The effect of electrochemically treated glassy carbon on the activity of supported Pt catalyst in methanol oxidation

Effect of electrochemical oxidation of glassy carbon on deposition of platinum particles and electrocatalytic activity of platinum supported on oxidized glassy carbon (Pt/GC_OX) were studied for methanol oxidation in H₂SO₄ solution. Platinum was potentiostatically deposited from H₂SO₄ + H₂PtCl₆ solution. Glassy carbon was anodically polarised in 0.5 M H₂SO₄ at 2.25 V vs. saturated calomel electrode (SCE) during 35 s. Electrochemical treatment of GC support, affecting not significantly the real Pt surface area, leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GC_OX electrode for methanol oxidation is larger than polycrystalline Pt and for more than one order of magnitude larger than Pt/GC electrode. This increase in activity indicates the pronounced role of organic residues of GC support on the properties of Pt particles deposited on glassy carbon.     

<Emphasis Type="Italic">o</Emphasis>-Phenylenediamine as a New Catalyst in the Highly Regioselective Conversion of Epoxides to Halohydrins with Elemental Halogens

Summary. The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]⁺·I₅^– is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon.     

A new kind of organophosphorus compounds as an efficient catalyst for asymmetric C-C bond formation reactions

A new class of chiral pyrrolidine-phosphite organocatalysts, available from commercially starting materials, has been synthesized and shown to be good catalytic activity for asymmetric Michael and Aldol reactions. The reactions proceeded to give the products in good yield and in a highly selective manner. Ionic liquid [Bmim][BF₄] as an efficient green solvent has been employed in the Michael addition.     

An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes

With the world’s focus on rapidly deploying second generation biofuels technologies, there exists today a good deal of interest in how yields, economics, and environmental impacts of the various conversion processes of lignocellulosic biomass to transportation fuels compare. Although there is a good deal of information regarding these conversion processes, this information is typically very difficult to use on a comparison basis because different underlying assumptions, such as feedstock costs, plant size, co-product credits or assumed state of technology, have been utilized. In this study, a rigorous comparison of different biomass to transportation fuels conversion processes was performed with standard underlying economic and environmental assumptions so that exact comparisons can be made. This study looked at promising second-generation conversion processes utilizing biochemical and thermochemical gasification technologies on both a current and an achievable state of technology in 2012. The fundamental finding of this study is that although the biochemical and thermochemical processes to ethanol analyzed have their individual strengths and weaknesses, the two processes have very comparable yields, economics, and environmental impacts. Hence, this study concludes that based on this analysis there is not a distinct economic or environmental impact difference between biochemical and thermochemical gasification processes for second generation ethanol production.     

乙酸稀土盐催化缩聚合成聚(对苯二甲酸乙二酯-co-己二酸乙二酯)

合成了一系列乙酸稀土盐(乙酸钇,乙酸镧,乙酸钕,乙酸镝),作为单组分催化剂,采用熔融缩聚法催化对苯二甲酸二甲酯、乙二醇和1,6-己二酸的共缩聚反应,制备了芳香族脂肪族共聚酯——聚(对苯二甲酸乙二酯-co-己二酸乙二酯)(PETA).通过1H-NMR,SEC,DSC及力学性能测试表征了聚合物的序列结构,分子量及分布,热性能及机械性能.结果表明,乙酸稀土盐单组分可催化共缩聚反应,效果优良,能够合成高分子量和较窄分子量分布的共聚酯,共聚酯具有较高的拉伸强度和断裂伸长率.     

乙醇在钯电极上的电氧化机理

利用循环伏安与现场傅里叶变换红外(FTIR)光谱对乙醇在Pd电极上的电氧化机理进行了研究. 循环伏安测量表明, 乙醇在Pd上氧化的性能受pH值与乙醇浓度的影响. 当溶液pH>11.0时, Pd对乙醇才具有催化性能, 而且乙醇在Pd上氧化的性能随着pH值和乙醇浓度的增加而提高. 现场红外光谱电化学测量结果证明, 乙醇在不同pH 溶液中的氧化反应机理和产物不同. 当溶液pH>13.0 时, 产物只有乙酸盐, 说明乙醇仅发生部分氧化, 乙醇中的C—C键没有断裂. 当溶液pH≤13.0时, 尽管乙醇在Pd电极上的氧化活性受到抑制, 却发生完全氧化而产生二氧化碳, 说明乙醇的C—C键在低碱环境中容易断裂, 最后乙醇被完全氧化. 实验中没有检测到CO, 表明该反应途径是一个非毒化过程.     

SBA-15介孔分子筛担载的钒基氧化物催化剂对乙烷选择氧化性能

用等体积浸渍法制备了SBA-15担载的钒基(V/SBA-15)和钾修饰的钒基氧化物(K-V/SBA-15)催化剂, 使用氮气吸附、小角X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis DRS)和紫外激光拉曼光谱对这些催化剂的结构进行表征, 并评价了这些催化剂对乙烷选择氧化的活性与选择性. 实验结果表明介孔结构SBA-15对乙烷选择氧化的活性优于常规的SiO2; 对于SBA-15担载的V/SBA-15和K-V/SBA-15催化剂, 极低钒担载量(nV:nSi≤0.1:100)时隔离的四配位钒氧化物是乙烷选择氧化生成醛类化合物的活性物种, 高钒担载量(nV:nSi≥2.5:100)时聚合的和微晶态的钒氧化物是乙烷氧化脱氢或深度氧化的活性物种.     

Production of valuable hydrocarbons by catalytic degradation of a mixture of post-consumer plastic waste in a fluidized-bed reactor

A mixture of post-consumer plastic waste (PE/PP/PS/PVC) was pyrolyzed over various catalysts using a fluid catalytic cracking (FCC) process operating isothermally at ambient pressure. Experiments with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A model based on kinetic and mechanistic schemes for the observed products associated with chemical reactions and catalyst deactivation has been developed. The model gives a good representation of experimental results. It is also an improvement on the currently available empirical “lumping” techniques which are usually severely restricted in terms of product definitions. Additionally, this model represents the benefits of product selectivity for the chemical composition in relation to the effect of structurally different catalyst types, and the performance of the reaction temperature used as well as the particle size of the catalyst selected.     

低含量高活性负载镍催化剂的制备及其加氢反应研究

以羰基镍为源, 制备了一系列高活性低含量负载镍催化剂. 采用BET、 XRD、 AAS和SEM等对催化剂进行表征. 以苯乙烯选择性加氢为探针反应, 考察了催化剂制备方法、镍含量、溶剂和反应温度、压力、时间对反应结果的影响. 结果表明, 用羰基镍制备的含镍为1%～5%的催化剂对苯乙烯的选择性加氢生成乙苯有很高的反应活性, 苯乙烯转化率和乙苯选择性分别达到了98%和99%以上.     

‘Click’ silica immobilisation of metallo-porphyrin complexes and their application in epoxidation catalysis

We present the synthesis, via Adler condensation reactions, of mono- and tetrakis-4-(ethynyl-phenyl)porphyrin ligands and the zinc and manganese complexes thereof. The formed complexes were immobilised on silica by reacting the ethynyl groups with azide-functionalised silica in a copper(I) catalysed Huisgens 1,3-dipolar cycloaddition reaction. The synthesised metallo-porphyrin containing materials were thoroughly characterised using various solid-state techniques (NMR, IR, UV-Vis, elemental content analysis). The manganese containing materials were applied as catalysts in the epoxidation of various alkenes (cyclooctene, cyclohexene, styrene) with various oxidants (iodosylbenzene, tert-butylperoxide). The heterogenised homogeneous catalysts show diminished activity and yields compared to the analogous homogeneous catalysts (71% yield cf. 92% for cyclooctene epoxidation, TOF 82 h⁻¹ cf. 230 h⁻¹). Upon recycling, the heterogenised catalysts become gradually less active over five cycles until they are catalytically inactive. The deactivation process is discussed, with spectroscopy suggesting that the catalysts themselves are intact and thus stable to the reaction conditions and recycling, however there is likely some decomplexation, and also both chemical and mechanical decomposition of the silica support resulting in inaccessibility to the catalytic site.