Result 1 - 6 of total 6
Results in Chemistry, Vol 4, Iss , Pp 100495- (2022)
2022
| Keywords | Chemistry ; QD1-999 |
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| Language | English |
| Publishing date | 2022-01-01T00:00:00Z |
| Publisher | Elsevier |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
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Frontiers in Catalysis, Vol
2022 Volume 2
Abstract: Molecular hydrogen (H2) is considered an ideal energy vector and a clean fuel, due to its zero-carbon combustion. Nevertheless, despite hydrogen is the most and one of the most abundant elements in the universe and in earth crust, respectively, it is ... ...
| Abstract | Molecular hydrogen (H2) is considered an ideal energy vector and a clean fuel, due to its zero-carbon combustion. Nevertheless, despite hydrogen is the most and one of the most abundant elements in the universe and in earth crust, respectively, it is always combined with other elements in our planet and never appears in its elemental state. This means that H2 must be produced through, almost always, endergonic processes, whose sustainability depend not only on the starting material but also on the source of energy necessary for these processes to occur. Colors have been assigned to identify the level of sustainability of H2 production with the green one indicating H2 produced from water using a renewable source of energy, preferably sunlight. Redox water splitting (WS) into H2 (hydrogen evolution reaction, HER) and O2 (oxygen evolution reaction, OER) is, nevertheless, an extremely difficult process not only from the thermodynamic but also from the kinetic point of view. Relevant kinetic barriers are present in both sides of the redox process, especially in OER. For this reason, performing WS in an efficient manner requires the development of active and robust catalysts capable of offering alternative reaction pathways to WS, lowering down the unfavorable kinetic barriers and thus maximizing the energy conversion efficiency. Inspiration for developing efficient catalysts for HER and OER has traditionally derived from Nature, who, over the course of many billions of years, according to the evolutionary theory, has assembled two molecular catalytic pools, namely oxygen evolving complex and ferredoxin/ferredoxin NADP+ reductase, which offer viable kinetic pathways to both OER and reduction of NADP+ (the “biological form” of H2). In reality, after several attempts of mimicking natural catalysts, the efforts of the researchers have been addressed to different molecular systems, which exhibit best performances, unfortunately often based on noble-metal atoms, especially for OER. In this contribution we review the ... |
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| Keywords | green hydrogen ; water oxidation ; hydrogen evolution ; homogeneous catalysis ; organometallics ; Chemistry ; QD1-999 |
| Subject code | 660 ; 541 |
| Language | English |
| Publishing date | 2022-05-01T00:00:00Z |
| Publisher | Frontiers Media S.A. |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
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Polymers, Vol 15, Iss 1378, p
2023 Volume 1378
Abstract: The dinuclear aluminum salt {[ i Bu 2 (DMA)Al] 2 ( μ -H)} + [B(C 6 F 5 ) 4 ] − ( AlHAl ... DMA = N , N -dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues ... ...
| Abstract | The dinuclear aluminum salt {[ i Bu 2 (DMA)Al] 2 ( μ -H)} + [B(C 6 F 5 ) 4 ] − ( AlHAl DMA = N , N -dimethylaniline) is the prototype of a new class of molecular cocatalysts for catalytic olefin polymerization, its modular nature offering easy avenues for tailoring the activator to specific needs. We report here, as proof of concept, a first variant ( s-AlHAl ) bearing p -hexadecyl- N , N -dimethylaniline (DMA C16 ) units, which enhances solubility in aliphatic hydrocarbons. The novel s-AlHAl was used successfully as an activator/scavenger in ethylene/1-hexene copolymerization in a high-temperature solution process. |
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| Keywords | olefin polymerization ; catalyst activation ; borate activators ; methylaluminoxane ; soluble cocatalyst ; Organic chemistry ; QD241-441 |
| Language | English |
| Publishing date | 2023-03-01T00:00:00Z |
| Publisher | MDPI AG |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
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Inorganics, Vol 7, Iss 10, p
2019 Volume 123
Abstract: Clean production of renewable fuels is a great challenge of our scientific community. Iridium complexes have demonstrated a superior catalytic activity in the water oxidation (WO) reaction, which is a crucial step in water splitting process. Herein, we ... ...
| Abstract | Clean production of renewable fuels is a great challenge of our scientific community. Iridium complexes have demonstrated a superior catalytic activity in the water oxidation (WO) reaction, which is a crucial step in water splitting process. Herein, we have used a defective zirconium metal−organic framework (MOF) with UiO-66 structure as support of a highly active Ir complex based on EDTA with the formula [Ir(HEDTA)Cl]Na. The defects are induced by the partial substitution of terephthalic acid with smaller formate groups. Anchoring of the complex occurs through a post-synthetic exchange of formate anions, coordinated at the zirconium clusters of the MOF, with the free carboxylate group of the [Ir(HEDTA)Cl] − complex. The modified material was tested as a heterogeneous catalyst for the WO reaction by using cerium ammonium nitrate (CAN) as the sacrificial agent. Although turnover frequency (TOF) and turnover number (TON) values are comparable to those of other iridium heterogenized catalysts, the MOF exhibits iridium leaching not limited at the first catalytic run, as usually observed, suggesting a lack of stability of the hybrid system under strong oxidative conditions. |
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| Keywords | metal–organic framework ; post-synthetic modification ; iridium catalysis ; water oxidation ; water splitting ; Inorganic chemistry ; QD146-197 |
| Subject code | 540 |
| Language | English |
| Publishing date | 2019-10-01T00:00:00Z |
| Publisher | MDPI AG |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
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Catalysts, Vol 11, Iss 2, p
Mechanisms and Implications for Catalysis
2021 Volume 215
Abstract: Even after several decades of intense research, mechanistic studies of olefin polymerization by early transition metal catalysts continue to reveal unexpected elementary reaction steps. In this mini-review, the recent discovery of two unprecedented chain ...
| Abstract | Even after several decades of intense research, mechanistic studies of olefin polymerization by early transition metal catalysts continue to reveal unexpected elementary reaction steps. In this mini-review, the recent discovery of two unprecedented chain termination processes is summarized: chain transfer to solvent (CTS) and chain transfer to monomer (CTM), leading to benzyl/tolyl and allyl type chain ends, respectively. Although similar transfer reactions are well-known in radical polymerization, only very recently they have been observed also in olefin insertion polymerization catalysis. In the latter context, these processes were first identified in Ti-catalyzed propene and ethene polymerization; more recently, CTS was also reported in Sc-catalyzed styrene polymerization. In the Ti case, these processes represent a unique combination of insertion polymerization, organic radical chemistry and reactivity of a M(IV)/M(III) redox couple. In the Sc case, CTS occurs via a σ-bond metathesis reactivity, and it is associated with a significant boost of catalytic activity and/or with tuning of polystyrene molecular weight and tacticity. The mechanistic studies that led to the understanding of these chain transfer reactions are summarized, highlighting their relevance in olefin polymerization catalysis and beyond. |
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| Keywords | olefin polymerization ; chain transfer ; solvent activation ; chain ends ; homolysis ; Ti(IV)/Ti(III) redox couple ; Chemical technology ; TP1-1185 ; Chemistry ; QD1-999 |
| Subject code | 540 |
| Language | English |
| Publishing date | 2021-02-01T00:00:00Z |
| Publisher | MDPI AG |
| Document type | Article ; Online |
| Database | BASE - Bielefeld Academic Search Engine (life sciences selection) |
Your chosen title can be delivered directly to ZB MED Cologne location if you are registered as a user at ZB MED Cologne.
Journal of the American Chemical Society. 2018 June 18, v. 140, no. 28
2018
Abstract: Twisted intramolecular charge transfer (TICT) chromophores exhibit uniquely large second-order optical nonlinearities (μβ). However, their promise as electro-optic (E-O) materials is yet untapped, reflecting a strong tendency to aggregate in low-polarity ...
| Abstract | Twisted intramolecular charge transfer (TICT) chromophores exhibit uniquely large second-order optical nonlinearities (μβ). However, their promise as electro-optic (E-O) materials is yet untapped, reflecting a strong tendency to aggregate in low-polarity media, leading to a dramatic fall in μβ. Until now, TICT chromophores in deaggregating polar solvents suffered decreased response due to polarity-driven changes in electronic structure. Here we report a new series of benzimidazolium-based TICT chromophores with interaryl torsional angles in the range of 64–77°. The most twisted, B2TMC-2, exhibits a large μβvec = −26,000 × 10–48 esu (at 1907 nm) in dilute nonpolar CH2Cl2 solution, which is maintained in polar DMF (μβvec= −20,370 × 10–48 esu) as measured by DC electric field-induced second harmonic generation (EFISH). Sterically enforced interaryl torsional angles are confirmed by single-crystal X-ray diffraction and solution phase Nuclear Overhauser Effect (NOE) NMR, and spectroscopic characterization reveals a zwitterionic/aromatic ground state electronic structure associated with the high μβ. We show that increasingly disrupted conjugation is correlated with increased μβ even at intermediate twist angles. The excellent performance and reduced aggregation in polar solvents opens new avenues for bridging microscopic and macroscopic chromophore performance. |
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| Keywords | methylene chloride ; nuclear magnetic resonance spectroscopy ; solvents ; spectral analysis ; X-ray diffraction ; zwitterions |
| Language | English |
| Dates of publication | 2018-0618 |
| Size | p. 8746-8755. |
| Publishing place | American Chemical Society |
| Document type | Article |
| ZDB-ID | 3155-0 |
| ISSN | 1520-5126 ; 0002-7863 |
| ISSN (online) | 1520-5126 |
| ISSN | 0002-7863 |
| DOI | 10.1021/jacs.8b04320 |
| Database | NAL-Catalogue (AGRICOLA) |
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