CeO2担载Cu纳米粒子电催化CO2还原产乙烯：CeO2不同暴露晶面对催化性能的影响

Fossil fuels are expected to be the major source of energy for the next few decades. However, combustion of nonrenewable resources leads to the release of large quantities of CO₂, the primary greenhouse gas. Notably, the concentration of CO₂ in the atmosphere is increasing annually at an astounding rate. Electrochemical CO₂ reduction (ECR) to value-added fuels and chemicals using electricity from intermittent renewable energy sources is a carbon-neutral method to alleviate anthropogenic CO₂ emissions. Despite the steady progress in the selective generation of C₁ products (CO and formic acid), the production of multi-carbon species still suffers from low selectivity and efficiency. As an ECR product, ethylene (C₂H₄) has a higher energy density than do C₁ species and is an important industrial feedstock in high demand. However, the conversion of CO₂ to C₂H₄ is plagued by low productivity and large overpotential, in addition to the severe competing hydrogen evolution reaction (HER) during the ECR. To address these issues, the design and development of advanced electrocatalysts are critical. Here, we demonstrate fine-tuning of ECR to C₂H₄ by taking advantage of the prominent interaction of Cu with shape-controlled CeO₂ nanocrystals, that is, cubes, rods, and octahedra predominantly covered with (100), (110), and (111) surfaces, respectively. We found that the selectivity and activity of the ECR depended strongly on the exposed crystal facets of CeO₂. The overall ECR Faradaic efficiency (FE) over Cu/CeO₂(110) (FE ≈ 56.7%) surpassed that of both Cu/CeO₂(100) (FE ≈ 51.5%) and Cu/CeO₂(111) (FE ≈ 48.4%) in 0.1 mol·L^-1 KHCO₃ solutions with an H-type cell. This was in stark contrast to the exclusive occurrence of the HER over pure carbon paper, CeO₂(100), CeO₂(110), and CeO₂(111). In particular, the FE toward C₂H₄ formation and the partial current density increased in the sequence Cu/CeO₂(111) < Cu/CeO₂(100) < Cu/CeO₂(110) within applied bias potentials from -1.00 to -1.15 V (vs. the reversible hydrogen electrode), reaching 39.1% over Cu/CeO₂(110) at a mild overpotential (1.13 V). The corresponding values for Cu/CeO₂(100) and Cu/CeO₂(111) were FE_C2H4 ≈ 31.8% and FE_C2H4 ≈ 29.6%, respectively. The C₂H₄ selectivity was comparable to that of many reported Cu-based electrocatalysts at similar overpotentials. Furthermore, the FE for C₂H₄ remained stable even after 6 h of continuous electrolysis. The superior ECR activity of Cu/CeO₂(110) to yield C₂H₄ was attributed to the metastable (110) surface, which not only promoted the effective adsorption of CO₂ but also remarkably stabilized Cu⁺, thereby boosting the ECR to produce C₂H₄. This work offers an alternative strategy to enhance the ECR efficiency by crystal facet engineering.     

Synthesis, structure, and complexation of a large 28-mer macrocycle containing two binding sites for either anions or metal ions

The "one-pot" synthesis and characterization of a large 28-mer macrocycle (H(4)L(2)) with oxamido units capable of complexing guest ions through oxygen or nitrogen donor atoms is reported. Single-crystal structure determination of H(8)L(2)(NO(3))(4) and (Cu(2)[H(2)L(2)](H(2)O)(2))(NO(3))(2) demonstrated that the macrocycle contains two sites capable of complexing two nitrate anions or two copper(II) ions, involving a large structural reorganization in the conformation of the macrocyclic framework on coordination of the copper(II) ions when compared to the nitrate. Electrochemical and magnetic susceptibility measurements on the dinuclear Cu(II) complex and the related mononuclear and trinuclear Cu(II) complexes derived from the related 14-mer macrocycle were carried out and illustrate the role of the oxamido groups in mediating metal-metal interaction and delocalization.     

An electron diffraction determination of the molecular structures of silyl- and germyl-manganese pentacarbonyl in the gas phase

The molecular structures of the title compounds have been determined by gas phase electron diffraction methods. The SiMn and GeMn bond lengths are 240.7 ? 0.5 and 248.7 ? 0.2 pm respectively and the CMnC angles in the silyl and germyl cases are 94.5 ± 2° and 97 ± 2° respectively. Comparisons are made with the reported structure of CH₃Mn(CO)₅ and He^I photoelectron spectra of these compounds in an attempt to determine the extent of d → d π-bonding in the SiMn or GeMn bonds.     

Platination of [3-X-7,8-Ph2-7,8-nido-C2B9H8] (X=Et, F): Synthesis and characterisation of slipped and 1,2→1,7 isomerised products

The reaction of the labelled carborane ligand [3-Et-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ with a source of {Pt(PMe₂Ph)₂}²⁺ affords non-isomerised 1,2-Ph₂-3,3-(PMe₂Ph)₂-6-Et-3,1,2-closo-PtC₂B₉H₈ (1). The analogous reaction between [3-F-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ and {Pt(PMe₂Ph)₂}²⁺ yields 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-F-2,1,8-closo-PtC₂B₉H₈ (3). Compound 1 has a heavily slipped structure (Δ 0.72 Å), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-Et-2,1,8-closo-PtC₂B₉H₈ (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB₂ face of an intermediate based on the structure of 1. Compounds 1–3 were characterised by a combination of spectroscopic and crystallographic techniques.     

次级键与晶体中锑(III)螯合物配位多面体研究

考虑立体活性孤对电子附近次级键配位原子的贡献, 对文献报道的三十个氨基多羧酸锑(III)螯合物的晶体结构中配位多面体描述进行了全面的修正. 配位多面体的几何构型指定采用了单位球内截多面体的两面角判据及其相关的ANVPDA程序. 所有配位多面体几何构型的修正均得到了键价计算的有力支持.     

Bis(cyclopentadienyl)titanium complexes of naphthalene-1,8-dithiolates, biphenyl 2,2'-dithiolates, and related ligands

Titanocene 1,8-dithiolato-naphthalene and titanocene 2,2'-dithiolato biphenyl are produced by the reaction of naphtho[1,8-cd]-1,2-dithiole [or the biphenyl] with titanocene dicarbonyl (Ti(II)) in toluene at room temperature. The pro-ligands 2,7-di(tert-butyl)naphtho[1,8-cd]-1,2-dithiole, 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole, 4,5-dithioacephenanthrylene, and 13,14-dithiapicene have been used in similar reactions with titanocene dicarbonyl to investigate the effect of steric bulk and of varying the naphthalene backbone on the final complex. The resulting Cp(2)TiS(2)Ar complexes (Ar = naphthalene) have been shown by temperature-dependent (1)H NMR spectroscopy to exist in solution in an envelope conformation with the six-membered TiS(2)C(3) rings undergoing inversion on the NMR time scale while the similar Cp(2)TiS(2)Ar complexes (Ar = biphenyl, binaphthalene) interconvert more rapidly. Titanocene 2,2'-disulfinato biphenyl has been synthesized by the salt elimination reaction of titanocene dichloride (Ti(IV)) and the disodium salt of biphenyl 2,2'-disulfinic acid. Finally, the effect of using pro-ligands where the sulfur atoms have been mono- or di-oxidized has been studied, and an interesting oxygen elimination reaction is observed for the S=O fragments but not for the SO(2) groups. All complexes have been characterized spectroscopically and seven X-ray structures are reported.     

Polymerization by alkaline earth metal compounds—I. Studies on the polymerization of methylmethacrylate by triphenylmethyl metal derivatives and related compounds of calcium,strontium and barium

A series of related organo-alkaline earth metal compounds of formula (Ph₃C)MX(THF)_η, (M = Ca, Sr, Ba; X = Cl: M = Ca, Sr; X = Br: M = Ba; X = CPh₃), has been isolated and characterized using analytical and spectroscopic techniques. The polymerization of methylmethacrylate (MMA) has been studied using these organometallic compounds as initiators. Investigations of the tacticity variations of polymethylmethacrylate (PMMA) produced in 1,2-dimethoxyethane or tetrahydrofuran (THF) at 210 K have shown that the syndiotacticity is higher in the former solvent, decreases with the following changes in initiator composition: Ca > Sr ? Ba; Cl > Br; in THF, it is dependent on the monomer concentration. The molecular weight distributions of the PMMA samples are broad and have distinct bi- or poly-modal features. The polymerization process appears to be anionic in nature but the evidence suggests that more than one type of propagation occurs and mechanistic aspects are discussed. Polymerization of bulk MMA by these same initiators is also reported. The initiators RMX(THF)_n (M = Sr, R = Me, n = 3 or R = Et, n = 2) and (C₃H₅)SrBr(THF)₂ are shown to be inefficient for polymerization of MMA. The glass transition temperatures of a range of PMMA samples of differing tacticity are presented and discussed.     

A stratospheric chemical reaction controlling climatic change

It has been established from geological studies that change in the atmospheric content of carbon dioxide gas commenced about one hundred million years ago. The likely origin of this change is advanced as being the onset of the Brewer circulation caused by the rise in terrain induced by tectonic plate movement. It is demonstrated that tectonic plate movement can be affected by impacts from external bodies which penetrate the crust of the Earth. The consequences of the change in atmospheric concentration of carbon dioxide are proposed as first, extinctions and reductions in animal numbers, including primates, as a result of changes in body chemistry of these animals and second, a change in the rate of weathering of rocks giving rise to changes in the availability of chemicals such as calcium and potassium which are essential for plant and animal life. This latter change contributing to the extinctions and reductions in animal numbers. It is shown that the change in weathering can account for the rise to dominance of angiosperm plants. It is concluded that there were several simultaneous evolutionary environments on Earth which were a function of altitude which gave rise to a vertical variation in atmospheric content of carbon dioxide. This variation disappeared with rise of terrain and the onset of the Brewer circulation. Such changes are advanced and being much more important than any changes in temperature caused by greenhouse effects since the disappearance of atmospheric variations in carbon dioxide allowed animal migration. It is demonstrated that the conditions of extinction could be reintroduced by human activities.     

Chloroplast Biogenesis 77: Two Novel Monovinyl and Divinyl Light-Dark Greening Groups of Plants and Their Relationship to the Chlorophyll a Biosynthetic Heterogeneity of Green Plants

Abstract— On the basis of the steady-state accumulation of divinyl (DV) or monovinyl (MV) protochlorophyllide (Pchlide) a in darkness (D) or in the light (L), green plants have been classified into three different greening groups namely dark divinyl-light divinyl (DDV-LDV), dark monovinyl-light divinyl (DMV-LDV) and dark monovinyl-light monovinyl (DMV-LMV) (Ionannides et al., Biochem. Syst. Ecol. 22, 211-220,1994). Interruption of the L phase of the photoperiod by a brief period of darkness (LD condition) revealed a predominance of different chlorophyll (Chl) a biosynthetic routes, depending upon the greening group affiliation of the plant species. For example, in DMV-LDV and DMV-LMV plants, the predominant Chl a biosynthetic routes under the LD condition appear to be the MV Chi a biosynthetic route and/or a mixed DV-MV Chi a biosynthetic route that bifurcates at the level of DV Pchlide a. On the basis of DV and MV Pchlide a accumulation rates after re-darkening, this greening group is designated as a light-dark MV (LDMV) subgroup. In DDV-LDV plants, the predominant LD Chi a biosynthetic routes appear to be the DV Chi a biosynthetic route and/or a mixed DV-MV Chi a biosynthetic route that bifurcates at the level of DV Chlide a. This greening group is designated as a light-dark DV (LDDV) subgroup. It is proposed that upon inhibiting the conversion of Pchlide a to Chi a by interruption of the L phase of the photoperiod by a brief period of D, the rates of DV and MV Pchlide a regeneration may reflect the carryover rates of DV and MV Pchlide a biosynthesis in L instead of reflecting a differential use of DV and MV carboxylic biosynthetic rates in D. It is also shown that in LDMV plants, MV Chlide a and MV Chi a are formed without the participation of [4-vinyl] Chlide a reductase. On the basis of recently published evidence, it is also argued that Pchlide oxidoreductase-A (POR-A) may be active in LDDV plants, while POR-B may predominate in LDMV plant species. The evolutionary significance of the LDDV and LDMV greening subgroups is discussed.