This defines a mechanism to tune the reactivity of metal active sites in microporous materials. Poly lactic acid PLA is extensively used as an eco-friendly compound for many applications. In this work, various materials including MOFs and simple bases have been applied as catalysts for the Lactide synthesis.
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The novel described procedure is even expected to be very efficient for industrial applications. A novel strategy to bio-based chemicals with a branched carbon skeleton is introduced. Hereto, small sugars, such as 1,3-dihydroxyacetone, are coupled catalytically to obtain branched C6 sugars, such as dendroketose, in high yield at mild conditions. By bringing this branching step up front, at the level of the sugar feedstock branching-first , new opportunities for the synthesis of useful chemicals arise.
Here, we show that the branched sugar can be efficiently valorized into i new branched polyols and ii short branched alkanes. These molecules are potentially interesting as plasticizers, crosslinkers or detergent precursors.
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The second valorization route demonstrates a facile hydrodeoxygenation of the branched sugars towards their corresponding branched alkanes e. In the short term, commercial integration of these mono-branched alkanes, in contrast to branched polyols, is expected to be straightforward, because of their drop-in character and well-known valuable octane booster role when present in gasoline. Accordingly, the branching-first concept is also demonstrated with other small sugars e.
This Editorial presents the Special Issue on Supported Molecular Catalysts as a forum to discuss recent advances in the immobilization and heterogenization of molecular catalysts. The scope ranges from organic synthesis and highly selective reactions through to photocatalysis and electrocatalysis, including advances in enzyme immobilization methodology. The outcome is a wide spectrum of papers encompassing all the old formal domains of catalysis research of both primary and secondary research.
Mesostructured silica—carbon nanocomposites with large mesopore interconnectivity are created from sucrose as sustainable carbon source using a mild vapor-phase assisted hydrothermal treatment procedure.
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A superior catalytic activity is demonstrated for the solvent-less condensation of 2-methylfuran with furfural; both product yield and conversion rate surpass that of reference catalysts such as their counterparts from dry pyrolysis and the commercial strong acid resins. The enhanced catalytic activity is attributed to the higher SO 3 H acid density 0. The origin of the well-developed large interconnecting mesopores is investigated and discussed.
The mild hydrothermal treatment causes local etching of the original mesopores in the precursor material, creating unexpected interconnectivity between the pores, while the original micropores are basically eliminated during the treatment. Therefore, the here specified hydrothermal treatment provides a promising method to conventional pyrolysis for the efficient and eco-friendly synthesis of highly mesoporous silica—carbon nanocomposites and modification of their physicochemical properties.
Selective dealkylation of alkylphenols, the opposite reaction of the more commonly studied phenol alkylation, may represent an important reaction in the production of base chemicals like phenol and olefins from fossilized and raw lignocellulosic matter. The reaction was studied deliberately in presence of steam to get stable time on stream catalysis.
The kinetic study examines the role of the catalytically active sites; it reveals the importance of site constraint on the activity, selectivity and stability, and shows the complex temperature dependency of the dealkylation. EP does not enter the micropores of ferrierite and ZSM, as suggested by adsorption experiments. Thus, in absence of intracrystalline diffusion limitation as verified by calculations using reported effective diffusivities, and substantiated by a comparably high apparent activation energy for all zeolites , the increased reaction turnover rate with increasing pore size from medium to large pore zeolites is largely explained by a change in reaction pathway from monolecular to bimolecular to convert EP to phenol and ethylene.
A pathway proceeding through fast thermodynamically favourable bimolecular reactions occurs in the spatially non-constrained pores and crystal surface, whereas monomolecular reactions take place in the micropores of ZSM Despite the lower rate, the selectivity over ZSM-5 strongly benefits from active site confinement, being responsible to achieve quantitative formation of phenol and ethylene from ethylphenol.
The excellent performance of ZSM-5 thus accords with its shape selective property that avoids undesired side reactions such as the sterically demanding bimolecular reactions like disproportionation, transalkylation and C-C cracking, and severe cokes formation. A catalytic reductive aminolysis of reducing monosaccharides into short ethylene diamines or C 2 diamines was recently communicated by our group Pelckmans et al.
Here, a general mechanism for this novel reaction is proposed based on the results of a combined experimental and theoretical study. The mechanism involves hemiaminal formation and subsequent dehydration to produce a zwitterionic iminium intermediate, which undergoes fast C—C cleavage as a result of intramolecular deprotonation, followed by hydrogenation of the formed unsaturated amine intermediate. The role of the amine in facilitating the C—C scission is explained in detail and supported by DFT calculations. Different catalysts, carbohydrate substrates, and reaction conditions were tested to validate the proposed reaction mechanism.
The reaction rate experiences a strong solvent dependency.
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DFT calculations show that presence of MeOH beneficially affects both the kinetics of the nucleophilic amine attack and the C—C bond scission. The high yield is explained by the formation of a heterocyclic oxazolidine intermediate. Iron-containing zeolites exhibit unprecedented reactivity in the low-temperature hydroxylation of methane to form methanol. Using nuclear resonance vibrational spectroscopy coupled to X-ray absorption spectroscopy, we probe the bonding interaction between the iron center, its zeolite lattice-derived ligands, and the reactive oxygen.
Density functional theory calculations clarify how the experimentally determined geometric structure of the active site leads to an electronic structure that is highly activated to perform H-atom abstraction. In previous works aiming at understanding the mesoporous network after alkaline treatment in the presence of organic additives, conventional bulk characterization techniques led to the conclusion that the dissolved zeolite does not undergo any kind of recrystallization [Verboekend, D.
The formation of a small amount of nanosized crystals or embryonic phases of silicalite-1 MFI zeolite is evidenced, as well as their homogeneous dispersion on the mesoporous surface of the beta zeolite. We think that these results may explain why a homogeneous mesopore size distribution is obtained, when organic pore-directing agents are used in the zeolite hierarchization process performed in an alkaline medium. Moreover, a connection is proposed between a broad range of multiple technologies and sustainable resources, with main attention to the native C skeleton and functionality of biomass.
Going deeper in sustainability, this paper selected four criteria, taking into account the entire valorisation route, to apply to the most promising carbohydrate-derived molecules. By doing this, the most promising chemicals and working points from a sustainable point of view are highlighted. The striking dimer selectivity is ascribed to the synergetic interplay between the activating methoxy groups and the oligomerisation-inhibiting propyl chain.
Lastly, to assess the functionality of the safe r bissyringol scaffold, it was converted into an APE. A new route to lactide, key building block of the bioplastic polylactic acid, is proposed via a continuous catalytic gas-phase transesterification of renewable alkyl lactates in a scalable fixed-bed setup. The solvent-free process allows for easy product separation and recycling of unconverted alkyl lactates and recyclable lactyl intermediates. Catalysts with high band gap energy of the supported TiO2 phase, indicative of a high surface spreading of isolated Ti centers, show the highest turnover frequency per Ti site.
In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely i lignocellulose fractionation, ii lignin depolymerisation, and iii upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations.
Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation i. During fractionation, this can be achieved by either i preserving the native lignin structure or ii by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates.
Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies. Amorphous aluminosilicates catalysts have been used industrially on a large scale for almost a century.
However, the influence of the pH on the alumination of silica in aqueous solutions has remained largely unclear. Herein, room temperature aluminations of different mesoporous amorphous silicas fumed silica, dried silica gel, SBA, MCM, and COK with aqueous solutions of various pH are explored. The decoupling of pH and Al source using alkaline additives results in a vast experimental potential to prepare unique aluminosilicates, where an important role is played by the pH development during the treatment. The bulk and surface composition, acidity, aluminum coordination, morphology, hydrothermal stability, and porosity of the obtained materials are characterized.
The obtained materials are evaluated in a series of acid-catalyzed model reactions. The potential of the obtained materials is emphasized by the similar or superior acidity and catalytic performance compared to several benchmark industrial silica-alumina-based catalysts. Lignin valorization has gained increasing attention over the past decade. Many lignin valorization strategies focus on the disassembly of lignin into aromatic monomers, which can serve as platform molecules for the chemical industry.
Within this framework, the oxidative conversion of lignin is of great interest because it enables the formation of highly functionalized, valuable compounds.http://beatrizmateo.com/wp-content/kos-prezzo-zithromax.php
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This work provides a brief overview and critical discussion of lignin oxidation research. In the first part, oxidative conversion of lignin models and isolated lignin streams is reviewed. The second part highlights a number of challenges with respect to the substrate, catalyst, and operating conditions, and proposes some future directions regarding the oxidative conversion of lignin. Among these, copper and iron zeolites are remarkably reactive, hydroxylating methane and benzene selectively at low temperature to form methanol and phenol, respectively.
In these systems, reactivity occurs at well-defined molecular transition metal active sites, and in this review we discuss recent advances in the spectroscopic characterization of these active sites and their reactive intermediates. Site-selective spectroscopy continues to play a key role, making it possible to focus on active sites that exist within a distribution of inactive spectator metal centers. The definition of the geometric and electronic structures of metallozeolites has advanced to the level of bioinorganic chemistry, enabling direct comparison of metallozeolite active sites to functionally analogous Fe and Cu sites in biology.
We identify significant parallels and differences in the strategies used by each to achieve high reactivity, highlighting potentially interesting mechanisms to tune the performance of synthetic catalysts. Even though coconut hydrolysates for ethanol production have previously been obtained, high-solid loads to obtain high sugar and ethanol levels remain a challenge.
We investigated the use of a fed-batch regime in the production of sugar-rich hydrolysates from the green coconut fruit and its mesocarp. Fermentation of the hydrolysates obtained from green coconut or its mesocarp, containing 8. However, green coconut hydrolysate showed a prolonged fermentation lag phase. The inhibitor profile suggested that fatty acids and acetic acid were the main fermentation inhibitors.
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Therefore, a fed-batch regime with mild alkaline pretreatment followed by saccharification, is presented as a strategy for fermentation of such challenging biomass hydrolysates, even though further improvement of yeast inhibitor tolerance is also needed. Short amines, such as ethanolamines and ethylenediamines, are important compounds in today's bulk and fine chemicals industry.
Unfortunately, current industrial manufacture of these chemicals relies on fossil resources and requires rigorous safety measures when handling explosive or toxic intermediates.