Catalysis Today

Ti-functionalized NH2-MIL-47: an effective and stable epoxidation catalyst

K. Leus, G. Vanhaelewyn, T. Bogaerts, Y-Y Liu, F. Esquivel, F. Callens, G.B. Marin, V. Van Speybroeck, H. Vrielinck, P. Van der Voort
Catalysis Today
208, 97-105
2013
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Abstract 

In this paper, we describe the post-functionalization of a V-containing Metal-organic framework with TiO(acac)2 to create a bimetallic oxidation catalyst. The catalytic performance of this V/Ti-MOF was examined for the oxidation of cyclohexene using molecular oxygen as oxidant in combination with cyclohexanecarboxaldehyde as co-oxidant. A significantly higher cyclohexene conversion was observed for the bimetallic catalyst compared to the non-functionalized material. Moreover, the catalyst could be recycled at least 3 times without loss of activity and stability. No detectable leaching of V or Ti was noted. Electron paramagnetic resonance measurements were performed to monitor the fraction of V-ions in the catalyst in the +IV valence state. A reduction of this fraction by ∼17% after oxidation catalysis is observed, in agreement with the generally accepted mechanism for this type of reaction.

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

K. Hemelsoet, A. Ghysels, D. Mores, K. De Wispelaere, V. Van Speybroeck, B.M. Weckhuysen, M. Waroquier
Catalysis Today
177 (1), 12-24
2011
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Abstract 

Theoretical and experimental IR data are combined to gain insight into the methanol and ethanol conversion over an acidic H-SAPO-34 catalyst. The theoretical simulations use a large finite cluster and the initial physisorption energy of both alcohols is calculated. Dispersive contributions turn out to be vital and ethanol adsorbs stronger than methanol with approximately 14 kJ mol(-1). Calculated IR spectra of the alcohols and of formed aromatic cations upon conversion are also analyzed and support the peak assignment of the experimental in situ DRIFT spectra, in particular for the C-H and C=C regions. Theoretical IR spectra of the gas phase compounds are compared with those of the molecules loaded in a SAPO cluster and the observed shifts of the peak positions are discussed. To get a better understanding of these framework-guest interactions, a new theoretical procedure is proposed based on a normal mode analysis. A cumulative overlap function is defined and enables the characterization of individual peaks as well as induced frequency shifts upon adsorption. (C) 2010 Elsevier B. V. All rights reserved.

Open Access version available at UGent repository

Catalytic and molecular separation properties of Zeogrids and Zeotiles

J.A. Martens, J.W. Thybaut, J.F.M. Denayer, S. Pulinthanathu Sree, A. Aerts, M-F. Reyniers, V. Van Speybroeck, M. Waroquier, A. Buekenhoudt, I. Vankelecom, W. Buijs, J. Persoons, G.V. Baron, S. Bals, G. Van Tendeloo, G.B. Marin, P.A. Jacobs, C. Kirschhock
Catalysis Today
168, 17-27
2011
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Abstract 

Zeogrids and Zeotiles are hierarchical materials built from assembled MFI zeolite precursor units. Permanent secondary porosity in these materials is obtained through self assembly of nanoparticles encountered in MFI zeolite synthesis in the presence of supramolecular templates. Hereon, the aggregated species are termed nanoslabs. Zeogrids are layered materials with lateral spacings between nanoslabs creating galleries qualifying as supermicropores. Zeotiles present a diversity of tridimensional nanoslab assemblies with mesopores. Zeotile-1, -4 and -6 are hexagonal mesostructures. Zeotile-1 has triangular and hexagonal channels; Zeotile-4 has hexagonal channels interconnected via slits. Zeotile-2 has a cubic structure with gyroid type mesoporosity. The behavior of Zeogrids and Zeotiles in adsorption, membrane and chromatographic separation and catalysis has been characterized and compared with zeolites and mesoporous materials derived from unstructured silica sources. Shape selectivity was detected via adsorption of n- and iso-alkanes. The mesoporosity of Zeotiles can be exploited in chromatographic separation of biomolecules. Zeotiles present attractive separation properties relevant to CO2 sequestration. Because of its facile synthesis procedure without hydrothermal steps Zeogrid is convenient for membrane synthesis. The performance of Zeogrid membrane in gas separation, nanofiltration and pervaporation is reported. In the Beckmann rearrangement of cyclohexanone oxime Zeogrids and Zeotiles display a catalytic activity characteristic of silicalite-1 zeolites. Introduction of acidity and redox catalytic activity can be achieved via incorporation of Al and Ti atoms in the nanoslabs during synthesis. Zeogrids are active in hydrocracking, catalytic cracking, alkylation and epoxidation reactions. Zeogrids and Zeotiles often behave differently from ordered mesoporous materials as well as from zeolites and present a valuable extension of the family of hierarchical silicate based materials.

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