Carbonyl‐precursor‐based W/Al2O3 and CoW/Al2O3 catalysts: characterization by temperature‐programmed methods

Carbonyl‐precursor‐based W/Al₂O₃ and bimetallic CoW/Al₂O₃ catalysts were prepared by gas‐phase adsorption in a fluidized‐bed reactor. The surface species formed during the gradual and controlled preparation process were studied by temperature‐programmed methods. Interactions on the surface were investigated as a function of metal loading by temperature‐programmed oxidation (TPO) and oxygen pulse chemisorption (PCO). A clear relationship was observed between decarbonylation treatment and the tungsten species formed. Total acidity of the samples was determined by temperature‐programmed desorption of ammonia (NH₃‐TPD). The NH₃‐TPD measurements, together with previous activity studies, suggest a relationship between total acidity and hydrotreating activity. The results of PCO and NH₃‐TPD measurements indicate that when the controlled gas‐phase preparation method is applied to zerovalent carbonyl precursor, the unfavourable formation of tungsten oxide can be minimized. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Metal‐ion Binding Properties of New N2S4O2‐ and N2S5O2‐Donor Macrocycles

Abstract

Synthetic procedures for new mixed‐donor macrocycle compounds were reported. The macrocyclic compounds were used in solvent extraction metal picrates such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Pb²⁺, and Co²⁺. The metal picrate extractions were investigated at 25±0.1°C with the aid of UV‐visible spectrometry. It was found that 6,7,9,10,12,13,23,24‐octahydro‐19H,26Hdibenzo[h,t](1,4,7,13,16,22,10,19) dioxatetrathiadiazasiclotetracosine‐20,27(21H,28H)‐dione showed selectivity towards Ag⁺, Hg²⁺, and Cd²⁺ among the other metals. The extraction constants (Log K_ex) and complex compositions were determined for the Ag⁺ and Hg²⁺ complexes for this compound and 9,10,12,13,23,24,26,27,29,30‐decahydro‐5H,15H‐dibenzo‐[h,w][1,4,7,13,16,19,25‐,10,22] dioxapentathiadiazacycloheptacosine‐6,16(7H,17H)‐dione.     

Vapour phase O‐methylation of 2‐naphthol over the solid bases alkali‐loaded silica and Cs‐loaded MCM‐41

O‐alkylation of 2‐naphthol has been investigated in the vapour phase over alkali‐loaded fumed silica and Cs‐MCM‐41. Both SiO₂ and MCM‐41 had low C‐alkylation activities and no O‐alkylation activity. The introduction of alkali ions considerably increases 2‐naphthol conversion with 2‐methoxynaphthalene being the major product. The activity of the catalysts increases with alkali loading and the basicity of the metal (Cs > K > Na > Li). Very high conversion (∼99%) of 2‐naphthol and selectivity (>95%) for 2‐methoxynaphthalene are obtained over Cs‐loaded fumed silica and MCM‐41. A small amount of 1‐methyl‐2‐hydroxynaphthalene is also formed over the Li‐, Na‐ and K‐loaded silica. This revised version was published online in July 2006 with corrections to the Cover Date.     

Promotional effect of H2O on the activity of In2O3‐doped Ga2O3–Al2O3 for the selective reduction of nitrogen monoxide

Effect of metal oxide additives on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by the sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. Of several metal oxide additives, the addition of In₂O₃ enhanced drastically the activity of Ga₂O₃–Al₂O₃ for NO reduction by propene in the presence of H₂O. In addition, the activity of In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was extremely intensified by the presence of H₂O below 350°C. The promotional effect of H₂O was interpreted by the suppression of undesirable propene oxidation and the removal of carbonaceous materials deposited on the catalyst surface. We also found that close interaction of In₂O₃ and Ga₂O₃ is necessary for the enhancement of activity by H₂O. A lot of hydrocarbons except methane and oxygenated compounds served as good reducing agents, among which propene and 2‐propanol were the most efficient ones. In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was capable of reducing NO into N₂ quite efficiently in the presence of H₂O at a very high space velocity. This revised version was published online in July 2006 with corrections to the Cover Date.     

High‐activity catalyst of SO 4 2− /ZrO2 supported on γ‐Al2O3 for n‐butane isomerization

A series of Al₂O₃supported SO ₄ ^2– /ZrO₂ superacid catalysts (named SZ/Al₂O₃) were prepared by a precipitation method and their catalytic behavior for nbutane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied in this paper. The catalytic activities of some of these catalysts were enhanced significantly at both low and high temperatures. At 250°C after 6 h on stream, the steady activity of the most active sample, 60%SZ/Al₂O₃, is about two times higher than that of conventional SZ. The texture properties of catalysts were studied by the methods of XRD and the adsorption of N₂. Experimental evidence of IR of adsorbed pyridine indicates that the significant activity enhancements of SZ/Al₂O₃ catalysts are caused by the increasing of the amount of strong acid sites.     

Simultaneous removal of N2O and CH4 as the strong greenhouse‐effect gases over Fe‐BEA zeolite in the presence of excess O2

Simultaneous catalytic removal of N₂O and CH₄ as the strong greenhouse‐effect gases was found to be possible over an Fe‐ion‐exchanged BEA zeolite (Fe‐BEA) by the selective catalytic reduction (SCR) of N₂O with CH₄. The direct decomposition of N₂O (2N₂O → 2N₂ + O₂) and the oxidation of CH₄ (CH₄ + 2O₂ → CO₂ + 2H₂O) over Fe‐BEA zeolite required high temperature above 400 and 450 °C, respectively. Nevertheless, the catalytic reduction of N₂O by adding CH₄ over Fe‐BEA zeolite readily occurred at much lower temperatures (ca. 250–350 °C) whether in the presence of O₂ or not. No oxidation of CH₄ by O₂ took place at these temperatures. On the basis of these results and the kinetic studies, it was concluded that CH₄ reacted selectively with N₂O to produce N₂, CO₂ and H₂O over Fe‐BEA zeolite even in the presence of excess O₂. Overall stoichiometry of the SCR of N₂O with CH₄ was determined as follows: 4N₂O + CH₄ → 4N₂ + CO₂ + 2H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Steady‐state N2O decomposition on Pt and Rh surfaces using a free‐jet molecular‐beam excited by nozzle heating

Steady‐state N₂O decomposition reaction on polycrystalline Pt and Rh surfaces has been studied using a supersonic free‐jet molecular beam (2.1 × 10¹⁸ molecules/cm² s). The energy of the incident N₂O beam was controlled by a nozzle heating technique in conjunction with a seeding technique. The decomposition rate shows both translational and vibrational energy dependence on the Pt surface. However, there is also the surface temperature dependence of the decomposition rate even varying the incident beam energy, indicating precursor‐mediated dissociation of N₂O on the Pt surface. On the other hand, no energy dependence was observed on the Rh surface, suggesting that the decomposition dynamics are different between Pt and Rh surfaces. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of Extraction of Chromatographic Materials Containing Bis(2‐ethyl‐1‐hexyl)Phosphoric Acid, 2‐Ethyl‐1‐Hexyl (2‐Ethyl‐1‐Hexyl) Phosphonic Acid,and Bis(2,4,4‐Trimethyl‐1‐Pentyl)Phosphinic Acid

Abstract

This work describes the uptake of a wide range of metal ions, including alkaline earths, transition metals, post‐transition metals, lanthanides and actinides, from acidic nitrate and chloride media on extraction chromatographic resins prepared from three different acidic organophosphorus compounds: bis(2‐ethyl‐1‐hexyl) phosphoric acid (HDEHP), 2‐ethyl‐1‐hexyl(2‐ethyl‐1‐hexyl)phosphonic acid, (HEH[EHP]) and bis(2,4,4‐trimethyl‐1‐pentyl)phosphinic acid (H[DTMPP]). The data is plotted in a format allowing for the easy comparison of the uptake of all metal ions under a given condition. Additionally, examples of several novel separations using the three extraction chromatographic materials are discussed.     

High activity and stability of the Rh‐free Co‐based ex‐hydrotalcite containing Pd in the catalytic decomposition of N2O

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over calcined hydrotalcite‐like compounds containing different combinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co‐precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N₂ adsorption at 77 K, and XRF. The presence of Rh, La, or Pd in the Co‐based HTlc's improves considerably the catalytic activity. Co–Rh,Al‐HTlc (Co/Rh/Al==3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex‐Co,Pd–La,Al‐HT (Co/Pd/La/Al=3/1/1/1) produces a similar catalytic activity to that of Rh‐containing catalyst, both in a N₂O‐containing stream and in one containing also SO₂ and O₂, but with a better performance in stability tests. PdO phase has been identified by XRD as being responsible for the considerable improvement in the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO₂ and O₂ are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Al2O3、Fe2O3、Si O2、Ti O2

选用氢氧化钠-过氧化钠熔融样品,热水浸取,酸化后用电感耦合等离子体发射光谱法测定几内亚红土型铝土矿中Al2O3、Fe2O3、SiO2、TiO2含量。对溶矿条件、分析谱线的选择和光谱干扰等各种因素进行了讨论,确定了试验的最佳条件。用本法测定国家标准物质和实际样品,测定值与标准值和其他化学方法测定值相符,方法的精密度5%(n=7),加标回收率在94. 96%～103. 07%。适合批量红土型铝土矿样品中硅铝铁钛的快速测定。     

Ozone formation with (V)UV‐enhanced dielectric barrier discharges in dry and humid gas mixtures of O2, N2/O2, and Ar/O2

The effect of (V)UV illumination at 172 run and 253.7 run on ozone formation with dielectric barrier discharges in air‐like mixtures of nitrogen/oxygen and argon/oxygen as function of the water concentration is presented. Although (V)UV at these wavelengths efficiently cleaves ozone, the ozone concentration in a combined (V)UV/dielectric barrier discharge in oxygen‐containing gases is reduced only very little. This corresponds to an enhanced concentration of atomic singlet oxygen, which, in presence of water, increases the production of hydroxyl radicals. This is confirmed by measurements of the removal rates of 2‐propanol and of its byproducts in dry and humid air in a combined (V)UV/dielectric barrier discharge treatment.     

Gas‐phase pinacol conversion on AlPO4, γ‐Al2O3 and SiO2 catalysts

Pinacol (2,3‐dimethyl‐2,3‐butanediol) conversion over AlPO₄ (Al/P = 1) and γ‐Al₂O₃ catalysts proceeded in two parallel reaction pathways with formation of 2,3‐dimethyl‐1,3‐butadiene (by 1,2‐elimination) and 3,3‐dimethyl‐2‐butanone (by rearrangement), the latter being the main reaction product. The activity was in accordance with the surface acidity data as measured versus cyclohexene skeletal isomerization reaction. Thus, AlPO₄ showed the highest activity (almost total conversion at 523 K). The 1,2‐elimination/rearrangement ratio depended on the type of catalyst used and diene formation increased with reaction temperature. Moreover, pinacolone was a reaction intermediate for diene production. This revised version was published online in July 2006 with corrections to the Cover Date.     

Possibility of Initiation of Combustion of CH4–O2 (Air) Mixtures with Laser‐Induced Excitation of O2 Molecules

The possibility of initiation of combustion of CH₄–O₂ mixtures with excitation of O₂ molecules to the states a¹_g and b¹⁺ _g by laser radiation with wavelengths of 1.268 m and 762 nm is considered. It is shown that excitation of O₂ molecules significantly decreases the induction period and ignition temperature because of accelerated formation of active atoms and radicals and intensification of the chain mechanism of the process. Even if the specific energy of laser radiation absorbed by the gas is low ( 0.1 eV per molecule), the ignition temperature of the CH₄–O₂ mixture with a ratio of 1:2 can be reduced from 1000 to 300 K.     

Fe2+/H2O2体系O2生成路径

掌握Fe²⁺/H₂O₂体系O₂的生成路径,可为避免H₂O₂无效分解,开发经济高效的Fe²⁺/H₂O₂体系利用技术指明方向。采用添加自由基捕获剂的方法,探究Fe²⁺/H₂O₂体系内各种自由基对O₂生成速率的影响,进而确定O₂的生成路径。结果表明:Fe²⁺/H₂O₂体系内不会产生大量O₂^-·,O₂^-·不是生成O₂的主要反应物质;O₂^-·被全部捕获后,体系中仍产生大量O₂^-·,但此时无O₂生成,证明生成O₂的反应由·OH和HO₂·两种自由基直接参与。分析认为反应·OH+HO₂·-H₂O+O₂是体系内O₂生成的主要路径。控制Fe²⁺/H₂O₂体系定向生成·OH,抑制HO₂·的产生,是提高Fe²⁺/H₂O₂体系中H₂O₂利用率的有效手段。     

Oxidative dehydrogenation of ethane by carbon dioxide over sulfate‐modified Cr2O3/SiO2 catalysts

The oxidative dehydrogenation of ethane into ethylene by carbon dioxide over unsupported Cr₂O₃, Cr₂O₃/SiO₂ and a series of Cr₂O₃/SiO₂ catalysts modified by sulfate was investigated. The results show that Cr₂O₃/SiO₂ is an effective catalyst for dehydrogenation of ethane and CO₂ in the feed promotes the catalytic activity. Sulfation of silica will influence the catalytic behavior of Cr₂O₃/SiO₂ in dehydrogenation of ethane with carbon dioxide depending on the amount of sulfate. Cr₂O₃/6 wt% SO ₄ ^2- –SiO₂ catalysts exhibit an excellent performance for this reaction, giving an ethylene yield of 55% at 67% ethane conversion at 650°C. Characterizations indicate that addition of sulfate changes the bulk and surface properties of Cr₂O₃/SiO₂, promoting the reduction of Cr⁶⁺ to Cr³⁺ and favoring the catalytic conversion. This revised version was published online in July 2006 with corrections to the Cover Date.     

K2O含量对B2O3-Al2O3-Na2O玻璃结构及物理性能的影响

选取B_2O_3-Al_2O_3-Na_2O三元玻璃系统,研究改变玻璃系统中K_2O的含量对硼酸盐低熔点封接玻璃性能的影响。通过XRD、DTA等手段对玻璃样品的膨胀系数、转变温度、软化温度、电阻率、介电常数等性能进行了测试。结果表明:在B_2O_3-Al_2O_3-Na_2O三元玻璃系统中,随着K_2O含量的增加,硼酸盐玻璃的膨胀系数呈先下降后上升的趋势,在K_2O含量位于5 mol%左右时,硼酸盐玻璃的膨胀系数小幅下降,这是硼反常现象的体现。K_2O含量在7～8 mol%左右时,膨胀系数出现最低值。玻璃的体积电阻率和介电常数的变化也存在着硼反常现象,随着K_2O含量的增加,均呈现先下降再上升后又下降的趋势。玻璃的转变温度T_g和软化温度T_f的变化趋势基本一致,均呈现先下降后上升再下降的趋势。     

CaC2O4—H2C2O4—H2O体系相平衡研究

测量了25 C时CaC_2O_4-H_2C_2O_4-H_2O三元系的固液平衡数据,实验数据用Pitzer模型进行了关联。     

K2O对Na2O-Al2O3-B2O3玻璃性质的影响

制备了添加K2O的Na2O—Al2O3-B2O3系统低熔点玻璃,研究了玻璃的转变温度（Tg）、热膨胀系数（仅）和玻璃的红外光谱,表明随着K20含量的增加Na2O—AlO3-B2O3玻璃熔化温度、转变温度也降低,添加K20玻璃的热膨胀系数较大,在近红外区有一水分的吸收带,在中红外区有B—O、A1-O的特征吸收带,玻璃的Tg、仅与玻璃中K2O含量的关系,混合碱效应对玻璃的性能的影响。