制备方法对镧钡共改性氧化铝性能的影响

The effect of preparation method on the properties of alumina modified by La₂O₃ and BaO was investigated by means of Low temperature nitrogen adsorption-desorption, NH₃-TPD, NO-TPD and XRD. The results show that alumina prepared by peptizing method exhibits the best textural properties, alumina obtained by co-precipitation method presents the strongest surface acidity and alumina derived from impregnation method shows the best ability of NO adsorption. After calcination at 1 100 ℃, all alumina except that from impregnation method have excellent thermal stability. When the specific surface area and pore volume of alumina are large enough, the activity of catalyst Pd/alumina is affected primarily by the surface acidity of alumina.     

蔗糖辅助制备大比表面积氧化铝

The preparation of alumina with large surface area, certain phase and porosimetry has always been one of important researches. A new method using much less sucrose (the molar ratio of sucrose to Al^3 =0.5) was developed to prepare γ-Al2O3 with large surface area and high thermal stability. Firstly, ammonium hydroxide was dropped to aqueous solution of aluminum nitrate and sucrose. The resulted precipitate in suspension washeated until a homogeneous gel was ohtained. Then the gel was dehydrated at 110℃ to get a fluffy black precursor. Finally, γ-Al2O3 with A=345m^2/g was prepared by calcining the preeursor at 600℃ for 24h. The precursor and the obtained γ-Al2O3 were characterized by DTA-TG, N2 adsorption-desorption isotherms, XRD and TEM, According to the dispersion behaviors of organic compounds on supports, the related mechanism was discussed.     

制备条件对SiO2改性氧化铝材料耐热性能的影响

The thermal stabilization mechanism of silica and effect of preparation conditions on the thermal stability of silica-modified alumina have been investigated by low temperature nitrogen adsorption-desorption, XRD, TEM and ²⁷Al MAS NMR. The results show that the addition of silica is effective in suppressing α phase transformation and therefore, in maintaining large surface area of alumina after heating at elevated temperatures. The stabilization effect of the silica species increases with the rise of silica content, however, the overabundance of silica species weakens its stabilization effect. The preparation conditions influence the thermal stability of alumina and stabilization effect of silica. Employing solgel and supercritical drying methods, silica-doped alumina materials with high thermal stability were prepared using NaAlO₂ and water-soluble sodium silicate.     

Al2O3 Effect on the Catalytic Activity of Cu-ZnO-Al2O3-SiO2 Catalysts for Dimethyl Ether Synthesis from CO2 Hydrogenation

The effect of Al2O3 on the Cu-ZnO-Al2O3-SiO2 catalysts prepared by a pseudo sol-gel method has been investigated and these catalysts were characterized by XRD, H2-TPR, XPS, NH3-TPD and CO2- TPD techniques. As revealed by XRD and H2-TPR, the added alumina produces high dispersion of CuO and makes the reduction of CuO difficult. XPS analysis detects a remarkably high Al^3＋ enrichment at the surface of calcined samples, along with a decrease of Eb of Cu 2p3/2, which confirms the Cu-Al interaction. Another important role of Al203 would be to incorporate into the SiO2 structure to form the acid-base sites for ether formation. The reaction results shows that the addition of Al2O3 exhibits a promoting effect on the CO2 conversion only when its content is below 1.4%, and an optimal DME selectivity is obtained when 4.0%Al2O3 is added, indicating a better ＇synergistic effect＇ is present between the methanol forming component and the acidic component in bifunctional catalysts. Possible relationship between the catalytic activity and the Cu-Al interaction as well as the surface acidity is discussed.     

一种新型高比表面积 TiO2载体在 NH3选择性催化还原反应中对 V2O5分散性的促进作用

A titania support with a large surface area was developed, which has a BET surface area of 380.5 m2/g, four times that of a traditional titania support. The support was ultrasonically impregnated with 5 wt%vanadia. A special heat treatment was used in the calcination to maintain the large sur‐face area and high dispersion of vanadium species. This catalyst was compared to a common V2O5‐TiO2 catalyst with the same vanadia loading prepared by a traditional method. The new cata‐lyst has a surface area of 117.7 m2/g, which was 38%higher than the traditional V2O5‐TiO2 catalyst. The selective catalytic reduction (SCR) performance demonstrated that the new catalyst had a wid‐er temperature window and better N2 selectivity compared to the traditional one. The NO conver‐sion was>80%from 200 to 450 °C. The temperature window was 100 °C wider than the traditional catalyst. Raman spectra indicated that the vanadium species formed more V‐O‐V linkages on the catalyst prepared by the traditional method. The amount of V‐O‐Ti and V=O was larger for the new catalyst. Temperature programmed desorption of NH3, temperature programmed reduction by H2 and X‐ray photoelectron spectroscopy results showed that its redox ability and total acidity were enhanced. The results are helpful for developing a more efficient SCR catalyst for the removal of NOx in flue gases.     

Cobalt supported on CNTs-covered γ-and nano-structured alumina catalysts utilized for wax selective Fischer-Tropsch synthesis

Cobalt supported on carbon nanotubes(CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis(FTS).Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications.In this investigation regularγ-and nano-structured(N-S)alumina as well as CNTs-covered regularγ-and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru.The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS.γ-Al2O3 was prepared by calcination of bohemite and N-S-Al2O3 was prepared by sol-gel method using aluminum chloride as starting material.Catalyst evaluations indicated that N-S-Al2O3 was superior to regularγ-Al2O3 and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity.These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation.Furthermore,TPR analysis indicated that the cobalt aluminate phase,which is responsible for the permanent deactivation of alumina supported Co-based catalysts,did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.     

Highly active porous nickel-film electrode via polystyrene microsphere template-assisted composite electrodeposition for hydrogen-evolution reaction in alkaline medium

A highly porous nickel-film electrode with satisfactory mechanical strength was prepared by a facile vertical template-assisted composite electrodeposition method using polystyrene(PS) microspheres templates, with the aim of improving the electrocatalytic activity for the hydrogen-evolution reaction(HER). During the composite electrodeposition process, the hydrophobic PS microspheres were highly dispersed in the electrolyte with the help of a surfactant, and then co-deposited with Ni to form the film electrode. After removing the PS templates by annealing, a porous Ni film containing large amount of uniformly dispersed pores with narrow size distribution was obtained, and then applied as the electrode for the HER in an alkaline medium. As evidenced by the electrochemical analysis, the porous Ni film electrode exhibits higher catalytic activity as compared to a dense Ni film electrode and is superior to a Ni/Ru O2/Ce O2 commercial electrode. The effect of temperature on the catalytic properties of the porous Ni film electrode was also investigated; the activation energy was calculated as 17.26 k J/mol. The enhanced activity toward the HER was attributed to the improved electrochemical surface area and mass transportation facilitated by the high porosity of the synthesized Ni film electrode.     

CO oxidation over Co3O4/SiO2 catalysts: Effects of porous structure of silica and catalyst calcination temperature

The catalytic performances of Co3O4/SiO2 catalysts prepared by incipient wetness impregnation for CO oxidation were investigated using three kinds of silica as carriers with different pore sizes of 7.7, 14.0 and 27.0 nm. The effects of calcination temperature on the catalyst surface and micro structure properties as well as catalytic performance for the oxidation of carbon monoxide were also studied. All catalysts were characterized by N2 adsorption-desorption, XRD, XPS, FTIR, H2-TPR and O2-TPD. It was found that the properties and crystal size of cobalt-containing species strongly depended on the pore size of silica carrier. While the silica pore size increased from 7.7 to 27.0 nm, the Co3O4 crystal size increased from 8.5 to 13.5 nm. Moreover, it was demonstrated that if the spinel crystal structure of Co3O4 was obtained at a calcination temperature as low as 150 ℃, the catalyst sample would have a high Co3O4 surface dispersion and a increase of surface active species, and thus exhibit a high activity for the oxidation of carbon monoxide.     

Nickel ferrite spinel as catalyst precursor in the dry reforming of methane:Synthesis,characterization and catalytic properties

Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction (XRD),Raman spectroscopy and X-ray photoelectron spectroscopy (XPS),among which X-ray diffraction (XRD) was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 (hematite) was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction (TPR) and in situ XRD,which showed the influence of the preparation method.The surface area (BET),particle size (Rietveld refinement),as well as surface Ni/Fe atomic ratio (XPS) and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.     

The first systhesis of a chromia-pillared layered niobate with porosity, acidity and high thermostability

Although the hydrated niobic acid is an unusual solid acid and making an impact onits application in catalysis, it is usually nonporous and has a rather low surface area andweak acidity upon heat treatment. To overcome these shortcomings, the layered nio-bate had been pillared with thermostable inorganic oxides such as alumina and silica.Chromia is also a suitable inorganic oxide which can be used as pillar and contributesnew properties to the resultant materials. Here, we report the first synthesis of achromia-pillared layered niobate with porosity, acidity and thermostability.