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Catalysis Science & Technology

The reactivity of a phenoxy-imine-ether system (FI)TiCl3/MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt%, 520–450 kg1-hexene gTi1 h−1) between 30 and 40 °C, to a moderate polyethylene formation (70–80 wt%, 60–70 kgpolyethylene gTi1 h−1) at a higher reaction temperature (T > 60 °C). Polymerization was investigated based on an original “polymer-to-catalyst” strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature 13C NMR analyses, polyethylenes were found to exhibit high molar masses (>105 g mol−1) and a low 1-hexene content (<1 mol%) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at a higher temperature. The increase of dispersity to 4.6 at 80 °C suggests a change from single to multi-site catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler–Natta or a bulky post-metallocene catalyst.

20 July, 2020

Chemical Communications Journal

The reaction of cyclic amides with acetylene under low pressure, using ruthenium-phosphine catalysts, afforded a broad variety of N-vinylated amides including (azabicyclic) lactams, oxazolidinones, benzoisoxazolones, isoindolinones, quinoxalinones, oxazinanones, cyclic urea derivatives (imidazolidinones), nucleobases (thymine), amino acid anhydrides and thiazolidinone.


15 July, 2020

Molecular Catalysis Journal

Diffusion and acidity of molecules are key parameters in organic synthesis; therefore, highly stable mesoporous HZSM-5 zeolites with ratios of Brønsted (CB) to Lewis (CL) acid sites tuned by alkaline desilication were employed for Friedel–Crafts acylation of anisole with acetic anhydride. Controlled zeolite desilication (Si/Al = 12 and 23) proceeded by varying the NaOH concentration, temperature, and treatment time. SEM/EDS, XRD, N2 physisorption, NH3-TPD, DRIFTS, and 29Si-MAS-NMR data were used to correlate the generated intracrystalline mesoporosity with the new textural, acidic, and catalytic properties. It was evidenced that desilication allowed the CB/CL ratio to vary from 21 to 2.3. During anisole acylation, the specific activity to 4-methoxyacetophenone (4-MAP), on a desilicated zeolite that preserved most of the original microstructure, markedly increased with increasing mesoporosity, even a decrease of the CB/CL ratio had occurred. The strong changes in the acid nature and textural properties did not change the anisole acylation acid mechanism and improved the internal diffusion of reactants and 4-MAP to or from the active sites, respectively. Thus, appropriate levels of mesoporosity with consequent acidity changes may be designed through controlled zeolite desilication, with the resultant hierarchical zeolite capable of being applied as a catalyst to a particular organic reaction mechanism.

1 July, 2020

CrystEngComm Journal

Although the concept of quantum confinement was introduced more than thirty years ago, a wide application of the quantum dots is still limited by the fact that monodisperse quantum dots with controlled optoelectronic properties are typically synthesized on a relatively small scale. Larger scale synthesis techniques are usually not able to produce monodisperse nanoparticles yet. In this contribution, we illustrate the capability of the combination of transmission electron microscopy and X-ray diffraction to reveal detailed and scale-bridging information about the complex microstructure of non-monodisperse quantum dots, which is the first step towards a further upscalling of the techniques for production of quantum dots with controlled properties. As a model system, CdSe quantum dots synthesized using an automated robotic hot-injection method at different temperatures were chosen. The combined microstructure analytics revealed the size and shape of the CdSe nanocrystals and the kind, density and arrangement of planar defects. The role of the planar defects in the particle coarsening by oriented attachment and the effect of the planar fault arrangement on the phase constitution, on the crystallographic coherence of the counterparts and on the optoelectronic properties are discussed.

11 June, 2020

Combinatorial Science Journal

Translation of a manual process to high throughput for research and development requires special consideration. One important and often unreported aspect is the establishment of an efficient cleaning routine. This becomes significant, as precious time and, in particular, material would be lost, that is, when low-quality high-throughput experimentation is involved. We present a fully automated cleaning routine of the challenging synthesis of cadmium selenide quantum dots. Manual, semiautomated, and fully automated cleaning protocols were executed and compared in terms of spectral similarities of the synthesized colloids. Only the fully automated protocol enabled true 24/7 operation.


1 June, 2020

ChemCatChem Journal

The selective hydroconversion of 5‐hydroxymethylfurfural (HMF) to biofuels is currently highly sought‐for. While the literature has demonstrated that this reaction is possible on promoted Ni catalysts, we show here that a monometallic, non‐promoted Ni/SBA‐15 catalyst, prepared by incipient wetness impregnation, can convert HMF to 2,5‐dimethylfuran (DMF) and to 2,5‐dimethyltetrahydrofuran (DMTHF) at 180 °C, in a consecutive way. Through a control over reaction time, high yields to DMF (71 %, at conversion of 93 %) or DMTHF (97 %, at conversion of 100 %) can be achieved. Kinetic modelling suggests a preferential route to DMF via 5‐methylfurfural (MFFR) as intermediate, though the route via 2,5‐bis(hydroxylmethyl)furan (BHMF) is also present. The favored route in the experimental conditions involves the hydrogenolysis of the hydroxyl group of HMF as first step, followed by the hydrogenation of the aldehyde function, to methylfurfuryl alcohol (MFOL). It is suggested a higher reaction rate of hydrogenation or hydrogenolysis of the side group is linked to the presence of a methyl group in the molecule. No hydrogenation of the furan ring is detected on the intermediates.

29 May, 2020

ACS Publications

An enzyme degassing method for oxygen-intolerant polymerizations was implemented in a commercially available automated parallel synthesizer and tested for reversible addition–fragmentation chain transfer (RAFT) polymerizations performed in open vessels. For this purpose, a recently reported methodology that employs the enzyme glucose oxidase (GOx) to deplete oxygen in reaction media was utilized. The effectiveness of this approach to perform unattended parallel polymerization reactions in open vessels was demonstrated by comparing experimental results to those obtained under similar experimental conditions but utilizing the common degassing method of sparging N2 to remove oxygen. The proposed experimental technique displayed good precision in performing RAFT polymerizations and good control of the obtained polymers and could be easily adapted to other systems where the removal of oxygen is mandatory. This alternative high-throughput/high-output method may have the potential to increase productivity in research projects where oxygen-intolerant reactions are involved.


30 April, 2020

ACS Publications

Hybrid, e.g. organic inorganic, perovskites from the type methylammonium lead iodide (CH3NH3PbI3), are promising solar cell materials. However, due to the large parameter space spanned by the manifold combinations of divalent metals with organic cations and anions, an efficient approach is needed to rapidly test and categorize new promising materials. Herein, we developed a high throughput approach for the automated synthesis of perovskite layers with different precursor ratios at varying annealing temperatures. The layers were analyzed by optical absorption and photoluminescence (PL) spectroscopy as well as X-ray diffraction (XRD) and evaluated using two different procedures. The first one is a stepwise exclusion of non-performing reactant ratios and synthesis conditions by using both spectroscopic techniques, followed by a final validation of the procedure by XRD. In the second procedure, only PL results were consulted in combination with high throughput screening using design of experiments (DoE) to reduce the total number of experiments needed and compared to the manual cascade approach. Noteworthy, by simple PL screening, it was possible to identify the best ratio of perovskite to byproducts and annealing temperature. Thus, only with PL more detailed results as with the manual protocol were reached, while at the same time the effort for characterization was significantly reduced (by 60 % of the experimental time). In conclusion, our approach opens a way towards fast and efficient identification of new promising materials at different reaction and process conditions.

19 March, 2020

ACS Publications

Copolymerization of isoprene (IP) with glycidyl methacrylate (GMA) was performed under RAFT (reversible addition–fragmentation chain-transfer) polymerization conditions in a platform for high-output experimentation. Covering the range between 1 and 0.2 molar fraction of IP in the feed, four sets of reactions were carried out at 10, 15, 20, and 30 h at 115 °C. The kinetic data obtained were used to estimate the reactivity ratios using a nonlinear least-squares approach (NLLS). Reactivity ratios rGMA = 0.61 and rIP = 0.74 indicate that both monomers tend to crosspropagate in agreement with known literature values. Concerning the RAFT study, relatively good control and livingness of the copolymerization was observed except for the experiment in which IP represents 20 mol % in the feed. 1H NMR characterization confirmed the presence of both monomers in the final copolymer, particularly the presence of the epoxy ring of GMA which is susceptible to post polymerization reactions. Finally, preliminary results on the hydrogenation of various polymers are discussed.

28 February, 2020

Carbohydrate Research Journal

Rhamnan and rhamnan sulfate are naturally occurring carbohydrates that have important biological functions and possible therapeutic applications, but studies are limited to the microheterogeneous mixtures from natural sources. This work reports the first synthesis of any sulfated rhamnan fragments and successful automation of the process with a recently developed automated solution-phase approach using N-iodosuccinimide/trimethylsilyl triflate (NIS/TMSOTf) promotor and levulinoyl ester deprotection conditions. The automated solution-phase activation/deprotection approach was initially able to create alpha 1 → 2, 1 → 3 type rhamnan di- and trisaccharide in moderate yields. Once these targets were achieved, a process to use SO3•pyridine complex in DMF for sulfation compatible with an automated solution-phase liquid handling system was developed and successfully applied to carbohydrate sulfation to create two rhamnan sulfate fragments with differing monosulfation patterns.


22 January, 2020