- The influence of long-term exposure of Mg–Al mixed oxide at ambient conditions on its transition to hydrotalcite: The long-term aging of Mg–Al mixed oxide
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The paper is focused on the study of long-term aging of Mg–Al mixed oxides, which causes the rebuilding of the hydrotalcite layered structure in the presence of humidity. The novelty consists in the description of influence during the long-term aging (6 m
- Bábelová, Monika,Hájek, Martin,Kocík, Jaroslav,Strejcová, Kate?ina,Ti?ler, Zdeněk,Velvarská, Romana
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- Optimized Cellulose Nanocrystal Organocatalysts Outperform Silica-Supported Analogues: Cooperativity, Selectivity, and Bifunctionality in Acid-Base Aldol Condensation Reactions
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Cellulose nanocrystals (CNCs) are demonstrated as effective, ordered supports for cooperative acid-base heterogeneous organocatalysis, offering an alternative to typical silica supports. CNC catalyst surface chemistry is optimized through quantitative control of the loadings of carboxylic acids, primary amines, and sulfate half-esters, as characterized by elemental analysis, conductometric titration, and FT-IR spectroscopy. Catalysts are evaluated in the liquid phase aldol condensation of 4-nitrobenzaldehyde or furfural with acetone. Carboxylic acids are effective cooperative acid partners in CNC organocatalysts, and site-specific activity is strongly correlated with the COOH:NH2 ratio. Partial sulfate half-ester removal, high acid/base ratios, and use of unprotected diamines in the catalyst synthesis lead to optimized CNC catalyst function (site-time yield = 1.0 × 10-4 s-1). High selectivities to dehydrated aldol products (>80%) are achieved due to the acid content of the CNC catalysts. CNC catalysts outperform analogous SBA-15-supported aminosilica catalysts in regard to both activity and selectivity. Crystalline surface structures and ordered chemical functionalization in CNCs appear advantageous for precise design and control of bifunctional acid-base cooperative catalysts.
- Ellebracht, Nathan C.,Jones, Christopher W.
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p. 3266 - 3277
(2019/03/26)
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- Upgrading of furfural to biofuel precursors: Via aldol condensation with acetone over magnesium hydroxide fluorides MgF2- x(OH)x
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Wastes from lignocellulosic materials, especially hemicellulose, are extremely promising resources to produce fuels from renewable raw materials. Furfural, resulting from the depolymerization of hemicellulose, is often considered as an extremely interesting platform molecule. Particularly, new biofuels containing molecules with 8 and 13 carbon atoms can be produced from aldol condensation of furfural and acetone followed by a deoxygenation reaction. In this work, several magnesium hydroxide fluorides MgF2-x(OH)x were prepared by a sol-gel method with various F/Mg ratios (0 to 2) at 100 °C. All solid samples were fully characterized by several techniques (nitrogen adsorption-desorption, TEM, IR, XRD and ICP). MgF2-x(OH)x were mainly composed of an intimate mixture of MgF2 and Mg(OH)2-x(OCH3)x and exhibited both acid-base properties and high surface areas. From CO2 adsorption experiments, a basicity scale corresponding to basic sites with moderate strength was established: MgF1.5(OH)0.5 > MgF(OH) ~ MgF1.75(OH)0.25 > MgF0.5(OH)1.5 > Mg(OH)2 ? MgF2. It was proposed that the presence of fluorine allowed stabilization of the basic sites with moderate strength at ambient atmosphere. The aldol condensation of furfural and acetone was carried out under mild reaction conditions (50 °C, Patm) over MgF2-x(OH)x. These catalysts were involved in this reaction without using a classical activation step for basic solid catalysts, which constitutes a major advantage of energy conservation and thus, economic efficiency. The solid with a F/Mg ratio equal to 1.5 (MgF1.5(OH)0.5) exhibited the highest activity, the furanic dimer (1,5-di(furan-2-yl)penta-1,4-dien-3-one) being the main product. A good correlation between the catalytic activity and the basicity scale was highlighted. Based on these results, the nature of active sites was proposed: a combination of a Lewis acid site (coordinatively unsaturated metal site) in the vicinity of a basic site (hydroxyl groups of Mg(OH)2-x(OCH3)x). The effect of the furfural/acetone ratio on the catalytic properties of MgF1.5(OH)0.5 was also investigated.
- Xu, Minrui,Célérier, Stéphane,Comparot, Jean-Dominique,Rousseau, Julie,Corbet, Matthieu,Richard, Frédéric,Clacens, Jean-Marc
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p. 5793 - 5802
(2019/11/05)
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- Study on thermal stabilities and symmetries of chemisorbed species formed on K-zeolites upon CO2 adsorption by TPD and in situ IR spectroscopy
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In the current study, K-zeolites with different structure, Si/Al ratio and morphology have been prepared and then characterized by different techniques including in situ IR spectroscopy upon CO2 sorption and CO2–TPD with the aim of u
- Ganjkhanlou, Yadolah,Bulánek, Roman,Kikhtyanin, Oleg,Frolich, Karel
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p. 355 - 364
(2017/11/15)
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- Nanosized TiO2—A promising catalyst for the aldol condensation of furfural with acetone in biomass upgrading
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Nanosized TiO2 catalyst was successfully prepared by a simple green procedure and used in liquid phase aldol condensation of furfural with acetone, a key step in bio-fuel processing. In order to determine the effect of calcination temperature on catalytic properties of TiO2, the as-prepared TiO2 and calcined TiO2 (150–900?°C) were studied by XRD, BET, TPD-CO2/NH3, TGA/DTG and FTIR evaluation. The catalytic performance of TiO2 samples in aldol condensation of furfural with acetone was evaluated and compared with that of Mg–Al hydrotalcites and a BEA zeolite. These experiments showed that uncalcined TiO2 possessed reasonable activity in aldol condensation of furfural to acetone and resulted in commonly produced condensation products. The observed catalytic behavior of TiO2 could be competitive with that reported for other inorganic solids. The calcination of TiO2 resulted, however, in a decrease in its catalytic activity due to extensive dehydration and surface dehydroxylation as well as due to changes of textural properties resulting in a decrease in the amount of accessible active sites. Thanks to its advanced properties, nanosized TiO2 is a promising catalyst for aldol condensation of furfural with acetone and could broaden possibilities for optimizing conditions for bio-fuel production.
- Nguyen Thanh, Dong,Kikhtyanin, Oleg,Ramos, Ruben,Kothari, Maadhav,Ulbrich, Pavel,Munshi, Tasnim,Kubi?ka, David
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- Toward understanding of the role of Lewis acidity in aldol condensation of acetone and furfural using MOF and zeolite catalysts
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The aldol condensation of furfural and acetone allow producing higher value products from simple organic compounds resulting from biomass processing. In this paper, a number of metal organic framework (MOF) materials possessing Lewis acidity were investigated as catalysts in this reaction. Experiments were carried out under batch reaction conditions in Parr stirred autoclave at 100 °C during 0-4 h. The catalytic results indicated that the aldol condensation over MOFs took place with the participation of acidic rather than basic centers. The catalytic performance of these materials exhibited could not be explained by their reported Lewis acidity. Experiments with heat-activated and re-hydrated samples showed that Br?nsted acid sites could also be present in MOFs as a consequence of interaction of metal cation with surrounding water molecules. As a consequence, the catalysts having such generated Br?nsted acidity exhibited enhanced activity in the reaction.
- Kikhtyanin, Oleg,Kubi?ka, David,?ejka, Ji?í
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p. 158 - 162
(2015/04/22)
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- Unprecedented selectivities in aldol condensation over Mg-Al hydrotalcite in a fixed bed reactor setup
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Aldol condensation of furfural with acetone (molar ratio 1:10) was carried out in a flow fixed bed setup at 50 °C using calcined hydrotalcite with Mg/Al of 3 as a catalyst. Complete conversion of furfural and stable catalyst performance was obtained during the initial 50 h on stream. This period was followed by a rapid catalyst deactivation. In contrast to previous reports, higher molecular weight products that were identified as products of successive aldol condensation of acetone with furfural were observed. Their concentration was time-dependent with a maximum formation after 10 to 30 h on stream.
- Kikhtyanin, Oleg,Hora, Luká?,Kubi?ka, David
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- Comparative study of physico-chemical properties of laboratory and industrially prepared layered double hydroxides and their behavior in aldol condensation of furfural and acetone
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In this article, properties of laboratory and industrially prepared Mg-Al layered double hydroxides (LDH) with Mg:Al molar ratios varied in the range from 2 to 4 were compared. Physico-chemical properties of the studied materials were investigated with XR
- Hora, Luk,Kikhtyanin, Oleg,apek, Libor,Bortnovskiy, Oleg,Kubika, David
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p. 221 - 230
(2015/03/14)
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- Aldol reactions mediated by a tetrahedral boronate
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The base is a key factor in aldol reactions in organic media, determining the selectivity. Here, we describe a tetrahedral phenylboronate salt as a mild non-nucleophilic base that is able to catalyse the aldol reaction and significantly decrease the formation of undesired elimination products. This journal is
- Mueller, Tobias,Djanashvili, Kristina,Arends, Isabel W.C.E.,Peters, Joop A.,Hanefeld, Ulf
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supporting information
p. 361 - 363
(2013/02/23)
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- Dried chitosan-gels as organocatalysts for the production of biomass-derived platform chemicals
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Aldol condensations between sugar-derived dehydrated aldehydes (e.g. furfural) and acetone have been proposed as a route to provide useful biomass-derived chemicals. In the quest of sustainable catalytic ways for such aldol condensations, this paper assesses the use of dried chitosan-gels as naturally-immobilized, readily available and non-hazardous amino-based organocatalysts. At room temperature chitosan dried gels are not suitable catalysts for the desired reaction. However, at higher temperatures (>90 °C) reaction proceeds efficiently either in solvent-free systems (with addition of catalytic amounts of water) or in water. The set-up of closed reactor set-ups (thermoshakers or microwave reactions) proved highly beneficial for the reaction outcome. Furthermore, chitosan dried gels were successfully re-used for a number of cycles. An efficient catalyst drying method (either lyophilization or scCO2 drying) was crucial to achieve virtually full conversions in 4 h. After pertinent further process optimization, dried chitosan-gels may become very useful catalysts for their use in biomass-based reactions in biorefineries.
- Kayser, Henning,Müller, Christoph R.,García-González, Carlos A.,Smirnova, Irina,Leitner, Walter,Domínguez De María, Pablo
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p. 180 - 186
(2013/02/23)
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- Silica-immobilized piperazine: A sustainable organocatalyst for aldol and Knoevenagel reactions
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Silica-supported piperazine was found to be an efficient catalyst for aldol reactions of aromatic aldehydes and ketones with straightforward product isolation and catalyst reuse. Furthermore, the catalyst is active in Knoevenagel-type reactions to afford coumarin derivatives, using 2-methyltetrahydrofuran (2-MeTHF) as a novel bio-based solvent.
- Shanmuganathan, Saravanakumar,Greiner, Lasse,De María, Pablo Domínguez
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experimental part
p. 6670 - 6672
(2011/02/21)
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- Chitosan hydrogel: A green and recyclable biopolymer catalyst for aldol and Knoevenagel reactions
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Chitosan hydrogel is efficiently utilized as an organocatalyst for aldol and Knoevenagel reactions, providing the products in high yields with a high chemoselectivity under biphasic conditions. The catalyst was recovered by simple filtration and reused several times without significant loss of activity. the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006.
- Reddy, K. Rajender,Rajgopal,Maheswari, C. Uma,Lakshmi Kantam
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p. 1549 - 1552
(2007/10/03)
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- Electron deficiency of aldehydes controls the pyrrolidine catalyzed direct cross-aldol reaction of aromatic/heterocyclic aldehydes and ketones in water
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A synthetically useful pyrrolidine catalyzed direct cross-aldol reaction of aromatic/heterocyclic aldehydes with ketones in water affords the aldol addition product in up to 93% yield. Electrophilicity of the aldehydes controls the course of the reaction.
- Chimni, Swapandeep Singh,Mahajan, Dinesh
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p. 5019 - 5025
(2007/10/03)
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- Efficient Wittig-Horner and Improved Claisen-Schmidt Synthesis of Acyclic α-Enones with a 2-Furyl or 3,4-Methylenedioxyphenyl Group at the β-Position.
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The Wittig-Horner and Claisen-Schmidt syntheses of acyclic α-enanes bearing a 2-furyl or 3,4-methylenedioxyphenyl group in the β-position have been achieved using activated barium hydroxide C-200 with good yields.The Wittig-Horner reaction in homogeneous phase is shown to be more efficient than the Claisen-Schmidt condensation under interfacial solid-liquid conditions.The 1H and the 13C megnetic parameters of compounds 5 and 6 are described.The use of 1H-13C correlation spectra helped in the unambiguous assignment of the olefinic and aromatic carbons of α-enones 5a and 6a.
- Alvarez-Ibarra, Carlos,Perez, Maria Selma Arias,Fernandez, Maria J.,Serrano, David,Sinisterra, Vicente
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p. 2674 - 2686
(2007/10/02)
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