Auswahl der wissenschaftlichen Literatur zum Thema „Salophen co-catalyst“

Single-atom catalysts are a family of heterogeneous electrocatalysts widely used in energy storage and conversion. The determination of the local structure of the active metal sites is challenging, which limits the establishment of the reliable structure-property relationship of single-atom catalysts. A carbon black-conjugated complex can be used as the model catalyst to probe the intrinsic activity of metal sites with certain local structures. In this work, we prepared carbon black-conjugated [Co(phenanthroline)Cl2], [Co(o-phenylenediamine)Cl2] and [Co(salophen)]. In these catalysts, the Co complexes with well-defined structures are anchored on the edge of carbon black by pyrazine moieties. The number of electrochemical accessible Co sites can be measured from the area of the redox peaks of pyrazine linkers in the cyclic voltammetry curve. Then, the intrinsic electrocatalytic activity of one Co site can be obtained. The catalytic performances of the three catalysts towards oxygen reduction reaction in alkaline conditions were measured. Carbon black-conjugated [Co(salophen)] showed the highest intrinsic activity with the turnover frequency of 0.72 s−1 at 0.75 V vs. the reversible hydrogen electrode. The strategy developed in this work can be used to explore and verify the possible local structure of active sites proposed for single-atom catalysts.

Abstract Catalysts based on porous polymeric microspheres were prepared from N,N′-Bis(3,3′-allyl-salicylidene)-o-phenylenediamine Pd(II) (PdAS) metallo-monomer, styrene (STY), and divinylbenzene (DVB) as co-monomers. The effects of the STY/PdAS mass ratio of co-monomers were investigated to synthesize the optimal catalyst. All the prepared materials were characterized by scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, inductively coupled plasma optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), solid-state diffuse-reflectance UV Vis (DRS UV-Vis) spectrometry, and X-ray photoelectron spectroscopy (XPS). Increasing the PdAS content from 1 to 5 wt%, based on the mass feed of monomers, produced well-defined spherical polymer resins with particle diameters of ~200 μm and high surface areas (>500 m2/g). XPS spectra shown a unique Pd2+ signal associated with the PdAS complex immobilized on a porous resin matrix. The catalytic performances of porous polymer microspheres were evaluated for Heck reaction between iodobenzene and methyl acrylate to produce methyl cinnamate, giving up to 100 % selectivity for the trans-isomer. The resin with 5 wt% PdAS showed the best catalytic activity in methyl cinnamate synthesis. Finally, the best catalytic system was evaluated in octinoxate production producing the target product with the same levels of conversion and selectivity for trans-isomer as was detected for methyl cinnamate synthesis.

Addition of a soluble or a supported CrIII-salophen complex as a co-catalyst greatly enhances the catalytic activity of Bu4NBr for the formation of styrene carbonate from styrene epoxide and CO2. Their combination with a very low co-catalyst:Bu4NBr:styrene oxide molar ratio = 1:2:112 (corresponding to 0.9 mol% of CrIII co-catalyst) led to an almost complete conversion of styrene oxide after 7 h at 80°C under an initial pressure of CO2 of 11 bar and to a selectivity in styrene carbonate of 100%. The covalent heterogenization of the complex was achieved through the formation of an amide bond with a functionalized {NH2}-SBA-15 silica support. In both conditions, the use of these CrIII catalysts allowed excellent conversion of styrene already at 50°C (69 and 47% after 24 h, respectively, in homogeneous and heterogeneous conditions). Comparison with our previous work using other metal cations from the transition metals particularly highlights the preponderant effect of the nature of the metal cation as a co-catalyst in this reaction, that may be linked to its calculated binding energy to the epoxides. Both co-catalysts were successfully reused four times without any appreciable loss of performance.

Ce projet a pour objectif la mise au point d’une réaction globale de synthèse de styrène carbonate à partir du styrène en présence de CO2 et d’un oxydant propre : O2. Les catalyseurs Salophen-R-M (R = Me2N, Et2N, tBu et M = Mn, Ni et Cr) ont été synthétisés et leur activité co-catalytique pour la réaction de cycloaddition de CO2 sur le styrène oxyde a été évaluée en présence de Bu4NBr ; Salophen-Me2N-Cr a présenté les meilleurs résultats : 99% de rendement obtenu après 3h à 80°C. Les complexes Salophen-R-M ont été greffés sur silice mésoporeuse {NH2}-SBA-15 par liaison covalente. En parallèle, le greffage de sels d’ammonium quaternaires a été optimisé par voie ex-situ sur SBA-OH. Ces matériaux catalytiques ont été testés pour la formation de styrène carbonate, avec des rendements supérieurs à ceux obtenus en solution grâce à l’effet de synergie lié à la présence de silanols. Le catalyseur Salophen-Me2N-Cr a été testé en réaction d’époxydation Mukaiyama du styrène en présence de O2 Un rendement en styrène oxyde de 50% a été obtenu dans des conditions de réaction similaires à celles utilisées en cycloaddition. La réaction globale a été effectuée en présence de catalyseurs Bu4NBr et Salophen-Me2N-Cr à 80°C sous 3,5 bar O2 et 11 bar CO2. Un rendement maximum en styrène carbonate de 31% a été obtenu après réaction en deux étapes distinctes d’oxydation (3h) puis de cycloaddition (20h)
The objective of this project is to develop a comprehensive reaction for the synthesis of styrene carbonate from styrene in the presence of CO2 and a clean oxidant: O2. Salophen-R-M (R = Me2N, Et2N, tBu and M = Mn, Ni and Cr) catalysts were synthesized and their co-catalytic activity for the cycloaddition reaction of CO2 on styrene oxide was evaluated in the presence of Bu4NBr; Salophen-Me2N-Cr showed the best results: 99% yield obtained after 3h at 80°C. Salophen-R-M complexes were grafted onto mesoporous silica {NH2}-SBA-15 by covalent bonding. In parallel, the binding of quaternary ammonium salts was optimized by ex-situ grafting on SBA-OH. These catalytic materials were tested for the formation of styrene carbonate, with yields higher than those obtained in solution thanks to the synergy effect linked to the presence of silanols. The Salophen-Me2N-Cr catalyst was tested in the Mukaiyama epoxidation reaction of styrene in the presence of O2. A 50% yield of styrene oxide was obtained under reaction conditions similar to those used in cycloaddition. The overall reaction was performed in the presence of Bu4NBr and Salophen-Me2N -Cr catalysts at 80°C under 3.5 bar O2 and 11 bar CO2. A maximum yield of styrene carbonate of 31% was obtained after a two-step reaction of oxidation (3h) and cycloaddition (20h)