A density functional theory investigation on the mechanism and kinetics of dimethyl carbonate formation on Cu2O catalyst

A theoretical analysis about the mechanism and kinetics of dimethyl carbonate (DMC) formation via oxidative carbonylation of methanol on Cu₂O catalyst is explored using periodic density functional calculations, both in gas phase and in solvent. The effect of solvent is taken into account using the conductor‐like screening model. The calculated results show that CO insertion to methoxide species to produce monomethyl carbonate species is the rate‐determining step, the corresponding activation barrier is 161.9 kJ mol^?1. Then, monomethyl carbonate species reacts with additional methoxide to form DMC with an activation barrier of 98.8 kJ mol^?1, above reaction pathway mainly contributes to the formation of DMC. CO insertion to dimethoxide species to form DMC is also considered and analyzed, the corresponding activation barrier is 308.5 kJ mol^?1, suggesting that CO insertion to dimethoxide species is not competitive in dynamics in comparison with CO insertion to methoxide species. The solvent effects on CO insertion to methoxide species involving the activation barriers suggest that the rate‐determining step can be significantly affected by the solvent, 70.2 kJ mol^?1 in methanol and 63.9 kJ mol^?1 in water, which means that solvent effect can reduce the activation barrier of CO insertion to methoxide species and make the reaction of CO insertion to methoxide in solvents much easier than that in gas phase. Above calculated results can provide good theoretical guidance for the mechanism and kinetics of DMC formation and suggest that solvent effect can well improve the performance of DMC formation on Cu₂O catalyst in a liquid‐phase slurry. © 2012 Wiley Periodicals, Inc.     

Potential energy surfaces for Rh?CO from DFT calculations

We present potential energy surfaces for Rh? CO obtained from density functional theory for two electronic states of Rh? CO. We have performed local spin-density calculations including relativistic as well as gradient corrections. The construction of a reasonably accurate atom–atom potential for Rh? CO is not possible. We were much more successful in constructing the potential energy surfaces by representing the potential as a spherical expansion. The expansion coefficients, which are functions of the distance between the rhodium atom and the carbon monoxide center of mass, can be represented by Lennard-Jones, Buckingham, or Morse functions, with an error of the fit within 10 kJ/mol. The potential energy surfaces, using Morse functions, predict that the electronic ground state of Rh? CO is ²Σ⁺ or ²Δ. This is a linear structure with an equilibrium distance of rhodium to the carbon monoxide center of mass of 0.253 nm. The bonding energy is ?184 kJ/mol. Further, Morse functions predict that the first exicted state is ⁴A′. This is a bent structure (∠Rh? CO = 14°) with an equilibrium distance of rhodium to the carbon monoxide center of mass of 0.298 nm. The bonding energy of this state is ?60 kJ/mol. Both these predictions are in good agreement with the actual density functional calculations. We found 0.250 nm with ?205 kJ/mol for ²Σ⁺ and 0.253 nm with ?199 kJ/mol for ²Δ. For ⁴A′, we found 0.271 nm, ∠Rh? CO = 30°, with ?63 kJ/mol. The larger deviation for ⁴A′ than for ²Σ⁺ or ²Δ is a consequence of the fact that the minimum for ⁴A′ is a very shallow well. © 1994 by John Wiley & Sons, Inc.     

Cu/活性炭催化剂：水合肼还原制备及催化甲醇氧化羰基化

以活性炭为载体,水合肼为还原剂制备了负载型Cu/活性炭催化剂,考察了水合肼/硝酸铜物质的量的比对催化甲醇气相氧化羰基化性能的影响,并采用XRD、XPS、H2-TPR和SEM等手段对催化剂进行了表征。结果表明,不加入还原剂水合肼时,催化剂中仅有CuO;随着水合肼/硝酸铜物质的量的比的增加,二价铜逐步被还原为Cu2O和/或单质Cu0,未被还原的Cu(OH)2在催化剂干燥过程中分解形成分散态CuO存在于催化剂表面。当水合肼/硝酸铜物质的量的比为0.75时,催化剂的催化性能最好,碳酸二甲酯的时空收率为120.62 mg.(g.h)-1,选择性为74.51%,甲醇转化率达到3.88%。在93 h反应时间内,催化剂都保持了较高的反应活性和选择性。此时铜物种以Cu2O和分散态CuO为主,Cu2O是主要的活性物种。     

Computational investigation of enantio‐ and regioselectivity of rhodium‐catalyzed asymmetric hydroformylation of vinyl formate with CHIRAPHOS‐type ligand

The potential energy profile for Rh‐catalyzed asymmetric hydroformylation of vinyl formate is mapped out using a nonlocal density functional method (B3LYP). This study focuses on the enantio‐ and regioselectivity of asymmetric hydroformylation. All the structures are optimized at the B3LYP/6‐31G(d,p) level(LANL2DZ(d) for Rh, P). As illustrated by computation, the olefin insertion step is irreversible because of higher activation free energy of the reverse reaction than that of forward reaction, so it is the determining step for both the regioselectivity and enantioselectivity in asymmetric hydroformylation. The lowest activation free energy in vinyl insertion is the path 2a → TS1a (ΔG^≠ = 47.92 kJ/mol), giving rise to the preferred product as (S)‐1‐formylenthyl formate. Throughout the catalytic cycle, the H₂ oxidative addition has the highest activation free energy, 77.24 kJ/mol, so it is the rate‐limiting step for the whole catalytic cycle. The calculation results are in agreement with many experiment investigations. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

淀粉基炭负载纳米铜催化合成碳酸二甲酯

以硝酸铜和可溶性淀粉为原料, 经过溶胶-凝胶化过程、高温炭化和KOH活化得到炭负载铜催化剂(Cu/C), 采用扫描电镜、透射电镜、X射线衍射、热重-差热分析仪、N₂吸附和CO程序升温脱附对催化剂结构进行了表征, 并考察了它在甲醇氧化羰基化合成碳酸二甲酯(DMC)反应中的催化活性. 结果表明, 活化温度和KOH用量对催化剂的表面结构及金属铜粒子尺寸影响显著, 当活化温度为850℃, KOH:C=1 (质量比)时, Cu/C催化剂的比表面积达到1690 m²/g, 铜纳米粒子平均晶粒尺寸为30.4 nm, 催化活性最高, DMC时空收率达到235.7 mg·g^-1·h^-1, 甲醇转化率和DMC选择性分别为1.6%和76.5%.     

Design and Synthesis of Copper–Cobalt Catalysts for the Selective Conversion of Synthesis Gas to Ethanol and Higher Alcohols

Combining quantum‐mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoO_x catalysts for the selective conversion of synthesis gas (CO+H₂) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non‐petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu–Co alloy sites, at Co‐enriched surfaces, as ideal for the selective production of long‐chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu²⁺ and Co²⁺ cations in a wide range of compositions. As revealed by energy‐dispersive X‐ray nanospectroscopy and temperature‐resolved X‐ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co‐rich surface compositions, for which Cu phase segregation is prevented.     

Density Functional Study of Catalytic Activity of Cu<Subscript>12</Subscript>TM for Water Gas Shift Reaction

Based on density functional theory calculations, we have systematically studied the WGS reaction on various nanosized Cu₁₂TM of Co, Ni, Cu (from the 3d row), Rh, Pd, Ag (from the 4d row), Ir, Pt, Au (from the 5d row). The reaction mechanism proposed by Langmuir–Hinshelwood has been followed, which corresponds to \({\text{CO* + OH* }} \to {\text{COOH*}} \to {\text{CO}}_{2} {\text{ + H*}}\). The comparison of the Gibbs free energy profiles of carboxyl mechanism on different Cu₁₂TM systems concludes that WGS reaction is determined by the steps of H₂ forming and OH* reacting with CO* to form COOH*. BEP relationship between activation barriers (Ea) and reaction energies (ΔH) on a series of Cu₁₂TM clusters is very good. What’s more, the activation barrier of rate-determining step of Cu₁₂Au is the smallest. TOF, with the aid of An Energetic Span Model (ESM), is used to estimate the efficiency of the different Cu₁₂TM clusters. The results show that the values of TOFs in doping Cu₁₂Rh, Cu₁₂Ir and Cu₁₂Pt are smaller than that in pure Cu. Moreover, the values of TOFs in doping Cu₁₂Co, Cu₁₂Ni, Cu₁₂Pd, Cu₁₂Ag, and Cu₁₂Au are higher than that in Cu₁₃. The higher value of TOF, the more favorable catalysts they are. This results shoud be helpful in developing efficient catalysts for WGS reaction. Finally, d-band center is used to explain the binding energy of CO and H₂O. It shows that there is a good liner relationship between d-band center and binding energy of CO but not for H₂O.     

Catalytic CO Oxidation by O2 Mediated by Noble‐Metal‐Free Cluster Anions Cu2VO3–5−

Catalytic CO oxidation by molecular O₂ is an important model reaction in both the condensed phase and gas‐phase studies. Available gas‐phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O₂ under thermal collision conditions. Herein, we identified the first example of noble‐metal‐free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu₂VO_3–5^? for CO oxidation by O₂. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu?Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O₂ activation during the catalysis.     

Low‐Temperature Oxidation of Carbon Monoxide with Gold(III) Ions Supported on Titanium Oxide

Au/TiO₂ catalysts prepared by a deposition–precipitation process and used for CO oxidation without previous calcination exhibited high, largely temperature‐independent conversions at low temperatures, with apparent activation energies of about zero. Thermal treatments, such as He at 623 K, changed the conversion–temperature characteristics to the well‐known S‐shape, with activation energies slightly below 30 kJ mol^?1. Sample characterization by XAFS and electron microscopy and a low‐temperature IR study of CO adsorption and oxidation showed that CO can be oxidized by gas‐phase O₂ at 90 K already over the freeze‐dried catalyst in the initial state that contained Au exclusively in the +3 oxidation state. CO conversion after activation in the feed at 303 K is due to Au^III‐containing sites at low temperatures, while Au⁰ dominates conversion at higher temperatures. After thermal treatments, CO conversion in the whole investigated temperature range results from sites containing exclusively Au⁰.     

Mechanism of CO oxidation in excess H2 over CuO/CeO2 catalysts: ESR and TPD studies

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO₂ catalysts in excess H₂ is studied. CO conversion increases and the temperature range of the reaction decreases by 100 K as the CuO content is raised. The maximal CO conversion, 98.5%, is achieved on 6.4% CuO/CeO₂ at 150°C. At T > 150°C, the CO conversion decreases as a result of the deactivation of part of the active sites because of the dissociative adsorption of hydrogen. CO is efficiently adsorbed on the oxidized catalyst to form CO-Cu⁺ carbonyls on Cu₂O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu⁰ of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O₂ on Cu⁰ at T ～ 150°C. The activation energies of CO, CO₂, and H₂O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu⁺ carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.     

A Highly Stable Copper‐Based Catalyst for Clarifying the Catalytic Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation

Identification of the active copper species, and further illustration of the catalytic mechanism of Cu‐based catalysts is still a challenge because of the mobility and evolution of Cu⁰ and Cu⁺ species in the reaction process. Thus, an unprecedentedly stable Cu‐based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu⁰ and Cu⁺ in the dehydrogenation of methanol to methyl formate by combining isotope‐labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu⁰ sites promote the cleavage of the O?H bond in methanol and of the C?H bond in the reaction intermediates CH₃O and H₂COOCH₃ which is formed from CH₃O and HCHO, whereas Cu⁺ sites cause rapid decomposition of formaldehyde generated on the Cu⁰ sites into CO and H₂.     

Effect of Temperature on Oxide Formation in Ligand-Deficient Cu|Cu(II), Ethylenediamine System

The influence of temperature on formation of oxide layers on copper electrode in solutions containing 0.01 M Cu(II), 0.005 M ethylenediamine, and 0.3 M K₂SO₄ as a supporting electrolyte at pH 5.3 is investigated. The rate of net process Cu + Cu²⁺ + H₂O Cu₂O + 2H⁺ proceeding under open-circuit conditions is supposedly controlled by interaction between copper electrode and Cu²⁺ aqua-ions. Well-defined voltammetric peak is observed at –0.75 V (SHE), the height of which may serve as a measure of Cu₂O formation rate. An activation energy and a formal rate constant of the process are found to equal 30 kJ mol^–1 and 0.17 s^–1.     

Pyrrolidone ligand improved Cu‐based catalysts with high performance for acetylene hydrochlorination

A series of Cu‐pyrrolidone/spherical activated carbon (SAC) catalysts were prepared via a simple incipient wetness impregnation method and then assessed in acetylene hydrochlorination, and the catalytic evaluation result indicated that the 1‐methyl‐2‐pyrrolidinone (NMP) ligand was found to be the most effective one to significantly improve the activity and stability of Cu catalyst. The catalyst with the optimal molar ratio of NMP/Cu = 0.25 showed 94.2% acetylene conversion at 180°C and an acetylene gas hourly space velocity of 180 h^?1. Moreover, the acetylene conversion of Cu‐0.25NMP/SAC remained stable over 99.1% for about 220 h under the industrial condition. Transmission electron microscopy (TEM) analyses proved that NMP ligand improved the dispersion of Cu species. In addition, hydrogen temperature‐programmed reduction (H₂‐TPR), X‐ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), and Brunner–Emmet–Teller (BET) indicated that the additive of NMP was preferential to stabilize the catalytic active Cu⁺ and Cu²⁺ species and inhibit the reduction of Cu^α+ to Cu⁰ during the preparation process and reaction, hence restraining the coke deposition. Furthermore, the steady coordination structure between Cu and NMP was confirmed by Fourier‐transform infrared spectra (FT‐IR) and Raman combining with density functional theory (DFT) calculation, which could effectively lower the adsorption energy of catalyst for C₂H₂ and inhibit the serious carbon deposition caused by excessive acetylene self‐accumulation. Our findings suggest that the efficient, well‐stabilized cost‐effective, and environmentally friendly Cu catalyst has great potential in acetylene hydrochlorination.     

Simultaneous removal of Cu2+ and Cr3+ ions from aqueous solution based on Complexation with Eriochrome cyanine‐R and derivative spectrophotometric method

TiO₂ nanoparticles deposited on activated carbon (TiO₂–NP–AC) was prepared and characterized by XRD and SEM analysis. Subsequently, simultaneous ultrasound‐assisted adsorption of Cu²⁺ and Cr³⁺ ions onto TiO₂‐NPs‐AC after complexation via eriochrome cyanine R (ECR) has been investigated with UV–Vis and FAA spectrophotometer. Spectra overlapping of the ECR‐Cu and ECR‐Cr complex was resolve by derivative spectrophotometric technique. The effects of various parameters such as initial Cu²⁺ (A) and Cr³⁺ (B) ions concentrations, TiO₂‐NPs‐AC mass (C), sonication time (D) and pH (E) on the removal percentage were investigated and optimized by central composite design (CCD). The optimize conditions were set as: 4.21 min, 0.019 mg, 20.02 and 13.22 mg L^?1 and 6.63 for sonication time, TiO₂–NP–AC mass, initial Cr³⁺ and Cu²⁺ ions concentration and pH, respectively. The experimental equilibrium data fitting to Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models show that the Langmuir model is a good and suitable model for evaluation and the actual behavior of adsorption process and maximum adsorption capacity of 105.26 and 93.46 mg g^?1 were obtained for Cu²⁺ and Cr³⁺ ions, respectively. Kinetic evaluation of experimental data showed that the adsorption processes followed well pseudo second order and intraparticle diffusion models.     

无氯 Cu/AC 催化剂的制备及其催化气相甲醇氧化羰基化反应性能

 以 Cu2(NO3)(OH)3/AC (活性碳) 为催化剂前驱体, 在惰性气氛中于不同温度热处理分别制得无氯的 CuO/AC, Cu2O/AC 和 Cu0/AC 催化剂, 并用于甲醇直接气相氧化羰基化合成碳酸二甲酯 (DMC) 反应. 结果表明, 200 °C 处理制得的催化剂中, Cu 物种以 CuO 为主. 随着处理温度的升高, 催化剂中 CuO 含量逐渐降低, 而 Cu2O 含量增加; 400 °C 制备的催化剂中, Cu 物种仅以 Cu2O 形式存在; 而 450 °C 以上处理时则以 Cu0 形式存在. 随着热处理温度的提高, 相应催化剂活性逐渐增加, 表明 CuO, Cu2O 和 Cu0 均具有催化活性, 其活性大小的顺序为 CuO < Cu2O < Cu0. 在 140 °C, CO:MeOH:O2 = 4:10:1, SV = 5 600 h1 条件下, 450 °C 处理制备的 Cu0/AC 催化剂表现出较高的催化甲醇氧化羰基化活性, 其中甲醇转化率达 11.5%, DMC 的时空收率和选择性分别为 261.9 mg/(g•h) 和 76.0%.     

Mechanochemical Activation of Cu–CeO<Subscript>2</Subscript> Mixture as a Promising Technique for the Solid-State Synthesis of Catalysts for the Selective Oxidation of CO in the Presence of H<Subscript>2</Subscript>

A new ecologically clean method for the solid-phase synthesis of oxide copper–ceria catalysts with the use of the mechanochemical activation of a mixture of Cu powder (8 wt %) with CeO₂ was developed. It was established that metallic copper was oxidized by oxygen from CeO₂ in the course of mechanochemical activation. The intensity of a signal due to metallic Cu in the X-ray diffraction analysis spectra decreased with the duration of mechanochemical activation. The Cu¹⁺, Cu²⁺, and Ce³⁺ ions were detected on the sample surface by X-ray photoelectron spectroscopy. The application of temperature-programmed reduction (TPR) made it possible to detect two active oxygen species in the reaction of CO oxidation in the regions of 190 and 210–220°C by a TPR-H₂ method and in the regions of 150 and 180–190°C by a TPR-CO method. It is likely that the former species occurred in the catalytically active nanocomposite surface structures containing Cu–O–Ce bonds, whereas the latter occurred in the finely dispersed particles of CuO on the surface of CeO₂. The maximum conversion of CO (98%, 165°C) reached by the mechanochemical activation of the sample for 60 min was almost the same as conversion on a supported CuO/CeO₂ catalyst.     

Variable‐Temperature Infrared Spectroscopy Studies on the Thermodynamics of CO Adsorption on the Zeolite Ca–Y

Variable temperature FT–IR spectroscopy (in the range of 298–380 K) is used to study the thermodynamics of formation of Ca²⁺???CO carbonyl species upon CO adsorption on the faujasite‐type zeolite Ca–Y, and also the (temperature‐dependent) isomerization equilibrium between carbonyl and isocarbonyl (Ca²⁺???OC) species. The standard enthalpy and entropy changes involved in formation of the monocarbonyl species resulted to be ΔH⁰=?50.3 (±0.5) kJ mol^?1 and ΔS⁰=?186 (±5) J mol^?1 K^?1, respectively. Isomerization of the (C‐bonded) Ca²⁺???CO carbonyl to yield the (O‐bonded) Ca²⁺???OC isocarbonyl involves an enthalpy change =+11.4 (±1.0) kJ mol^?1. These results are compared with previously reported data for the CO/Sr–Y system; and also, a brief analysis of enthalpy–entropy correlation for CO adsorption on zeolites and metal oxides is given.     

CuO‐Doped Mesoporous Silica Hybrid for Rapid and Sensitive Amperometric Detection of Phenolic Compounds

This work constructed an amperometric biosensing platform using CuO doped mesoporous silica hybrid (CuO/SBA‐15) as a carrier. The CuO/SBA‐15 showed a pair of redox peaks of Cu^2+/0. Upon immobilization of tyrosinase on the hybrid, the resulting biosensor exhibited a rapid (<0.5 s) and sensitive amperometric response to phenolic compounds under the optimized conditions. The linear response to catechol ranged from 1.2×10^?9 to 3.0×10^?5 M. The activation energy for enzymatic reaction was calculated to be 26.6 kJ mol^?1. The apparent Michaelis–Menten constants of the enzyme electrode were estimated to be 54.6, 145, 17.0, 74.8 and 633 µM for catechol, phenol, p‐cresol, m‐cresol and dopamine hydrochloride, respectively. The metal oxide doped mesoporous silica hybrid exhibited excellent performance for construction of new biosensors.     

Non-isothermal Kinetics of the Thermal Decomposition of 3-Nitro-1,2,4-triazol-5-one Magnesium Complex

Introduction3 Nitro 1,2 ,4 triazol 5 one (NTO)metalcomplexeshavemanyspecialstructuresandsomepotentialusesinammunition .1 4 Wepreviouslypreparedanddeterminedthecrystalstructureofitsmagnesiumcomplex ,5andinthispaper ,wediscusseditsthermalbehaviorbyDSCandTG/DTGtechniquesandstudieditsnon isothermalkineticsbythemeansoftheKissingermethod ,theOzawamethod ,thedifferentialmethodandtheintegralmethod .ExperimentalSample[Mg(H2 O) 6 ](NTO) 2 ·2H2 Owaspreparedasfollows :AcalculatedamountofMg(OH…