Oxygen states during thermal decomposition of Ag2O: XPS and UPS study

Using photoemission XPS and UPS methods, we have studied the oxygen states in the silver metal lattice during the thermal decomposition of Ag₂O. It has been shown that one half of the lattice oxygen inside subsurface layers of Ag₂O is transformed to subsurface oxygen in metallic silver characterized by a quasimolecular structure. Thermal annealing up to 1000 K did not result in the removal of the residual subsurface oxygen.     

EPR studies of the hydroperoxy radical in x-irradiated single crystals of BaCl2·2H2O

Electron paramagnetic resonance studies of X-irradiated single crystals of BaCl₂-2H₂O have been made at room temperature. Four resonance lines are observed which can be grouped into two hyperfine doublets. Angular variation studies were made in the crystallographic ab, bc and ac planes. There are two magnetically equivalent but physically inequivalent magnetic complexes in the crystal lattice which are mutually perpendicular to each other. The paramagnetic species is identified as the hydroperoxy radical and a detailed discussion is made at the end.     

纳米Cu2O催化二苯甲烷二氨基甲酸苯酯无溶剂热分解制备二苯甲烷二异氰酸酯

研究了无溶剂条件下纳米Cu₂O催化二苯甲烷二氨基甲酸苯酯(MDPC)热分解制备二苯甲烷二异氰酸酯(MDI),考察了纳米Cu₂O的制备条件与反应条件对MDPC热分解反应性能的影响.结果表明,水解法制备的纳米Cu₂O在Ar中于300℃焙烧2h,其催化性能最佳;最佳的反应条件为Cu₂O用量为原料总重的0.06%,反应温度220℃,反应压力0.6kPa,反应时间12min,此时MDPC转化率达到99.8%,MDI选择性86.2%.     

Thermal decomposition mechanisms of MgCl2·6H2O and MgCl2·H2O

The thermal decomposition mechanisms and the intermediate morphology of MgCl₂·6H₂O and MgCl₂·H₂O were studied using integrated thermal analysis, X-ray diffraction, scanning electron microscope and chemical analysis. The results showed that there were six steps in the thermal decomposition of MgCl₂·6H₂O: producing MgCl₂·4H₂O at 69 °C, MgCl₂·2H₂O at 129 °C, MgCl₂·nH₂O (1 ≤ n ≤ 2) and MgOHCl at 167 °C, the conversion of MgCl₂·nH₂O (1 ≤ n ≤ 2) to Mg(OH)Cl·0.3H₂O by simultaneous dehydration and hydrolysis at 203 °C, the dehydration of Mg(OH)Cl·0.3H₂O to MgOHCl at 235 °C, and finally the direct conversion of MgOHCl to the cylindrical particles of MgO at 415 °C. To restrain the sample hydrolysis and to obtain MgCl₂·H₂O, MgCl₂·6H₂O was first calcined in HCl atmosphere until 203 °C when MgCl₂·H₂O was obtained; HCl gas was then turned off and the calcination process continued, producing Mg₃Cl₂(OH)₄·2H₂O calcined at 203 °C, Mg₃(OH)₄Cl₂ at 220 °C and MgO at 360 °C. The temperature of producing MgO from calcination of MgCl₂·H₂O was lower (360 °C) than that from MgCl₂·6H₂O (415 °C) because of its more reactive intermediate products: the irregular shape and tiny needle-like Mg₃Cl₂(OH)₄·2H₂O particles and the uneven surface porous Mg₃(OH)₄Cl₂ particles. The MgO particles obtained at 360 °C had a flake structure.     

Ab initio molecular orbital and RRKM calculations of the thermal decomposition of CH2BrO radical

A theoretical study of the thermal decomposition and isomerization channels of bromomethoxy radical is carried out using ab initio molecular orbital methods and RRKM theory. Three kinds of reaction pathways are examined, bond scission, intramolecular three-center HBr elimination and isomerization. Energy-specific rate coefficients k(E) and thermal rate constants k(T,P) are evaluated using the ab initio data and RRKM theory. Relevance to existing experimental evidence is discussed.     

Co取代的六铁酸盐在N2O催化分解反应中的应用

采用溶胶-凝胶法制备了Co取代的Ba₂Mg_2-xCo_xFe₁₂O₂₂(x=0.0~2.0)催化剂,并考察了其在高浓度N₂O(30vol%)分解反应中的催化活性.结果表明,Co的取代显著提高了Ba₂Mg₂Fe₁₂O₂₂催化剂活性,当x=2时,N₂O的完全分解温度从1123K降至973K;提高催化剂焙烧温度会导致其表面积降低,进而降低其催化活性;但采用微波加热则能显著提高催化剂活性.     

Melting and thermal decomposition of [Ni(H2O)6](NO3)2

The two-stage melting process and the thermal decomposition of [Ni(H₂O)₆](NO₃)₂ was studied by DSC, DTA and TG. The first melting point at 328 K is connected with the small and the second melting point at 362 K with the large enthalpy and entropy changes. The thermal dehydration process starts just above ca. 315 K and continues up to ca. 500 K. It consists of three well-separated stages, but the sample mass loss at each stage depends on the experimental regime. However, irrespective of the chosen regime, the total of registered mass losses in stage one and two amounts to three H₂O molecules per one [Ni(H₂O)₆](NO₃)₂ molecule. The remaining three H₂O molecules are gradually freed in the temperature range of 440–500 K in the third stage of the dehydration. Above 580 K, anhydrous Ni(NO₃)₂ decomposes into NO and NiO. The gaseous products were identified by quadrupole mass spectrometer (QMS), and the solid product was identified by X-ray diffraction (XRD) analysis.     

Photo-oxidation of halomethanes at low temperature: the decomposition rate of CCl3O and CFCl2O radicals

The chlorine-photosensitized oxidation chains of CHCl₃ and CHFCl₂ were studied at 233 K and 253 K respectively to evaluate the decomposition rate of CCl₃O and CFCl₂O radicals:

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Various amounts of NO were introduced into the system to quench the chain reactions by introducing competition with the above reactions. In spite of the low temperature, these reactions were found to be fast and only lower limits of the rate constants could be determined: 1 × 10⁵ s⁻¹ at 233 K and 3 × 10⁴ s⁻¹ at 253 K for CCl₃O and CFCl₂O respectively at low pressure (about 7 Torr). This result shows that reactions other than these decompositions are highly unlikely for these species, either in the stratosphere or in any other reacting system.     

The overtone spectra of H2O,D2O and mixtures of H2O in D2O ice

The overtones of the stretching vibration of OH and OD were measured in solid solutions of H₂O in D₂O over a wide range of concentration and temperatures. The observed frequencies and the overall shape of the spectra were related to excitations of single OH or OD bonds (bound excitations) and those involving neighboring OH bonds extending over the crystal (non-bound excitations). The observed large anharmonicity of the bound state is interpreted as due to a low lying barrier in the double minimum potential curve for the hydrogen motion.     

N2O在Mg-Fe复合氧化物上的催化分解

用共沉淀法制备了一组Mg-Fe复合氧化物催化剂,用于N₂O催化分解,考察了催化剂组成、焙烧温度、负载助剂钾等参数对其催化活性的影响。采用N₂物理吸附、X射线衍射、H₂-程序升温还原等技术对催化剂进行了结构表征。结果表明,500 ℃焙烧的Mg_0.6Fe_0.4Fe₂O₄催化剂对于N₂O分解反应有较高活性,而K改性的催化剂活性均有所降低,且K的负载量越高,改性催化剂的活性越低,这是由于负载的K粒子抑制了表面铁物种的还原,降低了催化剂的比表面积。在有氧无水、水氧共存条件下连续反应10 h,Mg_0.6Fe_0.4Fe₂O₄的催化活性和稳定性均显著高于FeO_x催化剂。     

Zn-Fe尖晶石型复合氧化物催化分解N2O

用共沉淀法制备了Zn-Fe尖晶石型复合氧化物催化剂,用于有氧气氛中N₂O的分解反应;考察了复合氧化物的组成、焙烧温度及K改性对其催化活性的影响,并用氮气吸附、XRD和H₂-TPR等技术对催化剂结构进行了表征。结果表明,Zn-Fe尖晶石型复合氧化物具有良好的催化N₂O分解的活性;在优化出的Zn_0.8Fe_0.2Fe₂O₄-400催化剂上500℃下连续反应10 h时,有氧无水和有氧有水条件下N₂O转化率分别达到63.5%和22.2%。K改性Zn-Fe尖晶石型复合氧化物的催化活性均不及纯Zn-Fe氧化物,这是由于K改性催化剂的比表面积显著降低,而且K粒子迁移至催化剂表面,抑制了FeO_x的还原和表面氧物种的脱除。     

Derivatographic studies on transition metal complexes XV. Thermal isomerization of trans-[CrBr2pn2]Br.H2O in solid phase

The thermal trans-to-cis isomerization of [CrBr₂pn₂]Br·H₂O in a solid phase was studied by means of both derivatography and isothermal measurement. It was found that trans-[CrBr₂pn₂]Br·H₂O undergoes isomerization to the cis-complex by about 10% with complete dehydration followed by isomerization of the residual trans complex in the anhydrous state. It was characteristic of the complex, trans-[CrBr₂pn₂]Br·H₂O, that the thermal dehydration was remarkably rapid in comparison with that of the trans-[CoCl₂pn ₂](H₅O₂)Cl₂ and the isomerization of the cis complex occurred even in the anhydrous state though it did not in the corresponding cobalt(III) complex trans-[CoBr₂pn₂](H₅O₂)Br₂ in an analogous state.     

Thermal studies on sodium silicate hydrates. I. Trisodium hydrogensilicate pentahydrate,Na3HSiO4 · 5 H2O; Thermal stability and thermal decomposition reactions

Presented in this paper is a thermoanalytical study on Na₃HSiO₄ · 5 H₂O under a dry, inert nitrogen atmosphere, demonstrating the following thermal decomposition reactions and thermodynamically stable hydrate phases

This reaction behaviour was reproducibly observed by means of simultaneous thermal analysis (TG, DTG, DTA), differential scanning calorimetry (DSC) and X-ray heating experiments. Annealing of Na₃HSiO₄ · 5 H₂O at the above stability ranges yielded the subsequent hydrate phases as well as the dry silicate. The decomposition products were characterized by X-ray diffraction methods.     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.     

Co/Hβ催化剂上N_2O的分解性能研究

采用浸渍法制备了Hβ分子筛负载钴氧化物催化剂。考察了催化剂焙烧温度和钴负载量对催化剂催化分解N2O活性的影响,并采用XRD、NH3-TPD、H2-TPR、SEM等手段对催化剂的理化性质进行表征。结果表明,催化剂中的钴物种主要以Co3O4尖晶石型形态存在;催化剂焙烧温度显著影响其酸性和酸量及氧化还原性能,焙烧温度达到700℃后,催化剂中有难还原的Co-Al-O物种生成。焙烧温度和钴负载量对催化剂的催化活性均有影响,焙烧温度为600℃、钴负载量为10%~15%的催化剂催化活性好,N2O分解温度低,t10、t50和t95分别为325~329℃、364~367℃和406~408℃。     

Catalytic decomposition of N2O on La2CuO4 in the presence of LaNi5 alloy

Decomposition of N₂O has been studied on pure La₂CuO₄, La₂CuO₄ with 5 and 10 wt. % LaNi₅ and oxidized LaNi₅ in the temperature range of 240–490 °C at 50 and 200 Torr initial pressures of N₂O. The addition of LaNi₅ decreases the energy of activation compared to that of La₂CuO₄ which has been explained based on the dispersity of NiO over La₂CuO₄.

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N₂O La₂CuO₄ La₂CuO₄ LaNi₅ 5–10 .%, 240–490°C N₂O 50 200 . LaNi₅ , . NiO La₂CuO₄.

     

Theoretical studies on the stability of the H3O radical based on ab initio UHF-CI calculations

An UHF-CI investigation of parts of the energy surface for the H₃O radical is reported. Several types of basis sets have been used and the CI expansion included all singly and doubly replaced configurations using an UHF determinant as the reference state. H₃O, constrained-to C_3v symmetry is in the best approximation found to be 20.5 kcal/mol less stable than H₂O + H. A small local barrier of 4.6 kcal/mol for dissociation is found on the UHF level of approximation. Correlation effects lower this barrier to 3.4 kcal/mol making the existence of a quasibound state with a measurable lifetime improbable. The height of the barrier was found to be very sensitive to the detailed form of the diffuse singly occupied orbital.     

N_2O在Mg-Co和Mg-Mn-Co复合氧化物上的催化分解

用溶胶-凝胶法制备了不同组成的Mg-Co和Mg-Mn-Co复合氧化物,用于催化分解N_2O。在较高活性的Mg-Mn-Co表面浸渍K_2CO_3溶液,制备K改性催化剂。用X射线衍射(XRD)、N_2物理吸附(BET)、扫描电镜(SEM)、H_2程序升温还原(H_2-TPR)、O_2程序升温脱附(O_2-TPD)等技术表征催化剂结构,考察了复合氧化物的组成、K负载量等制备参数对催化剂活性的影响。结果表明,加入助剂K显著提高了催化剂活性,其中,0.02 K/MgMn_(0.2)Co_(1.8)O_4活性较高,有氧无水、有氧有水气氛400℃连续反应50 h,N_2O转化率分别保持97%和60%。有水-无水气氛交替实验表明,有水反应后再进行无水实验,K改性催化剂的稳定性较好。     

Thermal decomposition of barium oxalate hemihydrate BaC2O4·0.5H2O

The thermal behaviour of BaC₂O₄sd0.5H₂O and BaCO₃ in carbon dioxide and nitrogen atmospheres is investigated as part of a study about the thermal decomposition of barium trioxalatoaluminate. For this purpose thermogravimetry, differential thermal analysis, differential scanning calorimetry and high temperature X-ray diffraction were used. An infrared absorption spectrum of BaC₂O₄·0.5H₂O was scanned at room temperature.At increasing temperature, in dry nitrogen, the hydrate water of BaC₂O₄· 0.5H₂O is split off, followed by the oxalate decomposition. A part of the evolved carbon monoxide disproportionates, leaving carbon behind. At higher temperatures the latter reacts with barium carbonate, previously formed. Finally the residual solid barium carbonate decomposes into barium oxide and carbon dioxide.In dry carbon dioxide atmosphere an analogous dehydration occurs, followed by oxalate decomposition. Under these conditions the carbon formation is fully suppressed, and as a consequence no secondary reaction occurs. The barium carbonate decomposition is shifted to much higher temperatures, at a low rate in the solid phase, a strongly accelerated one at the onset of melting, and a moderated one when the melt is saturated with barium carbonate. The two phase transitions of BaCO₃ are detectable in both atmospheres mentioned.