H2S splitting on Cu(110): Insight from combined periodic density functional theory calculations and microkinetic simulation

Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H₂S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H₂S → H₂S* → SH* → S* and (2) 2H₂S → 2H₂S* → 2SH* → S* + H₂S* → S* + H₂S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H₂S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H₂S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H₂S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc.     

Thermal studies on the decomposition of aquopentamminecobalt(III) hexathiocyanatochromate(III)

The decomposition of [Co(NH₃)₅H₂O] [Cr(NCS)₆] has been studied using DSC and TG. The first step involves the loss of H₂O and NH₃ in a first-order process to produce [(NH₃)₅Co(SCN)₃Cr(NCS)₃]. A second step involves the loss of HSCN. Activation energies are presented and the mechanisms of the reactions are discussed in comparison to analogous cyanide complexes.     

Study on the thermal decomposition kinetics ofcis/trans-[Cu(gly)2] • H2O

The thermal decomposition reactions of the complexescis/trans-[Cu(gly)₂] • H₂O were studied by TG-DSC methods. The results showed that they have similar decomposition process, which occur in two steps. The first step is the loss of water and the second step is the decomposition of anhydrous complexes. But forcis-[Cu(gly)₂]•H₂O, the temperature of losing water is higher than that oftrans-isomer. Their reaction mechanisms of the two-step decomposition were also proposed.

     

Study on the thermal decomposition kinetics of<Emphasis Type="Italic">cis/trans-</Emphasis>[Cu(gly)<Subscript>2</Subscript>] • H<Subscript>2</Subscript>O

The thermal decomposition reactions of the complexescis/trans-[Cu(gly)₂] ? H₂O were studied by TG-DSC methods. The results showed that they have similar decomposition process, which occur in two steps. The first step is the loss of water and the second step is the decomposition of anhydrous complexes. But forcis-[Cu(gly)₂]?H₂O, the temperature of losing water is higher than that oftrans-isomer. Their reaction mechanisms of the two-step decomposition were also proposed.     

Investigations on Preparation,Crystal Structure and Thermal Stability of Bis(O-ethylcarbonodithiolato-S,S′)(1,10-phenanthroline-N~1,N~(10))cobalt(II) Complex:[Co(Et-XA)_2·phen]·H_2O (XA=xanthate)

IntroductionTheincreasingcommercialvalueoftransitionmetalcomplexesofxanthateshasarousedconsiderableinterestintheirchemistry .Whiletheiranalyticalapplicationsarewellknown ,1theyarenowfindingextensiveuseinvulcan izationofrubber ,frothfloatationprocessforconcentrationofsulphideores ,asantioxidants ,lubricants ,2 ,3andhavebeenfoundtopossessfungicidalandinsecticidalactivi ties .4 Recently ,molecularrecognitionbetweenhostandguestmolecules ,inclusionphenomenaandnoncovalentmolecularinteractionarefunda…     

Thermal studies on oxalate complexes. IV. Potassium bis(oxalato)cuprate(II) dihydrate

The dehydration and decomposition of K₂[Cu(C₂O₄)₂] · 2 H₂O have been studied using TG. The dehydration reaction gave the best fit to a second-order rate equation and has an activation energy of 411.5 ± 41.1 kJ mole^?1. Three distinct decomposition patterns were observed for the anhydrous complex. In the first case, K₂[Cu(C₂O₄)₂] decomposes to K₂CO₃ and CuO by loss of CO₂ and 2 CO. In the second case, decomposition leads to K₂C₂O₄ and Cu by loss of 2 CO₂. In the third case, the basic carbonate K₂[Cu(CO₃)_3/2O_1/2] is produced by loss of 2 CO and 0.5 CO₂. In the last case additional loss of CO₂ leads to the formation of K₂CO₃ and CuO in a separate reaction. Kinetic parameters are reported and discussed for all these reactions.     

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH₃, CO₂ and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH₃, CO₂, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H₂ and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.     

Solid state decomposition studies on metal salicylates. Thermal decomposition of some lanthanide salicylato complexes

The thermal stability and mechanism of thermal decomposition in air of the four lanthanide complexes of 2-hydroxybenzoic acid have been studied by TG, DSC, IR and MS techniques. An analysis of the prepared compounds show that Pr(III), Nd(III) and Tb(III) form anhydrous salicylato (Hsal)⁻ complexes while the corresponding holmium compound contains four water molecules. The TG curves show two (praseodymium, terbium), three (neodymium) or four (holmium) main stages of thermal decomposition. The most unstable among the complexes studied is Ho(Hsal)₃·4H₂O which releases four water molecules in an endothermic dehydration step. Ligand molecules decompose mainly in two stages of which the first is endothermic and is attributed to the release of the ligand acid and the second is a strongly exothermic decarboxylation process. The final decomposition product is the corresponding lanthanide(III) oxide, except in the case of terbium which decomposes to Tb₄O₇.     

Analyse und Optimierung von Gasphasen-Reaktionen,XVII. Selenoketen

Analysis and Optimization of Gasphase Reactions, XVII. — Selenoketene The thermal decomposition of 1,2,3-selenadiazole in the gaseous phase has been investigated by photoelectron and mass spectroscopy. At temperatures above 720 K selenoketene is formed, the PE spectrum of which can be assigned based on ab initio SCF calculations as well as on radical cation state comparison with the iso(valence) electronic heterocumulenes H₂C  C  O and H₂C  C  S. The 4-phenyl derivative decomposes above 820 K forming phenylacetylene.     

Determination of mechanism of thermal decomposition of Mg,Ca and Zn hydrazidocarbonates by evolved gas analysis

Hydrazo-carbonates are complex compounds and products of the reactions between solutions of metal ion and solutions of hydrazido-carbonic acid. The decomposition of Mg(N₂H₃COO)₂. 2H₂O, Ca(N₂H₃COO)₂·H₂O and Zn(N₂H₃COO)₂ in inert atmosphere were studied. By classical thermoanalytical methods and data on the composition of the intermediates and final products the mechanisms of the thermal decomposition could not be resolved therefore also evolved gas analysis was used (EGA). The first step of thermal decomposition of Ca and Mg hydrazidocarbonates is dehydration. With the heating the decomposition of the hydrazido-carbonates proceeds under evolution of the ammonia, carbon monoxide and/or nitrogen and carbon dioxide giving as the intermediates for calcium and magnesium compounds the corresponding carbonates oxides as the final products. The zinc compound decomposes to the oxide, ZnO but also zinc cyanamide was detected during to the thermal treatment.     

Low-temperature catalytic decomposition of hydrogen sulfide into hydrogen and diatomic gaseous sulfur

The thermodynamics of three pathways of the hydrogen sulfide decomposition reaction is considered. In the thermal process, the gas-phase dissociation of hydrogen sulfide yields hydrogen and diatomic singlet sulfur. Over sulfide catalysts, the reaction proceeds via the formation of disulfane (H₂S₂) as the key surface intermediate. This intermediate then decomposes to release hydrogen into the gas phase, and adsorbed singlet sulfur recombines into cyclooctasulfur. Over metal catalysts, H₂S decomposes via dissociation into surface atoms followed by the formation of gaseous hydrogen and gaseous triplet disulfur. The last two pathways are thermodynamically forbidden in the gas phase and can take place at room temperature only on the surface of a catalyst. An alternative mechanism is suggested for hydrogen sulfide assimilation in the chemosynthesis process involving sulfur bacteria. To shift the hydrogen sulfide decomposition equilibrium toward the target product (hydrogen), it is suggested that the reaction should be conducted at room temperature as a three-phase process over a solid catalyst under a layer of a solvent that can dissolve hydrogen sulfide and sulfur. In this case, it is possible to attain an H₂S conversion close to 100%. Therefore, hydrogen sulfide can be considered as an inexhaustible source of hydrogen, a valuable chemical and an environmentally friendly energetic product.     

Structure and fragmentation mechanism of [C3H7S]+ ions

From a comparison of the metastable ion bundance ratios for loss of C₂H₄ and H₂S from [C₃H₇S]⁺ ions in a series of alkyl thio ethers and thiols it was concluded that in most compunds these ion s isomerize to a common structure prior to decomposition in the first field free region. The mechanism for C₂H₄ loss from the [C₃H₇S]⁺ ion gen erated from CH₃SCH₂CH₃ was investigated in detail using ¹³C and ²H labelling. A rearrangement with formation of a cyclic intermediate prior to the decompistion reaction is proposed. The fragmentation is preceded by extensive hydrogen scrabling. The carbon atoms of the expelled C₂H₄ molecule are those of the CH₂?CH₃ moiety.     

Another Example for the Ability of the $\rm SbS^{3-}_{3}$ Anion to act as a Bidentate Ligand: Solvothermal Synthesis,Crystal Structure,Calculated and Experimental Raman Spectra of [Cr(tren)SbS3]·H2O

The new charge neutral complex [Cr(tren)SbS₃]·H₂O was synthesized under solvothermal conditions applying CrCl₃·6H₂O, Sb₂S₃, and S as starting material in an aqueous tren solution (tren = tris(2‐aminoethyl)amine)). The compound crystallizes in the non‐centrosymmetric space group P2₁2₁2₁ with a = 8.7779(15), b = 10.7122(17), c = 15.4286(18) Å, V = 1450.8(4) ų. In the structure the Cr³⁺ ion is surrounded by four N atoms of the amine molecules and by two S atoms of a trigonal pyramidal [SbS₃]^3? group, i.e., the latter acts as a bidentate ligand. A three‐dimensional network is formed via hydrogen bonds between the complexes and water molecules. The main resonances in the Raman spectrum can be explained on the basis of calculated data. The most intense band is due to the Sb‐S stretching vibration. The thermal properties were investigated by DTA‐TG measurements. On heating [Cr(tren)SbS₃]·H₂O decomposes in two distinct steps. The first step corresponds to the removal of the water molecules and the second step to the loss of the tren ligand.     

Pyrolysis Mass Spectrometry Analysis of BF4 − Doped Polythiophene

Abstract

Pyrolysis of electrochemically prepared BF₄ ^? doped polythiophene (PTh) by direct insertion probe and Currie point pyrolysis gas chromatography mass spectrometry techniques indicated that thermal decomposition of PTh occurs in two steps. In accordance with literature results, the first step is assigned to the loss of the dopant, and the second step to the degradation of the polymer backbone producing segments of various conjugation lengths. At elevated temperatures, detection of products such as H₂S and C₂H₂ indicating cleavage of the thiophene (Th) ring was associated with a network structure. For the dedoped samples, a significant increase in the relative intensities of the peaks characteristic to the counter ion of the dopant, N(C₄H₉)₄ ⁺ pointed out the inward diffusion of (C₄H₉)₄N⁺ during the dedoping process.     

Thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate. Part 3. Isothermal kinetics

The kinetics of the thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate in air were established from isothermal experiments. By heating the solution, first most of the water evaporates to a composition of equimolar amounts of water and manganese nitrate; this concentrated solution then decomposes to γ-Mn(NO₂, NO₂ and water, usually in two steps. The first step can be described best by the model [?ln(1 ? α)]^{$\text{1}\text{2}$} = 8.9 × 10¹¹ exp(?121000/RT)t, whereas the second step is described equally well by several models. The kinetic parameters of these models are quite similar, the average activation energy being 141 kJ mole^?1.The decomposition of anhydrous Mn(NO₃)₂, which proceeds in a single step, can also be described with several similar models. In this case the average activation energy is about 92 kJ mole^?1.     

Insights into the Mechanism of the Reaction between Tetrachloro‐p‐Benzoquinone and Hydrogen Peroxide and their Implications in the Catalytic Role of Water Molecules in Producing the Hydroxyl Radial

Detailed mechanisms for the formation of hydroxyl or alkoxyl radicals in the reactions between tetrachloro‐p‐benzoquinone (TCBQ) and organic hydroperoxides are crucial for better understanding the potential carcinogenicity of polyhalogenated quinones. Herein, the mechanism of the reaction between TCBQ and H₂O₂ has been systematically investigated at the B3LYP/6‐311++G** level of theory in the presence of different numbers of water molecules. We report that the whole reaction can easily take place with the assistance of explicit water molecules. Namely, an initial intermediate is formed first. After that, a nucleophilic attack of H₂O₂ onto TCBQ occurs, which results in the formation of a second intermediate that contains an OOH group. Subsequently, this second intermediate decomposes homolytically through cleavage of the O? O bond to produce a hydroxyl radical. Energy analyses suggest that the nucleophilic attack is the rate‐determining step in the whole reaction. The participation of explicit water molecules promotes the reaction significantly, which can be used to explain the experimental phenomena. In addition, the effects of F, Br, and CH₃ substituents on this reaction have also been studied.     

Kinetic and thermodynamic studies of MgHPO<Subscript>4</Subscript> · 3H<Subscript>2</Subscript>O by non-isothermal decomposition data

The thermal decomposition of magnesium hydrogen phosphate trihydrate MgHPO₄ · 3H₂O was investigated in air atmosphere using TG-DTG-DTA. MgHPO₄ · 3H₂O decomposes in a single step and its final decomposition product (Mg₂P₂O₇) was obtained. The activation energies of the decomposition step of MgHPO₄ · 3H₂O were calculated through the isoconversional methods of the Ozawa, Kissinger–Akahira–Sunose (KAS) and Iterative equation, and the possible conversion function has been estimated through the Coats and Redfern integral equation. The activation energies calculated for the decomposition reaction by different techniques and methods were found to be consistent. The better kinetic model of the decomposition reaction for MgHPO₄ · 3H₂O is the F _1/3 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the decomposition reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous without connecting with the introduction of heat.     

Mechanism of oxidation of iron(II) chelates by hexavalent chromium and heptavalent manganese in aqueous sulfuric acid and micellar media - a kinetic approach

Summary Oxidation of the Fe^II chelates [FeL] (L = phen or bipy) by Cr^VI and Mn^VII in H₂SO₄ medium was found to proceed through the formation of a bimetallic insertion complex which decomposes in the slow step, followed by electron transfer from [FeL] to the oxidant. The reactions are catalysed by both anionic and non-ionic micelles [SDS and triton-x (Tx), respectively]. A mechanism is suggested involving electrostatic stabilization of the cationic forms of the Fe^II chelates by anionic SDS and the partial anionic character of polyoxyethylene moiety of Tx, respectively. The marginal catalysis of cationic micelles (CTAB) is attributed to co-anion-micellar interactions.     

Beiträge zur Chemie der Oxid-halogenide von Molybdän und Wolfram. VII. Thermische Zersetzung und Bildungsenthalpie von WOCl3 und WOCl2

The thermal decomposition of WOCI₃ proceeds in the first decomposition step according to 2 WOCl₃,s = WOCl₂,s + WOCl₄,g. The second decomposition step of WOCI₃ is identical with the thermal decomposition of WOCI₂, equation see “Inhaltsübersicht” The interpretation of the decomposition equilibrium of WOCl₃ gives the heat of formation: ΔH°(WOCl₂,s,298) = ?155(±4) kcal/Mol. The heat of formation δH° (WOCl₃,s,298) = ?174,15(±0,8) kcal/Mol was determined from the solution enthalpy of WOCl₃ in 2n NaOH with 1% H₂O₂.     

Kinetic and spectroscopic analysis of NH3 decomposition under R.F. Plasma at moderate pressures

The plasma decomposition of NH₃ has been studied as a function of the residence time, power input, and pressure. The process follows apparently zero-order kinetics, which can be interpreted on the basis of a kinetic mechanism involving as initial step the rupture of an N-H bond from vibro-rotationally excited modecules. Simultaneous spectroscopic observations of the emission light due to electronically excited NH₂, NH, H, and N₂ have been used to confirm the suggested mechanism and to show that NH₂ and NH are successive intermediate species and that the final step of the decomposition process is the bimolecular recombination NH+NHN₂+H₂.