Selectivity control of carbonylation of methanol to dimethyl oxalate and dimethyl carbonate over gold anode by electrochemical potential

New and unique electrocatalysis of gold for the carbonylation of methanol to dimethyl oxalate (DMO) and dimethyl carbonate (DMC) was found. The selectivity to DMO and DMC could be controlled over gold anode by electrochemical potential, as you like. Drastic changes of gold electrocatalysis was due to changes of the oxidation state of gold, Au0 or Au3+.     

Vapor Phase Carbonylation Reactions Using Methyl Nitrite Over Pd Catalysts

Vapor phase carbonylation reactions using methyl nitrite (MN) as an oxidant have been developed by Ube Industries, Ltd. Dimethyl oxalate (DMO) and dimethyl carbonate (DMC) are synthesized efficiently over Pd(0) and Pd(II) catalysts under mild condition in gas phase, respectively. In these synthesis procedures, two kinds of separate reactions are involved. The first reaction is the catalytic synthesis of DMO or DMC from MN and CO; and the second reaction is non-catalytic MN synthesis from methanol, O₂ and NO, which is produced from the first reaction. The high DMO or DMC selectivity and suppression of catalyst deactivation originate from the facts that O₂ is not involved and H₂O is not produced in the first reaction.     

Mechanistic investigations on dimethyl carbonate formation by oxidative carbonylation of methanol over a CuY zeolite: an operando SSITKA/DRIFTS/MS study

The simultaneous combination of steady state isotopic transient kinetic analysis (SSITKA) with diffuse reflectance Fourier transform spectroscopy (DRIFTS) and mass spectrometric (MS) analysis was applied to study the oxidative carbonylation of methanol (MeOH) to dimethyl carbonate (DMC) on a CuY zeolite catalyst prepared by incipient-wetness impregnation of commercial zeolite NH(4)-Y. The interaction of the catalyst with different reactants and reactant mixtures (O(2), CO, CO/O(2), MeOH/O(2), MeOH/CO, and MeOH/CO/O(2)) was studied in detail using (16)O(2)/(18)O(2) as well as (12)CO/(13)CO containing gas mixtures. DMC is produced via a monodentate monomethyl carbonate (MMC) species as intermediate which is formed by the concerted action of adsorbed methoxide and CO with gas phase MeOH. Adsorbed bidentate MMC species were found to be inactive. Lattice oxygen supplied by CuO(x) species is involved in the formation of MMC. Gas phase oxygen is needed to re-oxidize the catalyst but favours also the oxidation of CO to CO(2) and unselective oxidation reactions of MeOH to methyl formate, dimethoxymethane, and CO(2). The appropriate choice of reaction temperature and of the oxygen content in the reactant gas mixture was found to be indispensable for reaching high DMC selectivities.     

Pt-Mo电极上CO、甲醛和甲醇的电催化氧化-微分电化学质谱研究

利用微分电化学质谱（DEMS）研究了Mo修饰的Pt电极上CO、甲醛和甲醇的电催 化氧化,证实了Mo(IV)是催化活性样品,而且它只对弱吸附CO的氧化起催化作用, 对强吸附CO的氧化没有催化活性。在低于0.4 V的电位下,吸附在Pt电极上的Mo结 甲醇和甲醛的催化氧化是通过弱吸附CO的氧化路径进行的。     

Cuβ催化剂上氧化羰基合成碳酸二甲酯的原位漫反射红外光谱研究

采用原位漫反射红外光谱法研究了Cuβ催化剂上氧化羰基合成碳酸二甲酯(DMC)的反应机理,考察了甲醇、一氧化碳和DMC的单独吸附及混合气吸附。结果表明,Cuβ催化剂上只存在一种活性位,位于六元环中;氧气能够氧化吸附态的甲醇产生甲氧基和水;DMC吸附在Cuβ催化剂上时,以羰基中的氧原子吸附在活性位上更加稳定;反应存在生成单甲氧基物种和双甲氧基物种两条路径,单甲氧基物种与CO反应生成单甲基碳酸盐物种(MMC),MMC再与甲氧基反应生成DMC;CO插入双甲氧基物种也可以得到DMC。在Cuβ催化剂上更倾向于进行CO插入双甲氧基物种这一路径。     

Investigation of the effect of carbon monoxide on the oxidative carbonylation of methanol to dimethyl carbonate over CuX and CuZSM-5 zeolites

Direct synthesis of dimethyl carbonate offers prospects for a “green chemistry” replacement to eliminate use of phosgene for polymer production and other processes. The carbonylation of methanol to produce dimethyl carbonate over Cu⁺X and Cu⁺ZSM-5 zeolites prepared by solid-state ion exchange has been investigated, focusing on the interaction of carbon monoxide with the Cu⁺ zeolites. The methanol carbonylation mechanism reported previously has been extended to account for carbon monoxide adsorption at high pressure. The comparison of the results obtained from Cu⁺X and Cu⁺ZSM-5 show that strong CO adsorption on the catalyst is not related to increased rate of dimethyl carbonate production. The rate limiting step for DMC production is best described as the Eley-Rideal reaction of gas-phase CO with surface methoxide.     

CuO-La_2O_3/AC催化剂上气相合成碳酸二甲酯的研究(英文)

制备出了用于甲醇气相氧化羰基化合成碳酸二甲酯反应的负载铜基催化剂ＣｕＯ－Ｌａ_2Ｏ_3／ＡＣ。考察了预处理的活性炭载体对反应性能的影响。采用ＸＰＳ技术表征了催化剂的表面性质。结果表明,ＣｕＯ－Ｌａ２Ｏ３／ＡＣ催化剂具有催化合成碳酸二甲酯的反应活性：反应性能依赖于催化剂表面的ＣｕＯ和Ｃｕ２Ｏ物种;用盐酸预处理的活性炭载体可明显提高催化剂的活性和稳定性。     

Carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes: an unexpectedly complex network of catalytic reactions, centred around a Pd-imido intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P₂) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N′‐diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co‐produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H₂O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P₂Pd⁰ compound formed in situ, oxidation to a palladium imido compound P₂Pd^II?NPh, can be achieved by de‐oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P₂Pd^II?NPh to P₂Pd⁰ makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd–imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.     

The local environment of Cu+ in Cu-Y zeolite and its relationship to the synthesis of dimethyl carbonate

Cu-exchanged Y zeolite was investigated in order to determine the location of the copper cations relative to the zeolite framework and to determine which Cu cations are active for the oxidative carbonylation of methanol to dimethyl carbonate (DMC). Cu-Y zeolite was prepared by vapor-phase exchange of H-Y with CuCl. The oxidation state, local coordination, and bond distances of Al and Cu were determined using Al K-edge and Cu K-edge X-ray absorption spectroscopy (XAS). Complimentary information was obtained by H2 temperature-programmed reduction and by in-situ infrared spectroscopy. Cu-Y has a Cu/Al ratio of unity and very little occluded CuCl. The average Al-O and Al-Cu bond distances are 1.67 angstroms and 2.79 angstroms, respectively, and the average Cu-O and Cu-Si(Al) bond distances are 1.99 angstroms and 3.13 angstroms, respectively. All of the Cu exchanged is present as Cu+ in sites I', II, and III'. Cu-Y is active for the oxidative carbonylation of methanol, and at low reactant contact time produces DMC as the primary product. With increasing reactant contact time, DMC formation decreases in preference to the formation of dimethoxy methane (DMM) and methylformate (MF). The formation of DMM and MF is attributed to the hydrogenation of DMC and the hydrogenolysis of DMM, respectively. Observation of the catalyst under reaction conditions reveals that most of the copper cations remain as Cu+, but some oxidation of Cu+ to Cu2+ does occur. It is also concluded that only those copper cations present in site II and III' positions are accessible to the reactants, and hence are catalytically active. The dominant adsorbed species on the surface are methoxy groups, and adsorbed CO is present as a minority species. The relationship of these observations to the kinetics of DMC synthesis is discussed.     

TBAB修饰的负载型Wacker催化剂催化甲醇羰基化合成碳酸二甲酯

自 1 95 9年 Smidt等 [1]发现均相 Pd Cl2 - Cu Cl2 体系可高效率直接选择性氧化乙烯制乙醛以来 ,Wacker催化过程已成为乙醛工业生产的主要方法 .为解决 Wacker催化体系腐蚀性强及催化体系与产物难以分离等弊端 ,将均相 Wacker(Pd Cl2 - Cu Cl2 )催化剂固载化成为备受关注的研究课题[2 ] .多相Wacker催化剂不仅成功地应用于选择性氧化低碳烯烃制醛和酮 [3 ,4 ] ,还用于 CO深度氧化 [5～ 7] .碳酸二甲酯 (DMC)的合成与应用研究是目前绿色化学前沿课题 .在众多的 DMC合成方法中 ,常压气相法因其工艺简单、对设备无腐蚀以及产品易分离…     

碘甲烷在碳酸二甲酯直接合成中的作用

Dimethyl carbonate (DMC) is an environmentally friendly compound and a substitutive intermediate for highly toxic phosgene or dimethyl sulfate in carbonylation and methylation reactions as well as a promising octane booster. The common methods for its preparation are the oxidative carbonylation of methanol catalyzed by a variety of transition metal ions and the transesterification of ethylene carbonate or propene carbonate with methanol[1]. The direct synthesis of DMC from carbon dioxide and methanol is a challenging route in which the most abundant carbon resources and a main greenhouse gas is used as feedstock. A new method for the direct synthesis of DMC catalyzed by the methoxide of main group metal has attracted more and more attention since it was reported[2～6] . However the lower conversion of the reaction has become the main obstacle for its application. In this letter, an efficient promoter for the direct synthesis of DMC is reported.     

Electrooxidation of carbon monoxide and methanol on platinum-overlayer-coated gold nanoparticles: effects of film thickness

The electrooxidation of carbon monoxide and methanol on Pt-coated Au nanoparticles attached to 3-aminopropyl trimethoxysilane-modified indium tin oxide electrodes was examined as a function of Pt film thickness and Au particle coverage. For the electrodes with medium and high Au particle coverages, the CO stripping peak position shifts to more negative values with increasing Pt film thickness, from ca. 0.8 V (vs Ag/AgCl) at 1 ML to 0.45 V at 10 ML. Accompanying this peak potential shift is the sharpening of the peak width from more than 150 to 65 mV. For the electrode with low Au particle coverage, similar peak width narrowing was also observed, but the peak potential shift is much smaller, from 0.85 V at 1 ML of Pt to 0.65 V at 10 ML. These observations are compared with the CO oxidation on bulk Pt electrodes and on Pt films deposited on bulk Au electrodes. The film-thickness-dependent CO oxidation is explained by d band theory in terms of strain and ligand effects, the particle size effect, and the particle aggregation induced by Pt film growth. Corresponding to the increasing CO oxidation activity, the current density of methanol oxidation grows with the Pt film thickness. The peak potential and current density reach the same values as those obtained on a polycrystalline bulk Pt electrode when more than 4 ML of Pt is deposited on the Au particle electrodes with a particle coverage higher than 0.25. These results suggest that it is feasible to reduce Pt loading in methanol fuel cells by using Pt thin films as the anode catalyst.     

Highly active Pd containing EMT zeolite catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate

Palladium containing EMT zeolite catalyst(Pd/EMT) was prepared and used for the indirect oxidative carbonylation of methanol to dimethyl carbonate(DMC).The EMT zeolite was employed as a new catalyst support and compared with the conventional Pd containing FAU zeolite catalyst(Pd/FAU).The Pd/EMT in contrast to the Pd/FAU catalyst exhibited high intrinsic activity with the turnover frequency of 0.25 s^-1 vs.0.11 s^-1.The Pd/EMT catalyst showed high CO conversion of 82% and DMC selectivity of 79%,that maintained for at least 130 h,while the activity of the Pd/FAU catalyst rapidly deteriorated within 12 h.The enhanced interactions between Pd and EMT zeolite inhibited the sintering of palladium clusters and maintained the Pd2+ active sites in the Pd/EMT catalyst.The stabilization of the mono-dispersed Pd clusters within the EMT zeolite is paramount to the excellent performance of the catalyst for the indirect oxidative carbonylation of methanol to DMC.     

碱性直接醇燃料电池非铂阳极催化剂

以纳米Pd,Pd-Ru,Au和Au-Ru为碱性直接醇燃料电池非Pt阳极催化剂,考察了其对甲醇、乙醇和乙二醇的电氧化性能.结果表明,Pd在酸中对醇电氧化的催化活性很低,但在碱中表现出较高的催化活性,起波电势约为0.4V(vsRHE);引入Ru助催化剂后,起波电势负移约0.15V;Pd-Ru对乙醇的电氧化表现出很高的活性,在0.3～0.4V电势范围内其活性为Pt-Ru的4倍.Au在酸中几乎不催化醇类分子的电氧化,但在碱中表现出一定的催化活性,在高于0.6V(vsRHE)的电势范围内可观察到醇氧化阳极电流.Au-Ru的催化活性高于Au,但起波电势没有明显负移,这可能表明当电势不足够正时醇分子在Au表面的吸附脱氢步骤是速率控制步骤.     

助剂含量对CuLi/AC 催化剂结构及甲醇氧化羰基化反应性能的影响

采用微波辐射法制备出不同助剂含量的CuLi/AC(活性炭)催化剂, 考察了其在甲醇气相氧化羰基化合成碳酸二甲酯(DMC)反应中的催化性能, 使用X射线衍射、 扫描电子显微镜、 比表面积、 H₂程序升温还原、 X射线光电子能谱和CO程序升温脱附对催化剂的结构进行了表征. 研究结果表明, 添加适量的Li有助于铜物种还原为低价态的Cu⁰, 形成颗粒尺寸更小、 分布更加均匀的铜纳米颗粒, 并高度分散在活性炭载体表面. 催化剂活性与表面单质铜的含量有关, 即Cu⁰是催化剂的主要活性物种, 并且Cu⁰的晶粒尺寸越小, 催化剂活性越好. 添加Li后增加了催化剂表面的CO弱吸附位, 有利于CO对Cu-OCH₃的插入反应, 因此提高了催化活性. 随着Li含量的增加, DMC的时空收率逐渐升高, 当Li添加质量分数达到0.15%时, DMC的时空收率达到最高值540.6 mg·g^-1·h^-1, 甲醇转化率为4.5%, DMC选择性为81.4%.     

Critical temperatures and pressures of reacting mixture in synthesis of dimethyl carbonate with methanol and carbon dioxide

Critical temperatures and pressures of nominal reacting mixture in synthesis of dimethyl carbonate （DMC） from methanol and carbon dioxide （quaternary mixture of carbon dioxide ＋ methanol ＋ water ＋ DMC） were measured using a high-pressure view cell. The results suggested that the critical properties of the reacting mixture depended on the reaction extent as well as its initial composition （initial ratio of carbon dioxide to methanol）. Such information is essential for determining the reaction conditions when one intends to carry out the synthesis of DMC with CO2 and methanol under supercritical conditions.     

CO and methanol oxidation at platinum-tin electrodes

Electrooxidation of dissolved CO and methanol at platinum-tin electrodes with different phase composition (a two-phase Sn/Pt-catalyst, Pt-Sn alloy, and Pt₃Sn intermetallic compound) is studied. All studied catalysts show higher catalytic activity in the CO oxidation at lower potentials (0.3–0.5 V against reversible hydrogen electrode (RHE)), as compared with platinum; no catalysis is observed at higher potentials (0.7 V); moreover, inhibiting is observed in some cases. The catalyst with the most strongly ordered structure (Pt₃Sn) demonstrated the highest catalytic activity; however, it appeared being less stable against oxidation at potentials more positive than 1.0 V. Catalytic effects were practically absent in the CO-adsorbate oxidation process. The sequence of catalyst activities in the methanol oxidation process differed from that in the CO oxidation; in particular, Pt3Sn appeared being the least active. The observed difference can be associated with the difference in the CO and methanol adsorption mechanisms. The effect of the carbonaceous support dispersion on the current-voltage curves is discussed.     

Novel fabrication of copper oxides on AC and its enhanced catalytic performance on oxidative carbonylation of methanol

Copper oxides(CuO_x) nanoparticles dispersed on activated carbon(AC) were prepared by using vaporphase methanol as the reducing agent. The CuO_x/AC as prepared exhibited an enhanced catalytic activity in oxidative carbonylation of methanol to dimethyl carbonate(DMC). The catalytic performance was significantly influenced by reduction conditions including temperature and time. With the similar selectivity of DMC, the space time yield(STY) under optimal reduction conditions reached up to 408 mg g~(-1)h~(-1), which is superior to conventional methods such as thermolysis and solvothermal reduction. Based on the characterization results of XRD, TEM and XPS, the good copper dispersion and high Cu~+ content obtained by vapor-phase methanol reduction were mainly responsible for the high catalytic activity.     

A DFT study of DMC formation on Rh‐doped Cu/AC surfaces

The activity and selectivity of heterogeneous catalysts can be significantly improved by dispersion of another active component in the metal substrate. The impact of Rh promoter on the formation of dimethyl carbonate (DMC) via oxidative carbonylation of methanol on Cu–Rh/AC (activated carbon) catalyst was investigated by density functional theory calculations. The most stable configurations of reacting species (CO, OH, CH₃O, monomethyl carbonate, and DMC) adsorbed on the Cu⁰(zero‐valent copper)/AC and Cu–Rh/AC surfaces were determined on the basis of the calculated results. The reaction energy and activation energy of the rate‐limiting steps on the Cu–Rh/AC and Cu⁰/AC surfaces were compared. The activation energies of the rate‐limiting step of CO insertion into dimethoxide are 206.3 and 304.8 kJ mol^?1 on the Cu–Rh/AC and Cu⁰/AC surfaces, respectively. The activation energies of the rate‐limiting step of CO insertion into methoxide are 78.5 and 92.7 kJ/mol on the Cu–Rh/AC and Cu⁰/AC surfaces, respectively. The calculated results indicate that the addition of Rh atom has a significant effect on decreasing the active energy the main pathway for DMC formation. © 2015 Wiley Periodicals, Inc.     

纳米晶枝CuAu合金催化剂对二氧化碳电催化还原性能的研究

利用可再生清洁能源将CO2转化为CO和其他小分子是合成含碳燃料的可观方法之一.间歇性可再生能源存储的重要策略之一是将二氧化碳进行电化学还原.选择具有高活性和稳定性的电催化剂对于电化学还原CO2至关重要.在这项研究中,我们使用简单的电沉积方法合成了具有纳米晶枝状结构的CuAu合金电极.各项表征显示原子比约为1∶1的CuA...