Thermal decomposition of Cu-based hydroxycarbonate catalytic precursors for the low-temperature co-shift reaction

The thermal decomposition of Cu-Zn-Al hydroxycarbonate precursors to obtain water-gas shift catalysts was studied by employing a variety of experimental techniques. A set of six samples containing 34 wt% of Cu and different Al/Zn ratios were prepared by coprecipitation. Depending on the cation ratio, the ternary precursors contained hydrotalcite, aurichalcite and/or rosasite phases. Malachite and hydrozincite were determined in binary Cu/Al and Cu/Zn samples, respectively. The precipitates decomposed in three endothermic transformations in the temperature ranges 363–453 K, 453–673 K and 673–923 K. In the first step (ΔW=0–9%), the hydrotalcite-containing samples lost the crystallization water of the hydrotalcite phase. In the middle-temperature transition (ΔW=18–30%), the samples were completely dehydroxylated and simultaneously eliminated a proportion of the carbonate ions through a two-step dehydroxylation/decarbonation process. The high-temperature transformation (ΔW=3–7%) corresponded to the final decarbonation of the samples. Mixed oxides with a high dispersion of copper were obtained from hydrotalcite-containing precursors: the higher the amount of hydrotalcite in the precursor, the lower the CuO crystallite size in the resulting mixed oxide.     

Thermal properties of jojoba wax

The thermal behaviour of Jojoba (Simmondsia chinensis) liquid wax was studied by differential scanning calorimetry (DSC), varying the annealing conditions. The fusion enthalpy (ΔHf) of the unannealed material was 27.1 cal/g; the relationship between heat capacity (Cp) and temperature could be expressed by the following equation:Cp=9.51×10^?4 T+0.129. It was found that Jojoba wax presents four endothermic transitions (α, β, γ andδ) including fusionα, estimable at low heating rates (1 K/min); the activation energies (Ea) for transitionsα andγ were 51.18 and 64.82 Kcal/mole respectively; and it was observed that the transition temperaturesα andγ maintained a lineal relationship with the square root of the heating rate (Hr).     

Vibrational energy exchange of the DF (ν=2) state with DF (ν=0)

The energy transfer rate for the reaction DF (ν=1) + DF (ν=1)^k_νν→ DF (ν=0) + DF (ν=2) + ΔE=91.6 cm^?1 has been studied in a combined shock-tube laser-induced fluorescence experiment at temperatures from 295 to 720°K. The rate coefficient k_νν for the exothermic reaction was found to vary as T^?1 when expressed in units of cm³/mole sec. At T=295°K, the probability of the reaction is approximately 0.2 per collision.     

Estimation of the critical rate of temperature rise for thermal explosion of nitrocellulose using non-isothermal DSC

The expressions to calculate the critical rate of temperature rise of thermal explosion $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for energetic materials (EMs) were derived from the Semenov’s thermal explosion theory and autocatalytic reaction rate equation of nth order, C_nB, B_na, first-order, apparent empiric-order, simple first-order, A_u, apparent empiric-order of m = 0, n = 0, p = 1 and m = 0, n = 1, p = 1, using reasonable hypotheses. A method to determine the kinetic parameters in the autocatalytic-decomposing reaction rate equations and the $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ in EMs when autocatalytic decomposition converts into thermal explosion from data of DSC curves at different heating rate was presented. Results show that (1) under non-isothermal DSC conditions, the autocatalytic-decomposing reaction of NC (12.97 % N) can be described by the first-order autocatalytic reaction rate equation dα/dt = 10^16.00exp(?174520/RT)(1 ? α) + 10^16.00exp(?163510/RT)α(1 ? α); (2) the value of $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for NC (12.97 % N) when autocatalytic decomposition converts into thermal explosion is 0.354 K s^?1.     

Kinetics of talc dehydroxylation

The kinetics of the dehydroxylation of talc have been measured in the temperature interval 1100–1160 K by means of isothermal weight-change determinations. The reaction follows first-order kinetics. Over the indicated temperature range the enthalpy of activation was found to be 101±4 kcal mol^?1, and the entropy of activation was found to be 16±4 cal mol^?1 K^?1. The error estimates correspond to one standard deviation. The enthalpy necessary to break the MgOH bond was estimated from the heat of reaction for MgOH(g) → Mg(g)+OH(g). This turns out to be 97 kcal mol^?1 in reasonable agreement with the measured enthalpy of activation.These activation parameters are consistent with the mechanism proposed for dehydroxylation of talc consisting of MgOH bond scission and subsequent migration of magnesium. These results contradict a previous report on the kinetics of talc dehydroxylation in which a diffusion-controlled expression was claimed to represent the rate of talc weight loss. It is suggested that the presence of adsorbed water on the talc used in the previous investigation is responsible for the discrepancy.     

Conformational properties of 1-methyl-1-germacyclohexane: low-temperature NMR and quantum chemical calculations

The conformational preference of the methyl group of 1-methyl-1-germacyclohexane was studied experimentally in solution (low-temperature ¹³C NMR) and by quantum chemical calculations (CCSD(T), MP2 and DFT methods). The NMR experiment resulted in an axial/equatorial ratio of 44/56 mol% at 114 K corresponding to an A value (A = G _ax ? G _eq) of 0.06 kcal mol^?1. An average value for ΔG _e→a ^#  = 5.0 ± 0.1 kcal mol^?1 was obtained for the temperature range 106–134 K. The experimental results are very well reproduced by the calculations. CCSD(T)/CBS calculations + thermal corrections resulted in an A value of 0.02 kcal mol^?1, whereas a ΔE value of ?0.01 kcal mol^?1 at 0 K was obtained.     

Tungsten(V) dimeric complexes with heterocyclic dithiocarbamates

In this paper we report the syntheses and study of a number of oxo- and sulphido-bridged tungsten(V) complexes with morpholine dithiocarbamate and piperidine dithiocarbamate as ligands. We assign the following formulae to the complexes: W₂O₃(Rdtc)₄, W₂O₄(Rdtc)₂, W₂O₂S₂(Rdtc)₂ and W₂O₃S(Rdtc)₂ (where R = morpholine and piperidine), based on the analytical data. We have studied the complexes by IR and electronic spectra, and magnetic susceptibility measurements. We assign in the IR spectra the following bands: W=O (ν_s=939–948 cm^?1), W-O_b(ν_a=813–819 cm^?1, ν_s = 431–448 cm^?1), W-S_b (ν_a=470–476 cm^?1, ν_s = 368–370 cm^?1, C-N (β = 1511–1519 cm^?1) and C-S (ν = 1090–1113 cm^?1). The low values of the magnetic moments (0.03–0.60 B.M.) are in accordance with a dimeric species of tungsten(V).     

Quantitative determination of specific heat by differential scanning calorimetry

The influence of some experimental parameters on the quantitative determination of specific heats by DSC is discussed. Conditions allowing measurement of the specific heat with a maximum relative error of 1.5 % are proposed. The specific heats of NaA zeolite,C _p=0.227±0.003 cal.°C^?1.g^?1, and AgA zeoliteC _p=0.205±0.003 cal.°C^?1.g^?1 have been determined.     

Kinetics and mechanism of the reaction of OH with ClO

The kinetics and mechanism of the following reactions have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium, using the discharge‐flow mass spectrometric method: 1a : (1a) 1b : (1b) The following Arrhenius expression for the total rate constant was obtained from the kinetics of OH consumption in excess of ClO radical, produced in the Cl + O₃ reaction either in excess of Cl atoms or ozone: k₁ = (6.7 ± 1.8) × 10^?12 exp {(360 ± 90)/T} cm³ molecule^?1 s^?1 (with k₁ = (2.2 ± 0.4) × 10^?11 cm³ molecule^?1 s^?1 at T = 298 K), where uncertainties represent 95% confidence limits and include estimated systematic errors. The value of k₁ is compared with those from previous studies and current recommendations. HCl was detected as a minor product of reaction (1) and the rate constant for the channel forming HCl (reaction (1b)) has been determined from the kinetics of HCl formation at T = 230–320 K: k_1b = (9.7 ± 4.1) × 10^?14 exp{(600 ± 120)/T} cm³ molecule^?1 s^?1 (with k_1b = (7.3 ± 2.2) × 10^?13 cm³ molecule^?1 s^?1 and k_1b/k₁ = 0.035 ± 0.010 at T = 298 K), where uncertainties represent 95% confidence limits. In addition, the measured kinetic data were used to derive the enthalpy of formation of HO₂ radicals: Δ H_f,298(HO₂) = 3.0 ± 0.4 kcal mol^?1. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 587–599, 2001     

Study on thermal decomposition and oxidation kinetics of cation exchange resins using non-isothermal TG analysis

Kinetics of two successive thermal decomposition reaction steps of cationic ion exchange resins and oxidation of the first thermal decomposition residue were investigated using a non-isothermal thermogravimetric analysis. Reaction mechanisms and kinetic parameters for three different reaction steps, which were identified from a FTIR gas analysis, were established from an analysis of TG analysis data using an isoconversional method and a master-plot method. Primary thermal dissociation of SO₃H⁺ from divinylbenzene copolymer was well described by an Avrami–Erofeev type reaction (n = 2, g(α) = [?ln(1 ? α)]^1/2]), and its activation energy was determined to be 46.8 ± 2.8 kJ mol^?1. Thermal decomposition of remaining polymeric materials at temperatures above 400 °C was described by one-dimensional diffusion (g(α) = α ²), and its activation energy was determined to be 49.1 ± 3.1 kJ mol^?1. The oxidation of remaining polymeric materials after thermal dissociation of SO₃H⁺ was described by a phase boundary reaction (contracting volume, g(α) = 1?(1 ? α)^1/3). The activation energy and the order of oxygen power dependency were determined to be 101.3 ± 13.4 and 1.05 ± 0.17 kJ mol^?1, respectively.     

水合烟酸铜Cu(Nic)2•H2O(s)(Nic＝烟酸)的合成、表征及热力学性质

近几十年来,烟酸盐类化合物或配合物由于优越的吸收率高和无毒副作用等特点使其在化妆品、药品和食品等领域作为营养添加剂具有重要应用前景。然而,这类化合物的基础热力学数据极其缺乏,从而限制了这类化合物的理论研究和应用开发的深入开展。为此,本论文利用室温固相合成方法和球磨技术合成了一种新化合物Cu(Nic)2•H2O(s),利用化学分析、元素分析、FTIR和X-射线粉末衍射技术表征了它的结构和组成,利用精密自动绝热热量计准确地测量了它在78-400 K温区的摩尔热容。在热容曲线的T ＝ 326-346 K温区观察到一个明显的固-液相变过程。利用相变温区三次重复实验热容的测量结果确定了此相变过程的峰温、相变焓和相变熵分别为：Tfus＝(341.290 ±0.873) K, DfusHm＝(13.582±0.012) kJ×mol-1, DfusSm＝(39.797±0.067) J×K-1×mol-1。通过最小二乘法将相变前和相变后的热容实验值分别拟合成了热容对温度的两个多项式方程。通过热容多项式方程的数值积分,得到了这个化合物的舒平热容值和相对于298.15 K的各种热力学函数值,并且将每隔5 K的热力学函数值列成了表格。     

Combustion synthesis and thermal expansion of RE6UO12 (RE = Dy and Tb)

Citrate–nitrate combustion method was adopted for the synthesis of RE₆UO₁₂ (RE = Dy and Tb). These compounds were characterized by X-ray diffraction. Thermal expansion coefficient of these compounds were measured in the temperature range of 298–1,273 K by high temperature X-ray powder diffractometry (HT-XRD) and compared with other rare earth compounds reported in the literature. There was no observed phase transition in Dy₆UO₁₂, but Tb₆UO₁₂ showed a second-order phase transition at 670 K which was confirmed using differential scanning calorimeter. The average volume thermal expansion coefficient of Dy₆UO₁₂ in the temperature range of 298–1,273 K is (29.82 ± 4.02) × 10^?6 and that of Tb₆UO₁₂ in the temperature range of 298–673 K is (13.76 ± 2.64) × 10^?6 K^?1.     

Calorimetric investigations of the MBr−NdBr3 melts (M=Li,Na, K,Cs)

Present work is a part of thermodynamic research program on the MX?LnX₃ system (M=alkali metal,X=Cl, Br andLn=lanthanide). Molar enthalpies of mixing in the LiBr?NdBr₃, NaBr?NdBr₃ and KBr?NdBr₃ liquid binary systems have been determined at temperature 1063 K by direct calorimetry in the whole range of composition. Investigated systems are generally characterized by negative enthalpies of mixing with minimum atX _NdBr3≈0.3–0.4. These enthalpies decrease with decrease of ionic radii of alkali metals. Molar enthalpies of solid-solid and solid-liquid phase transitions of K₃NdBr₆ and Cs₃NdBr₆ have been also determined by differential scanning calorimetry (DSC). K₃NdBr₆ is formed at 689 K from KBr and K₂NdBr₅ with enthalpy of 44.0 kJ·mol^?1 whereas Cs₃NdBr₆ is stable at ambient temperature and undergoes phase transition in the solid state at 731 K with enthalpy of 8.8 kJ·mol^?1. Enthalpies of melting have been also determined.     

The phase diagram of the AgNO3−KNO3 system determined by differential scanning calorimetry

The phase diagram for the AgNO₃?KNO₃ system has been determined using differential scanning calorimetry (DSC). Eutectic point has been found at 391 K andX _Ag=0.580 mole fraction AgNO₃. The DSC curves indicate the existence of an intermermediate compound (AgNO₃·KNO₃) in the KNO₃-rich region of the phase diagram. This compound was identified in the solid phase by X-ray diffraction. The melting and the crystallization processes were followed with the aid of a hot stage microscope, too.     

Kinetic study of the thermal dehydration of syngenite K2Ca(SO4)2·H2O under isothermal conditions

A study of the kinetics of the thermal dehydration of syngenite was carried out using the isothermal gravimetric method. Weight changes of the samples were followed by means of a Mettler Thermoanalyzer. The applicability of nine equations commonly used to describe the thermal decomposition of solids was investigated. The experimental results can be best represented, over the whole temperature range of the change, by the Avrami equation I $$[ - \ln (1 - \alpha )]^{1/2} = Kt$$ whereα=degree of decomposition,t=time, andK=rate constant. The activation energy deduced for the process is 51.8±3.7 kcal·mole^?1 and the log of the preexponential factor is 20.5±0.1.     

Kinetics and Mechanisms for the Reactions of Phenyl Radical with Ketene and its Deuterated Isotopomer: An Experimental and Theoretical Study

Kinetics and mechanism for the reaction of phenyl radical (C₆H₅) with ketene (H₂C_β?C_α?O) were studied by the cavity ring‐down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C₆H₅ transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD₂CO, can be expressed by the Arrhenius equation k=(5.9±1.8)×10¹¹ exp[?(1160±100)/T] cm³ mol^?1 s^?1 over a temperature range of 301–474 K. The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable, in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6‐31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C_α, C_β, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298–2500 K under atmospheric pressure by using the predicted transition‐state parameters and the adjusted entrance reaction barriers E_α=E_β=1.2 kcal mol^?1; they can be represented by the following expression in units of cm³ mol^?1 s^?1: k_α=6.2×10¹⁹ T^?2.3 exp[?7590/T] and k_β=3.2×10⁴ T^2.4 exp[?246/T].     

Kinetics and mechanism of the oxidation of formic acid by thallium(III). Reinvestigation of hydrogen ion dependence

The rate of the oxidation of formic acid by thallium(III) in (Li, H)ClO₄ solutions is not affected by variation in hydrogen ion concentration and the experimental rate law, $$\frac{{ - d\left[ {T\left( {III} \right)} \right]}}{{d t}} = \frac{{k_1 K\left[ {T\left( {III} \right)} \right]\left[ {HCOOCH} \right]}}{{1 + K\left[ {HCOOH} \right]}}$$ is consistent with the mechanism which requires the formation of intermediate complex [HCOOHTl]³⁺ in a rapid preequilibrium followed by its slow decomposition to yield the final products. At 75°,k ₁ andK have the values of 16±1×10^?5 sec^?1 and 7.3±0.5M ^?1 resp.     

Kinetics of catalyst-free thermal and photo-oxidation of cumene

Kinetics of thermal and photo-oxidation of cumene in the absence of catalyst was studied using high-pressure differential scanning calorimetry and low-pressure photocalorimetry. Kinetics of oxidation was followed by cumene hydroperoxide (CHP), acetophenone, and phenol formation. The amount of CHP formed was deduced from the total heat of reaction of thermal degradation of CHP at 453 K and using a new gas chromatographic method. CHP solution in cumene oxidized at 453 K and 680 psi of oxygen reproducibly with the heat of reaction linearly dependent on peroxide concentration in cumene. It was confirmed that cumene thermal oxidation was slow at <453 K, but at ≥453 K could occur explosively. Autocatalysis by CHP during thermo-oxidation was confirmed. Apparent activation energy of the photo-oxidation of cumene was found to be E _a = 22.3 kJ mol^?1. The value corresponds to radical chain process of the cumene autoxidation. Under assumption of pseudo-first order reaction, the rate constant of CHP formation was found to change from k _CHP ≈ 0.76 s^?1 during the first 4 h of photo-oxidation to k _CHP ≈ 0.2 s^?1 at the later stages at 2.0 W cm^?2 of UV exposure dose. It was established that the initial presence of the CHP in cumene does not change the photo-oxidation kinetics, but shifts the kinetic curve to earlier time. Finite difference method was employed to numerically model kinetics of cumene oxidation. The result indicated higher than expected thermal and photo-stability of both, cumene and CHP.     

Heat capacity of polynuclear Fe(HTrz)3(B10H10)·H2O and trinuclear [Fe3(PrTrz)6(ReO4)4(H2O)2](ReO4)2 complexes (HTrz=1,2,4-triazole, PrTrz=4-propyl-1,2,4-triazole) manifesting 1A1⇔5T2 spin transition

Low-temperature heat capacity of polynuclear Fe(HTrz)₃(B₁₀H₁₀)·H₂O (I) and trinuclear [Fe₃(PrTrz)₆(ReO₄)₄(H₂O)₂](ReO₄)₂ (II) spin crossover coordination compounds was measured in 80–300 K temperature range using a vacuum adiabatic calorimeter. For I, an anomaly of heat capacity with a maximum at T _trs=234.5 K (heating mode) was observed, Δ_trs H=10.1±0.2 kJ mol^?1 Δ_trs S=43.0±0.8 J mol^? K^?1. For II, a smooth anomaly between 150 and 230 K was found, Δ_trs H=2.5±0.25 kJ mol^?1 Δ_trs S=13.6±1.4 J mol^? K^?1. Anomalies observed in both compounds correspond to ¹A₁?⁵T₂ spin transition.     

Thermochemical study of some methoxytetralones

The standard (p^° = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of 5-, 6- and 7-methoxy-α-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated, 5-methoxy-α-tetralone -(244.8 ± 1.9) kJ · mol^?1, 6-methoxy-α-tetralone ?(243.0 ± 2.8) kJ · mol^?1 and 7-methoxy-α-tetralone ?(242.3 ± 2.6) kJ · mol^?1.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of 8-methoxy-α-tetralone. Similar calculations were done for the 5-, 6-, 7- and 8-methoxy-β-tetralone, for which experimental work was not done.