The Thermal Properties and Firing Characteristics of Zr/KClO4 Priming Compositions Containing Graphite,Fe2O3 and Al2O3 additives

Thermal decomposition of Zr/KClO₄ priming compositions containing different concentration of additives, such as graphite, Fe₂O₃ and Al₂O₃ have been studied by DSC/TG techniques. The firing characteristics of these primer mixtures have also been examined by Bruceton test and by adiabatic calorimeter. The results of these experiments suggest that strong interaction has been occurred between KClO₄ and Fe₂O₃ in the solid state. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic Effect of Some Chromites on the Thermal Decomposition of KClO4. Mechanistic and non-isothermal kinetic studies

The catalytic effect of two different groups of chromites on the non-isothermal decomposition of KClO₄was studied. TG and DSC curves of the thermal behaviour obtained for KClO₄-alkaline earth chromites (Series 1) mixtures indicate the formation of K₂Cr₂O₇, through a solid-solid interaction, before accelerating the decomposition stage of KClO₄. Such an accelerating effect becomes more pronounced in the case of admixing KClO₄ with some transition metal chromites (Series 2). The results were discussed taking into consideration the electronic configuration of cations and the electrical properties of the chromite catalysts. The presence of coordinatively active cations, able to form surface complex with the oxygen of the perchlorate anion, was proved to be necessary for obtaining an active catalyst. The kinetic parameters and models describing the catalyzed thermal decomposition process of KClO₄ were evaluated by using a computer program that allows the analysis using five different methods. It was found that the adopted kinetic model for pure KClO₄ and that mixed with catalysts from Series 1 is one-dimensional movement of phase boundary. On the other hand, random nucleation mechanism was achieved in the presence of catalysts from Series 2. Finally, a tentative reaction mechanism consistent with the obtained results was suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

Textural and catalytic properties of the FexOy/Fe-KClO4 system

Selected properties of commercial iron powders, standardised in the atmosphere of hydrogen, have been studied. The reactivity of iron oxides in the thermal decomposition of KClO₄ in the solid-state mechanical mixture of Fe and KClO₄ containing 9, 13, 17, 21 and 25 wt.% of KClO₄, respectively, has been tested by the differential thermal analysis (DTA) and thermogravimetric analysis (TG). It has been established that the Fe₃O₄ phase on the surface of the iron powder act as an effective catalysts in the thermal decomposition of KClO₄.     

Thermosonimetry and thermomicroscopy of the decomposition of NaClO4 and KClO4

Thermal decompositions of NaClO₄ and KClO₄ were followed by simultaneous TS-DTA and thermomicroscopy. For NaClO₄ TS curves corresponding to melting/decomposition and solidification of molten NaCl were found to consist of six peaks. During decomposition of KClO₄, three TS peaks appeared. The origin of these TS peaks is discussed on the basis of thermomicroscopic observations during which melting of the particles, evolution of bubbles of different sizes, formation of solid products of varied morphologies, vigorous vibration of these solids, and precipitation of NaCl or KCl were observed.     

Ba2Cu3O5+δ as an intermediate phase during the synthesis of YBa2Cu4O8

We propose a reaction model for the synthesis of YBa₂Cu₄O₈ under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide react to Ba₂Cu₃O_5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected to Ba₂Cu₃O_5+δ, which reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈ or decomposes to BaCuO₂ and CuO. In a last step parts of BaCuO₂ reacts with Y₂O₃ and CuO to YBa₂Cu₄O₈.     

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO₄/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG?CDSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700?°C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10?°C?min^?1, the peak temperatures for ignition and afterburning process of stoichiometric KClO₄/Mg (58.8/41.2) was 543 and 615?°C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530?°C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5?kJ?mol^?1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO₄/Mg-containing pyrotechnics.     

吸附法制备CuO-Ag/SiO2纳米复合物

利用吸附法原位制备CuO/SiO2、CuO-Ag/SiO2纳米复合物,研究了不同吸附质体系中预负载的纳米Ag粒子对CuO的影响。结果表明:Ag粒子对CuO的影响因吸附质的不同而不同。以Cu(Ac)2为吸附质,纳米Ag几乎没有影响;以NaOH为吸附质,纳米Ag使得CuO的晶粒粒径增大。这一结果与铜物种对Ag晶粒粒径的影响规律完全不同。通过比较不同吸附质的吸附行为,Cu(OH)2与硅胶表面的相互作用被认为是导致这一现象的原因。     

Efficient oxidative degradation of 2-chlorophenol and 4-chlorophenol over supported CuO-based catalysts

A series of metal oxide catalysts for catalytic oxidative degradation of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) were prepared, and the supported CuO catalysts were studied particularly. The supported CuO catalysts were characterized by XRD and NH3-TPD techniques, in which CuO/γ-Al2O3 exhibited high degradation activity. The addition of Na2O or K2O into CuO/γ-Al2O3 improved the oxidative degradation of CPs remarkably, in which Na2O was more efficient than K2O. Over CuO/γ-Al2O3-Na2O, CPs were completely converted and the liberation of the inorganic chloride from 2-CP or 4-CP reached 97% or 100% respectively at 30 ?C for 2 h. The supported CuO catalysts with good dispersion of CuO particles and less acid sites were favorable for the efficient oxidative degradation of CPs. In addition, the initial pH of the reaction solution was found to be an important factor which influenced the catalytic oxidative degradation of CPs and the initial pH of 11.2 and 9.8 was preferred for the oxidative degradation of 2-CP and 4-CP respectively over CuO/γ-Al2O3 catalyst.     

Reactivity of binary mixtures of Cu(II) oxalate and La(III) oxalate

Reactivity of binary mixtures of oxalates of Cu(II) and La(III) was studied by observing their thermal behaviours in decomposition using TG, DTA and XRD techniques to set the temperature conditions for preparations of various composites of oxides of Cu(II) and La(III). In the thermal behaviour it was found that the decomposition of Cu(II) oxalate is not affected while that of La(III) oxalate is drastically affected in the case of all the mixtures. The decomposition temperature at which La(III) oxide is formed is lowered by 250 K in the case of all the mixtures while the complete decomposition occurred at 723 K only in the case of mixtures containing excess Cu(II) oxalate.At 823 K La₂CuO₄ phase is developed in all the mixtures while -La and Cu₂La phases are also detected in mixtures containing excess Cu(II) oxalate. Therefore, the temperature 823 K was found to be suitable to prepare various composites viz. La₂CuO₄, La₂CuO₄·La₂O₃ and La₂CuO₄·CuO to study their electrical properties.Authors are thankful to the authorities of Department of Atomic Energy (DAE), Government of India, for providing the funds for research project and to Professor A. V. Phadke, Department of Geology, University of Poona, for valuable discussion.     

Improving safety performance of lactose-fueled binary pyrotechnic systems of smoke dyes

The lactose/KClO₃ is a widely used pyrotechnic mixture to vaporize organic materials, such as smoke dyes. However, because of low ignition temperature of this mixture, serious precaution should be taken into account to prevent its accidental self-ignition. In order to find a safe and efficient alternative of this conventional mixture, KClO₃ has been replaced by common oxidizing agents including KMnO₄, KNO₃, KClO₄, Ba(NO₃)₂, PbO₂ and NH₄ClO₄. TG and DTA analysis have been used to obtain thermal characteristic of the mixtures. Based on ignition temperature of the pyrotechnic mixtures we can divide them into four categories as follows: (1) the mixture igniting at low temperature, i.e., at about 200 °C. (2) Moderate temperature igniting mixture, in which ignition occurs at 300–400 °C. (3) High temperature igniting mixture with ignition temperature higher than 400 °C .(4) Not igniting mixtures. Also, the apparent activation energy (E), ΔG ^#, ΔH ^#, ΔS ^# and critical ignition temperature (T _b ) of the ignition processes of low and moderate temperature igniting mixtures were obtained from the DSC experiments. Finally, among the investigated mixtures, lactose/KNO₃ can be considered as a safe and efficient pyrotechnic composition for vaporization of organic materials, such as smoke dyes, due to its moderate safe ignition temperature.     

The influences of combinative effect of temperature and humidity on the thermal stability of pyrotechnic mixtures containing strontium nitrate as oxidizer

The influences of combinative effect of temperature and humidity on the thermal stabilities of three pyrotechnic compositions are investigated in the study. The thermal behavior for each pyrotechnic is analyzed by SETARAM thermal analyzer. Activation energy is determined by Kissinger method and critical temperature of thermal explosion (T _b) of pyrotechnic compositions is also calculated. The results of thermal analysis revealed that relative humidity could decrease the thermal stability of pyrotechnic mixtures. The critical temperature of thermal explosion (T _b) of each pyrotechnics decreased as the relative humidity increasing. Based on the value of T _b, the thermal stabilities of the pyrotechnic mixtures are in the order of S_r(NO₃)₂/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/S_rCO₃/KClO₄/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/KClO₄/Mg₄Al₃/PVC/PF. The thermal stability of S_r(NO₃)₂/Mg₄Al₃/PVC/PF show the best thermal stability than other two mixtures whether it is in the condition of humidity or not.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

溶剂极性对微波辐射老化制备前驱体及CuO/ZnO/Al2O3催化剂结构的影响

在制备CuO/ZnO/Al2O3催化剂的老化过程中,采用微波辐射老化技术,着重研究了溶剂极性对前躯体物相组成,烧后CuO/ZnO/Al2O3催化剂结构及其在浆态床合成甲醇工艺中催化性能的影响。通过XRD、DTG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂表征表明,沉淀母液在微波辐射条件下进行老化,溶剂的极性对前躯体物相组成及催化剂结构影响显著。随着溶剂极性的增大,Zn2+/Cu2+取代Cu2(CO3)(OH)2/Zn5(CO3)2(OH)6中Cu2+/Zn2+的取代反应增强,使得前躯体中(Cu,Zn)5(CO3)2(OH)6和(Cu,Zn)2(CO3)(OH)2物相的含量增多,结晶度提高,导致烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用增强,且CuO晶粒减小,表面Cu含量增加,催化剂活性和稳定性提高。水溶剂的极性最大,制备的催化剂活性和稳定性最好,甲醇的时空收率(STY)和平均失活率分别为320 mg.g-1.h-1和0.11%.d-1。     

Titania supported copper catalysts for methanol synthesis from carbon dioxide

The effect of co-catalyst (ZnO or ZrO₂) has been tested for hydrogenation of CO₂ on CuO/TiO₂ and CuO/Al₂O₃. CuO−ZnO/TiO₂ catalyst showed the highest activity for methanol synthesis. Kinetic parameters were also determined.     

CuO Catalysts Supported on Porous TiO2 Microspheres for Low-Temperature CO Oxidation

The porous TiO₂ microspheres were prepared by the reversed-phase suspension polymerization and sol-gel method using reversed-phase suspension droplets as the templates. The CO oxidation catalytic properties of the CuO/TiO₂ catalysts prepared by hydrothermal method and impregnation method were extensively investigated. The structure of CuO/TiO₂ catalysts was determined by TG-DTA, XRD, TEM, and XPS. The results indicated that the redox capacity of CuO/TiO₂ was greatly depended on the aqueous solution concentration of Cu(NO₃)₂ used in the preparation of CuO/TiO₂ and the calcination temperature of the CuO/TiO₂ catalysts.     

Preparation and characterization of CuO/SiO2 and NiO/SiO2 with bimodal pore structure by sol-gel method

CuO/SiO₂ and NiO/SiO₂ with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO₂ with the presence of PEO_, CuO crystalline sizes were larger than those of NiO/SiO_2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the CuO/SiO₂ with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.     

铜物种对Cu/Fe2O3水煤气变换反应催化剂性能的影响

采用共沉淀法制备了系列铜负载量不同的Cu/Fe₂O₃水煤气变换(WGS)催化剂,并考察了铜负载量对催化剂结构和水煤气变换反应性能的影响. 结果表明,Cu/Fe₂O₃催化剂呈现出良好的水煤气反应性能,当CuO质量分数为20%时,催化剂的WGS性能最优,250 ℃时CO转化率高达97.2%,同时热稳定性也最好. 运用X射线粉末衍射(XRD)、N₂物理吸脱附和H₂程序升温还原(H₂-TPR)等手段对Cu/Fe₂O₃催化剂的物相、织构特征及还原性能进行了表征,结果表明,CuFe₂O₄物种的存在极大地改善了催化剂的还原性能和WGS反应活性. 这是由于CuFe₂O₄特殊的尖晶石结构有利于Cu微晶的稳定;同时,CuFe₂O₄在低温下即被还原为单质铜,有利于促进催化剂体系中电子的转移. 此外,通过(NH₄)₂CO₃溶液处理,研究了独立相CuO对Cu/Fe₂O₃催化剂WGS反应性能的影响,结果发现,独立相CuO的存在,有利于H原子在各组分传递,从而促进催化剂的CuFe₂O₄的还原,改善Cu/Fe₂O₃催化剂的WGS反应性能.     

Preparation of ethyl levulinate from wheat stalk over Zr(SO4)2/SiO2

A series of Zr(SO₄)₂/SiO₂ solid acid catalysts with different Zr(SO₄)₂ loadings were prepared by water-soluble-impregnation method at room temperature. Then, the prepared catalysts were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectrum, X-ray diffraction, adsorption/desorption of N₂, and temperature-programmed desorption of NH₃. The results showed that the active component Zr(SO₄)₂ was successfully adhered to the mesoporous SiO₂, and the acid amount of Zr(SO₄)₂/SiO₂ increased with the increasing of the Zr(SO₄)₂ loadings. Finally, the wheat stalk was used as raw material and depolymerized over Zr(SO₄)₂/SiO₂ to produce ethyl levulinate (EL). The reaction mixture was separated and purified by filtration and vacuum distillation. The kinetic characteristics and the reaction pathway were also studied. A comparative study showed that 20 wt.% Zr(SO₄)₂/SiO₂ exhibited higher catalytic activity. When reaction temperature, time, catalyst dosage and Zr(SO₄)₂ loadings were 190 °C, 50 min, 20 wt.% and 30 wt.%, the EL yield reached a maximum of 17.14%. The relative content of EL exceeded 90% after three steps of distillation.     

制备方法对CuO/CeO_2-ZrO_2催化CO低温氧化活性的影响

采用微波加热分解法(一步法)和微波加热处理共沉淀+浸渍法(两步法)制备了CuO/CeO2-ZrO2催化剂,并对其进行了X射线衍射、低温氮气吸附/脱附和程序升温还原等表征,采用色谱流动法考察了催化剂的催化CO低温氧化性能.结果表明,一步法比两步法更有利于使催化剂表面CuO高度分散,CuO与CeO2-ZrO2间的相互作用更强,CuO更容易被还原,从而具有更高的催化CO氧化活性.与CeO2-ZrO2有相互作用的高分散和小颗粒CuO有利于催化剂活性的提高,与CeO2-ZrO2无相互作用的大颗粒CuO对催化剂的活性有抑制作用.     

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.