Synthesis and Characterization of Sol-Gel Cu-ZrO2 and Fe-ZrO2 Catalysts

Fe-ZrO₂ and Cu-ZrO₂ xerogels were prepared by a sol-gel method. The effect of the hydrolysis catalyst during the gelation step, namely H₂SO₄ or NH₄OH, on the properties of the resulting materials was investigated by XRD, BET, TGA/DTA, TPD of ammonia, FTIR, and TPR. Fe-ZrO₂ and Cu-ZrO₂ xerogels, with sulfuric acid introduced as the hydrolysis catalyst, mainly crystallyzed in the tetragonal phase and exhibited larger surface area and acid amount than those obtained with NH₄OH. Ammonia TPD shows that copper promoted sulfated zirconia is the most acidic material. TGA and FTIR reveal that under oxidizing conditions sulfated zirconia promoted with iron and copper retains more sulfate species than unpromoted sulfated zirconia. Regardless of the hydrolysis catalyst employed, copper promoted catalysts calcined at 600°C, contain a large fraction of copper oxide specieseasily reduced at low temperatures. These copper oxide species are believed to have different environment and interactions with the surface oxygen vacancies of the zirconia support. A FeO-like phase appears to be the most probable one after reduction of Fe-ZrO₂ catalysts prepared with NH₄OH as the hydrolysis catalyst. The formation of Fe° species may be hindered by the high dispersion and interaction of Fe²⁺ ions with the zirconia support. On the other hand, the reduction peaks of iron oxide and sulfate species exhibit a considerable overlap in the TPR profiles of sulfated Fe-ZrO₂ samples. Hence, the nature of the supported phase in the latter samples is rather uncertain.     

氧化钇掺杂块状SiO2气凝胶的制备与表征

以正硅酸四乙酯（TEOS）为前驱体,YCl₃·6H₂O为掺杂剂,采用溶胶-凝胶法并结合CO₂超临界干燥工艺得到了块状Y₂O₃-SiO₂气凝胶,其中Y₂O₃掺杂含量控制在5wt%~30wt%范围内。利用扫描电镜（SEM）、透射电镜（TEM）、X射线衍射（XRD）、比表面积测定（BET）、X射线荧光分析（XRF）等测试手段对样品进行表征。结果表明：经过氧化钇掺杂后得到的Y₂O₃-SiO₂气凝胶,不仅维持了SiO₂气凝胶原有的空间网络结构,而且具有更高的热稳定性,经过900℃热处理2h后,10wt%Y₂O₃（0.447g的YCl₃·6H₂O）掺杂的Y₂O₃-SiO₂气凝胶仍然处于无定形态,平均孔径约为21.3nm,比表面积高达643.8m₂·g^-1。     

氧化钇掺杂块状SiO_2气凝胶的制备与表征

以正硅酸四乙酯(TEOS)为前驱体,YCl3·6H2O为掺杂剂,采用溶胶-凝胶法并结合CO2超临界干燥工艺得到了块状Y2O3-SiO2气凝胶,其中Y2O3掺杂含量控制在5wt%~30wt%范围内。利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、比表面积测定(BET)、X射线荧光分析(XRF)等测试手段对样品进行表征。结果表明:经过氧化钇掺杂后得到的Y2O3-SiO2气凝胶,不仅维持了SiO2气凝胶原有的空间网络结构,而且具有更高的热稳定性,经过900℃热处理2 h后,10wt%Y2O3(0.447 g的YCl3·6H2O)掺杂的Y2O3-SiO2气凝胶仍然处于无定形态,平均孔径约为21.3 nm,比表面积高达643.8 m2·g-1。     

Acidity and Structure of Ca-Doped V2O5/ZrO2 Catalysts

Acidity and structure of Ca-doped V₂O₅/ZrO₂ catalysts have been studied by FTIR. Both Lewis and Brønsted acidity decreased with Ca loading. New surface vanadate species seemed to be formed by Ca addition.     

Application of Alumina Aerogels as Catalysts

Al₂O₃ gels prepared by hydrolysis of Al-alkoxide were applied as catalysts for NO reduction by hydrocarbon. Xerogels were obtained by drying at 90°C, for 24 h, in air. Aerogels were prepared by supercritical drying of the wet gels in ethanol, using an autoclave. The catalyst activity of the gels for NO reduction with C₃H₆ as determined at 200–600°C in a fixed bed flow reactor. NO conversion to N₂ was about 60% at 550°C with both catalysts, and at 600°C it was better with the aerogel than with the xerogel. The specific surface area of the xerogel, which was larger than that of the aerogel as-dried, decreased to 1/3 by annealing at >500°C. However, the surface area of the aerogel hardly changed by annealing at temperatures up to 700°C. The bimodal pore size distribution of the aerogel hardly changed by annealing, too. The microstructure of the aerogels is stable at high temperatures, and they are better catalysts at high temperatures.     

Preparation,Characterization, and Catalytic Behavior of Nanostructured Mesoporous CuO/ZrO2 Catalysts for Low-Temperature CO Oxidation

High-surface area mesoporous 20 mol% CuO/ZrO₂ catalyst was prepared by a surfactant-assisted method of nanocrystalline particle assembly, and characterized by x-ray powder diffraction (XRD), N₂ adsorption, transmission electron microscopy (TEM), H₂-TPR, TG-DTA, and x-ray photoelectron spectra (XPS) techniques. The catalytic properties of the CuO/ZrO₂ nanocatalysts calcined at different temperature were evaluated by low-temperature carbon monoxide oxidation using a CATLAB system. The results showed that these mesoporous nanostructured CuO/ZrO₂ catalysts were very active for low-temperature CO oxidation and the CuO/ZrO₂ catalyst calcined at 400°C exhibited the highest catalytic activity.     

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H₂SO₄. The samples prepared with HCl were additionally sulfated with a 1 M solution of H₂SO₄. Characterization was performed with FTIR and ²⁹Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO₂-SiO₂ system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m²/g were obtained.     

Synthesis of Silica Aerogels: Influence of the Supercritical CO2 on the Sol-Gel Process

The synthesis of silica aerogels was modified by addition of supercritical CO₂ during the sol-gel process. It was shown, that CO₂ acts as a catalyst and accelerates the gelation significantly. This effect was studied under a multitude of experimental conditions. The influence of the precursor concentration, temperature and the nature of the catalysts and solvent on the gel formation in presence of CO₂ was studied. Several gels obtained by this method were dried and transparent silica aerogels were produced.     

介孔交联蒙脱土固体酸催化剂的结构与性能

采用溶胶凝胶法制备介孔钛交联蒙脱土，再采用SO₄^2-和CeO₂进行两次改性，然后以之为载体，制备铜基交联蒙脱土介孔固体酸催化剂。 催化剂的结构通过BET、XRD、TPR、Py-IR、FTIR、XPS和SEM等手段进行表征，并研究了它们在富氧条件下对丙烯选择还原NO的催化性能。结果表明，钛交联剂能很好地撑开蒙脱土的土层，形成良好的介孔结构，其孔径分布集中在3～7 nm，并且使制得的交联蒙脱土载体的比表面积明显增大；SO₄     

Scaling Properties and Structure of Aerogels

Young’s modulus as well as solid thermal and electrical conductivity of aerogels have been observed to scale with density. No quantitative explanations were available up to now for these experimental findings. To establish a quantitive relationship between morphological and topological features of fractal gel networks, a simulation procedure is introduced that allows to produce three-dimensional gel structures, from which two important parameters can be extracted: i) the fraction α of interconnected mass of the gel network and ii) the ratio γ of Pythagorean distance to minimum path length on the gel backbone. Surprisingly the product αγ, which enters important macroscopic parameters such as elasticity or solid thermal (and electrical) conductivity, was found to scale with an exponent that is only a function of the mass fractal dimensionD. Also, an analytical relation between modulus and conductivity can be derived.     

ZrO_2负载Pt催化巴豆醛选择性加氢

以高比表面积ZrO2为载体,采用浸渍法制备了负载型Pt催化剂,应用于常压下气相巴豆醛加氢反应,考察了Pt负载量和H2还原温度等对巴豆醛选择性加氢性能的影响.实验结果表明,Pt负载量(质量分数)为3%的3Pt/ZrO2催化剂经500℃还原后,具有较高的巴豆醛选择性加氢性能:巴豆醛转化率为27%,巴豆醇的选择性为55%.X射线粉末衍射(XRD)分析,CO化学吸附,NH3程序升温脱附(NH3-TPD)表征结果表明Pt/ZrO2催化剂上Lewis强酸中心和适宜的Pt颗粒(约为8nm)有利于巴豆醛选择性加氢生成巴豆醇.     

Decomposition of Nitrous Oxide on CoOX/ZrO2, CuOX/ZrO2 and FeOX/ZrO2 Catalysts

On CoO_x/ZrO₂, CuO_x/ZrO₂ and FeO_x/ZrO₂ catalysts, below the limits shown by characterization to have high metal dispersion, the turnover frequency for N₂O decomposition is nearly independent of metal content.     

CO and Methane Oxidation Over CeXZr1-XO2 Mixed Oxide Supported PdO Catalysts

In this paper, the Ce_XZr_1-XO₂-supported PdO catalysts were prepared and the effect of Ce/Zr ratio on catalytic activity for CO and methane oxidation was studied, both activity and the reduction behavior of catalyst depend on the Ce/Zr ratio. The reduction behavior of those catalysts was characterized by means of TPR.     

Zr对CuO/ZnO/Al_2O_3前驱体物相、催化剂结构及其合成甲醇性能的影响

采用并流共沉淀法,在CuO/ZnO/Al2O3三元催化剂中加入第四组分Zr,考察了沉淀温度对四元催化剂的前驱体物相组成及浆态床合成甲醇催化活性的影响。通过XRD、DTG、TPR、FTIR、CO-TPD、XPS、HR-TEM等对所制备催化剂及其前驱体的微观结构进行了表征。研究表明:Zr促进了绿铜锌矿(Cu,Zn)5(CO3)2(OH)6物相的生成,使催化剂前驱体中绿铜锌矿含量增加,焙烧后的催化剂铜锌协同作用增强,CuO分散度提高,CuO晶粒平均直径只有4.18nm,同时还原温度显著降低为150℃,CO吸附能力增强,结果显著提高了浆态床合成甲醇催化活性和稳定性。与CuO/ZnO/Al2O3三元催化剂相比,80℃沉淀制备的含4%Zr的CuO/ZnO/Al2O3/ZrO2四元催化剂的甲醇时空收率提高了8.67%,失活率降低了65.12%。     

P123软模板对CuO-CeO2结构及其CO催化氧化性能的影响

采用软模板水热法制备了不同Cu/Ce物质的量之比的CuO-CeO₂(n_Cu:n_Ce=1:9、2:8、3:7、4:6、5:5、6:4、7:3)催化剂。考察了n_Cu:n_Ce和制备方法(软模板水热法和无模板共沉淀法)对CuO-CeO₂催化剂低温催化氧化CO性能的影响,并采用XRD、N₂-吸附脱附、TEM、H₂-TPR和XPS等表征手段对催化剂的结构、氧化还原特性和表面化学状态等进行了分析。结果表明,随着nCu:nCe的增加,CuO-CeO₂催化剂的CO催化氧化活性先升高后降低。当n_Cu:n_Ce=5:5时,催化剂在100℃时CO转化率即达到90%以上。采用软模板水热法制备的CuO-CeO₂催化剂大的比表面积、狭窄的孔道分布结构、活性CuO物种高的分散状态和CuO与CeO₂之间存在强相互作用是其具有优异的CO催化氧化活性的主要原因。     

轻质高强度C/Al2O3复合气凝胶的制备及表征

采用溶胶-凝胶法和CO2超临界干燥工艺制备RF/Al2O3复合气凝胶,再经高温热处理过程得到轻质高强度C/Al2O3复合气凝胶,研究了不同热处理温度对气凝胶结构的影响,利用氮气吸附、X射线衍射、扫描电子显微镜和透射电子显微镜等手段对气凝胶的结构和性能进行了分析并且测试了不同热处理温度样品的压缩强度。实验结果表明:C/Al2O3复合气凝胶具有均匀的三维网络结构且成块性好,随着热处理温度的升高,气凝胶比表面积和强度均先增大后减小,当1 400℃时,C/Al2O3复合气凝胶比表面积最高,为831 m2.g-1,压缩强度最大,为9.5 MPa。     

Planar ZrO2 Waveguides Prepared by the Sol-Gel Process: Structural and Optical Properties

ZrO₂ waveguides are prepared by the sol-gel process from a solution containing zirconiumn-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300°C and the pure ZrO₂ tetragonal crystalline phase appears beyond 400°C. Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38 Å at 400°C to 53 Å at 600°C. Waveguides are at least monomode TE₀ at 632.8 nm. At this wavelength, optical losses are about, 0.8±0.2dB/cm for amorphous layers and increase up to 2.5±0.4 dB/cm for 600°C heat-treated waveguides.     

自生纳米纤维增强SiO_2气凝胶的制备及性能研究

采用溶胶-凝胶法和乙醇超临界干燥工艺制备ZrOX/SiO2复合气凝胶,再经1 200℃高温热处理得到自生纳米纤维增强SiO2复合气凝胶。利用扫描电子显微镜、透射电子显微镜、X射线衍射、热重和氮气吸附等手段对气凝胶的结构和性能进行了分析,并且测试了样品的压缩强度及真密度。实验结果表明:自生纳米纤维增强SiO2复合气凝胶具有均匀的多孔网络结构,锆氧纳米纤维是以化学键连接复合的方式无序穿插在气凝胶中,对复合气凝胶的机械强度和隔热性能有明显的改善。经1 200℃热处理后的ZrOX/SiO2复合气凝胶比表面积为827.22 m2·g-1,压缩强度为9.68 MPa,真密度为0.23 g·cm-3。     

自生纳米纤维增强SiO2气凝胶的制备及性能研究

采用溶胶-凝胶法和乙醇超临界干燥工艺制备ZrO_X/SiO₂复合气凝胶,再经1200℃高温热处理得到自生纳米纤维增强SiO₂复合气凝胶。利用扫描电子显微镜、透射电子显微镜、X射线衍射、热重和氮气吸附等手段对气凝胶的结构和性能进行了分析,并且测试了样品的压缩强度及真密度。实验结果表明：自生纳米纤维增强SiO₂复合气凝胶具有均匀的多孔网络结构,锆氧纳米纤维是以化学键连接复合的方式无序穿插在气凝胶中,对复合气凝胶的机械强度和隔热性能有明显的改善。经1200℃热处理后的ZrO_X/SiO₂复合气凝胶比表面积为827.22m₂·g^-1,压缩强度为9.68MPa,真密度为0.23g·cm^-3。     

ZrO_2-Al_2O_3复合氧化物的合成及其性能研究

采用表面活性剂改性的沉淀法合成了系列掺杂钇、镧、钡的氧化锆铝复合氧化物。通过XRD、XRF、低温N2吸附和CO脉冲化学吸附等手段考察了表面活性剂、助剂、焙烧温度对复合材料结构、孔结构以及负载0.5%铑催化剂的分散性能等的影响。研究表明:与采用常规沉淀法合成的氧化锆铝复合氧化物相比,添加表面活性剂合成的样品具有更大的比表面积、孔容和适合的孔径分布。分别或同时掺杂La、Ba、Y合成的氧化锆铝复合氧化物都能抑制氧化铝的α相变,提高复合材料和催化剂表面金属Rh的高温抗烧结能力,特别是同时掺杂La、Ba、Y合成的Rh/LBYZA样品经1100℃4h焙烧后仍有17.82%的金属分散度。以LBYZA为载体制备的新鲜催化剂(600℃4h焙烧样品)在CO选择还原NO反应中NO和CO的起燃温度分别为240、243℃,完全燃烧温度分别为273、280℃,表现出较高的催化活性。