Widely Controllable Syngas Production by a Dye‐Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible‐Light Irradiation

Visible‐light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂ evolving Co^III catalyst and a CO‐producing Re^I catalyst on TiO₂ have been found to produce both H₂ and CO (syngas) in CO₂‐saturated N ,N ‐dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^I and Co^III catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂ to each of the CO₂‐reduction and hydrogen‐evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.     

Distinct Proton and Water Reduction Behavior with a Cobalt(III) Electrocatalyst Based on Pentadentate Oximes

A new pentadentate oxime has been designed to drive the preferential coordination favored by Co^I in catalysts used for proton/water reduction. The ligand incorporates water upon metal coordination and is water soluble. This Co^III species is doubly reduced to Co^I and exhibits H⁺ reduction activity in the presence of weak acids in MeCN and evolves H₂ upon protonation suggesting that the ligand design increases catalyst effectiveness. Superior catalysis is observed in water with a turnover number (TON) of 5700 over 18 h. However, the catalyst yields Co‐based nanoparticles, indicating that the solvent media may dictate the nature of the catalyst.     

Structural and Electronic Influences on Rates of Tertpyridine−Amine CoIII−H Formation During Catalytic H2 Evolution in an Aqueous Environment

In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺ species results in the formation of [Co^II(κ⁴-L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴-L)(OH₂)]⁺, which undergoes a rate-limiting structural rearrangement to [Co^I(κ⁵-L)]⁺ before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺ formation is similar for all complexes in the series. Using E_1/2 values of various Co species and pK_a values of [Co^III−H]²⁺ estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺ is unfavorable, [Co^II−H]⁺ reacts with protons to produce H₂. The catalytic activity for H₂ evolution tracks the hydricity of the [Co^II−H]⁺ intermediate.     

Microsecond X‐ray Absorption Spectroscopy Identification of CoI Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time‐resolved X‐ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the Co^I intermediate of cobaloxime, which is a non‐noble metal catalyst for solar hydrogen production from water. Distances between cobalt and the nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X‐ray absorption and UV/Vis data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive Co^I state under similar conditions. Possible deactivation mechanisms are discussed.     

Highly dispersed Mn2O3−Co3O4 nanostructures on carbon matrix as heterogeneous Fenton-like catalyst

This work reports the synthesis of various carbon (Vulcan XC-72 R) supported metal oxide nanostructures, such as Mn₂O₃, Co₃O₄ and Mn₂O₃−Co₃O₄ as heterogeneous Fenton-like catalysts for the degradation of organic dye pollutants, namely Rhodamine B (RB) and Congo Red (CR) in wastewater. The activity results showed that the bimetallic Mn₂O₃−Co₃O₄/C catalyst exhibits much higher activity than the monometallic Mn₂O₃/C and Co₃O₄/C catalysts for the degradation of both RB and CR pollutants, due to the synergistic properties induced by the Mn−Co and/or Mn (Co)−support interactions. The degradation efficiency of RB and CR was considerably increased with an increase of reaction temperature from 25 to 45°C. Importantly, the bimetallic Mn₂O₃−Co₃O₄/C catalyst could maintain its catalytic activity up to five successive cycles, revealing its catalytic durability for wastewater purification. The structure–activity correlations demonstrated a probable mechanism for the degradation of organic dye pollutants in wastewater, involving •OH radical as well as Mn²⁺/Mn³⁺ or Co²⁺/Co³⁺ redox couple of the Mn₂O₃−Co₃O₄/C catalyst.     

Chiral Bicyclo[2.2.2]octane-Fused CpRh Complexes: Synthesis and Potential Use in Asymmetric C−H Activation

A new class of chiral cyclopentadienyl rhodium(I) complexes (CpRh^I) bearing C₂-symmetric chiral bridged-ring-fused Cp ligands was prepared. The complexes were successfully applied to the asymmetric C−H activation reaction of N-methoxybenzamides with quinones, affording a series of chiral hydrophenanthridinones in up to 82 % yield with up to 99 % ee. Interestingly, structure analysis reveals that the side wall of the optimal chiral CpRh^I catalyst is vertically more extended, horizontally less extended, and closer to the metal center in comparison with the classic binaphthyl and spirobiindanyl CpRh^I complexes, and may thus account for its superior catalytic performance.     

SN2 or Electron Transfer?? A new technique discriminates the mechanisms of oxidative addition of alkyl halides to corrinato- and porphyrinatocobalt(I)

A fast electrochemical technique for the discrimination of one- and two-electron mechanisms in the oxidative addition of alkylating agents (RX) to corrinato- and porphyrinatocobalt(I) ([Co^IL]) is described. It is based on single-scan voltammograms of [Co^IIL] in the presence of RX and variable amounts of the radical trap acrylonitrile. In the first part of the voltammogram, [Co^IIL] is reduced, and fast oxidative addition of RX to [Co^IL] is triggered. If the reaction proceeds via a two-electron mechanism, [R Co^IIIL] is formed independently of acrylonitrile concentration, but if a transient free radical R is involved, R is competitively trapped by acrylonitrile and [Co^IIL] to yield, at high enough acrylonitrile concentration, exclusively the olefin-inserted [R_CN Co^IIIL]. [R_CN Co^IIIL] is reducible in the intermediate potential range, [R Co^IIIL] at the negative end of the single-scan voltammogram. Hence, from the appearance of the reduction waves due to [R_CN Co^IIIL] and [R Co^IIIL], the mechanism of oxidative addition of RX to [Co^IL] is easily deduced. The method is applied to the study of the mechanistic borderline of oxidative addition using a series of 15 RX and 4 [CoL]'s, i.e. cobalamin (Cbl), heptamethyl cobyrinate (‘Cby’), (tetraphenylporphyrinato) cobalt ([Co(tpp])), and (octaethylporphyrinato) cobalt ([Co(oep)]). All non-activated primary alkyl iodides and bromides exhibit, at room temperature, pure two-electron mechanisms with all [Co^IL]'s, except neopentyliodide with Cb1^I and ‘Cby’^I. All secondary alkyl iodides involve free radicals with Cb1^I and ‘Cby’^I, but a pure two-electron mechanism or a mixed one-electron two-electron mechanism with [Co^I(tpp)] and [Co^I(oep)]. The mechanistic switch from a two-electron to a one-electron mechanism for increasingly sterically demanding RX's occurs earlier with the supernucleophilic Cb1^I and ‘Cby’^I than with [Co^I(tapp)] and [Co^I(oep)].     

Cobalt tetrasulfophthalocyaninate as a catalyst of the reduction of nitrite with thiourea dioxide

The kinetics of reduction of nitrite with thiourea dioxide in the presence of cobalt tetrasulfophth-alocyaninate was studied. The process was shown to involve the Co^II ↔ Co^I catalytic cycle. The kinetic parameters of the reduction of Co^II and Co^I tetrasulfophthalocyaninates were determined     

Facile synthesis of nanostructured Ni-Co/ZnO material: An efficient and inexpensive catalyst for Heck reactions under ligand-free conditions

A simple, efficient and economically viable method for the Heck reaction has been accomplished in the absence of phosphine ligand. The Heck reaction was performed using nanostructured Ni-Co/ZnO material as a heterogeneous catalyst in a DMF/H₂O solvent system and in the presence of K₂CO₃, at 120 °C. The Ni-Co/ZnO nanostructures were prepared by the facile reduction-impregnation method. The structural and morphological properties of Ni-Co/ZnO nanostructure were investigated using various physico-chemical characterization techniques. Structural studies displayed the formation of hexagonal (wurtzite) ZnO. Electron microscopy imaging showed the presence of agglomerated clusters of Ni-Co nanoparticles over the surfaces of elliptical, flower bud-like and irregularly shaped sub-micron sized particle bundles of ZnO. The elemental composition analysis (EDX) confirmed the loading of Ni and Co nanoparticles over the nanocrystalline ZnO. The surface chemical state analysis of Ni-Co/ZnO material validated that Ni nanostructure exists in Ni²⁺ and Ni³⁺ species, whereas, Co nanostructure exists in Co²⁺ and Co³⁺ species. UV–Vis diffuse reflectance spectroscopy displays red shift in the light absorption edge of Ni-Co/ZnO catalyst compared to pure ZnO. The as-prepared Ni-Co bimetallic supported ZnO nanostructure showed better catalytic activity and stability for the Heck reactions under phosphine ligand-free conditions. Ni-Co/ZnO catalyzed Heck reactions afforded the corresponding cross-coupled products with moderate to good yields (up to 92%). Ni-Co/ZnO catalyst could be reused for five successive runs without significant loss of catalytic activity.     

CuCl2和HY分子筛的表面反应及Cu/Y分子筛的制备及其催化甲醇氧化羰基化

以CuCl₂为前驱物与HY分子筛进行固相离子交换制备了Cu/Y催化剂,采用热重方法研究了CuCl₂与HY分子筛的表面固相离子交换反应,结合活性测试表明催化剂中高度分散的CuCl和离子交换形式的Cu⁺物种是甲醇氧化羰基化合成碳酸二甲酯的催化活性中心。X射线光电子能谱表征和元素分析结果表明,活性金属Cu主要以CuCl形式存在于分子筛外表面,而在分子筛笼内则以交换的Cu⁺和少量吸附的CuCl形式存在。与以CuCl为交换铜源所制催化剂相比,以CuCl₂为铜源制备的催化剂Cu含量低,催化活性更高。     

Rhodium-terpyridine Catalyzed Transfer Hydrogenation of Aromatic Nitro Compounds in Water

A rhodium terpyridine complex catalyzed transfer hydrogenation of nitroarenes to anilines with i-PrOH as hydrogen source and water as solvent has been developed. The catalytic system can work at a substrate/catalyst (S/C) ratio of 2000, with a turnover frequency (TOF) up to 3360 h⁻¹, which represents one of the most active catalytic transfer hydrogenation systems for nitroarene reduction. The catalytic system is operationally simple and the protocol could be scaled up to 20 gram scale. The water-soluble catalyst bearing a carboxyl group could be recycled 15 times without significant loss of activity.     

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal–Support Interactions and C−H Bond Activation at Low Temperature

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO₂) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO₂ at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO₂(111) exhibits the best performance and Cu/CeO₂(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO₂(111) at temperatures as low as 300 K—generating CH_x and CO_x species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co²⁺/CeO₂(111), and to only 0.05 eV on Co⁰/CeO_2−x (111). At 700 K, under methane dry reforming conditions, CO₂ dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CH_x formed on the Co⁰/CeO_2−x (111) catalyst recombines to yield ethane or ethylene.     

Efficient Selective Oxidation of Aromatic Alkanes by Double Cobalt Active Sites over Oxygen Vacancy-rich Mesoporous Co3O4

The development of efficient catalyst for selective oxidation of hydrocarbon to functional compounds remains a challenge. Herein, mesoporous Co₃O₄ (mCo₃O₄-350) showed excellent catalytic activity for selective oxidation of aromatic-alkanes, especially for oxidation of ethylbenzene with a conversion of 42 % and selectivity of 90 % for acetophenone at 120 °C. Notably, mCo₃O₄ presented a unique catalytic path of direct oxidation of aromatic-alkanes to aromatic ketones rather than the conventional stepwise oxidation to alcohols and then to ketones. Density functional theory calculations revealed that oxygen vacancies in mCo₃O₄ activate around Co atoms, causing electronic state change from Co³⁺_(Oh)→Co²⁺_(Oh). Co²⁺_(Oh) has great attraction to ethylbenzene, and weak interaction with O₂, which provide insufficient O₂ for gradual oxidation of phenylethanol to acetophenone. Combined with high energy barrier for forming phenylethanol, the direct oxidation path from ethylbenzene to acetophenone is kinetically favorable on mCo₃O₄, sharply contrasted to non-selective oxidation of ethylbenzene on commercial Co₃O₄.     

Oxidation of CO and hydrocarbons over perovskite-type complex oxides

The catalytic activity of perovskites M^IM^IIO₃ (M^I=La; M^II=Co, Mn, Cr, Al, Ni, and V) and M^ICoO₃ (M=Y, Nd, Sm, and Er) in the oxidation of CO, propylene, and ethylbenzene was investigated. The highest activity was observed for the M^ICoO₃ catalysts with perfect perovskite structure. The nature of the rare-earth element has no influence on the catalytic activity. Deformation of the octahedral coordination of the metal was found for the less active catalysts. The interaction of gases (CO, CO+air) with the catalyst surface was investigated. The more active catalysts adsorb a greater amount of O₂, and the adsorption occurs in the temperature region of the oxidation reaction. The activities of the perovskite- and spinel-type catalysts were compared under similar conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 698–701, April, 1999.     

Ionic Polymer Microspheres Bearing a CoIII–Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides

We report a unique strategy to obtain the bifunctional heterogeneous catalyst TBB‐Bpy@Salen‐Co (TBB=1,2,4,5‐tetrakis(bromomethyl)benzene, Bpy=4,4’‐bipyridine, Salen‐Co=N,N’‐bis({4‐dimethylamino}salicylidene)ethylenediamino cobalt(III) acetate) by combining a cross‐linked ionic polymer with a Co^III–salen Schiff base. The catalyst showed extra high activity for CO₂ fixation under mild, solvent‐free reaction conditions with no requirement for a co‐catalyst. The synthesized catalyst possessed distinctive spherical structural features, abundant halogen Br^? anions with good leaving group ability, and accessible Lewis acidic Co metal centers. These unique features, together with the synergistic role of the Co and Br^? functional sites, allowed TBB‐Bpy@Salen‐Co to exhibit enhanced catalytic conversion of CO₂ into cyclic carbonates relative to the corresponding monofunctional analogues. This catalyst can be easily recovered and recycled five times without significant leaching of Co or loss of activity. Moreover, based on our experimental results and previous work, a synergistic cycloaddition reaction mechanism was proposed.     

ESIMS Studies and Calculations on Alkali‐Metal Adduct Ions of Ruthenium Olefin Metathesis Catalysts and Their Catalytic Activity in Metathesis Reactions

Electrospray ionization mass spectrometry (ESIMS) and subsequent tandem mass spectrometry (MS/MS) analyses were used to study some important metathesis reactions with the first‐generation ruthenium catalyst 1 , focusing on the ruthenium complex intermediates in the catalytic cycle. In situ cationization with alkali cations (Li⁺, Na⁺, K⁺, and Cs⁺) using a microreactor coupled directly to the ESI ion source allowed mass spectrometric detection and characterization of the ruthenium species present in solution and particularly the catalytically active monophosphine–ruthenium intermediates present in equilibrium with the respective bisphosphine–ruthenium species in solution. Moreover, the intrinsic catalytic activity of the cationized monophosphine–ruthenium complex 1 a ?K⁺ was directly demonstrated by gas‐phase reactions with 1‐butene or ethene to give the propylidene Ru species 3 a ?K⁺ and the methylidene Ru species 4 a ?K⁺, respectively. Ring‐closing metathesis (RCM) reactions of 1,6‐heptadiene ( 5 ), 1,7‐octadiene ( 6 ) and 1,8‐nonadiene ( 7 ) were studied in the presence of KCl and the ruthenium alkylidene intermediates 8 , 9 , and 10 , respectively, were detected as cationized monophosphine and bisphosphine ruthenium complexes. Acyclic diene metathesis (ADMET) polymerization of 1,9‐decadiene ( 14 ) and ring‐opening metathesis polymerization (ROMP) of cyclooctene ( 18 ) were studied analogously, and the expected ruthenium alkylidene intermediates were directly intercepted from reaction solution and characterized unambiguously by their isotopic patterns and ESIMS/MS. ADMET polymerization was not observed for 1,5‐hexadiene ( 22 ), but the formation of the intramolecularly stabilized monophosphine ruthenium complex 23 a was seen. The ratio of the signal intensities of the respective with potassium cationized monophosphine and bisphosphine alkylidene Ru species varied from [I _4a ]/[I ₄ ]=0.02 to [I _23a ]/[I ₂₃ ]=10.2 and proved to be a sensitive and quantitative probe for intramolecular π‐complex formation of the monophosphine–ruthenium species and of double bonds in the alkylidene chain. MS/MS spectra revealed the intrinsic metathesis catalytic activity of the potassium adduct ions of the ruthenium alkylidene intermediates 8 a , 9 a , 10 a , 15 a , and 19 a , but not 23 a by elimination of the respective cycloalkene in the second step of RCM. Computations were performed to provide information about the structures of the alkali metal adduct ions of catalyst 1 and the influence of the alkali metal ions on the energy profile in the catalytic cycle of the metathesis reaction.     

Effects of Activation Atmospheres on Structure and Activity of Mo-based Catalyst for Synthesis of Higher Alcohols

Activated carbon supported Mo-based catalysts were prepared and reduced under different activation atmospheres, including pure H₂, syngas (H₂/CO=2/1), and pure CO. The catalysts structures were characterized by X-ray diffraction, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic performance for the higher alcohol synthesis from syngas was tested. The pure H₂ treatment showed a high reduction capacity. The presence of a large amount of metallic Co⁰. and low valence state Mo^φ+ (0<φ<2) on the surface suggested a super activity for the CO dissociation and hydrogenation, which promoted hydrocarbons formation and reduced the alcohol selectivity. In contrast, the pure CO-reduced catalyst had a low reduction degree. The Mo and Co species at the catalyst mainly existed in the form of Mo⁴⁺ and Co²⁺. The syngas-reduced catalyst showed the highest activity and selectivity for the higher alcohols synthesis. We suggest that the syngas treatment had an appropriate reduction capacity that is between those of pure H₂ and pure CO and led to the coexistence of multivalent Co species as well as the enrichment of Mo^δ+ on the catalyst's surface. The synergistic effects between these active species provided a better cooperativity and equilibrium between the CO dissociation, hydrogenation and CO insertion and thus contributed beneficially to the formation of higher alcohols.     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

高分散的炭载Au纳米催化剂的制备、表征和催化活性

采用柠檬酸钠还原-胶体负载法, 制备了高分散的炭载Au纳米催化剂, 并以液相催化氧化葡萄糖为葡萄糖酸钠的反应评价了Au/C催化剂的活性. 研究结果表明, 金溶胶制备过程中柠檬酸钠的用量对粒子尺寸以及所获催化剂的催化活性有重要影响; 催化剂在多次使用之后活性的降低可能是由于在活性炭表面金粒子活性位点上形成的Au^δ＋-O^δ－化合态减少的缘故. 同时比较了制备的Au/C和商业Pd/C催化剂对葡萄糖的液相催化氧化反应, 证明Au/C催化剂明显优于Pd/C催化剂.