Effect of H2S-uptake on the conversion of cyclohexene on Ru- and Pd-promoted molybdena-alumina catalysts

The effect of H₂S on the activity and selectivity of catalysts (Ru/Al₂O₃, Pd/Al₂O₃ and Ru and Pd promoted molydena-alumina) was different (on differnt catalysts and different conversions of cyclohexene). Ru-containing catalysts showed higher sulfur sensitivities than the Pd-containing ones. The sequence of catalysts by their H₂S uptake related to mass of catalyst was PdMo/Al₂O₃RuMo/Al₂O₃Mo/Al₂O₃>Pd/Al₂O₃Ru/Al₂O₃.     

Fabrication,morphology and mechanical properties of Al2O3–Al graded coatings on China low activation martensitic steel substrates

Al₂O₃, Al₂O₃/Al and Al₂O₃–Al graded coatings were fabricated on China low activation martensitic steel and silicon substrates by RF magnetron sputtering. The coating composition and cross‐section morphologies were investigated using X‐ray photoelectron spectroscopy, Auger electron spectroscopy and field‐emission scanning electron microscopy. The mechanical properties of the coatings were studied using nanoindentation, wafer‐curvature measurements and microscratch tests. The results show that usable Al₂O₃–Al graded coatings could be fabricated. With a more continuous compositional gradient, the interface zone was more compact. The hardness and elastic modulus of Al₂O₃–Al graded coatings were less than those of Al₂O₃ coatings, but greater than those of Al₂O₃/Al coatings. After annealing at 773 K for 3 h, the hardness of Al₂O₃–Al graded coating showed a small increase. The residual stresses in Al₂O₃–Al graded coatings declined to about 0.3 GPa, compared with the 6.6 GPa for Al₂O₃ coating. The adhesion of Al₂O₃ was improved by deposition of Al or Al compositional gradient oxide layers. Copyright © 2011 John Wiley & Sons, Ltd.     

焙烧气氛对Ru/Al2O3催化剂上甲烷部分氧化制合成气反应性能的影响

采用气相色谱、质谱和原位时间分辨红外光谱等技术对空气和Ar气氛中焙烧的Ru/Al2O3催化剂样品上甲烷部分氧化(POM)制合成气反应进行了跟踪,并采用化学吸附、X射线衍射、拉曼光谱和H2-程序升温还原等技术对催化剂进行了表征.结果表明,在Ru/Al2O3-Air上POM反应出现振荡现象,而在Ru/Al2O3-Ar上则可...     

A density functional study on the aggregation of alumina clusters

A calculation has been performed to explore the mechanism of aggregation reaction between two small molecular clusters [(Al₂O₃) _n1 and (Al₂O₃) _n2] by the density functional theory method. Five pathways of aggregation reactions between two different (Al₂O₃)₁ clusters isomers were identified. The detailed process of (Al₂O₃)₁ interaction with (Al₂O₃)₂ were also obtained. All the products of the aggregation reactions between two cage structures are cage-dimer structures. We calculated the thermodynamic properties of all the aggregate clusters. The Gibbs free energy changes of aggregation reactions in 0–1000 K were negative and increased with the temperature increase. The energy changes of enthalpy and entropy were also obtained.     

P改性对Mo-Ni/Al2O3煤焦油加氢脱氮性能的影响

在磷含量1.34%下,采用分步浸渍法按磷添加顺序不同制备了3种改性催化剂:MoP-Ni/Al₂O₃、Mo-NiP/Al₂O₃、Mo-Ni/PAl₂O₃.通过X射线衍射(XRD)、程序升温脱附(NH₃-TPD)、程序升温还原(H₂-TPR)、氮气吸附等技术对催化剂进行了表征.以新疆中低温煤焦油为原料,考察了不同磷改性方式对催化剂加氢脱氮(HDN)性能的影响.结果表明,适宜的磷添加方式能够改变催化剂的酸性分布,提高10~13 nm加氢脱氮有效孔的比例,并且减弱活性组分与载体的相互作用,同时使得活性组分更易被还原,进而提高催化剂加氢脱氮性能.加氢脱氮活性顺序为Mo-Ni/PAl₂O₃(74.36%)>Mo-NiP/Al₂O₃(72.74%)>Mo-Ni/Al₂O₃(71.72%)>MoP-Ni/Al₂O₃(56.13%).     

Reactivity of amorphous aluminas prepared by the thermal decomposition of aluminum chloride and nitrate

The physicochemical properties and reactivity of amorphous aluminas, Al₂O₃(C1) and Al₂O₃(N), which were prepared by the thermal decomposition of AlCl₃ · 6 H₂O and Al(NO₃)₃ · 9 H₂O at 600°C for 2–300 h, were investigated by means of TG, DTA, X-ray diffraction, SEM and IR. The reactivity of Al₂O₃(Cl) for ZnAl₂O₄ formation was, in general, higher than that of Al₂O₃(N) and was influenced by the content of residual chlorine in Al₂O₃(Cl). The rate of ZnAl₂O₄ formation followed the Avrami—Erofeev equation in the ZnOAl₂O₃(Cl) system and the Jander equation ZnOAl₂O₃(N) system, respectively.     

Elucidation of sulfur mobility on Cr, Mo and W-based catalysts in hydrodesulfurization using a35S pulse tracer method

In hydrodesulfurization of radioactive³⁵S-labeled dibenzothiophene catalyzed by CrO₃/Al₂O₃, it was found that sulfur on sulfided CrO₃/Al₂O₃ was more labile than those on MoO₃/Al₂O₃ and WO₃/Al₂O₃, while the amount of sulfur was less than that on MoO₃/Al₂O₃. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

A study of the properties of active sites on PtY/Al2O3

The catalytic performance and the properties of active sites on PtY/Al₂O₃ have been studied using a pulse microreactor, TEM and poisoning technique. The study shows that PtY/Al₂O₃ shows higher activity and selectivity for n-hexane conversion and the dehydrogenation of cyclohexane, as compared to Pt/Al₂O₃. The changes in PtY/Al₂O₃ geometric patterns and in both the total numbers of active sites (TNAS) and the active site distribution (ASD) caused by Y are likely to be responsible for the catalytic improvements.     

Activity of Au,Ni, and Au-Ni catalysts in the water-gas shift reaction and carbon monoxide oxidation

Au/Al₂O₃, NiO _x /Al₂O₃, and (Au + NiO _x )/Al₂O₃ composites have been prepared by ion exchange and impregnation. Their structural and electronic properties, including the size and shape of supported metal particles and the oxidation state and ligand environment of the Au and Ni atoms, have been investigated. The catalytic action of Au/Al₂O₃, NiO _x /Al₂O₃, and (Au + NiO _x )/Al₂O₃ in the water-gas shift reaction and carbon monoxide oxidation is reported. At 300–450°C, the CO conversion over (Au + NiO _x )/Al₂O₃ exceeds the sum of the CO conversions over the monometallic catalysts Au/Al₂O₃ and NiO _x /Al₂O₃ by a factor of 2–3. An explanation is suggested for the nonadditive increase in the CO conversion over the Au-Ni catalysts.     

氧化铝载体和氧化钡助剂对钌基氨合成催化剂结构和性能的影响

采用不同来源γ-Al2O3(市售Al2O3-1,合成Al2O3-2)作为钌基氨合成催化剂载体,利用浸渍法制备了一系列添加不同BaO助剂含量的Ba-Ru/Al2O3催化剂.通过X射线衍射(XRD)、N2-低温物理吸附、X射线荧光光谱(XRF)、透射电镜(TEM)、H2程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)等方法研究了不同来源的Al2O3以及BaO助剂含量对负载型钌基催化剂的物相结构、织构性质、微观形貌、表面性质和催化剂的氨合成活性等方面的影响.结果表明,载体的物理化学性质对制备的钌基氨合成催化剂的结构以及活性有较大影响.BaO助剂对催化剂的影响主要表现在两个方面:添加量不同导致BaO与γ-Al2O3的作用力不同,从而进一步影响催化体系的比表面积和孔结构性质;BaO助剂会对体系的Ru物种还原性质以及催化剂表面酸碱性质进行调节,适量BaO的加入能够极大提高反应活性,而这种最佳量与载体性质密切相关.     

Catalytic Performance and Characterization of Pt‐Co/Al2O3 Catalysts for CO2 Reforming of CH4 to Synthesis Gas

Pt‐Co/Al₂O₂ catalyst has been studied for CO₂ reforming of CH₄ to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al₂O₃ was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al₂O₃ and Pt/Al₂O₃ catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al₂O₃ > Pt/Al₂O₃ > Co/Al₂O₃. With 9% Co, the Co/Al₂O₃ calcined at 923 K was also active for CO₂ reforming of CH₄, however, its carbon formation was much more fast man that of the Pt‐Co/Al₂O₃ catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl₂O₄, formed during calcining of Co/Al₂O₃ at high temperature before Pt addition. Promoted by Pt, Co/Al₂O₄ in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al₂O₄ reduction are responsible for high activity of the Pt‐Co/Al₂O₃ catalyst, and the remain Co/Al₂O₄ is beneficial to suppression of carbon deposition over the catalyst.     

High photocatalytic activity and stability for decomposition of gaseous acetaldehyde on TiO2/Al2O3 composite films coated on foam nickel substrates by sol-gel processes

A set of anatase titanium dioxide (TiO₂) films coated on foam nickel that modified by Al₂O₃ films as transition layer (indicated as TiO₂/Al₂O₃ films) were synthesized via sol-gel route. The bulk and surface properties of the TiO₂/Al₂O₃ films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO₂/Al₂O₃ films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO₂/Al₂O₃ composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO₂ films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al₂O₃ transition layer, which concentrates the target substances around TiO₂ particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al₂O₃ modified foam nickel are 0.12 and 113.7 m²/g, respectively) to provide more sites for TiO₂ loading.     

不同硅铝比Al-ITQ-13分子筛的甲醇制丙烯反应催化性能

采用晶种法直接合成了硅铝比(SiO_2/Al_2O_3物质的量比)为137、224和309的三种Al-ITQ-13分子筛,并采用粉末X射线衍射(XRD)、扫描电镜(SEM)、N_2吸附-脱附、固体核磁共振(MAS NMR)和NH_3-程序升温脱附(NH_3-TPD)等分析方法对不同硅铝比分子筛进行了表征,并在固定床微型反应评价装置上,考察了硅铝比对甲醇转化制丙烯反应性能的影响。结果表明,不同硅铝比Al-ITQ-13分子筛呈现出相似的织构性质,酸量及酸强度随着硅铝比的升高逐渐下降。硅铝比对甲醇转化反应的产物分布存在较大的影响;随着硅铝比的升高,氢转移反应和芳构化反应活性降低,使得乙烯选择性下降,而丙烯和丁烯的选择性升高。硅铝比由137提高到309,丙烯的选择性(质量分数)由46.04%增加到55.52%,而丙烯/乙烯比由3.39提高到6.57。     

Effect of Al2O3 nanoparticles on the steel-glass/epoxy composite joint bonded by a two-component structural acrylic adhesive

This paper reports a study on the effect of Al₂O₃ nanoparticles on the adhesion strength of steel-glass/epoxy composite joints bonded by a two-component structural acrylic adhesive. The addition of Al₂O₃ nanoparticles to the two-component acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strength of the adhesive joints increased by addition of Al₂O₃ up to 1.5 wt%, which decreased by further addition of the nanofiller. Introduction of the nanoparticles caused a reduction in the peel strength of the joints. DSC analysis revealed that the glass transition temperature (Tg) of the adhesives rose by increasing the nanofiller content. The advancing water contact angle was decreased for adhesives containing nanoparticles. SEM micrographs indicated good dispersions of the Al₂O₃ nanoparticles within the acrylic matrix in the specimens with up to 1.5 wt% Al₂O₃ and revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Organic reactions in a solid matrix—IV: Oxirane rearrangement on modified-alumina

Rearrangement of methyldialkyl-substituted oxiranes to the corresponding allylic secondary alcohols with active Al₂O₃ is accompanied by carbonium ion rearrangements. The effect of modifying the Al₂O₃ with various bases or salts has been studied. With NaOH-modified Al₂O₃, the carbonium ion-rearrangements are significantly suppressed, and rearrangement to the allylic alcohols becomes the major pathway. Rearrangement of 2,10-epoxypinane (both isomers) on Al₂O₃-NaOH is reported.     

Roles of surface nitrogen oxides in propene activation and NO reduction on Ag/Al2O3

The activation of propene in selective catalytic reduction (SCR) of NO on 4% Ag/Al₂O₃ has been studied by in situ infrared (IR) spectroscopy. Distinctive propene activation products were detected in the SCR of NO, depending on the nature of surface oxygen and nitrogen oxide species on Ag/Al₂O₃. C₃H₆ was oxidized to acetate species in an O₂ + C₃H₆ atmosphere on Ag/Al₂O₃ above 573 K. The addition of NO to the C₃H₆ + O₂ feed gas suppressed the formation of acetate species but increased the proportion of acrylate species. Acrylate species were further confirmed to be formed preferentially from C₃H₆ oxidation without the O₂ atmosphere on Ag/Al₂O₃ or nitrate-adsorbed Ag/Al₂O₃. On the other hand, adsorption of NO led to the formation of nitrito species on Ag/Al₂O₃, but the nitrito was barely oxidized to nitrate species unless there was an O₂ atmosphere at 473–673 K. Thus, the oxidation of propene to acetate species, or the formation of nitrate from nitrito, is attributed to two competitive electrophilic reactions. The formation of nitrate from nitrito species decreased electrophilic oxygen species that oxidized propene to acetate. Nevertheless, the first dehydrogenation of propene to form acrylate species on nitrate-adsorbed Ag/Al₂O₃ is a nucleophilic reaction, as it is on Ag/Al₂O₃. Furthermore, there was no decrease in reaction activity for formation of acrylate species on nitrate-adsorbed Ag/Al₂O₃ compared to Ag/Al₂O₃. This led to the total reaction occurring easily through the propene nucleophilic oxidation branch because the presence of the adsorbed nitrogen oxides changed selectively the formation rates of the surface reductants. IR spectra data further demonstrate that acrylate and acetate species, as the surface reductants, reacted with nitrate to generate isocyanate intermediates in the SCR of NO. The effect of structures of different reductants on NO reduction is discussed.     

Effect of surface treatments on interfacial characteristics and band alignments of atomic‐layer‐deposited Al2O3 films on GaAs substrates

The GaAs surfaces were passivated by two kinds of chemical pretreatments (using NH₄OH and (NH₄)₂S as passivation agents) for atomic layer deposited (ALD) Al₂O₃ dielectric film growth. The chemical information at Al₂O₃/GaAs interfaces was carefully characterized. The impact of surface treatments on the band alignments of ALD Al₂O₃ films on n? GaAs (100) substrates was also investigated. After postdeposition annealing, the NH₄OH passivated samples not only have a slight increase of the As? As peaks with an appearance of As suboxide (AsO_x) feature at Al₂O₃/GaAs interfaces but also exhibit a serious interfacial interdiffusion between Al₂O₃ and GaAs. However, the (NH₄)₂S passivated samples produce the Ga? S and As? S overlayers on GaAs, effectively preventing from the intermixed diffusion between Al₂O₃ films and GaAs substrates with a sharper interface. Both NH₄OH and (NH₄)₂S passivated Al₂O₃ samples show the same band gap of 6.67 eV. The conduction band offset at Al₂O₃/GaAs interface for the (NH₄)₂S passivated samples have a slight enhancement of 0.14 eV in comparison to NH₄OH passivated ones. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of the homogeneity of the distribution of doped elements in oxide single crystals

Summary The homogeneity of the distributions of doped V and Ti in Al₂O₃:V³⁺, Y₃Al₅O₁₂:V³⁺, Al₂O₃:Ti³⁺, Y₃Al₅O₁₂:Ti³⁺ single crystals was studied by means of laser emission microanalysis. The applied statistical methods include one-way variance analysis, two-way variance analysis, regression models and the gradient method.     

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al₂O₃, Al₂O₃—F, SiO₂, WO₃/ZrO₂, and La₂Î₃/ZrO₂, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al₂O₃. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al_;>2O₃ and Pt/La₂Î₃/ZrO₂ catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al₂O₃ catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.