Elena Gobechiya

Direct Patterning of Oriented Metal–Organic Framework Crystals via Control over Crystallization Kinetics in Clear Precursor Solutions

[*] Prof. D. E. De Vos, R. Ameloot, Dr. E. Gobechiya, Prof. J. A. Martens, Dr. L. Alaerts, Prof. B. F. Sels Department of Microbial and Molecular Systems Center for Surface Chemistry and Catalysis Katholieke Universiteit Leuven Kasteelpark Arenberg 23, B-3001 Leuven (Belgium) E-mail: Dirk.DeVos@biw.kuleuven.be Dr. H. Uji-i, Prof. J. Hofkens Department of Chemistry Katholieke Universiteit Leuven Celestijnenlaan 200F, B-3001 Leuven (Belgium)

Biobutanol Separation with the Metal–Organic Framework ZIF‐8

Bioalcohols, such as bioethanol and biobutanol, are a promising alternative to petroleum-based chemicals. As a fuel, biobutanol has superior properties compared to bioethanol, including a higher energy density and a lower volatility. A major challenge in the economical production of biobutanol as chemical or fuel is its separation from the aqueous medium in which it is produced by the fermentation of biomass. Given the low concentration of the alcohols in the fermentation broth, separation of the butanol fraction via distillation would be energyand cost-intensive. Among alternative separation methods to recover butanol from fermentation broth, adsorption has been identified as the most energy-efficient technique. This requires adsorbents that, besides a high adsorption capacity and stability, have a high affinity towards alcohols (typically, the final butanol concentration is at most 20 g L ) and a low affinity for water. Typical adsorbents (i.e. , most zeolites, silica, and alumina) have a high preference to water and so are not suitable for this particular application. Oudshoorn et al. reported that among the commercially available hydrophobic zeolites, silicalitetype zeolites are the most selective for alcohols, but their adsorption capacity remains low. Although active carbon selectively adsorbs alcohols from water, the recovery of adsorbed alcohols is problematic. Metal–organic frameworks (MOFs) offer new opportunities in adsorption technology, with unprecedented capacities and chemical and structural tunability. Herein, it is demonstrated that the MOF ZIF-8, a member of the zeolitic imidazolate framework (ZIF) family, has promising features for the production of pure biobutanol from its fermentation medium. ZIFs contain tetrahedral Zn atoms linked by imidazolate ligands. A large variety of zeolite-like structures can be obtained by modification of the ligands. ZIFs offer high hydrothermal, chemical, and thermal stabilities. ZIF-8, discovered by Huang et al. , crystallizes into the zeolite sodalite topology, generating a resistant structure with cages of 12.5 connected via hexagonal windows of 3.3 . (Figure S2). Adsorption isotherms on ZIF-8 have been reported for Ar, CO2, CH4, N2, C2H6, C2H4, and H2, and also for longer alkanes, alkenes, and organic compounds. b, 7] Molecular simulations have been used to identify the adsorption sites of H2, N2, and CH4. [8] Selective ZIF-8-membranes have been designed, and their permeability for light gasses has been investigated. 9] ZIF-8 shows an only very low [a] J. Cousin Saint Remi, T. R my, V. Van Hunskerken, S. van de Perre, T. Duerinck, Prof. Dr. G. V. Baron, Prof. Dr. J. F. M. Denayer Department of Chemical Engineering Vrije Universiteit Brussel Pleinlaan 2, 1050 Brussel (Belgium) Fax: (+ 32) 2 629 17 98 E-mail : joeri.denayer@vub.ac.be [b] Dr. M. Maes, Prof. Dr. D. De Vos, Dr. E. Gobechiya, Prof. Dr. C. E. A. Kirschhock Centre for Surface Chemistry and Catalysis Katholieke Universiteit Leuven Kasteelpark Arenberg 23, 3001 Heverlee (Belgium) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201100261. Figure 1. Vapor-phase adsorption on ZIF-8. Full symbols: adsorption; open symbols: desorption. a) Adsorption isotherms at 50 8C. b) Adsorption capacity at 50 8C. c) Butanol isotherms at varying temperature. d) Isosteric heat of adsorption as a function of pore filling.

Design of zeolite by inverse sigma transformation

Although the search for new zeolites has traditionally been based on trial and error, more rational methods are now available. The theoretical concept of inverse σ transformation of a zeolite framework to generate a new structure by removal of a layer of framework atoms and contraction has for the first time been achieved experimentally. The reactivity of framework germanium atoms in strong mineral acid was exploited to selectively remove germanium-containing four-ring units from an UTL type germanosilicate zeolite. Annealing of the leached framework through calcination led to the new all-silica COK-14 zeolite with intersecting 12- and 10-membered ring channel systems. An intermediate stage of this inverse σ transformation with dislodged germanate four-rings still residing in the pores could be demonstrated. Inverse σ transformation involving elimination of germanium-containing structural units opens perspectives for the synthesis of many more zeolites.

NH2-MIL-53(Al): A High-Contrast Reversible Solid-State Nonlinear Optical Switch

The metal-organic framework NH(2)-MIL-53(Al) is the first solid-state material displaying nonlinear optical switching due to a conformational change upon breathing. A switching contrast of at least 38 was observed. This transition originates in the restrained linker mobility in the very narrow pore configuration.

Adsorption and Separation of Light Gases on an Amino-Functionalized Metal–Organic Framework: An Adsorption and In Situ XRD Study

The NH(2)-MIL-53(Al) metal-organic framework was studied for its use in the separation of CO(2) from CH(4), H(2), N(2)C(2)H(6) and C(3)H(8) mixtures. Isotherms of methane, ethane, propane, hydrogen, nitrogen, and CO(2) were measured. The atypical shape of these isotherms is attributed to the breathing properties of the material, in which a transition from a very narrow pore form to a narrow pore form and from a narrow pore form to a large pore form occurs, depending on the total pressure and the nature of the adsorbate, as demonstrated by in situ XRD patterns measured during adsorption. Apart from CO(2), all tested gases interacted weakly with the adsorbent. As a result, they are excluded from adsorption in the narrow pore form of the material at low pressure. CO(2) interacted much more strongly and was adsorbed in significant amounts at low pressure. This gives the material excellent properties to separate CO(2) from other gases. The separation of CO(2) from methane, nitrogen, hydrogen, or a combination of these gases has been demonstrated by breakthrough experiments using pellets of NH(2)-MIL-53(Al). The effect of total pressure (1-30 bar), gas composition, temperature (303-403 K) and contact time has been examined. In all cases, CO(2) was selectively adsorbed, whereas methane, nitrogen, and hydrogen nearly did not adsorb at all. Regeneration of the adsorbent by thermal treatment, inert purge gas stripping, and pressure swing has been demonstrated. The NH(2)-MIL-53(Al) pellets retained their selectivity and capacity for more than two years.

Interplay of metal node and amine functionality in NH2-MIL-53: modulating breathing behavior through intra-framework interactions.

A series of amino-functionalized MIL-53 with different metals as nodes has been synthesized. By determining adsorption properties and spectroscopic characterization, we unequivocally show that the interaction between the amines of the organic linker and bridging μ(2)-OH of the inorganic scaffold modulates metal organic framework (MOF) flexibility. The strength of the interaction has been found to correlate with the electropositivity of the metal.

Gallium Oxide Nanorods: Novel, Template‐Free Synthesis and High Catalytic Activity in Epoxidation Reactions

Gallium oxide nanorods with unprecedented small dimensions (20-80 nm length and 3-5 nm width) were prepared using a novel, template-free synthesis method. This nanomaterial is an excellent heterogeneous catalyst for the sustainable epoxidation of alkenes with H2 O2 , rivaling the industrial benchmark microporous titanosilicate TS-1 with linear alkenes and being much superior with bulkier substrates. A thorough characterization study elucidated the correlation between the physicochemical properties of the gallium oxide nanorods and their catalytic performance, and underlined the importance of the nanorod morphology for generating a material with high specific surface area and a high number of accessible acid sites.

Reduction of Se(IV) in Boom Clay: XAS solid phase speciation.

The geochemical fate of selenium is of key importance for todays society due to its role as a highly toxic essential micronutrient and as a significant component of high level radioactive waste (HLRW) originating from the operation of nuclear reactors. Understanding and prediction of the long-term behavior of Se in natural environments requires identification of the in situ speciation of selenium. This article describes an XAS-based investigation into the solid phase speciation of Se upon interaction of Se(IV) with Boom Clay, a reducing, complex sediment selected as model host rock for clay-based deep geological disposal of HLRW in Belgium and Europe. Using a combination of long-term batch sorption experiments, linear combination XANES analysis and ITFA-based EXAFS analysis allowed for the first time to identify Se0 as the dominant solid phase speciation of Se in Boom Clay systems equilibrated with Se(IV).

New mesoporous composites of gallia nanoparticles: high-throughput synthesis and catalytic application

A new class of mesoporous materials constituted by gallia nanoparticles was synthesised and tested as epoxidation catalysts. The results prove that these materials can bridge the gap between Ga(2)O(3) nanoparticles and MCM-41-like materials, coupling the benefits of particles in the nanoscale to their organisation in a mesoporous structure.

Biogas upgrading through kinetic separation of carbon dioxide and methane over Rb- and Cs-ZK-5 zeolites

Eight-membered ring (8 MR) zeolites hold large potential for industrial CO2 separations such as biogas separation. They offer large selectivity due to the constrained environment for adsorption, especially when large cations are present in the interconnecting windows. The Rb- and Cs-exchanged ZK-5 zeolites (8 MR KFI type zeolites) were studied for kinetic CO2/CH4 separation. First, Rb-ZK-5 and Cs-ZK-5 were thoroughly characterized via chemical analysis, argon porosimetry, X-ray diffraction and Rietveld refinements. Afterwards, the CO2/CH4 separation potential of both adsorbents was assessed via the measurement of kinetic and equilibrium data (T = 261.15 - 323 K), breakthrough measurements at 303 K (P = 1 - 8 bar), and simulations of their performance. The high occupation of the central 8 MR sites with large cations causes strong diffusional limitations for CH4 on Rb-ZK-5 and Cs-ZK-5. As a result, both zeolites effectively separate CH4 from CO2 with very high selectivities (α = 17 at 1 bar and 303 K). Despite their very large CO2 selectivities, the performance of Rb-ZK-5 and Cs-ZK-5 was still lower than for the benchmark 13X zeolite on a larger scale. Future research needs to further unravel the adsorption mechanism on low-silica 8 MR zeolites and their corresponding potential in separation processes such as biogas purification.