied with few perovskite phase when calcined at 1 400 ℃ for 3 hours. H2-TPR profiles of the Fe-doping and Co-doping catalysts showed that the reduction peaks appeared in the range of 400 ℃ and 800 ℃, instead of that there weren’t any reduction peaks of no-doping catalyst. Compared with no-doping catalyst, not only the high-temperature activity of Fe-doping and Co-doping catalysts increased obviously, but also was methane half conversion temperature below 700 ℃ and was methane complete conversion temperature at 800 ℃. However, the high-temperature activity of Fe-doping catalyst is better than Co-doping catalyst within 700 ℃, and theirs the high-temperature activity are almost same over 700 ℃. Fe-doping catalyst formed single phase of hexaaluminate LaFeAl11O19.展开更多
By calcinatng conunerial silica at 1500 t or adding sodium oxalate and calcinating at 85Ot, α-cristobalite was obtained. The Raman and IR spectra of arnorphous silica and α-cristobalite were studied. The Raman and I...By calcinatng conunerial silica at 1500 t or adding sodium oxalate and calcinating at 85Ot, α-cristobalite was obtained. The Raman and IR spectra of arnorphous silica and α-cristobalite were studied. The Raman and IR spectra showed obvious changes. While amorphous silica transformed to α-cristobalite. The peak posihons and peak shape changed, and new vibration mode appeared in the crystal phase. For amorphous silica, the Raman spectrum has a broad band between 210-515 cm- 1 and two weak peaks at 793 and 966 cm -1. After phase tfansition, the broad band split into two strong peaks at 416 and 231 cm-1, and the positions of weak peaks changed. The IR spectrum of SiO2 has two strong peaks at about 1100 and 480 cm-1 and a weak peak at 800 cm-1. For α-cristobalite, a strong new peak appeared at 620 cm-1, and the adsorption at 800 cm-1 increased considerably. α-cristobalite also has two adsorption peaks in far-infrared.展开更多
A series of catalysts,hexaaluminates LaCexFe1-xAl11O19（x=0,0.2,0.4,0.6,0.8,1） were prepared by the co-precipitation method.The influences of the Ce doped on structure and catalytic performance of catalysts were stud...A series of catalysts,hexaaluminates LaCexFe1-xAl11O19（x=0,0.2,0.4,0.6,0.8,1） were prepared by the co-precipitation method.The influences of the Ce doped on structure and catalytic performance of catalysts were studied by XRD,FT-IR,H2-TPR,UV-DRS,XPS,EC（Electrical conductivity） and methane combustion activity test.The result shows that rare earth Ce species are more readily to exist in the form of CeO2over the catalysts than to enter the bulks of LaFeAl11O19hexaaluminates to substitute Al and Fe.Compared with catalyst LaFeAl11O19 without Ce doped,the Ce doped catalysts are being higher catalytic activity for methane combustion.Under reaction conditions of 4800h-1air velocity,and LaCe0.8Fe0.2Al11O19 showed the highest activity.It indicated that the CeO2,was contributed to improve the catalytic activity of LaCe0.8Fe0.2Al11O19 .Meanwhile,with Ce-containing increasing,the FT-IR spectra of each sample move forward the direction of higher wave-numbers slightly.Catalysts reduced proceeding becomes difficult.XPS and EC（Electrical conductivity） tests found that charge density of Fe3+ was added and Fe2P3 binding energy shifted to minus direction,electrical conductivity performance revealed that La-Fe hexaaluminates belonged to n-type semiconductor.After doped Ce,we found that electrical conductivity decline.When content of Ce reaches to x=0.8,the sample’s electrical conductivity becomes zero.展开更多
By calcinating commercial silica gel at 1500℃or adding Na2C2O4 and then calcinating at 850℃,α cristobalite was formed.On the basis of the vibration spectroscopy of silica support,Na W Mn/SiO2 catalyst was character...By calcinating commercial silica gel at 1500℃or adding Na2C2O4 and then calcinating at 850℃,α cristobalite was formed.On the basis of the vibration spectroscopy of silica support,Na W Mn/SiO2 catalyst was characterized by Raman spectroscopy.The results show that the structure of support and the interaction among metal components have significant effect on the dispersion and the structure of metal sites,and the tetrahedrally coordinated formed on α cristobalite surface is the most possible site of methane activation with high C2 selectivity.展开更多
文摘LaAl12O19 hexaaluminate was prepared by reverse microemulsion method in the water/TritonX-100/n-butoanol/cyclohexane. LaMAl11O19 were prepared using transition-metal M(M=Fe,Co) to substitute Al in the hexaaluminate lattice with same method. The LaAl12O19 hexaaluminate and effects of M on phase composition, specific surface area and activities evaluation for methane combustions were investigated by means of XRD, BET, H2-TPR and eatalytic reaction of methane combustion. Reverse microemulsion method is beneficial to maintain high surface area. The specific surface areas of prepared catalysts have about 11.6～16.3 m2·g-1. XRD spectrum analysis of Co-doping and no-doping catalyst indicated that hexaaluminate phase catalysts were dominated and companied with few perovskite phase when calcined at 1 400 ℃ for 3 hours. H2-TPR profiles of the Fe-doping and Co-doping catalysts showed that the reduction peaks appeared in the range of 400 ℃ and 800 ℃, instead of that there weren’t any reduction peaks of no-doping catalyst. Compared with no-doping catalyst, not only the high-temperature activity of Fe-doping and Co-doping catalysts increased obviously, but also was methane half conversion temperature below 700 ℃ and was methane complete conversion temperature at 800 ℃. However, the high-temperature activity of Fe-doping catalyst is better than Co-doping catalyst within 700 ℃, and theirs the high-temperature activity are almost same over 700 ℃. Fe-doping catalyst formed single phase of hexaaluminate LaFeAl11O19.
文摘By calcinatng conunerial silica at 1500 t or adding sodium oxalate and calcinating at 85Ot, α-cristobalite was obtained. The Raman and IR spectra of arnorphous silica and α-cristobalite were studied. The Raman and IR spectra showed obvious changes. While amorphous silica transformed to α-cristobalite. The peak posihons and peak shape changed, and new vibration mode appeared in the crystal phase. For amorphous silica, the Raman spectrum has a broad band between 210-515 cm- 1 and two weak peaks at 793 and 966 cm -1. After phase tfansition, the broad band split into two strong peaks at 416 and 231 cm-1, and the positions of weak peaks changed. The IR spectrum of SiO2 has two strong peaks at about 1100 and 480 cm-1 and a weak peak at 800 cm-1. For α-cristobalite, a strong new peak appeared at 620 cm-1, and the adsorption at 800 cm-1 increased considerably. α-cristobalite also has two adsorption peaks in far-infrared.
文摘A series of catalysts,hexaaluminates LaCexFe1-xAl11O19（x=0,0.2,0.4,0.6,0.8,1） were prepared by the co-precipitation method.The influences of the Ce doped on structure and catalytic performance of catalysts were studied by XRD,FT-IR,H2-TPR,UV-DRS,XPS,EC（Electrical conductivity） and methane combustion activity test.The result shows that rare earth Ce species are more readily to exist in the form of CeO2over the catalysts than to enter the bulks of LaFeAl11O19hexaaluminates to substitute Al and Fe.Compared with catalyst LaFeAl11O19 without Ce doped,the Ce doped catalysts are being higher catalytic activity for methane combustion.Under reaction conditions of 4800h-1air velocity,and LaCe0.8Fe0.2Al11O19 showed the highest activity.It indicated that the CeO2,was contributed to improve the catalytic activity of LaCe0.8Fe0.2Al11O19 .Meanwhile,with Ce-containing increasing,the FT-IR spectra of each sample move forward the direction of higher wave-numbers slightly.Catalysts reduced proceeding becomes difficult.XPS and EC（Electrical conductivity） tests found that charge density of Fe3+ was added and Fe2P3 binding energy shifted to minus direction,electrical conductivity performance revealed that La-Fe hexaaluminates belonged to n-type semiconductor.After doped Ce,we found that electrical conductivity decline.When content of Ce reaches to x=0.8,the sample’s electrical conductivity becomes zero.
文摘By calcinating commercial silica gel at 1500℃or adding Na2C2O4 and then calcinating at 850℃,α cristobalite was formed.On the basis of the vibration spectroscopy of silica support,Na W Mn/SiO2 catalyst was characterized by Raman spectroscopy.The results show that the structure of support and the interaction among metal components have significant effect on the dispersion and the structure of metal sites,and the tetrahedrally coordinated formed on α cristobalite surface is the most possible site of methane activation with high C2 selectivity.
