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1.
Summary Two different processes of the thermal decomposition of synthetic bayerite, i.e., the non-isothermal decomposition of mechanically ground sample in flowing N 2 and the controlled rate thermal decomposition of crystalline bayerite under vacuum, were investigated comparatively. In comparison with the conventional non-isothermal decomposition of crystalline bayerite in flowing N 2, the reaction temperature of the thermal decomposition was lowered by the individual effects of mechanical grinding of the sample and the reaction rate control. These decomposition processes indicated similar behavior characterized by the restricted changes of the specific surface area during the course of decomposition reaction and the formation of an amorphous alumina as the decomposition product. Different thermal behaviors were observed for those amorphous Al 2O 3 produced by the respective decomposition processes. 相似文献
2.
The aluminate hydrotalcites are proposed to have either of the following formulas: Mg 4Al 2(OH) 12(CO 3
2−)· xH 2O or Mg 4Al 2(OH) 12(CO 3
2−, SO 4
2−)· xH 2O. A pure hydrotalcite phase forms when magnesium chloride and aluminate solutions are mixed at a 1:1 volumetric ratio at
pH 14. The synthesis of the aluminate hydrotalcites using seawater results in the formation of an impurity phase bayerite.
Two decomposition steps have been identified for the aluminate hydrotalcites: (1) removal of interlayer water (230 °C) and
(2) simultaneous dehydroxylation and decarbonation (330 °C). The dehydration of bayerite was observed at 250 °C. X-ray diffraction
techniques determined that the synthesis of aluminate hydrotalcite with seawater and a volumetric ratio of 4.5 results in
very disordered structures. This was shown by a reduction in the mass loss associated with the removal of interlayer water
due to the reduction of interlayer sites caused by the misalignment of the metal-hydroxyl layers. 相似文献
3.
The hydrotalcite based upon manganese known as charmarite Mn 4Al 2(OH) 12CO 3·3H 2O has been synthesised with different Mn/Al ratios from 4:1 to 2:1. Impurities of manganese oxide, rhodochrosite and bayerite at low concentrations were also produced during the synthesis. The thermal stability of charmarite was investigated using thermogravimetry. The manganese hydrotalcite decomposed in stages with mass loss steps at 211, 305 and 793 °C. The product of the thermal decomposition was amorphous material mixed with manganese oxide. A comparison is made with the thermal decomposition of the Mg/Al hydrotalcite. It is concluded that the synthetic charmarite is slightly less stable than hydrotalcite. 相似文献
4.
研究了利用铝酸钠溶液碳酸化产生的沉淀, 经胶溶作用制备出纳米氢氧化铝溶胶的过程. 分析了铝酸钠溶液滴加到大量碳酸氢钠溶液中时发生的反应. X射线衍射研究结果表明, 在纳米氢氧化铝溶胶制备过程中, 从无定形氢氧化铝沉淀到拟薄水铝石的晶型转变过程是氢氧化铝沉淀胶溶时溶解再析出的过程. 将碳酸氢钠加入到苛性比为1.7的铝酸钠溶液中, 中和至苛性比为1.3后, 溶液诱导期中的紫外光谱显示270 nm处的Al(OH)3-6吸收增强. 经与含铝原子六配位的晶体紫外光谱对比后表明, 在铝酸钠分解生成氢氧化铝的过程中, 其铝的配位结构从四配位转化为六配位. 拟薄水铝石溶胶粒子的形貌与胶溶所用的酸和分散剂有关. 相似文献
5.
The influences of atmospheric CO 2 and H 2O on the kinetics of the thermal decomposition of zinc carbonate hydroxide, Zn 5(CO 3) 2(OH) 6, were investigated by means of controlled rate evolved gas analysis (CREGA) coupled with TG. Although CO 2 and H 2O were evolved simultaneously in a single mass-loss step of the thermal decomposition, different effects of those evolved
gases on the kinetic rate behavior were observed. No distinguished effect of atmospheric CO 2 was detected within the possible range of self-generated CO 2 concentration. On the other hand, apparent acceleration effect by the increase in the concentration of atmospheric H 2O was observed as the reduction of reaction temperature during the course of constant rate thermal decomposition. The catalytic
effect was characterized by the decrease in the apparent activation energy for the established reaction with increasing the
concentration of atmospheric H 2O, accompanied by the partially compensating decrease in the pre-exponential factor. 相似文献
6.
The mixed oxide LaNiO3 with perovskite structure was prepared by two relatively new and unconventional methods including preparation and thermal decomposition of mixed metal oxalate or carbonate precursors. The intermediates were prepared by reaction in a highly concentrated suspension (paste). The thermal decomposition conditions of these intermediates were described, and the final calcination temperatures were determined, which were done using thermal analysis methods and X-ray diffraction. During the decomposition of mixed carbonates, one-phase LaNiO3 is produced directly, and in case of decomposition of oxalates, a mixture of LaNiO3 and La2O3 is produced due to the formation of La2O2CO3 during the heating. Catalytic decomposition of nitrous oxide at high temperature (650–930 °C) and high loading (GHSV?=?350,000 h?1) has shown high LaNiO3 activity, even at lower temperatures. The results were compared with the same compound obtained by co-precipitation and by solid-state reaction. Methods of preparation based on decomposition of oxalate and carbonate intermediates lead to the preparation of materials with appropriate composition, morphology, specific surface and high catalytic activity. 相似文献
7.
The layered double hydroxides (LDHs) of Li and Al can be synthesized from the four polymorphs of Al(OH) 3, namely gibbsite, bayerite, nordstrandite, and doyleite. The crystal structure of this class of compounds depends on the type of the precursor used due to their topotactic reaction mechanism. While the LDHs derived from gibbsite and bayerite yield different crystal structures, the incorporation of Li into nordstrandite was expected to yield new LDH structures different from those derived from gibbsite and bayerite. The structure of nordstrandite derived LDHs were however identical to that derived from the bayerite counterpart. The absence of symmetry in the interlayer of nordstrandite ( C1) makes it unsuitable to accommodate the intercalating anions with different molecular symmetries. To make the interlayer gallery suitable for the anions, the metal hydroxide layers of the nordstrandite translate, transforming nordstrandite to bayerite. The bayerite with site symmetries Oh and C2 stabilizes the anions in the interlayer by hydrogen bonding. The transformation of nordstrandite to bayerite, when soaked in lithium salt solution is, therefore, a manifestation of the intercalating anions. 相似文献
8.
Conclusions It was shown that the size of the deposited bayerite particles remains constant during the entire time of its precipitation from aluminum nitrate solution at a constant pH, and the morphological changes that take place in the particles during the aging, washing, and conversion of the precipitate to -Al 2O 3 were described. 相似文献
9.
The decomposition of CO 2 in a dielectric packed-bed plasma reactor has been studied. It was found that the dielectric properties and morphology of
packing dielectric pellets play important roles in the reaction due to their influence on the electron energy distribution
in the plasma. The acid–base properties of the packing materials also affect the reaction through the chemisorption of CO 2 on basic sites of the materials. Heterogeneous reactions on the solid surfaces of the dielectric materials also play a role
in the reaction, which was also confirmed through the investigation of the influence of the discharge length on the reaction.
The reverse reaction of CO 2 decomposition, the oxidation of CO, was also investigated to further understand the role of dielectric materials in the plasma
and their effect on plasma reactions. Both the decomposition of CO 2 and the oxidation of CO in non-packed or dielectric packed reactors are first-ordered. 相似文献
10.
An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG‐DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu 2(OH) 2CO 3, was subjected to the measurements of CREGA‐TG under controlled concentrations of H 2O and CO 2 in the reaction atmosphere with taking account of self‐generated H 2O and CO 2 during the course of reaction. By a series of CREGA‐TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H 2O and CO 2, respectively. From the kinetic analysis of the CREGA‐TG curves and results of high temperature X‐ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H 2O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA‐TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self‐generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005 相似文献
11.
The kinetic behavior of the thermal decomposition of synthetic malachite was investigated by means of CRTA under different
conditions of reduced pressure, flowing gases and quasi-isobaric atmospheres. The thermal decomposition was found to proceed
at lower temperatures under the influence of the self-generated gases, CO 2 and H 2O. From a viewpoint of chemical equilibrium, the normal and opposite effects on the overall kinetics were observed for the
self-generated CO 2 and H 2O, respectively. The complexity of the present reaction is also reflected by the variations of the apparent kinetic parameters
which depend on the applied and self-generated atmospheric conditions. The practical usefulness of CRTA when applied to a
complicated thermal decomposition is discussed as exemplified by the kinetic approaches to the present reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
This paper presents a non-aqueous Li-air battery model that considers the side reactions of lithium carbonate (Li2CO3) formation from both electrolyte decomposition and carbon dioxide (CO2) in the ambient air. The deposition and decomposition behaviors of discharge products, the voltage, and capacity evolutions during the cycling operation of the Li-air batteries are investigated. The deposition behavior analysis implies that the Li2CO3 generated by electrolyte decomposition is mainly distributed near the separator side, while it is dominantly generated by Li-O2/CO2 reaction near the air side. The formation of Li2CO3 by side reactions makes the Li-air batteries exhibit a peak discharge deposition inside the cathode. Moreover, Li2CO3 is difficult to decompose and gradually accumulates with cycles, especially near the air side. The severe accumulation of Li2CO3 near the air side significantly reduces the O2 diffusion into the electrode, which induces severe cycling performance decay of the Li-air batteries. According to the distribution and evolution of the deposition, three simple hierarchical cathode structures with high porosities near the air side are finally studied. The simulation results indicate that the increase of the local porosity near the air side substantially improves the cycling performance of the Li-air batteries. 相似文献
13.
The processes, which influence the decomposition of 4MgCO 3 ·-Mg(OH) 2 · 4H 2O, could be determined by systematical variation of the analytical parameters. The original crystal structure exists in a wide temperature range during the decomposition. The formation of magnesite is a secondary reaction of the gaseous phase with the reaction product.H 2O and CO 2, are released simultaneously in different proportions during the decomposition to 500°C. Stoichiometric intermediates were not found. The original crystal structure collapsed, when the last H 2O escapes. The ratio of MgCO 3: MgO can be influenced by partial pressure of CO 2 in a wide range. 相似文献
14.
The present study investigated the preparation of 2,5-furandicarboxylic acid (FDCA) via the Henkel reaction between furoic acid alkali metal salts and zinc chloride under a continuous CO 2 flow at atmospheric pressure. The results obtained were compared with those of previous studies that used high-pressure conditions or toxic cadmium catalysts. The pathways and rate-determining steps of the reaction are revealed for the first time. Furthermore, the enhanced formation of FDCA through the promotion of carboxyl exchange and rearrangement during the reaction under a CO 2 flow was examined. The CO 2-rich environment afforded a high FDCA yield of 86.30 %, which is the highest yield obtained to date using the Henkel reaction. The findings of this study offer economically improved conditions for large-scale FDCA production. 相似文献
15.
The amount of carbon deposited on hexaaluminate LaNiAl 11O 19 catalyst in CH 4 decomposition and CO 2 reforming of methane was determined by means of thermogravimetric analysis (TGA). The properties of carbon formed on the catalysts were characterized by X-ray photoelectron spectroscopy (XPS), temperature-programmed CO 2 reaction (TPR-CO 2), and temperature-programmed oxidation (TPO) techniques. The experimental results showed that hexaaluminate LaNiAl 11O 19 catalyst possessed high resistance to carbon deposition in CO 2 reforming of methane to synthesis gas at high temperatures, and CO 2 played an important role in eliminating carbon during the reaction. At least two forms of the deposited carbon, graphite and carbide, were produced during methane reforming with CO 2. 相似文献
16.
The thermal decomposition of the malonates of bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn) was investigated by mainly TG-DTA, X-ray diffraction analysis and evolved gas analysis in atmospheres of N 2, CO 2 and O 2 and in the air. It was shown that CO 2 has an inhibiting effect on the decomposition whereas O 2 and air have the accelerating effects on the basis of N 2. The decomposition of the salts investigated can be classified into three groups from solid decomposition products: Mn and Zn malonates gave the metal oxides including 1–1.5 moles of elementary carbon, while Cu and Ni malonates gave the metals with 1–1.5 moles of the carbon. Fe and Co malonates in the last group gave once the metal oxides with 1-0.5 moles of the carbon and the oxides produced were subsequently reduced to the metals by the carbon. A possible reaction mechanism for the malonates was discussed and compared with those of the corresponding oxalates and succinates. 相似文献
17.
In this study, the preparation by grafting of amino-functionalized SBA-15 molecular sieves was carried out. Amino-functionalized molecular sieves were synthesized using a silane coupling agent and different types of amination reagents which react with modified SBA-15. These composites were characterized by FT-IR spectroscopy, X-ray diffraction at low angles, nitrogen physisorption at 77 K, and evaluated by the adsorption of CO2 and its temperature-programmed desorption—TPD. Thermal stability was investigated by TGA and DTA methods. In the view of a possible use of these amino-functionalized molecular sieves as sorbents for CO2 removal, their adsorption–desorption properties towards CO2 were also investigated by the TPD method. The mass loss of amino-functionalized molecular sieves above 215 °C was due to the oxidation and decomposition of amino propyl functional groups. This means that these composites could be used for adsorption of CO2 at temperatures below 215 °C. The adsorption of CO2 and its temperature programmed desorption using thermogravimetry were studied for amino-functionalized molecular sieves at 60 °C. The evolved gases during the adsorption–desorption of CO2 on amino-functionalized molecular sieves were identified by online mass spectrometry coupled with thermogravimetry. CO2 adsorption isotherms of functionalized samples at 60 °C showed that both the adsorption capacity (mg CO2/g adsorbent) and the efficiency of amino groups (mol CO2/mol NH2) depend on the type of amination reagents and the amount of organic compound used. 相似文献
18.
To improve the energy yield (EY) of plasma volatile organic compound decomposition, a dielectric barrier discharge plasma driven by pulse-modulated AC power was used to experimentally study the abatement of benzene in atmospheric pressure air and at room temperature. The effects of the duty cycle on decomposition efficiency, EY, CO 2 selectivity and the formation of ozone and NO 2 were investigated. The results show that applying pulse modulation improves the EY and the CO 2 selectivity and greatly reduces the wall temperature of the reaction chamber. 相似文献
19.
A new asymmetric diamine containing diarylimodazole pendant was synthesized from the nucleophilic substitution reaction of 1-fluoro-4-nitrobenzene and 2,4-dihydroxy benzaldehyde in the presence of K 2CO 3, followed by reaction with benzil and ammonium acetate for the preparation of imidazole ring. This novel diamine was used to prepare poly(amide-ether) (PAE) in reaction with different commercially available dicarboxylic acids via direct polycondensation using triphenyl phosphite and pyridine (Py) as catalyst. The PAEs were fully characterized and their properties such as inherent viscosity, solubility, optical, thermal and kinetics of thermal decomposition, and electrochemical oxidation were investigated. The polymers had inherent viscosity in the range of 0.47–0.65 dL/g and were noncrystalline with excellent solubility in various polar aprotic organic solvents. Their T g values ranged from 200 to 355°C and 10% weight loss temperature above 450°C in nitrogen and left more than 70% residue at 650°C. The kinetic parameters of thermal degradation such as activation energy, entropy, enthalpy and Gibbs free energy of thermal decomposition have been evaluated using different equations. We also report electrochemical oxidation of the resulting polymers in aqueous solution by using cyclic voltammetry technique on the multi-walled carbon nanotube-modified glassy carbon electrode. 相似文献
20.
制备了不同Ni/Al原子比的NiAl类水滑石样品,焙烧获得NiAl复合氧化物,用于N 2O分解反应,研究了NiAl复合氧化物组成对催化活性的影响。在活性较高的NiAl复合氧化物表面浸渍碱金属碳酸盐溶液,制备改性NiAl复合氧化物,考察了碱金属类型(Na、K、Cs)和钾前驱物(K 2CO 3、K 2C 2O 4、CH 3COOK、KNO 3)对改性催化剂活性的影响。用XRD、ICP-AES、FT-IR、BET、H 2-TPR、XPS技术表征了催化剂的组成结构。结果表明,Ni/Al原子比为2.7的NiAl复合氧化物催化活性较高;Na、K、Cs碳酸盐改性NiAl复合氧化物均提高了催化剂活性,其中K的助剂效应最强。钾前驱物对K改性NiAl复合氧化物的催化活性有显著影响,其中碳酸钾、醋酸钾、草酸钾的加入明显提高了改性催化剂的催化活性,而加入硝酸钾反而降低了催化剂活性。 相似文献
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