Marjo C. Mittelmeijer-Hazeleger

Efficient three-component coupling catalysed by mesoporous copper-aluminum based nanocomposites

Traditional synthesis methods for propargylamines have several drawbacks. A recently developed alternative route is the so-called “A3 coupling” in which an alkyne, an aldehyde, and an amine are coupled together. Typically, these reactions are catalysed by homogeneous gold salts, organogold complexes or silver salts. But these homogeneous catalysts are expensive and their separation is difficult. Here we report the discovery that solid Cu/Al/oxide mesoporous “sponges” are excellent A3 coupling catalysts. These materials are robust, inexpensive, and easy to make. They give good to excellent yields (87–97%) for a wide range of substrates. Being heterogeneous, these catalysts are also easy to handle and separate from the reaction mixture, and can be recycled with no loss of activity.

Mechanisms of adsorption of CO2 in the micropores of activated anthracite

The combined use of n-nonane preadsorption and CO2 adsorption at 273 K allows interpretation of the mechanism of adsorption of CO2 in narrow micropores of a series of CO2-activated carbons prepared from an anthracite. The mechanism depends on the shape and size of the pores. In narrow micropores of molecular dimensions (1σ), CO2 is probably adsorbed by micropore filling — as proposed for the adsorption of N2 at 77 K — which is associated with curved CO2 isotherms at 273 K. With increasing degree of activation, the microporosity widens and the adsorption of CO2 in narrow micropores of supramolecular dimensions (> 2σ) probably occurs by surface coverage, which is associated with rectilinear isotherms.

The microporous structure of organic and mineral soil materials

Microporous properties of soil materials are considered important to the physical sequestration processes of contaminants and the influence on risk assessment for chemicals in the environment. We studied the microporous properties of five organic soil materials and two agricultural topsoils and thei

Sieving di-branched from mono-branched and linear alkanes using ZIF-8: experimental proof and theoretical explanation

We study the adsorption equilibrium isotherms and differential heats of adsorption of hexane isomers on the zeolitic imidazolate framework ZIF-8. The studies are carried out at 373 K using a manometric set-up combined with a micro-calorimeter. We see that the Langmuir model describes well the isotherms for all four isomers (n-hexane, 2-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane). The linear and mono-branched isomers adsorb well, but 2,2-dimethylbutane is totally excluded. Plotting the differential heat of adsorption against the loading shows an initial plateau for n-hexane and 2-methylpentane. This is followed by a slow rise, indicating adsorbate-adsorbate interactions. For the di-branched isomers the differential heat of adsorption decreases with loading. To gain further insight, we ran molecular simulations using the grand-canonical Monte Carlo approach. Comparing the simulation and the experimental results shows that the ZIF framework model requires blocking of the cages, since 2,2-dimethylbutane cannot fit through the sodalite-type windows. Practically speaking, this means that ZIF-8 is a highly promising candidate for enhancing gasoline octane numbers at 373 K, as it can separate 2,2-dimethylbutane and 2,3-dimethylbutane from 2-methylpentane. Our results prove the potential of ZIF-8 as a new adsorbent that can be employed in the upgrade of the Total Isomerization Process for the production of high octane number gasoline, by blending di-branched alkanes in the gasoline.

Microporosity development by CO2 activation of an anthracite studied by physical adsorption of gases, mercury porosimetry, and scanning electron microscopy

A series of CO2-activated carbons (18%–97% burn-off) prepared from a low-ash-content anthracite has been characterized by macerai analysis, physical adsorption of gases (Ar/77 K, N2/77 K, n-butane/273 K, CO2/273 K), n-nonane preadsorption, mercury porosimetry and scanning electron microscopy. Apparent surface areas greater than 1600 m2/g and pore volumes near 1 cm3/g were obtained. There is a continuous increase in adsorption capacity with the burn-offdue to the enlargement of the micropores of the carbons. The meso- and macroporosity were poorly developed and almost exclusively microporosity was created in the carbons. The development of this microporosity was produced in three consecutive stages: for burn-off values smaller than 35% only small micropores were created and the carbons exhibited molecular sieve properties towards n-butane; at burn-off percentages between 35% and 60% medium micropores were developed and for greater activation degrees large micropores were produced. The small micropores can be evaluated from the CO2/273 K. adsorption isotherms by application of the Dubinin-Radushkevich (DR) eqn. Medium micropores can be obtained from application of the DR eq to the adsorption isotherms of Ar/77 K, N2/77 K or n-butane/273 K. Large micropores are evaluated either by n-nonane preadsorption or from the αs, plots of Ar/77 K, N2/77 K or n-butane/273 K adsorption. On the other hand, the total pore volumes of carbons evaluated from the He and Hg densities were in good agreement with the gas volumes adsorbed at P/P0 = 0.95 (Ar/77 K, N2/77 K and n-butane/273 K). The results obtained for these carbons are very similar to those previously reported for different series of CO2 activated carbons prepared from lignocellulosic materials.

Highly selective water adsorption in a lanthanum metal-organic framework.

We present a new metal-organic framework (MOF) built from lanthanum and pyrazine-2,5-dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)1.5(H2O)2]⋅2 H2O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single-crystal X-ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g(-1) MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF.

Poly(vinylidene fluoride)/nickel nanocomposites from semicrystalline block copolymer precursors

The fabrication of nanoporous poly(vinylidene fluoride) (PVDF) and PVDF/nickel nanocomposites from semicrystalline block copolymer precursors is reported. Polystyrene-block-poly(vinylidene fluoride)-block-polystyrene (PS-b-PVDF-b-PS) is prepared through functional benzoyl peroxide initiated polymerization of VDF, followed by atom transfer radical polymerization (ATRP) of styrene. The crystallization of PVDF plays a dominant role in the formation of the block copolymer structure, resulting in a spherulitic superstructure with an internal crystalline-amorphous lamellar nanostructure. The block copolymer promotes the formation of the ferroelectric β-polymorph of PVDF. Selective etching of the amorphous regions with nitric acid leads to nanoporous PVDF, which functions as a template for the generation of PVDF/Ni nanocomposites. The lamellar nanostructure and the β-crystalline phase are conserved during the etching procedure and electroless nickel deposition.

Microporous structure and enhanced hydrophobicity in methylated SiO2 for molecular separation

Methylated microporous silica with high thermal stability and tuneable hydrophobicity was obtained by acid-catalysed sol–gel hydrolysis and condensation of mixtures of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES). The gels exhibited a trend towards smaller ultramicropores with increasing methyl content, while in addition some supermicropores were formed with sizes of around 2 nm. For low MTES concentration, dilution prior to gelation and ageing resulted in materials with clearly smaller ultramicropores, whereas only a minor effect of dilution on structure was found at high MTES concentration. The small ultramicropore size in ‘diluted’ materials can be associated with a higher extent of condensation of mainly TEOS monomers. Stable structures formed from MTES in an early stage of synthesis may explain the particular micropore structure of MTES-rich gels. With increasing methyl content and with dilution of the sol, the affinity of the surface to water was strongly decreased. The applicability of microporous silica in wet atmospheres may thus be improved by methylation, and their pore structure modified by adaptation of the recipe, which would be highly relevant for industrial gas and liquid separation by inorganic membranes.

A facile building-block synthesis of multifunctional lanthanide MOFs

We report a building blocks approach providing a direct route to multifunctional MOFs, that display photoluminescent properties, robustness, porosity and in some cases unique magnetic properties. The self-assembly of [Mo(CN)8]4− with several in situ prepared lanthanide building blocks gives 3D robust porous networks with open channels. This approach solves the coordination problem, allowing exact placement of the lanthanide ions within the structure. Our MOFs feature good thermal stability and permanent porosity thanks to the strong carboxylate and cyanide linkages. The fact that we have both nitrogen-containing ligand and a π-system means that these MOFs can be excited using low-energy photons. Efficient visible emission was observed for MOFs containing Eu(III) and Tb(III). Surprisingly, the Tb-MOF shows ferromagnetic behavior, proving that the magnetic interaction between Tb(III) ions is strong enough to compensate the ligand field effects.

Porous texture of activated carbons modified with carbohydrates

Abstract A modification of the porous texture of activated carbons to develop meso- and macroporosity is described. Three gas-activated carbons of different origin, have been modified by impregnation with two carbon compounds ( d -glucose and d -glucosamine) from aqueous solution followed by carbonization at 1173 K and activation with CO 2 . The most important results of this procedure are (1) the development of meso- and macroporosity depends on the mesopore size distribution of the original activated carbon; (2) the gasification rates are different for each impregnated carbon in the activation step, and (3) there was no or little development of the original microporosity.