Photoinduced Electron‐Transfer Oxidation of Olefins with Molecular Oxygen Sensitized by Tetrasubstituted Dimethoxybenzenes: A Non‐Singlet‐Oxygen Mechanism

α‐Methylstyrene ( 1 ) was photo‐oxidized in the presence of a series of alkylated dimethoxybenzenes as sensitizers in an oxygen‐saturated MeCN solution to afford the cleaved ketone 2 , epoxide 3 , as well as a small amount of the ene product 4 in ca. 1 : 1 : 0.04 ratio. The relative rate of conversion was well‐correlated with the fluorescence quantum yield of sensitizers. Thus, a non‐singlet‐oxygen mechanism is proposed, in which an excited sensitizer is quenched by (ground‐state) molecular oxygen to produce a sensitizer radical cation and a superoxide ion (O), the former of which oxidizes the substrate, while the latter reacts with the resulting olefin radical cation ( 1 ^{+ .}) to give the major oxidation products. Photodurability of such electron‐donating sensitizers is dramatically improved by substituting four aromatic H‐atoms in 1,4‐dimethoxybenzene with Me or fused alkyl groups, which provides us with an environmentally friendly, clean method of photochemical functionalization with molecular oxygen, alternative to the ene reaction via singlet oxygenation.     

固载化阳离子金属卟啉/杂多阴离子复合催化剂在分子氧氧化乙苯过程中的催化特性

以交联聚苯乙烯微球(CPS)为基质载体, 采用同步合成与固载的方法, 简捷地制得了固载化阳离子苯基卟啉, 继而通过与钴盐的配合反应, 制备了固载化阳离子钴卟啉. 在此基础上, 以Keggin 型杂多酸磷钨酸(HPW)及磷钼酸(HPMo)为试剂, 凭借阳离子钴卟啉(CoP)与杂多阴离子之间的静电相互作用, 制备与表征了固载化的由阳离子钴卟啉与杂多阴离子复合而成的固体催化剂CoPPW-CPS和CoPPMo-CPS. 将两种复合催化剂用于分子氧氧化乙苯的氧化反应, 考察研究了催化特性. 结果表明: 在分子氧氧化乙苯的氧化反应中, 复合催化剂具有很高的催化活性, 可使乙苯高选择性地转化为苯乙酮, 反应12 h, 苯乙酮的产率达30.1%; 复合催化剂的催化活性比单纯的固载化钴卟啉高75%; CoPPW-CPS的催化活性高于CoPPMo-CPS. 在复合催化剂结构组分中, 固载化的杂多阴离子并无催化活性, 起催化作用的组分是钴卟啉; 但是, 杂多阴离子可有效保护钴卟啉, 使其免于被氧化失活, 从而使其保持稳定的高催化活性. 复合催化剂具有最适宜的投加量, 过量催化剂的加入, 会抑制钴卟啉的催化活性. 复合催化剂还具有良好的循环使用性能.     

Direct Observation of Oxygen Dissociation on Non‐Stoichiometric Metal Oxide Catalysts

Oxygen dissociation on metal oxides is a key reaction step, limiting the efficiency of numerous technologies. The complexity of the multi‐step oxygen reduction reaction (ORR) makes it difficult to investigate the oxygen dissociation step independently. Direct observation of the oxygen dissociation process is described, quantitatively, on perovskites La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ and (La_0.8Sr_0.2)_0.95MnO_3±δ, using gas‐phase isotope‐exchange with a 1:1 ¹⁶O₂:¹⁸O₂ ratio. Oxygen transport mechanisms between gas–surface reactions and surface–bulk exchange are deconvoluted. Our findings show that regardless of participation of lattice oxygen, La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ is better at oxygen dissociation than (La_0.8Sr_0.2)_0.95MnO_3±δ. Heteroexchange, involving lattice oxygen, dominates on La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ. In contrast, (La_0.8Sr_0.2)_0.95MnO_3±δ shows both homoexchange and heteroexchange, with the latter only happening above 600 °C. Using a 1:1 isotope mixture, a simple method is presented for separation of the oxygen dissociation step from the overall ORR.     

Bismuth‐Containing SBA‐15 Mesoporous Silica Catalysts for Solvent‐Free Liquid‐Phase Oxidation of Cyclohexane by Molecular Oxygen

Bismuth (Bi)‐containing SBA‐15 mesoporous silica catalysts, Bi/SBA‐15, with different Bi loadings were synthesized by a direct hydrothermal method. The materials were characterized in detail by various techniques. Powder‐X‐ray‐diffraction (PXRD), N₂‐adsorption/desorption, and transmission‐electron‐microscopic (TEM) analyses revealed that the well‐ordered hexagonal structure of SBA‐15 is maintained after Bi incorporation. Diffuse‐reflectance UV/VIS, Raman, and X‐ray photoelectron spectroscopy (XPS) showed that the incorporated Bi‐atoms are highly dispersed, most of them entering the internal surface of SBA‐15. The new, very stable catalysts were found to be highly efficient for the oxidation of cyclohexane in a solvent‐free system, molecular oxygen (O₂) being used as oxidant.     

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

The selective oxidation of propylene with O₂ to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu₂O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O₂: Cu₂O octahedra exposing {111} crystal planes are most selective for acrolein; Cu₂O cubes exposing {100} crystal planes are most selective for CO₂; Cu₂O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu₂O(111), three‐coordinated O on Cu₂O(110), and two‐coordinated O on Cu₂O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO₂, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.     

Regenerating Spent Solutions of Vanadium‐containing Heteropoly Acids in the Presence of Additives

Vanadium‐containing heteropoly acid solutions of Keggin H_3+xPMo_12–xV_xO₄₀ and modified H_aP_zMo_yV_xO_b types (P‐Mo‐V HPAs) are promising nanosized inorganic metal‐oxygen cluster compounds with the property of reversible oxidability (V^V ↔ V^IV). The oxidation of reduced P‐Mo‐V HPAs at a temperature of 130–170 °C and an oxygen pressure of 4 atm is a convenient method for their regeneration, but results in regeneration degree of only 75–88 %. Various materials with electron transfer or oxidative properties, such as nitrogen doped carbon nanofibers (N‐CNFs), Sibunit‐4, HNO₃, and MoO₂, were investigated as additives to facilitate and accelerate the regeneration of HPA solutions. Among the studied additives HNO₃ was found to show the best efficiency, resulting in regeneration degree of higher 95 %. Rapid and efficient regeneration of spent HPA catalysts is an important criterion for achieving high productivity and sustainability of oxidative processes on their basis.     

Complexes of Copper(I) with Dimercapto Compounds as Catalysts for Oxidation of Mercaptans and Hydrogen Sulfide with Molecular Oxygen in Aqueous Solutions

The conditions for formation of complexes of copper(I) with mercapto compounds in aqueous- alkaline solutions and the catalytic activity of these complexes in oxidation of mercaptans and hydrogen sulfide was studied. The kinetic characteristics of these catalysts were compared with those of catalysts based on cobalt phthalocyanines. A method was proposed for suppressing formation of the thiosulfate ion in oxidation of H₂S to elemental sulfur.     

Solvent‐Mediated Control of the Electrochemical Discharge Products of Non‐Aqueous Sodium–Oxygen Electrochemistry

The reduction of dioxygen in the presence of sodium cations can be tuned to give either sodium superoxide or sodium peroxide discharge products at the electrode surface. Control of the mechanistic direction of these processes may enhance the ability to tailor the energy density of sodium–oxygen batteries (NaO₂: 1071 Wh kg^?1 and Na₂O₂: 1505 Wh kg^?1). Through spectroelectrochemical analysis of a range of non‐aqueous solvents, we describe the dependence of these processes on the electrolyte solvent and subsequent interactions formed between Na⁺ and O₂^?. The solvents ability to form and remove [Na⁺‐O₂^?]_ads based on Gutmann donor number influences the final discharge product and mechanism of the cell. Utilizing surface‐enhanced Raman spectroscopy and electrochemical techniques, we demonstrate an analysis of the response of Na‐O₂ cell chemistry with sulfoxide, amide, ether, and nitrile electrolyte solvents.     

单取代杂多化合物在以分子氧为氧化剂的环己烯氧化反应中的催化作用

单取代杂多化合物在以分子氧为氧化剂的环己烯氧化反应中的催化作用秦笃捷,王国甲,吴越（吉林大学化学系,长春,１３００２３）关键词杂多化合物,环己烯,催化氧化单取代杂多化合物作为＂卟啉无机同系物＂而用于均相及相转移催化已引起人们的关注［１～３］．由于这类...     

Iron‐Based Molecular Water Oxidation Catalysts: Abundant,Cheap, and Promising

An efficient and robust water oxidation catalyst based on abundant and cheap materials is the key to converting solar energy into fuels through artificial photosynthesis for the future of humans. The development of molecular water oxidation catalysts (MWOCs) is a smart way to achieve promising catalytic activity, thanks to the clear structures and catalytic mechanisms of molecular catalysts. Efficient MWOCs based on noble‐metal complexes, for example, ruthenium and iridium, have been well developed over the last 30 years; however, the development of earth‐abundant metal‐based MWOCs is very limited and still challenging. Herein, the promising prospect of iron‐based MWOCs is highlighted, with a comprehensive summary of previously reported studies and future research focus in this area.     

Stability and Activity of Non‐Noble‐Metal‐Based Catalysts Toward the Hydrogen Evolution Reaction

A fundamental understanding of the behavior of non‐noble based materials toward the hydrogen evolution reaction is crucial for the successful implementation into practical devices. Through the implementation of a highly sensitive inductively coupled plasma mass spectrometer coupled to a scanning flow cell, the activity and stability of non‐noble electrocatalysts is presented. The studied catalysts comprise a range of compositions, including metal carbides (WC), sulfides (MoS₂), phosphides (Ni₅P₄, Co₂P), and their base metals (W, Ni, Mo, Co); their activity, stability, and degradation behavior was elaborated and compared to the state‐of‐the‐art catalyst platinum. The non‐noble materials are stable at HER potentials but dissolve substantially when no current is flowing. Through pre‐ and post‐characterization of the catalysts, explanations of their stability (thermodynamics and kinetics) are discussed, challenges for the application in real devices are analyzed, and strategies for circumventing dissolution are suggested. The precise correlation of metal dissolution with applied potential/current density allows for narrowing down suitable material choices as replacement for precious group metals as for example, platinum and opens up new ways in finding cost‐efficient, active, and stable new‐generation electrocatalysts.     

Fast and Simple Preparation of Iron‐Based Thin Films as Highly Efficient Water‐Oxidation Catalysts in Neutral Aqueous Solution

Water oxidation is the key step in natural and artificial photosynthesis for solar‐energy conversion. As this process is thermodynamically unfavorable and is challenging from a kinetic point of view, the development of highly efficient catalysts with low energy cost is a subject of fundamental significance. Herein, we report on iron‐based films as highly efficient water‐oxidation catalysts. The films can be quickly deposited onto electrodes from Fe^II ions in acetate buffer at pH 7.0 by simple cyclic voltammetry. The extremely low iron loading on the electrodes is critical for improved atom efficiency for catalysis. Our results showed that this film could catalyze water oxidation in neutral phosphate solution with a turnover frequency (TOF) of 756 h^?1 at an applied overpotential of 530 mV. The significance of this approach includes the use of earth‐abundant iron, the fast and simple method for catalyst preparation, the low catalyst loading, and the large TOF for O₂ evolution in neutral aqueous media.     

A Bio‐inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn₄CaO₅ cluster of natural oxygen‐evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M₄O₄ cubane‐like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M₄O₄ clusters, however, copper‐based molecular catalysts are poorly understood. Now, bio‐inspired Cu₄O₄ cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s^?1 for [(L_Gly‐Cu)₄] at 1.70 V and 105 s^?1 for [(L_Glu‐Cu)₄] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two‐electron transfer process in the Cu₄O₄ cubanes to form high‐valent Cu^III and Cu^IIIO^. intermediates during the catalysis.     

Synthesis of Orthorhombic Mo‐V‐Sb Oxide Species by Assembly of Pentagonal Mo6O21 Polyoxometalate Building Blocks

Mix and match : The pentagonal [Mo₆O₂₁]^n? polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo‐V‐Sb oxide. The first single‐crystal X‐ray analysis of an orthorhombic Mo–V‐based oxide, a promising catalyst for light alkane selective oxidation known as the “M1 phase”, revealed the structure of the compound.