Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO₂ emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO₂ by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO₂ with H₂ was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO₂ reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH₄ formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H₂O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions.     

光学活性Ugi胺的简便合成方法

本试验报道了一种可公斤级制备光学活性Ugi胺的方法。以课题组自制的手性二茂铁PNN配体(L1或L2)与贵金属Ir组成的复合物为催化剂CAT-1或CAT-2,叔丁醇锂为碱,异丙醇为溶剂,促进乙酰二茂铁的不对称氢化,分别以高收率、高立体选择性得到(S)-或(R)-1-二茂铁基乙醇;再经过简单的酯化、二甲胺取代,即可公斤级制备(S)-和(R)-Ugi胺,ee值高达99.2%,具有工业化应用前景。     

A synthesis of [14C]formamidine acetate

The one-step synthesis of [¹⁴C]formamidine acetate from [¹⁴C]barium cyanamide is described with product characterization by TLC and proton NMR.     

不对称氢化、氢转移反应制备(R)-邻氯扁桃酸甲酯：(S)-氯吡格雷关键中间体的不对称合成

目的 用不对称氢化、氢转移方法制备合成(S)-氯吡格雷的关键中间体——(R)-邻氯扁桃酸甲酯。方法 以α-邻氯扁桃酮酸甲酯为起始原料,分别用不对称氢化和氢转移方法制备(R)-邻氯扁桃酸甲酯。结果与结论 使用不对称氢化方法制备(R)-邻氯扁桃酸甲酯,对映选择性为64.8% ,用氢转移方法,优化催化条件后目标产物的ee值高达92.6%,从而为(S)-氯吡格雷的不对称合成奠定了基础。     

姜酮的超声波法合成

姜酮(zingerone,1),化学名为4-(4-羟基-3-甲氧基苯基)丁酮,是抗炎药6-姜酚(gingerol)~([1])的重要中间体,也是一种新型香料,可用于食品、饮料及化妆品行业~[2].天然的1主要存在于生姜的提取物姜油中,但含量甚微,且不易提纯.工业合成大多以香兰素(2)为原料,与丙酮缩合制得脱氢姜酮(3),3再经Pd/C或Raney-Ni催化氢化得1~([1,3,4]),反应时间长(制备3需24 h,还原3需9 h),操作要求高.     

Chemical storage of hydrogen in few-layer graphene

Birch reduction of few-layer graphene samples gives rise to hydrogenated samples containing up to 5 wt % of hydrogen. Spectroscopic studies reveal the presence of sp³ C-H bonds in the hydrogenated graphenes. They, however, decompose readily on heating to 500 °C or on irradiation with UV or laser radiation releasing all the hydrogen, thereby demonstrating the possible use of few-layer graphene for chemical storage of hydrogen. First-principles calculations throw light on the mechanism of dehydrogenation that appears to involve a significant reconstruction and relaxation of the lattice.     

Essential oils from Schinus terebinthifolius leaves – chemical composition and in vitro cytotoxicity evaluation

Context: In folk medicine, Schinus terebinthifolius Raddi (Anacardiaceae), has been used as a remedy for ulcers, respiratory problems, wounds, rheumatism, gout, diarrhea, skin ailments and arthritis, as well as to treat tumors and leprosy.

Objective: To investigate the chemical composition and cytotoxicity of essential oil from leaves of S. terebinthifolius as well as the identification of active compounds from this oil.

Material and methods: Essential oil from S. terebinthifolius leaves, obtained by hydrodistillation using a Clevenger-type apparatus, was characterized in terms of its chemical composition. Also, the crude oil was subjected to chromatographic separation procedures to afford an active fraction composed of α- and β-pinenes. These compounds, including hydrogenation (pinane) and epoxydation (α-pinene oxide) derivatives from α-pinene, were tested in vitro against murine melanoma cell line (B16F10-Nex2) and human melanoma (A2058), breast adenocarcinoma (MCF7), leukemia (human leukemia (HL-60) and cervical carcinoma (HeLa) cell lines.

Results: Forty-nine constituents were identified in the oil (97.9% of the total), with germacrene D (23.7%), bicyclogermacrene (15.0%), β-pinene (9.1%) and β-longipinene (8.1%) as the main compounds. The crude essential oil showed cytotoxic effects in several cell lines, mainly on leukemia and human cervical carcinoma. Fractions composed mainly of α- and β-pinenes as well as those composed of individually pinenes showed effective activities against all tested cell lines. Aiming to determinate preliminary structure/activity relationships, α-pinene was subjected to epoxydation and hydrogenation procedures whose obtained α-pinene oxide showed an expressive depression in its cytotoxicity effect, similar as observed to pinane derivative.

Discussion and conclusion: The obtained results indicated that the monoterpenes α- and β-pinenes could be responsible to the cytotoxic activity detected in the crude oil from leaves of S. terebinthifolius. In addition, it was possibly inferred that the presence of double bond in their structures, mainly at endocyclic position, is crucial to cytotoxic potential detected in these derivatives.     

萘普生拆分试剂葡辛胺的制备

目的：制备萘普生拆分试剂葡辛胺。方法：采用葡萄糖与正辛胺原位催化加氢制备的正交试验。结果与结论：通过五因素和五水平的正交试验表明，最佳的催化反应条件是：添加剂三乙胺用量0．5m1、反应温度60℃、反应氢压1．5MPa、催化剂用量0．7g，在60ml乙醇中，37．2mmolD—葡萄糖和31mmol正辛胺反应6h，葡辛胺的产率可达53．9％。     

醋酸乙酯加氢制乙醇气液固三相反应过程

采用Cu-ZnO/Al₂O₃催化剂,在高压搅拌釜中进行了醋酸乙酯加氢制乙醇气液固三相反应过程的研究,考察了溶剂效应、内外扩散和反应条件对醋酸乙酯转化率和乙醇选择性的影响。实验结果表明,醋酸乙酯在四乙二醇二甲醚溶剂中的转化率要高于在液体石蜡介质中的转化率。以四乙二醇二甲醚为溶剂,当催化剂粒径小于120 μm,搅拌转速大于800 r/min时,反应的内外扩散阻力可忽略;在最佳的反应条件（温度250℃,压力5.0 MPa,醋酸乙酯液时空速1.0 h^-1,氢气与醋酸乙酯的物质的量之比（氢酯比）10：1,搅拌转速800 r/min）下,醋酸乙酯的转化率为83.5%,乙醇的选择性为96.5%。在醋酸乙酯加氢制乙醇反应中引入液相介质,能够较好地解决气固相反应中催化剂床层的移热问题,且能有效降低反应的氢酯比。     

Reversible catalytic dehydrogenation of alcohols for energy storage

Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.Hydrogenation and dehydrogenation reactions are fundamental in synthetic organic chemistry and used in a variety of large- and small-scale processes for manufacturing chemicals, pharmaceuticals, foods, and fuels. An increased need for energy storage technologies, in large part because of the recent deployment of intermittent renewable energy sources, has generated a renewed interest in hydrogen as a form of chemical energy storage. Hydrogen, which may be used in fuel cells or internal combustion engines, is best-suited for longer-term energy storage and can be stored in the form of a compressed gas or a cryogenic liquid or chemically bonded in hydrides (1). The most attractive hydrogen storage media are liquid organic hydrogen carriers (LOHCs), because they have relatively high hydrogen content and can be transported and distributed using the existing liquid fuel infrastructure (2–5).Two strategies for coupling the chemical energy stored in these LOHCs with an energy storage device include thermal dehydrogenation to provide H₂(g) for a polymer electrolyte membrane (PEM) fuel cell (expression 1) (6) and electrochemical dehydrogenation to yield protons and electrons in a direct alcohol fuel cell (expressions 2 and 3) (2, 7). In the former (acceptorless strategy), hydrogen release from LOHCs frequently requires high reaction temperatures and expensive platinum group metal (PGM) catalysts. Regeneration of the hydrogen-depleted compounds can be achieved with both PGM and less expensive non-PGM catalysts (e.g., nickel-based); however, elevated hydrogen pressures are needed (8, 9). The latter was the basis for an Energy Frontier Research Center around Electrocatalysis, Transport Phenomena, and Materials for Innovative Energy Storage funded by the Department of Energy (Acknowledgments), which assumed the use of a single electrocatalyst for dehydrogenation and hydrogenation of LOHCs that would also simplify the conventional hydrogen storage process (10). The envisioned partial electrochemical dehydrogenation of LOHCs typically involves expensive PGM catalysts (11–18), with weak bases to serve as proton scavengers in lieu of a proton exchange membrane. Reversing the applied potential in the presence of these same components provides a mechanism for regenerating the LOHCs without the need for elevated hydrogen pressure:LH_n ? L + n/2?H₂, [1]LH_n ? L + n?H⁺ + n?e^?, [2]andn/2?O₂ + n?H⁺ + n?e^? ? n/2?H₂O.[3]A thermodynamic analysis of a variety of potential LOHCs showed that cyclic hydrocarbons exhibit high hydrogen contents but that nitrogen heterocycles exhibit lower reaction enthalpies (9, 10). Nitrogen heterocycles are also more practical, because they display energy densities that are comparable with those of liquid hydrogen, and the theoretical open cell potentials of these materials are calculated to be close to or exceed the potential of the hydrogen–oxygen fuel cell (11). In addition, the overpotential of their electrooxidation is also smaller compared with cyclic hydrocarbons (12). However, basic nitrogen heterocycles are not compatible with commonly used acidic proton exchange membranes because of the formation of a nonconductive salt. One alternative class of LOHCs that does not suffer from this problem is hydroxyl-containing compounds (e.g., alcohols and diols) that feature reasonable hydrogen content and low oxidation potentials. Both mono- and polysubstituted alcohols have been proposed as hydrogen storage materials (13) and used as fuel for direct alcohol fuel cells, usually in the form of an aqueous alkaline solution (14).Homogeneous catalysts for the acceptorless dehydrogenation of primary and secondary alcohols for the most part contain precious metals, such as Ru (19), Rh (20), and Ir (21). By comparison, the same reaction with nonprecious, earth-abundant metal catalysts is, so far, a relatively unexplored area in the literature. The first cobalt catalyst bearing a noninnocent bis(dicyclohexylphosphino)amine (PNP^Cy) ligand for acceptorless dehydrogenation of alcohols was reported by Hanson and coworkers (22, 23). Recently, Beller and coworkers (24) have shown hydrogen production from methanol in the presence of KOH with octahedral iron complexes (PNP^iPr)Fe(H)(CO)X [X = BH₄ (1) and X = Br (2)]. Remarkably, very low catalyst loadings (parts per million level) were used, and catalysis was performed at 91 °C, which suggests high thermal stability of these iron complexes and related intermediate species. However, Guan and coworkers (25) have accomplished ester hydrogenation using catalyst 1. In addition to these studies, it was recently shown that the same iron complexes can also efficiently catalyze the reversible dehydrogenation–hydrogenation of N-heterocycles (26). Yamaguchi et al. (27) have also reported Cp*Ir complexes with substituted pyridonate ligands that catalyze the reversible acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to quinoline in boiling xylene. Dehydrogenation is harder and routinely produced lower yields than hydrogenation, but with the 5-trifluoromethylpyridonate ligand, a quantitative yield was achieved in both directions (27). A computational analysis of the proposed catalytic cycle showed that two major pathways are possible: through a bifunctional species with coordinated pyridonate ligand or through a monomeric Cp*Ir(H)Cl complex (28).As part of our ongoing effort to develop another strategy, specifically electrocatalysts for reversible partial oxidation (dehydrogenation) of alcohol-based fuels, we concentrated on the possibility of converting a known dehydrogenation catalyst to an electrocatalyst through separation of protons and electrons. We regard separately extracting protons and electrons in a catalytic dehydrogenation reaction together with the microscopic reverse (29) (i.e., separately injecting protons and electrons to effect substrate hydrogenation) as fundamental in the development of a reversible alcohol dehydrogenation–hydrogenation electrocatalyst. It was clear at the outset that the possibility of oxidation of intermediate species containing metals in low-oxidation states during dehydrogenation and the competing proton reduction to H₂ in the reverse reaction substantially limited our selection of possible candidates. We recently reported electrocatalytic properties of an iridium amino-olefin complex [Ir(trop₂DACH)][OTf], which is capable of catalyzing alcohol dehydrogenation with chemical oxidants as well as electrocatalytic dehydrogenation of primary alcohols with excellent faradaic efficiency (30). Two catalytic systems capable of oxidizing alcohols with a chemical oxidant (ferrocenium cation) in the presence of a base as a proton acceptor have been very recently described in literature (30, 31).In this report, we describe catalytic systems that address both strategies outlined above as part of a unified effort to develop catalysts for reversible dehydrogenation of organic fuels in energy generation and storage reactions. These catalysts show reversible acceptorless (expression 1) and partial oxidative (expression 2) dehydrogenation of alcohols using non-PGM (iron-based) and PGM (iridium-based) catalysts, respectively.