Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al-Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol-gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N₂ adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350-410 m²/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al-Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ?220 °C and as the temperature was raised to 300 °C, some CH₄ and CO₂ formed on the account of DME.     

Investigation on the electrolysis voltage of electrocoagulation

The relation between electrolysis voltage and the other variables of an electrocoagulation process was analyzed. Theoretical models describing such a relation were established. Experiments were conducted to confirm the theoretical analysis and to determine the constants in the models. Both the theoretical analysis and experiments demonstrated that water pH and flow rate had little effects on the electrolysis voltage within a large range. The electrolysis voltage depends primarily on the inter-electrode distance, conductivity, current density and the electrode surface state. The models obtained can be used to calculate the total required electrolysis voltage for an electrocoagulation process.     

高铝砖高温弯曲应力-应变关系

采用研制的高温弯曲应力-应变测试仪研究了Ⅰ等高铝砖DL-80、Ⅱ等高铝砖GL-75和Ⅲ等高铝砖GL-55在不同温度下的力学性能,包括应力-应变曲线、弹性模量、抗折强度和断裂时的最大变形量。结果表明:高铝砖在不同温度下的应力-应变关系可以分为弹性阶段、塑性阶段和粘滞流动阶段;在低、中温范围内,高铝砖的弹性模量和抗折强度随温度的上升而增加,到达某一转折温度后,随温度的上升而明显下降;3种高铝砖高温力学性能从高到低的排列顺序为:Ⅱ等>Ⅰ等>Ⅲ等。     

等离子体改性对活性炭纤维低温选择性催化还原脱除NO的影响

采用介质阻挡放电(DBD)低温N2、O2等离子体技术对黏胶基活性炭纤维(V-ACF)进行表面改性,运用BET、SEM、NH3-TPD和FT-IR对催化剂进行表征,并对催化剂低温选择性催化还原(SCR)NO性能进行了研究。结果表明,N2、O2等离子体最佳改性时间分别为5 min与10 min,最佳反应温度为100℃,低温等离子体改性能明显提高ACF上NO转化率,且N2等离子体改性ACF催化效率高于O2等离子体改性ACF。     

低温熔盐法制备片状氧化铝

研究了以氢氧化铝为原料,氯化钠-氯化钾为熔盐,以及熔盐加入量对试样物相的影响。研究结果表明,熔盐加入量为67%时,在1000℃保温4h,得到了结晶完整的,边长为5～10μm,厚度为0.6～1.4μm的片状α-Al2O3;熔盐加入量为50%时,不能得到片状氧化铝。     

Characterization of high strength mortars with nano alumina at elevated temperatures

In this study, the effect of elevated temperatures on chemical composition, microstructure and mechanical properties of high strength mortars with nano alumina was investigated. Mortars with 1, 2 and 3% nano alumina as cement replacement were prepared and then exposed to 100 °C, 200 °C, 300 °C, 400 °C, 600 °C, 800 °C and 1000 °C. XRD, DSC and SEM tests were carried out to identify chemical composition and microstructure changes in the cement matrix after being exposed to elevated temperatures. Residual compressive strength, relative elastic modulus and gas permeability coefficient of samples were also obtained. A brittleness index was defined to monitor changes in brittleness of samples after being exposed to elevated temperatures. Nano alumina enhanced compressive strength of samples up to 16% and improved residual compressive strength. An increase in the relative elastic modulus, higher energy absorption and lower permeability were also observed when 1% nano alumina was added.     

Fundamental studies of NOx storage at low temperatures

A commercial NO_x storage catalyst (Pt, BaO and alumina containing) was investigated by temperature programmed desorption (TPD) experiments in the temperature range 100–400 °C. The catalyst stored a substantial amount of NO_x at 100 °C using NO + O₂. Nitrites or loosely bound NO species are suggested for this storage, since no NO was oxidised at this low temperature. In addition, the released NO_x during the temperature ramp consisted of mainly NO and at lower temperatures the NO₂ dissociation is limited. Water and CO₂ was found to decrease the storage substantially, 92% for the NO + O₂ adsorption at 100 °C. The total storage for 60 min using NO₂ + O₂ at 200 °C was similar when introducing CO₂ and H₂O. However, the initial total uptake of NO_x was decreased. Initially we probably formed loosely bound NO_x species, which likely are strongly influenced by water and CO₂. After longer time periods are barium nitrates probably formed and they can remove the carbonates by forming stable nitrates, thus resulting in the same total uptake of NO_x.     

The fracture toughness of alumina coatings plasma-sprayed at different in situ temperatures

Alumina coatings were prepared by atmospheric plasma spraying through controlling the surface temperature of the coatings during spraying. Both the polished and fractured cross-section microstructures of the coatings were characterized by scanning electron microscopy (SEM). The phase structures of the coatings and the feedstock were analyzed by X-ray diffraction technique (XRD). The microstructure and phase structure of the coatings prepared at different substrate temperatures were examined. SEM observations show that the intersplat bonding within the coatings was significantly improved by increasing the substrate temperature. The fracture toughness of the deposits was measured by indentation methods. For the coatings prepared at low substrate temperatures, the fracture toughness increased with the substrate temperature due to the improvement in the intersplat bonding. However, a significant decrease in the fracture toughness was found for the coatings prepared at high substrate temperatures. The change in phase structure of the coatings suggested that the residual tensile stress mainly resulted from phase transformation from γ-alumina to α-alumina at high substrate temperature should answer for the decline in the fracture toughness.