以乌洛托品为扩孔剂合成SiO2气凝胶的研究

以正硅酸乙酯为硅源,用溶胶—凝胶法通过常压干燥制备SiO2气凝胶,在溶胶—凝胶的过程中加入扩孔剂,着重考察以乌洛托品作为扩孔剂的用量、水解时间、水解温度、焙烧温度等因素对SiO2气凝胶孔径的影响。采用红外波谱(FTIR)表征了样品具有SiO2气凝胶的骨架结构和特定的表面基团,电镜(SEM)说明了样品有很好的分散性,热重(TG)说明经过扩孔的SiO2气凝胶依然有良好的热稳定性、BET对SiO2气凝胶表征显示了样品有较大的比表面积(400～1 200m2/g)、孔径(10～21nm)、孔容(0.5～2.5cm3/g)。     

ZrO_2–Al_2O_3复合气凝胶的制备与表征

以锆酸四丁酯、仲丁醇铝为原料,采用丙酮-苯胺原位生成水法结合乙醇超临界干燥技术制备了Zr O2-Al2O3复合气凝胶。利用扫描电子显微镜、氮气吸附-脱附比表面积与孔径分析仪和X射线衍射仪等对气凝胶的微观形貌、结构进行表征。结果表明:制得的Zr O2-Al2O3复合气凝胶比表面积为558 m2/g;1 000℃热处理后,比表面积仍高达129 m2/g,晶粒尺寸在7~14 nm之间;晶相从无定型态变为四方相氧化锆。通过纯Zr O2气凝胶与Zr O2-Al2O3复合气凝胶的对比发现,掺杂氧化铝可有效抑制氧化锆高温热处理过程中的晶体生长和晶相转变,提高耐温性能。     

水玻璃为源的超疏水型SiO2气凝胶块体制备与表征

采用廉价的水玻璃为硅源,通过乙醇溶剂替换及六甲基二硅醚和盐酸混合液对湿凝胶的表面基团改性,常压干燥出疏水介孔的SiO2气凝胶块体。制得的SiO2气凝胶块体具有超疏水性,在0～400℃附近,疏水角约155°～130°,其密度为80～200 mg/cm3,比表面积为568 m2/g,孔体积为2.9cm3/g,其室温下的热导率为0.026W/（m K）。     

疏水型SiO_2/TiO_2复合气凝胶的制备及光催化性能研究

采用溶胶-凝胶法,以甲基三甲氧基硅烷(MTMS)为前驱体,甲醇(Me OH)为溶剂,将SiO_2湿凝胶与纳米TiO_2复合,通过常压干燥法制备疏水型SiO_2/TiO_2复合气凝胶。利用扫描电镜(SEM)、X射线衍射仪(XRD)、红外光谱仪(FT-IR)、热重分析仪(TG)、比表面积及孔径分析仪(BET)等对所制备的复合气凝胶结构和形貌进行测试,同时研究其光催化性能与疏水性。结果表明,复合气凝胶具有三维空间网络多孔结构,孔洞尺寸大都为微纳米级,TiO_2均匀分散在气凝胶中,XRD与FT-IR证实了SiO_2/TiO_2复合气凝胶的成功制备,SiO_2/TiO_2复合气凝胶具有较好的热稳定性。所制备的SiO_2/TiO_2复合气凝胶的比表面积为479. 79 m2/g,表现出较好的疏水性,接触角可达153. 5°,并具有优异的光催化性能,光照3 h后对亚甲基蓝光催化降解率达98. 13%。     

疏水SiO2气凝胶的制备及表征

以正硅酸乙酯(TEOS)为硅源,三甲基氯硅烷(TMCS)为改性剂,经老化、表面疏水改性,常压干燥制备了高比表面积疏水SiO2气凝胶.用傅立叶变换红外光谱仪(FT-IR)、扫描电镜(SEM)、比表面及孔径分布仪、热重分析仪(TG-DSC)对其疏水特性及结构进行表征.结果表明:疏水SiO2气凝胶与水的接触角达145°,在空气中的热稳定温度为269 ℃;且比表面积达1035 m2/g,具有典型的气凝胶结构特征,孔径尺寸和密度分别达9.7 nm和0.129 g/cc,骨架颗粒尺寸小于30 nm.     

Na2CO3?10H2O-Na2HPO4.12H2O/SiO2复合定形相变材料的制备及应用研究

以十水合碳酸钠(SCD)、十二水合磷酸氢二钠(DHPD)为相变主体,制备了低过冷度,无相分离的共晶水合盐(EHS),以九水合硅酸钠为成核剂。进一步使用气相SiO₂为支撑材料,采用浸渍法制备了相变前后形状稳定的 EHS/SiO₂定形相变储能材料(SSPCM)。所得SSPCM的相变温度为 24.08 ℃,焓值为 146.6 J/g,过冷度为 0.55 ℃,热导率为 0.5454 W/m?K。同保温泡沫相比,其可将模拟房内部中心温度的升温时间延长 3.26 倍,降温时间延长 1.39 倍,具有优异的“热缓冲”性能,在建筑节能领域具有广阔的应用前景。     

含钴硅酸乙酯的Sol-Gel法制备Co/SiO_2纳米复合气凝胶

气凝胶 (aerogels)是一种结构可控的新型轻质纳米多孔性非晶固态材料 ,而金属 /氧化物复合气凝胶由于其高的比表面积 ,可作为高效催化剂 .本工作首次采用含钴硅酸乙酯 (Co_TEOS)进行溶胶 -凝胶反应来制备高钴含量的纳米级Co/SiO2 复合气凝胶 ,制备的Co/SiO2 复合气凝胶中n(Co)∶n(Si)的比例最高可达 2∶1,且复合气凝胶中的Co含量可在小于 6 6 % (质量分数 )的范围内任意调节 ,并系统研究了水量、催化剂浓度、溶剂量及含钴硅酸乙酯的组成对溶胶 -凝胶过程的影响 .所制备的高钴含量的Co/SiO2 复合气凝胶的比表面积和孔体积均随钴含量的降低而增加 ,分别可达到 6 0 0m2 /g以上和 1.0m3/g以上 .该方法简单、可靠、金属保留率高 ,可制备所需金属含量的金属 /SiO2 复合气凝胶、多元金属 /SiO2 复合气凝胶 ,以及金属氧化物 /SiO2 复合气凝胶 .     

SiO_2掺杂Al_2O_3气凝胶改性研究

以仲丁醇铝与正硅酸乙酯为原料,选取甲酰胺为干燥控制化学添加剂和调凝剂,采用溶胶-凝胶法制备SiO_2-Al_2O_3凝胶,并通过老化、超临界干燥工艺得到了乳白色、轻质、块状无裂纹的硅铝二元气凝胶。将气凝胶进行高温热处理,从室温到1300°C范围内,气凝胶能够保持块状无坍塌、微裂纹产生,其1300°C比表面积维持在55 m~2/g。采用SEM、TEM、XRD、BET等手段系统探究了SiO_2含量对Al_2O_3气凝胶性能与结构的影响,着重分析了硅元素掺杂对热稳定性的改善机理。     

甲基三乙氧基硅烷改性制备疏水SiO2气凝胶

采用原位聚合法结合超临界干燥工艺,以正硅酸四乙酯为硅源、甲基三乙氧基硅烷为改性剂制备出疏水型SiO2气凝胶．采用比表面积及微孔物理分析仪、接触角分析仪、热分析仪和红外光谱仪对其性能和结构进行表征．结果表明：所制备出的SiO2气凝胶是接触角为160°、比表面积为674．47m^2／g和孔体积为4．13cm^3／g@疏水型气凝胶．疏水SiO2气凝胶的热稳定温度为244．5℃．     

ZrO_2/SO_4~(2-)固体超强酸制备方法的改进

通过比表面积、热失重、红外光谱等分析方法,进行了Zr(OH)_4低温干燥350℃烧结对失水、比表面积、浸渍硫酸时锆的损失变化的研究。证实样品低温干燥失水转化ZrO_2,干燥时间与失水量、比表面积的大小成正比,与锆的损失成反比。样品经过350℃、3 h烧结,其比表面积、失水转化成的ZrO_2的量显著增加,失锆量降低。将两种条件制备的ZrO_2/SO_4~(2-)代替硫酸用于净化粗苯,以检验其催化活性。实验表明:两种方法制备的催化剂用于苯净化反应时苯乙烯的转化率有明显差异,采用350℃、3 h烧结的样品浸渍硫酸得到的催化剂,苯乙烯的转化率达50％以上。本研究为固体超强酸的应用开拓了新的领域。     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Mixed oxides Ca2Fe2O5 and Ca2Co2O5 as anode materials for Li-ion batteries

The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data.     

Al2O3-coated SnO2/TiO2 composite electrode for the dye-sensitized solar cell

A novel Al₂O₃-coated SnO₂/TiO₂ composite electrode has been applied to the dye-sensitized solar cell. In such an electrode, two kinds of energy barriers (SnO₂/TiO₂ and TiO₂/Al₂O₃) were designed to suppress the recombination processes of the photo-generated electrons and holes. After the SnO₂ was modified by colloid TiO₂, the photoelectric conversion efficiency of the SnO₂/TiO₂ composite cell increased to 2.08% by a factor of 2.8 comparing with that of the SnO₂ cell. The Al₂O₃ layer on the SnO₂/TiO₂ composite electrode further suppressed the generation of the dark current, resulting in 37% improvement in device performance comparing with the SnO₂/TiO₂ cell.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

SO2 and NO removal from flue gas over V2O5/AC at lower temperatures — role of V2O5 on SO2 removal

Supporting V₂O₅ onto an activated coke (AC) has been reported to significantly increase the AC's activity in simultaneous SO₂ and NO removal from flue gas. To understand the role of V₂O₅ on SO₂ removal, V₂O₅/AC is studied through SO₂ removal reaction, surface analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) techniques. It is found that the main role of V₂O₅ in SO₂ removal over V₂O₅/AC is to catalyze SO₂ oxidation through a VOSO₄-like intermediate species, which reacts with O₂ to form SO₃ and V₂O₅. The SO₃ formed transfers from the V sites to AC sites and then reacts with H₂O to form H₂SO₄. At low V₂O₅ loadings, a V atom is able to catalyze as many as 8 SO₂ molecules to SO₃. At high V₂O₅ loadings, however, the number of SO₂ molecules catalyzed by a V atom is much less, due possibly to excessive amounts of V₂O₅ sites in comparison to the pores available for SO₃ and H₂SO₄ storage.     

Dynamic corrosion of Al2O3-ZrO2-SiO2 and Cr2O3-containing refractories by molten frits. Part I: Macroscopic analysis

Manufacturing of enamels and frits has undergone dramatic changes since the 1980s. This has required significant efforts in research and development. Typical compositions of frits for ceramic tiles are silica-based with fluxing agents; some of the components are highly corrosive. Improvements in the production of frits would imply the selection of the most adequate refractories as a function of the chemical composition of the considered frit and the fabrication procedure.The refractories currently used in frit furnaces are Al₂O₃-ZrO₂-SiO₂ (AZS) fused cast materials and Cr₂O₃-based materials. In this work, results on dynamic corrosion studies of AZS and Cr₂O₃-based materials by two ZnO-containing frits are described. Experiments have been performed using the “Merry Go Round” test at ≅1500 °C. Macroscopic results are analysed in terms of the remaining volume after the tests, as usually done in the glass industry. The significance and limits of such an approach are discussed.     

Dynamic corrosion of Al2O3-ZrO2-SiO2 and Cr2O3-containing refractories by molten frits. Part II: Microstructural study

In this work results on dynamic corrosion studies of fused cast Al₂O₃-SiO₂-ZrO₂ and isostatically pressed and sintered Cr₂O₃-based refractories by two crystalline (transparent) frits are described. Experiments have been performed using the “Merry Go Round” test at ≅1500 °C.Microstructural and mineralogical analyses of selected areas from the corroded regions of the studied refractories were performed by reflected light optical microscopy and scanning electron microscopy with analysis by X-ray dispersive energy.Significant differences between the corrosion mechanisms acting in the two types of materials were found. In the fused cast Al₂O₃-SiO₂-ZrO₂ specimens corrosion took place by the dissolution of alumina and zirconia in the frit and in the glass formed by the reaction between the frit and the refractory. In the Cr₂O₃-based materials the corrosion process was controlled by the capillar penetration of the molten frit through the open pores. The reaction between the ZnO from the frits and Cr₂O₃ led to the formation of spinel (ZnCr₂O₄), a high-melting point bonding phase that retarded the frit penetration. Results are discussed using the relevant phase equilibrium diagrams.     

The catalytic performance in oxidative coupling of methane and the surface basicity of La2O3, Nd2O3, ZrO2 and Nb2O5

The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ has been investigated under various conditions. The results confirmed that the activity of La₂O₃ and Nd₂O₃ was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO₂. Both methods showed that La₂O₃ and Nd₂O₃ had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO₂ had only negligible amount of weak basic sites and Nb₂O₅ was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO₂ it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

Electrocatalytic activity of IrO2-RuO2 supported on Sb-doped SnO2 nanoparticles

Electrocatalytic IrO₂-RuO₂ supported on Sb-doped SnO₂ (ATO) nanoparticles is very active towards the oxygen evolution reaction. The IrO₂-RuO₂ material is XRD amorphous and exists as clusters on the surface of the ATO. Systematic changes to the surface chemical composition of the ATO as a function of the IrO₂:RuO₂ ratio suggests an interaction between the IrO₂-RuO₂ and ATO. Cyclic voltammetry indicates that the electrochemically active surface area of IrO₂-RuO₂ clusters is maximised when the composition is 75 mol% IrO₂-25 mol% RuO₂. Decreasing the loading of IrO₂-RuO₂ on ATO reduces the electrochemically active surface area, although there is evidence to support a decrease in the clusters size with decreased loading. Tafel slope analysis shows that if the clusters are too small, the kinetics of the oxygen evolution reaction are reduced. Overall, clusters of IrO₂-RuO₂ on ATO have similar or better performance for the oxygen evolution reaction than many previously reported materials, despite the low quantity of noble metals used in the electrocatalysts. This suggests that these oxides may be of economic advantage if used as PEM water electrolysis anodes.