Enhanced electrocatalytic oxidation of methanol on Pd/polypyrrole–graphene in alkaline medium

The new electrocatalyst of Pd nanoparticles supported on polypyrrole-functionalized graphene (Pd/PPy–graphene) was reported. Microstructure, morphology and crystallinity of the synthesized materials were investigated by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The elements of the composite were characterized using energy dispersive X-ray spectroscopy (EDS). The results showed that the polypyrrole-wrapped graphene support successfully discrete Pd nanoparticles with the crystallite size of about 6 nm. Catalyst activity for methanol electro-oxidation in fuel cells was investigated by cyclic voltammetry (CV) and chronoamperometry. The fundamental electrochemical test results indicated that the electrocatalytic activity of Pd/PPy–graphene is much better than that of commercial catalyst for methanol oxidation.     

PWA/silica doped sulfonated poly(ether sulfone) composite membranes for direct methanol fuel cells

A novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica composite membranes for direct methanol fuel cells (DMFCs) application were prepared. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), water uptake, proton conductivity, and methanol permeability. Compared to a pure SPES membrane, PWA and SiO₂ doped membranes had a higher thermal stability and glass transition temperature (T_g) as revealed by TGA‐FTIR and DSC. The morphology of the composite membranes indicated that SiO₂ and PWA were uniformly distributed throughout the SPES matrix. Proper PWA and silica loadings in the composite membranes showed high proton conductivity and sufficient methanol permeability. The selectivity (the ratio of proton conductivity to methanol permeability) of the SPES‐P‐S 15% composite membrane was almost five times than that of Nafion 112 membrane. This excellent selectivity of SPES/PWA/silica composite membranes indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Prediction of Experimental Methanol Decomposition Rates on Platinum from First Principles

A microkinetic model for methanol decomposition on platinum is presented. The model incorporates competitive decomposition pathways, beginning with both O–H and C–H bond scission in methanol, and uses results from density functional theory (DFT) calculations [Greeley and Mavrikakis, J. Am. Chem. Soc. 124 (2002) 7193, Greeley and Mavrikakis, J. Am. Chem. Soc. 126 (2004) 3910]. Results from reaction kinetics experiments show that the rate of H₂ production increases with increasing temperature and methanol concentration in the feed and is only nominally affected by the presence of CO or H₂ with methanol. The model, based on the values of binding energies, pre-exponential factors and activation energy barriers derived from first principles calculations, accurately predicts experimental reaction rates and orders. The model also gives insight into the most favorable reaction pathway, the rate-limiting step, the apparent activation energy, coverages, and the effects of pressure. It is found that the pathway beginning with the C–H bond scission (CH₃OH→H₂COH→HCOH→CO) is dominant compared with the path beginning with O–H bond scission. The cleavage of the first C–H bond in methanol is the rate-controlling step. The surface is highly poisoned by CO, whereas COH appears to be a spectator species.     

B(C6F5)3催化Si-H/Si-OR缩聚反应机理及产物结构

根据DFT理论,用量子化学的方法对B(C₆F₅)₃催化Si—H/Si—OR缩聚反应的机理进行了研究,用²⁹Si NMR对1,4-双（二甲基硅基）苯（BDSB）与二甲基二甲氧基硅烷、甲基乙烯基二甲氧基硅烷、二苯基二甲氧基硅烷缩聚产物的微观结构进行了表征,结合反应机理,对单体的结构与缩聚产物的微观结构的关系进行了讨论。B(C₆F₅)₃先与Si—H形成弱加合物,然后Si—OR进攻Si—H/B(C₆F₅)₃加合物使Si—H断裂,形成氧钅翁离子中间体,最后H^-向正电中心迁移形成产物。H^-迁移方向的不同将导致3种反应：缩合、交换、逆反应。烷氧基硅烷中的乙烯基、苯基可以增加烷氧基C的正电性,并使C—O键伸长,减少Si—H/Si—OR交换反应的发生,使得缩聚产物具有更为交替的结构。     

Adsorption and decomposition of H2S on Pd(1 1 1) surface: a first-principles study

Gradient-corrected density functional theory was used to investigate the adsorption of H₂S on Pd(1 1 1) surface. Molecular adsorption was found to be stable with H₂S binding preferentially at top sites. In addition, the adsorption of other S moieties (SH and S) was investigated. SH and S were found to be preferentially bind at the bridge and fcc sites, respectively. The reaction pathways and energy profiles for H₂S decomposition giving rise to adsorbed S and H were determined. Both H₂S_(ad) → SH_(ad) + H_(ad) and SH_(ad) → S_(ad) + H_(ad) reactions were found to have low barriers and high exothermicities. This reveals that the decomposition of H₂S on Pd(1 1 1) surface is a facile process.     

MMAl在NH2与H混合覆盖的AlN(0001)-Al表面的吸附与扩散研究

利用量子化学的密度泛函理论(DFT),对AlN的MOCVD生长中表面反应前体AlCH₃(简称MMAl)在NH₂和H混合覆盖AlN(0001)-Al面的吸附与扩散进行计算分析。通过分析表面吸附能、扩散能垒及Mulliken数量比例等,确定可能的稳定吸附结构和扩散路径。研究发现：在NH₂与H混合覆盖的AlN(0001)-Al面,随着NH₂与H的覆盖度变化,MMAl均稳定吸附在T4位和H3位,吸附概率相近。随着NH₂比例增多、H比例减少,MMAl吸附后都向AlN表面转移电荷,同时其吸附变得相对容易,扩散变得逐渐困难。与吸附前相比,吸附后MMAl中的Al-C键长缩短,键能增强,不利于CH₃的脱离,导致引入C杂质的概率增高,表明MMAl既可能是生长中主要反应物质之一,同时也是引入C杂质的主要来源之一。若AlN表面存在覆盖H,吸附后的MMAl会促使表面覆盖的H原子倾向于脱离AlN表面,有利于后续生长。     

BrONO_2与Br(~2P_(3/2))气相反应的密度泛函理论研究

采用密度泛函理论计算方法B3LYP和基组6 31G(d),对BrONO2+Br(2P3/2)的反应机理进行了理论计算,得到各种可能反应途径的过渡态,并经过频率振动分析和内禀反应坐标(IRC)分析加以确认。结果表明:该反应是3通道反应,其中BrONO2+Br→Br2+NO3的反应活化能(5.25kJ/mol)最低,是反应主通道。     

Performance of direct methanol fuel cells prepared by hot-pressed MEA and catalyst-coated membrane (CCM)

The effect of the fabrication methods of the conventional hot-pressed membrane-electrode-assembly (hot-pressed MEA) and catalyst-coated membrane (CCM) on the utilization efficiency of Pt electrocatalysts, methanol crossover and performance of direct methanol fuel cells (DMFCs) is studied under the condition of the same Pt electrocatalysts loading. Cyclic voltammetric and electrochemical impedance studies showed that the cell with CCM exhibited significantly higher electrochemical surface area and lower electrode polarization resistance for the methanol oxidation reaction, in comparison to that with the hot-pressed MEA. Compared with the hot-pressed MEA, the methanol crossover of the cell with CCM is decreased by 55% and the power density of DMFC is enhanced by 36%. The improvement of the DMFCs with CCM is probably due to the significantly higher electrochemical reaction sites and the increased three-phase boundaries through the reduction in the loss of the Pt electrocatalysts in the gas diffusion layers and enhanced electrode/membrane interface.     

Preparation and solubility of water–methanol mixtures in sulfonated poly(etherketone) containing a cardo‐ring structure

The preparation and solubility of water–methanol mixtures in sulfonated (1,3‐dihydro‐3‐oxoisobenzofuran‐1,1‐diyl‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenyleneoxy‐1,4‐phenylene) (C‐PEK) was systematically studied. The sulfonation was carried out by reacting C‐PEK with 98% sulfuric acid at 60°C. This reaction obeys a first‐order reaction mechanism up to 4 h. The sulfonic acid group was uniformly dispersed in a sulfonated C‐PEK (SC‐PEK) membrane. The introduction of sulfonic acid groups in C‐PEK could increase polymer segmental gaps because of the size of a bulky sulfonic acid group or decrease polymer segmental gaps as a result of polar interactions. The former effect is dominant for SC‐PEK with low sulfonic acid content, whereas the latter occurs for SC‐PEK with high sulfonic acid content. The uptake of pure water or an aqueous methanol solution (e.g., 3, 5, and 10 wt % methanol concentration) in the sulfonated C‐PEK membranes increases with increasing sulfonic acid group content. However, the sulfonated C‐PEK with high sulfonic acid content selectively sorbs water rather than methanol in the membrane. This suggests that the sulfonated C‐PEK membrane could prevent crossover of methanol through the membrane and has potential as a polymer electrolyte for the direct methanol fuel cell. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1113–1123, 2006     

(Ni-P)-Co/WC纳米颗粒复合电刷镀层的组织性能分析

采用电刷镀技术制备(N i-P)-Co/W C纳米颗粒复合镀层,用扫描电子显微镜、X-射线衍射仪和电子探针测定了复合刷镀层表面形貌、微观组织结构及成分分布。结果显示,复合镀层中的组织结构更加致密,显微硬度比镍-磷合金镀层有较大程度的提高。     

Pd(OAc)_2/P(t-Bu)_3催化合成空穴传输材料APB的研究

以二苯基联苯二胺(DPB)和9-溴蒽为原料,在叔丁醇钠强碱环境下,以Pd(OAc)2/P(t-Bu)3为催化剂合成了新型空穴传输材料N,N’-二苯基-N,N’-二蒽基-1,1’-联苯-4,4’-二胺(APB)。得到优化的催化反应条件为:以二甲苯为溶剂在130~138℃回流反应3 h,Pd(OAc)2∶P(t-Bu)3=1∶1.2(摩尔比),P(t-Bu)3/9-溴蒽=0.24%;经元素分析、GC-MS、1H NMR等表征了结构;差示扫描量热仪(DSC)分析结果显示其熔点为324℃,具有良好的热稳定性。     

Pt/Au(111)表面合金电化学稳定性的第一性原理研究

利用密度泛函理论(DFT)对Pt/Au (111)表面合金的电化学稳定性进行了初步研究。形成能计算结果表明,Au与Pt不易在块体中形成合金,但能在Pt (111)面形成表面合金。溶解电位计算结果进一步表明,Pt/Au (111)面上Pt原子的溶解电位与其第一近邻Au原子数有很好的线性关系,而Au对第二近邻及更远近邻的Pt溶解电位的影响可忽略。这些结果意味着可建立表面配位环境与表面原子溶解电位间的标度关系,为揭示表面合金的结构-电化学稳定性构型关系奠定了基础。     

The adsorption of methyl nitrite on the Au(111) surface

The interaction of the methyl nitrite molecule (CH₃ONO) with the gold(111) surface has been studied by means of density functional calculations. The perfect Au(111) surface has been represented by a rather large cluster model, Au₂₂, that was in turn used to extract information about the preferred adsorption geometry of the CH₃ONO species. Vibrational frequencies and adsorption energy are also reported. The calculated adsorption energies are 31.2 kJ/mol with respect to gas phase cis-conformer and 35.1 kJ/mol with respect to trans-methyl nitrite, very close to the experimental adsorption energy of 33.5 kJ/mol. From the analysis of vibrational frequencies of gas phase and adsorbed species it is concluded that only the cis-conformer is present at the Au(111) surface.     

钯/竹炭催化剂催化湿地松松香歧化反应研究

研究钯/竹炭(Pb/BC)催化剂对湿地松松香的歧化反应,确定了最佳反应条件,催化剂用量为原料松香质量的 0.4%,搅拌速率 500 r/min,反应温度 270℃,反应时间 3 h,此时湿地松香歧化松香脱氢枞酸达到 56% 以上,枞酸降到 2% 左右,但枞酸指标仍未达到国家标准(枞酸含量≤0.5%)。在其他条件相同,催化剂用量为 0.3% 的反应条件下,采用Pd/BC催化剂也可以催化马尾松松香进行歧化反应,马尾松歧化松香中的枞酸含量为 0.43%, 可以达到国家标准。     

Synthesis of methoxysilanes by the reaction of metallic silicon with methanol using copper(II) acetate as the catalyst

The reaction of methanol with silicon was studied using various copper compounds other than the halides. Copper(II) acetate and copper(I) oxide gave high silicon conversions (82%) though the selectivities for trimethoxysilane were low (<19%). The selectivity was appreciably improved by addition of a small amount of thiophene or propyl chloride to the methanol feed.     

Samarium doped ceria (SDC) synthesized by a metal triethanolamine complex decomposition method: Characterization and an ionic conductivity study

Samarium doped ceria (SDC) powders as solid electrolyte ceramics were successfully prepared via thermal decomposition of metal organic complexes containing triethanolamine (TEA) as a ligand. The SDC powders synthesized using various samarium doping contents were characterized by X-ray diffractometry, scanning electron microscopy, X-ray absorption spectroscopy, energy dispersive X-ray spectroscopy and Brunauer-Emmett-Teller (BET) analysis. The influences of samarium doping and the calcination temperature on the characteristics of the SDC materials were thoroughly investigated. An appropriate temperature for SDC powder calcination was identified by thermogravimetric analysis to be 600 °C. After sintering the calcined SDC powders at 1500 °C to obtain highly dense ceramic pellets, the electrical conductivity of the materials was examined by impedance spectroscopy. The influence of percentage of Sm³⁺ dopants in SDC materials on the observed conductivity were explained by correlating with the detailed analysis of the local structure and environment of Sm³⁺ within the SDC materials by using X-ray absorption spectroscopy. The conductivities of the SDC products reported in this work indicate that they are promising candidates for solid electrolytes in solid oxide fuel cell applications.     

吡啶类缓蚀剂及其在Al(111)表面吸附行为的密度泛函理论分析

利用密度泛函理论方法研究了3种吡啶类缓蚀剂分子(吡啶、3-甲基吡啶和4-甲基吡啶)的反应活性及溶剂条件下在Al(111)表面的吸附行为。分子反应活性的量化计算结果表明,3种缓蚀剂分子的前线轨道均分布在吡啶环上,亲核和亲电活性中心均位于吡啶环的N原子上。分子与Al表面吸附的量化计算结果表明,3种分子均能与Al(111)面发生化学吸附,吸附强度顺序与实验测得的缓蚀效率顺序相一致,且缓蚀剂分子与Al(111)面的相互作用是由成键原子的轨道杂化所致。此外,3-甲基吡啶和4-甲基吡啶两个分子还能平行于Al(111)面发生物理吸附。     

WC含量对Ti(C,N)基金属陶瓷组织和性能的影响研究

用传统的粉末冶金方法制备了不同WC含量的超细Ti(C,N)基金属陶瓷试样,运用SEM,EDX等手段对材料的显微组织进行了表征分析,并用这些显微组织的特征和差异解释了材料宏观力学性能的特点.结果表明,金属陶瓷的组织为典型的两相结构特征,其中陶瓷相的芯、壳结构(core/timstructure)与溶解析出机制有关.少量WC的加入能提高材料的力学性能.断口SEM分析表明:断裂机理为典型的混合型断裂(穿晶断裂和沿晶断裂),金属相存在着明显撕裂的痕迹.     

Mechanism of hydrogen adsorption/absorption at thin Pd layers on Au(1 1 1)

Hydrogen adsorption and absorption at thin palladium deposits of 0.8-10 monolayers (ML) on Au(1 1 1) was studied in 0.1 M H₂SO₄ and HClO₄ using cyclic voltammetry, ac voltammetry, and impedance spectroscopy in the absence and in the presence of poison, crystal violet. Hydrogen adsorption on palladium is more reversible in sulfuric acid than in perchloric acid but it occurs at potentials 30 mV more positive in latter. The charge-transfer resistance exhibits a minimum at ∼0.27 V versus RHE and decreases with increasing in Pd deposit thickness in both acids. Adsorption capacitance at 0.8 ML Pd reaches maximum at the same potential. At other deposits the pseudo-capacitance starts to increase at lower overpotentials indicating the beginning of absorption, even at 2 ML Pd. The double layer capacitance is similar for all the deposits in sulfuric acid and it has a sharp maximum at 0.27 V versus RHE. In perchloric acid a broad maximum is observed. Crystal violet inhibits hydrogen adsorption but makes hydrogen absorption more reversible. The results suggest a fast direct hydrogen absorption mechanism that proceeds in parallel with slower hydrogen adsorption and indirect absorption.     

Effect of feed composition on PHB production from methanol by HCDC of Methylobacterium extorquens (DSMZ 1340)

BACKGROUND: Poly‐β‐hydroxybutyrate (PHB), produced by several species of bacteria, has attracted great attention as a biodegradable and biocompatible compound with similar properties to polypropylene. Unfortunately, its use is currently limited due to high production costs. One of the most common methods for overcoming this constraint is the use of inexpensive substrates, like methanol, in high cell density cultivations (HCDC). RESULTS: Fermentation was carried out with optimized feed composition (639 g l^?1 methanol, 4 g l^?1 MgSO₄.7H₂O, 41 mL L^?1 trace elements, 5.6 g L^?1 NaH₂PO₄.H₂O and 24.3 g L^?1 K₂HPO₄) and a feeding strategy based on the detection of substrate limitation by dissolved oxygen (DO). After 35 h, at which dry cell weight (DCW) reached a value of 70 g L^?1, PHB production was stimulated, and biomass and PHB productivities of 2.8 and 0.98 g L^?1 h^?1 were obtained, respectively. These results surpassed those reported in the literature for PHB production from methanol by Methylobacterium species. CONCLUSION: The proposed feed composition and feeding strategy for PHB production from methanol by Methylobacterium extorquens 1340 in fed‐batch cultivation resulted in high biomass and PHB productivity. They can be implemented for recombinant bioproducts (proteins) produced by M. extorquens due to the lack of PHB accumulation in the growth phase. Copyright © 2009 Society of Chemical Industry