Transfer Of Catalyst Research Articles

Sensitive detection of persulfate by a novel self-powered electrochemical sensor with carbon cloth electrodes modified with tin-doped cobalt tetroxide.

The accurate and rapid detection of persulfate concentration is important for environmental decontamination and human health protection. In this work, a novel self-powered electrochemical sensor for the sensitive monitoring of persulfate was developed, which utilized cobalt tetroxide (Co3O4@CC) or tin-doped cobalt tetroxide (SnxCo3-xO4@CC) cathode as the sensing element and anode with electrogenic microorganisms as the power supplier. The Co3O4@CC and SnxCo3-xO4@CC electrodes were fabricated by in situ growing nanostructured Co3O4 or SnxCo3-xO4 catalysts on carbon cloth. Electrochemical tests revealed that these electrodes exhibited excellent catalytic reduction performance toward persulfate because of the synergistic catalysis by Co3O4 and electrode electrons, well-exposed Co2+/Co3+ catalytic sites, and high electron transfer efficiency. Tin doping could enhance the catalytic persulfate reduction by improving the conductivity and electron transfer of the Co3O4 catalyst. The electrode prepared at a hydrothermal temperature of 90°C and a tin dosage of 0.286g·cm-2 achieved the highest persulfate reduction activity under pH 7. The sensing properties of the self-powered sensors toward persulfate were explored in detail. Results showed that under the optimal external load of 300 Ω, the proposed sensor could display a broad detection range of 0 to 1500μmol L-1 K2S2O8 with sensitivities of 1.13 and 0.12 μA μmol-1 L, a detection limit of 1.11μmol L-1 (S/N = 3), and a fast response time within 30s. The sensors also presented satisfactory reproducibility and selectivity during the detection of persulfate. The proposed sensor will provide a new approach for sensitive, on-site, and real-time monitoring of persulfate for a wide range of applications.

Boryl radical catalysis enables asymmetric radical cycloisomerization reactions.

The development of functionally distinct catalysts for enantioselective synthesis is a prominent yet challenging goal of synthetic chemistry. In this work, we report a family of chiral N-heterocyclic carbene (NHC)-ligated boryl radicals as catalysts that enable catalytic asymmetric radical cycloisomerization reactions. The radical catalysts can be generated from easily prepared NHC-borane complexes, and the broad availability of the chiral NHC component provides substantial benefits for stereochemical control. Mechanistic studies support a catalytic cycle comprising a sequence of boryl radical addition, hydrogen atom transfer, cyclization, and elimination of the boryl radical catalyst, wherein the chiral NHC subunit determines the enantioselectivity of the radical cyclization. This catalysis allows asymmetric construction of valuable chiral heterocyclic products from simple starting materials.

In-situ preparation of N-rich nano-activated carbon on negative-charged montmorillonite with enhanced activation of peroxymonosulfate for antibiotics degradation

N-rich nano-activated carbon/montmorillonite nanosheet with high ability for PMS activation and TC degradation was prepared via in-situ polymerization of ANI and calcination, creating open access for PMS to react with the fully exposed active sites. The prepared catalyst exhibited comparable catalytic ability to metal-based catalysts, achieving 86% degradation of TC (40 mg/L) in just 10 min using 0.3 g/L catalyzer and 0.3 g/L PMS. The degradation rate of TC reached 0.35 min−1, which was higher than that of most catalyst. The reason was attributed to the abundant active sites of graphitic N, pyridinic N, pyrrolic N, nitric oxide, and defects, improving the charge distribution and electron transfer of catalyst, and promoting the self-decomposition of PMS into the radical (•OH, •SO4−) and non-radical (1O2, predominant) species for TC degradation. Such catalyzer provided a novel design of metal-free catalysts with significant improvements, achieving the efficient bio-safety disposal of antibiotics from wastewater.

Insights into different toxic molecular gases on the Fe-dimer anchored at C2N monolayer as potential sorbents and gas sensors: A theoretical approach

The fundamental aspects, including geometric structure, adsorption energy, thermodynamic properties, charge transfer, and magnetic properties of carbon nitride C2N and double-atom catalyst (Fe2@C2N) monolayers with the adsorption of CO, NO, HCN, CS2, and SO2 molecules, were investigated using DFT and DFT-D3 correction dispersion methods. Compared to pristine C2N, the Fe2@C2N monolayer is more energetically efficient with high adsorption energies and has apparent charge transfer with these toxic gases. Our results revealed that NO preferred to be adsorbed on the Fe2@C2N with a superior Eads of −7.006 eV. The electric conductivity, sensitivity, and selectivity of C2N are significantly influenced by CO, NO, HCN, CS2, and SO2 molecules. Moreover, the opening of band gaps induced by the adsorption of NO gas molecules at Fe2@C2N can be used as an electronic signal to detect NO gas. Intriguingly, the partial density of states (PDOS) indicated that the NO adsorption of pristine C2N and Fe2@C2N monolayers exhibited half-metallicity behavior and magnetic properties. Non-covalent interactions (NCI) and the quantum theory of atoms in molecules (QTAIM) descriptors were examined to analyze the interaction process. This study can provide a new avenue for synthesizing and developing highly sensitive candidates and inexpensive green double-atom catalysts to capture and detect CO, NO, HCN, CS2, and SO2 molecules from the atmosphere at ambient temperature.

PdNi alloys with surface segregation of Pd@hydrophilic N, O doped carbons toward hydrogen production with high current densities

A series of catalysts, which consist of PdNi alloy cores and N, O co-doped carbon (NOC) shells, are developed by pyrolysis of metal–organic framework (PdNi) for hydrogen production with high current densities. The bulk or surface Pd compositions (Pd/(Pd + Ni) molar ratios) of PdNi alloys can be well controlled by the fed ones. Meanwhile, some structural features that are favorable to HER activity, especially to achieving high HER current densities under low overpotentials, are further adjusted by the Pd compositions, including d-band center (εd) of PdNi alloy affected by surface segregation of Pd, hydrophilicity of NOC shell, and charge transfer and mass diffusion efficiency of an entire catalyst. When the bulk Pd/(Pd + Ni) molar ratio is ∼ 0.21, Pd0.21Ni0.79@NOC has a moderate εd, the highest hydrophilicity, the highest charge transfer and mass diffusion efficiency, and finally the highest electric double-layer capacitance (or electrochemical active surface area). Accordingly, it affords the optimal apparent or specific activity for hydrogen production with high current densities under low overpotentials in 0.5 M H2SO4, including a low apparent η1000 of ∼ 240 mV or specific η2500(BET) of ∼ 240.9 mV, and a high current density of ∼ 1590 mA cm−2 at only ∼ 242 mV.

Sulfadiazine removal efficiency with persulfate driven by electron-rich Cu-beta zeolites

Surface electron transport and transfer of catalysts have important consequences for persulfate (PS) activation in PS system. In this paper, an electron-rich Cu-beta zeolites catalyst was synthesized utilizing a straightforward solid-state ion exchange technique to efficiently degrade sulfadiazine. The X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) results revealed that Cu element substitutes Al element and enters the beta molecular sieve framework smoothly. Furthermore, the X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the Cu-beta catalyst is primarily Cu0. Cu-beta zeolites catalyst can exhibit excellent catalytic activity to degrade sulfadiazine with the oxidant of PS. The optimal sulfadiazine removal performance was explored by adjusting reaction parameters, including sulfadiazine concentration, catalyst dosage, oxidant dosage, and solution pH. The sulfadiazine removal efficiency in the Cu-beta zeolites/PS system could reach 90.5% at the optimal reaction condition ([PS]0 = 0.5 g/L, [Cu-beta zeolites]0 = 1.0 g/L, pH = 7.0) with 50 mg/L of sulfadiazine. Meanwhile, The degradation efficiency was less affected by anionic interference (Cl−, SO4−, HCO3−). The surface electron transport and transfer of the Cu-beta zeolites catalyst were significant causes for the remarkable degradation performance. According to electron paramagnetic resonance (EPR) and quenching studies, the Cu-beta zeolites/PS system was mostly dominated by SO4•- in the degradation of sulfadiazine. Furthermore, two possible pathways for sulfadiazine degradation were proposed according to the analysis of intermediate products detected by the liquid chromatography–mass spectrometry (LC-MS).

Manipulation of an electron by photoirradiation in the electron-catalyzed cross-coupling reaction.

An electron has recently been shown to catalyze the cross-coupling reaction of organometallic compounds with aryl halides. In terms of green and sustainable chemistry, the electron catalysis is much more desirable than the inevitably used transition metal catalysis but a high temperature of more than 100°C is required to achieve it. Here, we disclose that visible light photoirradiation accelerates the electron-catalyzed reaction of arylzinc reagents with aryl halides with the aid of a photoredox catalysis. Photoexcitation of a photoredox catalyst and an anion radical intermediate respectively affects the supply and transfer of the electron catalyst, promoting the cross-coupling reaction to proceed at room temperature. The supply of the electron catalyst by the photoredox catalysis makes the scope of aryl halides wider.

Preparation of thermally stable organic-inorganic hybrid nanocomposites from chemically functionalized oxidized graphite by in situ catalytic oxidative decarboxylation

ABSTRACT In this study, the preparation of thermally stable organic-inorganic hybrid nanocomposites from chemically functionalized oxidized graphite is carried out by in-situ catalytic oxidative decarboxylation of 3,5-dinitrobenzoic acid (reactant) in the presence of potassium persulfate (oxidant), silver nitrate (catalyst) and graphite (support) under thermal or microwave conditions. The effects of heat transfer and dosages of reactant, catalyst and oxidant on the crystalline structure and the morphology of nanocomposites are studied in detail. The prepared nanocomposites are characterized by EDS, elemental mapping, FE-SEM, FT-IR and XRD. The thermal stability of nanocomposites is examined by TGA and DSC. EDS shows that nanocomposites are composed of C, O, N, S, K and Ag elements. FT-IR exhibits that the graphitic layers in nanocomposites are mainly oxidized and functionalized with carboxyl, carbonyl, hydroxyl, epoxy, sulfate, nitrate and nitroaryl groups. Addition of nitroaryl groups to nanocomposites is also supported by an increase found in their C and N contents. XRD demonstrates the coexistence of both oxidized amorphous carbon and graphite in combination with different levels of organic and inorganic phases. The prepared nanocomposites show good thermal stability. The total area of the DSC curve in these nanocomposites compared to graphite is enhanced.

Cu As Co-Catalyst for the Photo-Electrochemical CO Reduction on Multi-Junction Photoabsorbers

Substantial research effort has been dedicated to the electrochemical reduction of CO2 (CO2R) to higher carbon products throughout the recent years, baring the promise of a production pathway for green fuels and chemicals.1 However, only little progress has been achieved in the light driven heterogeneous CO2R catalysis, especially considering selective processes towards C2+ products. This arises from the additional complexity of photo-electrochemical reactions, which means that not only the sluggish reaction kinetics, high overpotentials and low selectivity of CO2R, but also the insufficient voltage and sensitivity towards harsh electrolyte conditions of photoabsorbers have to be encountered. Considering CO2R as multi-step process with CO as intermediate mitigates some issues of the process, e.g. the necessary overpotential is reduced and a higher selectivity towards valuable products can be achieved.2 Multi-junction solar stacks can provide operating voltages >2 V, which is sufficient for reducing CO2 to CO with high efficiencies or even produce multi-carbon products from CO while oxidizing water as anode reaction.3 In this work, we designed a process for photo-electrochemical CO reduction with multi-junction photoabsorbers. We start out by showing photo-electrochemical modelling of tandem photoabsorbers that emphasizes the advantages of CO as reactant compared to CO2. Further, we focus on the preparation of a nano-structured Cu catalyst, the most common material for reducing CO to C2+. Therefore, the electrochemical deposition and surface characterization using SEM, EDX and XPS of the catalyst on a dark model electrode coated with a sputter deposited TiO2 protection layer will be presented. Moreover, the CO reduction performance of the model at different potentials are characterized. In addition, the light transmission of the model electrode is reported, baring the possibility of illuminating the photoelectrode from the catalyst front side in mind. Lastly, the transfer of the model catalyst to a photoabsorber as well as the design of a photo-electrochemical flow-cell are discussed. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Rev. 119, 7610–7672 (2019)1.Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catal. 8, 7445–7454 (2018)Seger, B., Hansen, O. & Vesborg, P. C. K. A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. RRL 1, e201600013 (2017). Figure 1

Fenton micro-reactor on a bubble: A novel microbubble-triggered simultaneous capture and catalytic oxidation strategy for recalcitrant organic pollutant removal

A novel catalyst-functionalized microbubble system was developed to trigger both of the Fenton reaction and the flotation separation on the gas-liquid interface of bubbles for efficiently removing the recalcitrant organic pollutants from waters. The Fe(II)-functionalized colloidal microbubbles (FCMBs) were featured as large specific surface area, great bubble density and high ·OH activation capacity. Approximately 98.2% and 93.1% of the triphenylmethane and aromatic azo pollutants were removed within 0.5 min, respectively. Particularly, at the lowest Fe(II) dose of 0.2 mmol/L, the FCMB-triggered Fenton still achieved 7.4–20.6% higher removal than the traditional Fenton method at 0.5 min. In addition to the Fenton oxidative degradation mechanism, the FCMBs themselves were able to capture and remove 20.1–36.8% of pollutants from water. Thus, FCMBs served as micro-reactors in terms of: (i) the target molecules and intermediates were adhered and separated by FCMBs; and (ii) the FCMBs enhanced the mass transfer of catalyst and exposed sufficient active sites on the bubble surface for catalytic oxidation reaction. Compared with the traditional Fenton, the present method showed the robust tolerance of pH (4.0–9.5) and salinity (up to 40‰) at decreased Fe(II) doses, and the bio-toxicity of intermediates was obviously lower. The FCMB-triggered pollutant capture and catalytic oxidation technology exhibited a great potency in engineering implementation given the flexible bubble construction, the integration and simplification of treatment unit, as well as the decreased chemical doses.

Carbon dots regulate the interface electron transfer and catalytic kinetics of Pt-based alloys catalyst for highly efficient hydrogen oxidation

The regulation of interface electron-transfer and catalytic kinetics is very important to design the efficient electrocatalyst for alkaline hydrogen oxidation reaction (HOR). Here, we show the Pt-Ni alloy nanoparticles (PtNi2) have an enhanced HOR activity compared with single component Pt catalyst. While, the interface electron-transfer kinetics of PtNi2 catalyst exhibits a very wide electron-transfer speed distribution. When combined with carbon dots (CDs), the interface charge transfer of PtNi2-CDs composite is optimized, and then the PtNi2-5 mg CDs exhibits about 2.67 times and 4.04 times higher mass and specific activity in 0.1 M KOH than that of 20% commercial Pt/C. In this system, CDs also contribute to trapping H+ and H2O generated during HOR, tuning hydrogen binding energy (HBE), and regulating interface electron transfer. This work provides a deep understanding of the interface catalytic kinetics of Pt-based alloys towards highly efficient HOR catalysts design.

Identifying the Dominant Role of Pyridinic-N-Mo Bonding in Synergistic Electrocatalysis for Ambient Nitrogen Reduction.

For electrochemical nitrogen reduction reaction (NRR), hybridizing transition metal (TM) compounds with nitrogen-doped carbonaceous materials has been recognized as a promising strategy to improve the activity and stability of electrocatalysts due to the synergistic interaction from the TM-N-C active sites. Nevertheless, up to date, the fundamental mechanism of this so-called synergistic electrocatalysis for NRR is still unclear. Particularly, it remains ambiguous which configuration of N dopants, either pyridinic N or pyrrolic N, when coordinated with the TM, predominately contributes to this synergy. Herein, a self-assembled three-dimensional 1T-phase MoS2 microsphere coupled with N-doped carbon was developed (termed MoS2/NC), showing an impressive NRR performance in neutral medium. The hybridization of MoS2 and N-doped carbon can synergistically enhance the NRR efficiency by optimizing the electron transfer of catalyst. Acidification/blocking/poisoning experiments reveal the decisive role of pyridinic-N-Mo bonding, rather than pyrrolic-N-Mo bonding, in synergistically enhancing NRR electrocatalysis. The electrochemical-based in situ Fourier transform infrared spectroscopy (in situ FTIR) technology provides deep insights into the substantial contribution of pyridinic-N-MoS2 sites to NRR electrocatalysis and further uncover the underlying mechanism (associative pathway) at a molecular level.

Modelling of kinetics, mass transfer and flow pattern on open foam structures in tubular reactors: Hydrogenation of arabinose and galactose on ruthenium catalyst

Open foam structures are very beneficial as heterogeneous catalysts for three-phase processes, because they have high efficiency and low pressure drop. A mathematical model for open foam catalyst structures was developed. It was based on the concept of axial dispersion as flow pattern, on liquid-solid mass transfer effects and intrinsic kinetics on the active sites of the catalyst. Rate equations were presented for the hydrogenation of individual sugars and binary sugar mixtures on Ru/C catalysts and they were implemented in the mass transfer and flow models of the open foam catalyst. The flow pattern in the foam structure was confirmed with step change experiments with an inert tracer. The multiphase model was applied on the hydrogenation of arabinose and galactose in a laboratory-scale open foam catalyst bed. The model was able to reproduce the main features of the experimental observations, both for individual sugars and binary sugar mixtures.

Development of Mass-Production-Scale High Performance and Reliable Catalyst Coated Membrane (CCM) for PEMFC Via Optimized Electrode Slurry for Direct Coating Process

The mass production of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction in the materials cost. The most costly component of a PEMFC is the membrane electrode assembly (MEA), which contains the precious metal catalyst, platinum. Most related research is focused on cost-reduction of the catalysts, or cost-reduction of the proton exchange membranes (PEMs), and little fundamental research has focused on alternative MEA manufacturing routes as a means of cost-reduction. The MEAs are generally manufactured by decal transfer method. The decal transfer method necessitates coating wider catalyst layers to address alignment tolerance stack up and membrane shrinkage issues at lamination. The costs of existing processes are too high and not scalable and the film quality can be too low for long life. In order to support large scale manufacturing, alternative methods for MEA fabrication are imperative. Available fabrication techniques, such as direct coating by brushing, screen printing, spraying and reactive spray deposition. The direct coating method is more simple and efficient than indirect coating process, decal transfer method and has no risk of uneven and incomplete transfer of catalyst in the catalyst layer (CL). Furthermore, it also produces a higher MEA performance than the conventional decal transfer method due to an easier controllability of the CL thickness as well as a better ionic connection between the CLs and the membrane resulted from a strong attachment of the solvent on the membrane. However, the direct coating of electrode slurry onto the membrane has a critical problem that the membrane has a high tendency to swell or wrinkle with a contact of many solvents in the electrode slurries, which could give rise to the deformation of the CL by fast volume changes of the membrane. Therefore, the optimization of electrode slurry and control of dry process is very important in the direct coating method for the high quality MEA fabrication. Additionally, the effects of direct roll-to-roll coating conditions on the electrode structure and PEMFC performance are poorly understood in many systems. This provides a detailed protocol and materials for the fabrication of reproducible, high-performance, mass-production-scale catalyst coated membranes (CCMs) through implementation of an advance slot-die coating approach of the CLs directly onto PEMs. And this work is to investigate the influence of direct coating parameters on CCM structure and performance, with a particular focus on the slot-die system because of its ability to produce very high performance CCMs at low initial capital cost, particularly at mass-production-scale. The CCMs were analyzed by scanning electron microscopy (SEM) to assess surface morphology, as well as cross-section thickness and porosity. The performance of these CCMs was tested in PEMFCs with standard protocols and their resistance during PEMFC testing was studied by electrochemical impedance spectroscopy. Figure 1. (a) Procedure of direct roll-to-roll coating process, and (b) catalysts coated membrane. Figure 1

Still Unconquered: Enantioselective Passerini and Ugi Multicomponent Reactions.

The Passerini three-component (P-3CR) and the Ugi four-component (U-4CR) are two of the most prominent isocyanide-based multicomponent reactions (IMCRs). The P-3CR transforms isocyanides, aldehydes (ketones), and carboxylic acids to α-acyloxy carboxamides, while the U-4CR converts isocyanides, aldehydes (ketones), amines, and carboxylic acids to α-acetamido carboxamides. Conversion of the high energy formal divalent isocyano carbon into a tetravalent amide carbonyl carbon provides the driving force for these reactions. While the prototypical P-3CR and U-4CR provide linear adducts, many heterocycles and macrocycles are now readily synthesized by modifying these truly versatile reactions. As one stereocenter is generated by the nucleophilic addition of the isocyanide to the carbonyl and imine functions, the search for enantioselective versions of these reactions has become a much sought after goal among synthetic chemists. This seemingly trivial endeavor turns out to be extremely difficult to achieve, in sharp contrast to the remarkable progress documented in the field of asymmetric synthesis in general and catalytic enantioselective nucleophilic addition to C═X bond in particular. Since Denmark's first report in 2003 on the catalytic enantioselective Passerini two-component reaction of isocyanides with aldehydes, several Lewis acid (LA) and Brønsted acid-catalyzed enantioselective protocols have been developed. However, it is fair to say that truly catalytic enantioselective P-3CR and U-4CR with wide application scope remain elusive. In this Account, we summarize the progress recorded in this field over the past 15 years. We entered the field by investigating the enantioselective reaction of α-isocyanoacetamides with aldehydes and imines, which was previously developed in our lab for the synthesis of functionalized 5-aminooxazoles. Our initial experimental results, in conjunction with Dömling's and Schreiber's earlier findings, prompted us to assume that the low turnover number in LA-catalyzed asymmetric IMCRs is a main hurdle for enantioselectivity. We speculated that the LA incapable of forming chelates would be the catalyst of choice for enantioselectivity, the rational being that the P-3CR and the U-4CR afforded bidentate intermediates (α-hydroxy imidates, α-amino imidates) and products (α-acyloxy carboxamides, α-acetamido carboxamides) from nonchelating inputs. Therefore, the transfer of catalyst from these chelating intermediates or products to the monocoordinating starting materials would be difficult, hence the problem with catalyst turnover. This working hypothesis turned out to be a valuable guide that allowed us to develop Al-salen and Al-phosphate-catalyzed enantioselective P-3CR and enantioselective construction of chiral heterocycles such as oxazoles and tetrazoles. Nevertheless, all our attempts to apply these LA catalysts to the Ugi reaction failed. Indeed, to date, no reports on the successful LA-catalyzed asymmetric Ugi-type reactions exist in the literature. However, significant progress has been made in recent years employing organocatalysts. We developed a chiral phosphoric acid (CPA)-catalyzed enantioselective three-component synthesis of 2-(1-aminoalkyl)-5-aminooxazoles, a four-component synthesis of epoxy-tetrahydropyrrolo[3,4- b]pyridin-5-ones and a Ugi four-center, three-component reaction of isocyanides, anilines, and 2-formylbenzoic acids for the synthesis of isoindolinones. Other groups have found that chiral dicarboxylic acid and BOROX are effective catalysts for truncated Ugi three-component reactions.

Intramolecular Transfer of Pd Catalyst on Carbon–Carbon Triple Bond and Nitrogen–Nitrogen Double Bond in Suzuki–Miyaura Coupling Reaction

Intramolecular transfer of t-Bu3P-ligated Pd catalyst on a carbon–carbon triple bond (C≡C) and nitrogen–nitrogen double bond (N=N) was investigated and compared with the case of a carbon–carbon double bond (C=C), which is resistant to intramolecular transfer of the Pd catalyst. Suzuki–Miyaura coupling reaction of equimolar 4,4’-dibromotolan (1a) or 4,4’-dibromoazobenzene (1b) with 3-isobutoxyphenylboronic acid (2) was carried out in the presence of t-Bu3P-ligated Pd precatalyst 3 and KOH/18-crown-6 as a base at room temperature. In both cases, the diphenyl-substituted product was selectively obtained, indicating that the Pd catalyst walked from one benzene ring to the other through the C≡C or N=N bond after the first substitution with 2. Taking advantage of this finding, we conducted unstoichiometric Suzuki–Miyaura polycondensation of 1.3 equiv. of 1 and 1.0 equiv. of phenylenediboronic acid (ester) 6 in the presence of 3 and CsF/18-crown-6 as a base, obtaining high-molecular-weight conjugated polymer with a boronic acid (ester) moiety at both ends, contrary to the Flory principle.

Mechanistic Investigation of Catalyst-Transfer Suzuki-Miyaura Condensation Polymerization of Thiophene-Pyridine Biaryl Monomers with the Aid of Model Reactions.

We have investigated the requirements for efficient Pd-catalyzed Suzuki-Miyaura catalyst-transfer condensation polymerization (Pd-CTCP) reactions of 2-alkoxypropyl-6-(5-bromothiophen-2-yl)-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (12) as a donor-acceptor (D-A) biaryl monomer. As model reactions, we first carried out the Suzuki-Miyaura coupling reaction of X-Py-Th-X' (Th=thiophene, Py=pyridine, X, X'=Br or I) 1 with phenylboronic acid ester 2 by using tBu3 PPd0 as the catalyst. Monosubstitution with a phenyl group at Th-I mainly took place in the reaction of Br-Py-Th-I (1 b) with 2, whereas disubstitution selectively occurred in the reaction of I-Py-Th-Br (1 c) with 2, indicating that the Pd catalyst is intramolecularly transferred from acceptor Py to donor Th. Therefore, we synthesized monomer 12 by introduction of a boronate moiety and bromine into Py and Th, respectively. However, examination of the relationship between monomer conversion and the Mn of the obtained polymer, as well as the matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra, indicated that Suzuki-Miyaura coupling polymerization of 12 with (o-tolyl)tBu3 PPdBr initiator 13 proceeded in a step-growth polymerization manner through intermolecular transfer of the Pd catalyst. To understand the discrepancy between the model reactions and polymerization reaction, Suzuki-Miyaura coupling reactions of 1 c with thiopheneboronic acid ester instead of 2 were carried out. This resulted in a decrease of the disubstitution product. Therefore, step-growth polymerization appears to be due to intermolecular transfer of the Pd catalyst from Th after reductive elimination of the Th-Pd-Py complex formed by transmetalation of polymer Th-Br with (Pin)B-Py-Th-Br monomer 12 (Pin=pinacol). Catalysts with similar stabilization energies of metal-arene η2 -coordination for D and A monomers may be needed for CTCP reactions of biaryl D-A monomers.

Alternating Intramolecular and Intermolecular Catalyst-Transfer Suzuki-Miyaura Condensation Polymerization: Synthesis of Boronate-Terminated π-Conjugated Polymers Using Excess Dibromo Monomers.

The Suzuki-Miyaura coupling polymerization of dibromoarene 1 and arylenediboronic acid (ester) 2 with a Pd catalyst having a high propensity for intramolecular catalyst transfer is reported. The polymerization of excess 1 with 2 affords high-molecular-weight π-conjugated polymer having boronic acid (ester) moieties at both ends, contrary to Flory's principle. This unstoichiometric polycondensation behavior is accounted for by intramolecular transfer of the Pd catalyst on 1. In the polymerization of 1 and 2 having different aryl residues, high-molecular-weight polymer is obtained when the stronger donor aromatic is used as the dibromo monomer and the weaker donor or acceptor aromatic is used as diboronic acid (ester) monomer. The pinacol boronate moieties at both ends of the obtained poly(p-phenylene) (PPP) can be converted to benzoic acid ester, hydroxyl group, and bromine. Furthermore, the reaction of the pinacol boronate-terminated PPP with poly(3-hexylthiophene) (P3HT) having bromine at one end yields a triblock copolymer of P3HT-b-PPP-b-P3HT.

Preparation and evaluation of a metallic foam catalyst for steam-CO2 reforming of methane in GTL-FPSO process

A metallic foam catalyst was used to improve the heat transfer of a reactor for the steam-CO2 reforming (SCR) of methane in the GTL-FPSO (gas to liquid-floating production storage and offloading) process. The metallic foam catalyst was prepared and examined by scanning electron microscopy, fall-off test and SCR reaction. The radial heat transfer was characterized in terms of the Nusselt number and was compared with the pellet catalyst to confirm the improvement in the heat transfer of the metallic foam catalyst. As a result of the fall-off test, the adhesion strength was highest at an Al2O3/AIP molar ratio of 5. The Nusselt number of the metallic foam catalyst was higher than that of the conventional pellet catalyst. Therefore, the reformer had a uniform temperature distribution along the catalyst-bed when the metallic foam catalyst was used.

Reaction Mechanism for the Dual Gold‐Catalyzed Synthesis of Dibenzopentalene: A DFT Study

A wide range of gold-catalyzed reactions based on a dual activation mechanism has recently been reported in the literature. Herein, we present a computational investigation of the mechanism for the formation of dibenzopentalenes from 1-ethynyl-2-(phenylethynyl)benzene. Transition states have been found, which substantiate the dual activation mechanism previously published and furthermore point towards a continuous presence of two gold moieties throughout the mechanistic cycle, an observation of high importance for all reactions in the field of dual activation. The initial activation of the diyne has been shown to proceed via an intermolecular transfer of a cationic gold catalyst from the thermodynamically preferred geminal-σ,π-acetylide complex to the active non-geminal analogue. Furthermore, the regioselectivity of a 5-endo versus a 6-endo cyclization has been addressed, and the 5-endo cyclization was found to be most favorable both thermodynamically and with regard to the activation barrier.