Binary Catalytic Systems Research Articles

Iron(III) Complexes with Pyridine Group Coordination and Dissociation Reversible Equilibrium: Cooperative Activation of CO2 and Epoxides into Cyclic Carbonates.

Herein, a series of [ONSN]-type iron(III) complexes were synthesized. A binary catalytic system in combination with iron complexes and tetrabutylammonium bromide (TBAB) exhibited high activity for the synthesis of cyclic carbonates from CO2 (1 atm) and terminal epoxides at room temperature. Additionally, single-component iron complexes without using additional TBAB as nucleophiles also showed high activity for the cycloaddition of CO2 and terminal epoxides under 80 °C and 0.5 MPa of CO2. This study demonstrates that single-component iron catalysts provide a competitive alternative to binary catalytic systems for the synthesis of cyclic carbonates from CO2 and epoxides. Mechanistic studies on a single-component iron catalytic system suggest that the temperature serves as a role of responsive switch for controlling the coordination and dissociation of pyridine bearing iron catalysts detected using in situ infrared spectroscopy, and uncoordinated pyridine activates CO2 to form carbamate. Studies of electrospray ionization high-resolution mass spectrometry reveal that an iron center was used as a Lewis acidic site, free halogen anions from the iron center were used as a nucleophilic site, and coordinated pyridine was released from iron complexes to activate CO2.

Peroxymonosulfate assisted pesticide breakdown: Unveiling the potential of a novel S-scheme ZnO@CoFe2O4 photo-catalyst, anchored on activated carbon

A ternary hetero-junction was prepared by anchoring ZnO@CoFe2O4 (ZCF) on activated carbon (AC) and employed as a UV-assisted peroxymonosulfate (PMS) activator to boost the degradation of diazinon (DZN) pesticide. The structure, morphology, and optical properties of the ZCFAC hetero-junction were characterized through a series of techniques. The highest degradation efficiency of DZN (100% in 90 min) was achieved by the PMS-mediated ZCFAC/UV system, superior to other single or binary catalytic systems due to the strong synergistic effect between ZCFAC, PMS, and UV. The operating reaction conditions, synergistic effects, and the possible pathways of DZN degradation were investigated and discussed. Optical analysis showed that the band-gap energy of the ZCFAC hetero-junction not only enhanced the absorption of UV light but also reduced the recombination of photo-induced electron/hole pairs. Both radical and non-radical species (HO•, SO4•−, O2•−, 1O2, and h+) took part in the photo-degradation of DZN, assessed by scavenging tests. It was found that AC as a carrier not only improved the catalytic activity of CF and ZnO nanoparticles and conferred high stability for the catalyst but also played a crucial role in accelerating the catalytic PMS activation mechanism. Moreover, the PMS-mediated ZCFAC/UV system showed good reusability, universality, and practical applicability potential. Overall, this work explored an efficient strategy for the best use of hetero-structure photo-catalysts towards PMS activation to achieve high performance in decontaminating organic compounds.

Cycloalkanes oxidation with O2 in high-efficiency and high-selectivity catalyzed by 3D MOFs with limiting domain and Zn(AcO)2 through synergistic mode

To achieve efficient and selective cycloalkane oxidation, binary catalytic systems had been constructed on the basis of 3D MOFs [Zr6O4(μ3-OH)4(Metalloporphyrin)2(μ1-OH)4(μ1-H2O)4] and Zn(AcO)2. MOFs were prepared to construct limiting domains to suppress diffusiveness of free radicals under disorder state, and Zn(AcO)2 had been employed as synergistic catalysis sites. Catalytic system constructed by PCN-222-d(Co) and Zn(AcO)2 exhibited excellent catalytic performance. In contrast to T(4-COOCH3)PPCo as homogeneous catalyst, an enhancement from 3.83% to 5.51% was obtained from conversion, meanwhile selectivity was increased from 79.9% to 94.4% in cyclohexane oxidation. Primary source of the excellent performance were inhibition of diffusiveness of free radicals under disorder state, and enhancement on C-H bonds oxidation with oxidation intermediate R-OOH catalyzed by Zn(II). Synergistic catalysis process and catalytic mechanism were investigated via controlled experiments, radical trapping, and EPR analyses. This study provides a useful reference for oxidative functionalization of cycloalkanes with O2, and a significant contribution for other chemical conversions involving in free radicals.

Binary catalytic systems for the industrial cyclohexane oxidation process

This paper proposes the possibility of creating an efficient binary catalytic system for the industrial oxidation process of cyclohexane based on a compound of a metal of variable valence and a salt of perfluorinated sulfonic acid. Two-component binary mixtures of the main component and additive were used for the study. In addition to industrial cobalt naphthenate, other salts of metals of variable valences, such as manganese naphthenate, as well as stearates of copper, nickel, and cerium, were used as the main component of the binary mixture. A number of salts of perfluorinated sulfonic acids were used as an additive to the binary mixture. Chromoxane is shown to be the most efficient additive to cobalt naphthenate. In the presence of this binary system at the 50th minute of the process, the conversion of raw materials increased to 10.4 mol.%, which is 22% more than the oxidation of pure cobalt naphthenate, while the selectivity with respect to the target products remains high (79.5 mol.%). It is shown that of a number of compounds of metals of variable valence, the most effective main components of binary systems are cobalt naphthenate and cobalt-cerium catalyst. Carrying out the oxidation of cyclohexane in the presence of such systems allows increasing the conversion of the initial cyclohexane by 1.13 to 1.5 times and thus increasing the rate of oxidation of the hydrocarbon in comparison with the industrial process. It is also important that the use of such catalysts allows conducting the oxidation of cyclohexane to high conversions without losing the yield of the target products.

Binary catalytic systems constructed by porphyrin cobalts(II) with confining nano-region and Zn(OAc)2 for oxygenation of cycloalkanes with O2 in relay mode

To produce partly oxygenated products of cycloalkanes utilizing O2 in high-efficiency and high-selectivity, binary catalytic systems possessing bimetallic centers were constructed based on porphyrin cobalts(II) and Zn(OAc)2. Porphyrin cobalts(II) possessing bulky substituents had been synthesized to construct confining nano-regions to inhibit the spread of free radical in shambolic state, and Zn(OAc)2 was utilized to catalyze transformation of oxygenation intermediates cycloalkyl hydroperoxides. For cycloalkanes oxygenation using O2, binary system constructed by T2-NaPBr8Co(II)&Zn(OAc)2 exhibited superior catalytic performance. Both conversion and total selectivity to partly oxygenated products were raised. Compared with metalloporphyrin TPPBr8Co(II) with small substituents, conversion was increased from 5.13 to 6.21% and selectivity to partly oxygenated products was raised from 86.9 to 95.8% in classical cyclohexane oxygenation. The excellent performance of binary catalytic system constructed by T2-NaPBr8Co(II) and Zn(OAc)2 was mainly due to lower temperature, inhibited spread of free radical in confining catalytic region of T2-NaPBr8Co(II) and catalytic conversion of cycloalkyl hydroperoxides. The relay oxygenation path and catalytic mechanism were systematically investigated via EPR analyses and control experiments. This study is not only a significant contribution to construction of efficient and selective catalytic systems for cycloalkane oxygenation, but also a useful reference for other chemical conversion containing free radicals.

Immortal polymerization of LA: the influence of steric effects, electronic effects and pKaon chain transfer agents

In this paper, we systematically investigated the iROP of l-LA based Ca[N(SiMe3)2]2(THF)2/CTAs binary catalytic systems for the first time. The steric effect, electronic effect and pKa of CTAs all had great influences on the iROP of LA.

Ti and Zr amino-tris(phenolate) catalysts for the synthesis of cyclic carbonates from CO2 and epoxides

Herein, we report the application of four amino-tris(phenolate)-based metal complexes incorporating Ti(IV) or Zr(IV) centres (2a-3b) as homogeneous catalysts for the conversion of CO2 and epoxides into cyclic carbonates. The four complexes were synthesised, characterised and then evaluated in combination with tetrabutylammonium iodide, bromide or chloride as binary catalytic systems for the reaction of CO2 with 1,2-epoxyhexane as epoxide substrate at 12 bar CO2 pressure and 90 °C for 2 h. The catalytic systems comprising the two Ti(IV) complexes (2a and 2b) showed similar performance. One notable exception was the catalytic system consisting of titanium complex 2b, bearing an axial Cl-ligand, and tetrabutylammonium chloride, which displayed higher catalytic activity compared to other titanium-based systems. Even higher activity was achieved with Zr(IV) complex 3a, bearing an axial isopropoxide ligand, which reached turnover numbers (TONmetal) up to 1920 for the reaction of CO2 with 1,2-epoxyhexane at 12 bar CO2 pressure and 90 °C for 2 h. This performance is comparable with that of state-of-the-art catalysts for this reaction. The catalytic system consisting of complex 3a and tetrabutylammonium bromide was explored further by investigating its applicability with a broad substrate scope, achieving quantitative conversion of several epoxides with CO2 into cyclic carbonate products at 90 °C and 12 bar CO2 pressure for 18 h. The selectivity towards the cyclic carbonate products was ≥ 98% for all studied terminal epoxides and ≥ 80% for all examined cyclohexene-type epoxides.

Influence of Amino Acids and Alcohols on Catalytic Oxidation of Cyclohexane

Conducted experiments and collected data show that use of catalytic systems that contain individual amino acids and industrial catalyst – solution of cobalt naphtenate with cyclohexanone – have certain influence on the process of liquid-phase homogeneous oxidation of cyclohexane. The results of spectral studies of binary catalytic systems based on NC using additives of different nature (alcohols and nitrogen-containing modifiers) allow us to propose structural formulas of catalytic complexes.

Supported transition metals oxides and N-hydroxyphthalimide as binary catalytic systems for the liquid-phase oxidation of cumene

• Transition metal oxide (TMO) activates NHPI molecule producing PINO • radical • Surface acidity and redox properties of the metal oxide catalyst influence activation of NHPI • PINO • radical activated at the surface initiates/propagates homogeneous oxidation • Synergistic effect of NHPI-TMO couple increases oxidation rate • The efficiency of TMO as a cocatalyst decreases in order V 2 O 5 ≈ MnO x > CuO x The heterogeneous catalysts based on single active component such as V 2 O 5, MnOx and CuOx and bi-components V 2 O 5 -MoO 3 V 2 O 5 -WO 3 and V 2 O 5 -SbO x supported onto TiO 2 , TiO 2 -SiO 2 and Al 2 O 3 -SiO 2 was prepared and characterized. The aerobic liquid-phase oxidation of cumene (RH) in the presence of binary catalytic system containing N-hydroxyphthalimide (NHPI) and supported V, Mn and Cu oxides has been studied. It was observed that catalytic activities of the mono metallic systems decreases in order V 2 O 5 ≈ MnO x > CuO x , bi-metallic catalysts showed no catalytic activities. The effect of catalytic system composition comprising MnO x or VO x and NHPI, AIBN on the oxidation rate was studied . The major oxidations product was cumene hydroperoxide, whereas dimethyl phenyl carbinol and acetophenone were found as minor ones. The reactions scheme that summarizes the oxidation chemistry identifying the related role of heterogeneous initiation and homogeneous propagation and termination steps for oxidation of cumene via free-radical mechanism are presented.

Copolymerization of Phthalic Anhydride with Epoxides Catalyzed by Amine-Bis(Phenolate) Chromium(III) Complexes.

The effect of ligand structure on the catalytic activity of amine-bis(phenolate) chromium(III) complexes in the ring-opening copolymerization of phthalic anhydride and a series epoxides was studied. Eight complexes differing in the donor-pendant group (R1) and substituents (R2) in phenolate units were examined as catalysts of the model reaction between phthalic anhydride and cyclohexane oxide in toluene. They were used individually or as a part of the binary catalytic systems with nucleophilic co-catalysts. The co-catalyst was selected from the following organic bases: PPh3, DMAP, 1-butylimidazole, or DBU. The binary catalytic systems turned out to be more active than the complexes used individually, and DMAP proved to be the best choice as a co-catalyst. When the molar ratio of [PA]:[epoxide]:[Cr]:[DMAP] = 250:250:1:1 was applied, the most active complex (R1-X = CH2NMe2, R2 = F) allowed to copolymerize phthalic anhydride with differently substituted epoxides (cyclohexene oxide, 4-vinylcyclohexene oxide, styrene oxide, phenyl glycidyl ether, propylene oxide, butylene oxide, and epichlorohydrin) within 240 min at 110 °C. The resulting polyesters were characterized by Mn up to 20.6 kg mol−1 and narrow dispersity, and they did not contain polyether units.

Influence of alumina addition on structural and catalytic properties of sulphated zirconia in isomerization of n-hexane

New binary catalytic systems based on sulphated zirconia-alumina were synthesized by controlled hydrolysis of alkoxides using relative molar ratios of constituents 1:1, 1:2 and 1:3 in favour of zirconia. The obtained differences in the final catalytic material?s properties may be related to organic precursor memory effect, the applied calcinations temperatures and used alumina contents. The addition of alumina to zirconia affected the structural and surface properties stabilizing bare zirconia by means of slower phase transformation of tetragonal zirconia crystal phase into monoclinic one, further resulting in smaller crystallites sizes and higher surface density of acidic function (sulphates). The best alumina impact on physico-chemical properties was achieved when the highest amount of alumina (e.g. 50%) and lower calcination temperature (500?C) were used, causing relatively high steady-state activity in isomerization of n-hexane at reaction temperature 250 ?C. On the other hand, higher calcination temperature (600 ?C) played a role in the genesis of greater sulphate density. Catalytic activity and selectivity are expressed as a complex synergistic function of relative density of acid sites together with positive status of other optimized physico-chemical properties of the catalytic material (by activation and calcination temperatures).

Reactor Blend and Nanocomposite of Polyethylene Using a Binary Catalyst of Metallocene/Nickel

The present study aimed to conduct the ethylene polymerization using two binary catalytic systems to evaluate the resulting reactor blend of polyethylene. Subsequently, the study continued to explore the effects of catalyst to monomer molar ratio, reaction temperature, ethylene pressure and nanofillers on the catalysts activity, molar mass, thermal behavior, structural and morphological properties of the obtained polyethylene. The catalytic system containing α-diimine catalyst based on nickel showed higher activity, higher melting point (75.6 × 104 g polyethylene/(mol catalyst h), 125°C, respectively) and the extent of crystallinity (up to 48.5%) in comparison with the analogous system bearing pyridine-imine catalyst. The augmentation of nanoparticles increased the branching content in the system with α-diimine catalyst based on nickel, while these trends were reverse in pyridine-imine catalyst system, so that the branches were reduced as the nanoparticle concentration was increased. SEM images revealed distinct fibrous phases and the presence of obvious and well dispersed nanoparticles in the prepared nanocomposites. The synthesized polyethylene blend exhibited high thermal stability.

Evaluation of Transition Metal Catalysts in Electrochemically Induced Aromatic Phosphonation.

Voltammetry provides important information on the redox properties of catalysts (transition metal complexes of Ni, Co, Mn, etc.) and their activity in electrocatalytic reactions of aromatic C–H phosphonation in the presence of a phosphorus precursor, for example, dialkyl-H-phosphonate. Based on catalytic current growth of oxidation or reduction of the metal catalysts (CoII, MnII, NiII, MnII/NiII, MnII/CoII, and CoII/NiII), quantitative characteristics of the regeneration of catalysts were determined, for example, for MnII, NiII and MnII/NiII, CoII/NiII pairs. Calculations confirmed the previously made synthetic observations on the synergistic effect of certain metal ions in binary catalytic systems (MnIIbpy/NiIIbpy and NiIIbpy/CoIIbpy); for mixtures, the observed rate constants, or TOF, were 690 s−1 and 721 s−1, respectively, and product yields were higher for monometallic catalytic systems (up to 71% for bimetallic catalytic systems and ~30% for monometallic catalytic systems). In some cases, the appearance of pre-waves after adding H-phosphonates confirmed the preceding chemical reaction. It also confirmed the formation of metal phosphonates in the time scale of voltammetry, oxidizing or reducing at lower potentials than the original (RO)2P(O)H and metal complex, which could be used for fast diagnostics of metal ion and dialkyl-H-phosphonate interactions. Electrochemical transfer of an electron to (from) metal phosphonate generates a phosphonyl radical, which can then react with different arenes to give the products of aromatic C–H phosphonation.

Study on single and binary catalytic systems of pyridine‐imine catalysts based on nickel and iron in synthesis of reactor blends and low‐density polyethylene nanocomposites

ABSTRACTIn the presence of modified methylaluminoxane as cocatalyst, the behavior of a binary catalytic system based on pyridine‐imine nickel (N) and iron (F) catalysts was evaluated in order to reach a proper mixture of polyethylene (PE). A computational study along with kinetic profile suggested that the catalyst F with higher electron affinity (A) and electrophilicity (ω) in the methyl cationic active center and stronger interaction with the monomer led to high integrated monomer consumption and higher activity. In addition, the samples produced by the mixture of catalysts showed a higher value of [19.4 × 104 g (PE) mol (Fe+Ni)−1 h−1)], melting point (127.8 °C), and crystallinity extent (41.29%) than the samples produced by the single catalysts. The addition of multiwalled carbon nanotubes (MWCNT) into the polymerization media reduced the activity of catalysts [from 7.50 × 104 to 0.66 × 104 g (PE) mol (Fe+Ni)−1 h−1] and the thermal properties of the low‐density polyethylene nanocomposite samples. However, the sample containing 2.33% MWCNT20‐30 improved the total thermal stability of the neat polyethylene blend up to 400 °C. Scanning electron microscope images of the samples demonstrated irregular to virtually uniform morphologies were obtained through the in situ and solution‐mixing techniques. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47376.

Aromatic guanidines as highly active binary catalytic systems for the fixation of CO2 into cyclic carbonates under mild conditions

The formation of hydrogen bonding causes a considerable decrease in the reaction temperature and CO2 pressure used in this process.

Elucidating the Copper–Hägg Iron Carbide Synergistic Interactions for Selective CO Hydrogenation to Higher Alcohols

CO hydrogenation to higher alcohols (C2+OH) provides a promising route to convert coal, natural gas, shale gas, and biomass feedstocks into value-added chemicals and transportation fuels. However, the development of nonprecious metal catalysts with satisfactory activity and well-defined selectivity toward C2+OH remains challenging and impedes the commercialization of this process. Here, we show that the synergistic geometric and electronic interactions dictate the activity of Cu0–χ-Fe5C2 binary catalysts for selective CO hydrogenation to C2+OH, outperforming silica-supported precious Rh-based catalysts, by using a combination of experimental evidence from bulk, surface-sensitive, and imaging techniques collected on real and high-performance Cu–Fe binary catalytic systems coupled with density functional theory calculations. The closer is the d-band center to the Fermi level of Cu0–χ-Fe5C2(510) surface than those of χ-Fe5C2(510) and Rh(111) surface, and the electron-rich interface of Cu0–χ-Fe5C2(510) due to...

Stereorigid OSSO-Type Group 4 Metal Complexes in the Ring-Opening Polymerization of rac-Lactide.

The synthesis and characterization of a series of group 4 metal complexes of general formula {OSSOX}M(OR)2 (X = R = tBu, M = Zr (1); X = cumyl, M = Zr, R = tBu (2); X = cumyl, M = Ti, R = iPr (4); X = cumyl, M = Hf, R = tBu (5)) and {OSSOX}2Zr (X = Cl (3)) supported by o-phenylene-bridged bis(phenolato) ligands (OSSOtBu-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-di-tert-butyphenol); OSSOCum-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenol); OSSOCl-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-dichlorophenol)) are described herein. Complexes 1-5 were readily obtained by σ-bond metathesis reactions between the proligand and the appropriate homoleptic metal precursor. The reaction with OSSOCl yielded the bis-ligand complex{OSSOCl}2Zr (3) regardless of the OSSOCl-H/Zr(OtBu)4 molar ratio or experimental conditions. All complexes were characterized in solution using NMR spectroscopy and, in the case of 2, by single-crystal X-ray diffraction experiments. These complexes show a fac-fac ligand wrapping and a cis relationship between the other two monodentate ligands; zirconium and hafnium complexes 1-3 and 5 are configurationally stable, whereas titanium complex 4 is fluxional in solution at room temperature. The complexes tested in the ring-opening polymerization (ROP) of racemic-lactide showed, except in the case of 3, moderate rates and good levels of polymerization control. Upon addition of an exogenous alcohol (isopropyl alcohol or tert-butyl alcohol) efficient binary catalytic systems were achieved. Polymerizations were well-controlled, as testified by the linear growth of the molecular weight as polymerization proceeded, narrow polydispersity indices, and molecular weights close to those expected on the basis of added alcohol amounts. Experimental and theoretical evidence is provided that ROP reactions operate according to an activated monomer mechanism.

Production of bimodal polyethylene on chromium oxide/metallocene binary catalyst: Evaluation of comonomer effects

A novel option to produce bimodal polyethylene is by using binary catalytic systems, able to generate polyethylene chains with different predominant molecular weights in only one-step polymerization process. In this work, we explore in depth the catalytic behavior of a binary chromium-metallocene catalyst in the co-polymerizations of ethylene with 1-butene or 1-hexene looking for the production of bimodal polyethylene with an adequate comonomer profile across its molecular weight distribution. Likewise, the effect of the hydrogen together with comonomers was also evaluated for controlling polymers properties. Results indicate that the relative contribution of chromium and metallocene sites in the binary catalyst is strongly affected by using comonomers. Specifically, chromium contribution noticeably increases when using 1-hexene or 1-butene due to the positive comonomer effect observed in the individual chromium catalyst. The methodology used for hydrogen supply (continuous or discontinuous addition) plays a key role for tuning catalytic activity and polyethylene bimodality. Finally, comonomer placement across the molecular weight distribution of bimodal polyethylenes shows a growing profile, with a higher SCB concentration in the longest polymer chains than that obtained for a commercial PE100 sample.

Catalytic Activity of Binary and Triple Systems Based on Redox Inactive Metal Compound, LiSt and Additives of Monodentate Ligands-Modifiers: DMF, HMPA and PhOH, in Selective Ethylbenzene Oxidation with Dioxygen

Mechanism of catalysis with binary and triple catalytic systems based on redox inactive metal (lithium) compound {LiSt+L2} and {LiSt+L2+PhOH} (L2=DMF or HMPA), in the selective ethylbenzene oxidation by dioxygen into -phenylethyl hydroperoxide is researched. The results are compared with catalysis by nickel-lithium triple system {NiII(acac)2+LiSt+PhOH} in selective ethylbenzene oxidation to PEH. The role of H-bonding in mechanism of catalysis is discussed. The possibility of the stable supramolecular nanostructures formation on the basis of triple systems, {LiSt+L2+PhOH}, due to intermolecular H-bonds, is researched with the AFM method.

Bimodal polypropylene through binary metallocene catalytic systems: comparison between hybrid and mixed heterogeneous catalysts

Polypropylene with wider or bimodal molecular weight distribution is required for numerous applications since low molecular weight chains improve processability and high molecular weight fraction is required to get good mechanical properties. There are several routes to achieve a bimodal resin but the use of a binary catalytic system seems to be the most attractive, particularly with metallocenes combination. From a previous work two metallocenes were selected because they lead to polypropylenes with average molecular weights that differ in one order of magnitude. Two types of binary systems have been investigated, hybrid catalysts (two metallocenes loaded on the same support) and physical mixtures (two independent supported metallocenes that are introduced to the reactor and start the polymerization together), using different ratios, i.e., 25–75, 50–50, 75–25, at three reaction temperatures, i.e., 30, 50 and 70 °C. Most of the binary catalytic systems lead to bimodal molecular weight distributions. Polypropylenes produced by mixed catalysts are greatly influenced by the most active catalyst, while in PP coming from hybrid catalysts, as there is a strong interaction between both metallocenes, each one contributes according to its presence in the hybrid catalyst. Therefore, properties of obtained bimodal polypropylenes are quite influenced by the ratio between both metallocenes.