Manfred Meisel

Bio: Manfred Meisel is an academic researcher from Humboldt University of Berlin. The author has contributed to research in topics: Catalysis & Ammoxidation. The author has an hindex of 12, co-authored 117 publications receiving 628 citations. Previous affiliations of Manfred Meisel include Humboldt State University.

FTIR investigation of surface intermediates formed during the ammoxidation of toluene over vanadyl pyrophosphate

Abstract: The mechanism of formation of surface intermediates, appearing during the interaction of vanadyl pyrophosphate (VO) 2 P 2 O 7 with feed components of the toluene ammoxidation was studied by FTIR spectroscopy. The investigation of ammonia adsorption at elevated temperature showed protonated and coordinated ammonia as expected as well as the generation of amido species; all could be so called ‘nitrogen insertion species’ or a source of these at least. The interaction of toluene and possible reaction intermediates such as benzaldehyde and benzylamine with (VO) 2 P 2 O 7 was studied. The investigations revealed that the ammoxidation of toluene probably proceeds via the formation of a benzaldehyde intermediate. Afterwards, benzylimine surface species were probably formed by a N-insertion, using NH + 4 surface species followed by the formation of benzonitrile by subsequent oxidative dehydrogenation. However, no benzamide species were observed. The surface species generated upon adsorption of benzaldehyde were similar to those formed from toluene, indicating the role of the former as intermediate in the nitrile formation path. Otherwise, the adsorption of benzylamine in the presence of oxygen did not lead to the formation of benzonitrile. Therefore, an ammoxidation mechanism of toluene via a benzaldehyde intermediate is preferred and reaction pathways via benzamide or benzylamine as intermediates seem to be improbable.

Effect of the position of Cl-substituents on the nitrile formation during the ammoxidation of chlorotoluenes

Abstract: The conversion of isomeric chlorotoluenes to the corresponding benzonitriles by heterogeneous catalytic ammoxidation was studied. The reaction was carried out over (NH4)2[(VO)3(P3O7)2] as catalyst generated under the applied ammoxidation conditions by a solid-state reaction of the precursor compound VOHPO4· 0.5H2O. Activity and selectivity of the ammoxidation of chlorotoluenes are shown to depend on the position of the Cl-substituents causing a changed accessibility of the methyl group and a possible different electronic stabilization of the reaction intermediates.

An Extension of the Consistent Valence Force Field (CVFF) with the Aim to Simulate the Structures of Vanadium Phosphorus Oxides and the Adsorption of n‐Butane and of 1‐Butene on their Crystal Planes

Abstract: A specific force field of Consistent Valence Force Field type was developed with the aim to simulate the structures of catalysts of vanadium phosphorus oxide type and the reversible adsorption of organic compounds on specific crystallographic planes of such catalysts by molecular modeling. The appropriate parameters were derived for the bonded (stretching, bending, and torsional deformations) and nonbonded (attractive and repulsive van der Waals and Coulomb forces) atomic interactions for V—O and P—O bonds in typical fragments of these catalysts with the vanadium atom in the oxidation state IV. The parameters for bonded interactions were computed from Hessian matrices, supplied by the program DMol for performing Density Functional Theory, by means of a program for non-linear regression. The DMol program was applied to energy minimize structures of known vanadium phosphorus oxides, which were compared with X-ray structures, and to obtain their Hessian matrices as a basis for the force constants needed. Some hypothetical structural models had to be added. The van der Waals parameters were estimated by means of correlations between van der Waals radii and the repulsive parameters and between polarizabilities and the dispersive parameters from the literature. The force field obtained was applied to simulate the crystal structure of vanadyl pyrophosphate and to compute the heat of adsorption of n-butane and of 1-butene on its (100) plane (computer codes of company Biosym/MSI/Accelrys). The experimental crystal structure and the adsorption energies were fairly well reproduced, except that the a lattice constant proves somewhat too large. Eine Erweiterung des Kraftfeldes “Consistent Valence Force Field” (CVFF) fur die Simulation von Vanadium Phosphoroxid-Strukturen und der Adsorption von n-Butan und 1-Buten an ihren Kristallflachen Es wurde eine Erweiterung des bekannten Kraftfeldes vom Typ CVFF fur Molecular Modeling mit Festkorperstrukturen von Katalysatoren vom Vanadiumphosphoroxid-Typ mit Vanadium im Oxidationszustand IV und fur die Simulation der Adsorption von organischen Molekulen an ausgewahlten Kristallflachen erarbeitet. Die notwendigen Parameter fur die sog. bonded (stretching-, bending- und Torsions-Deformationen) und fur die sog. nonbonded Wechselwirkungen (van der Waals- und Coulomb-Wechselwirkungen) in V—O-, P—O- und O—H- Gruppen in typischen Fragmenten solcher Katalysatoren wurden abgeleitet. Hesse-Matrizen wurden mittels der Dichtefunktionalmethode erstellt. Dazu dienten V-, P-, O- und H-Atome enthaltenden Testmolekule, die geometrie-optimiert wurden. Der Parameter fur die van der Waals-Repulsion des Vanadiumatoms wurde uber eine literaturbekannte Korrelation mit van der Waals-Radien und der Dispersionsparameter uber eine Korrelation mit Atompolarisierbarkeiten bestimmt. Das erhaltene Kraftfeld wurde zur Simulation der Kristallstruktur des wichtigen Katalysators Vanadylpyrophosphat und zur Berechnung der Adsorptionswarmen von n-Butan bzw. von 1-Buten auf seiner (100)-Oberflache eingesetzt (Programme der Firma Biosym/MSI/Accelrys). Die Ergebnisse stehen in befriedigender Ubereinstimmung mit experimentellen Literaturwerten.

Reaction pathway of benzonitrile formation during toluene ammoxidation on vanadium phosphate catalysts

Abstract: The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH4+ ions located on BrOnsted sites, coordinatively bound NH3 on Lewis sites and NH2− groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH4+ ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.

Secondary building units, nets and bonding in the chemistry of metal–organic frameworks

Abstract: This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal–organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal–organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).

Hybrid Organic−Inorganic Polyoxometalate Compounds: From Structural Diversity to Applications

Abstract: Polyoxometalates (POMs) are discrete anionic metaloxygen clusters which can be regarded as soluble oxide fragments. They exhibit a great diversity of sizes, nuclearities, and shapes. They are built from the connection of {MOx} polyhedra, M being a d-block element in high oxidation state, usually VIV,V, MoVI, or WVI.1 While these species have been known for almost two centuries, they still attract much interest partly based on their large domains of applications. They play a great role in various areas ranging from catalysis,2 medicine,3 electrochemistry,4 photochromism,5 to magnetism.6 This palette of applications is intrinsically due to the combination of their added value properties (redox properties, large sizes, high negative charges, nucleophilicity...). Parallel to this domain, the organic-inorganic hybrids area has followed a similar expansion during the last 10 years. The concept of organic-inorganic hybrid materials * To whom correspondence should be addressed. E-mail: dolbecq@ chimie.uvsq.fr. Chem. Rev. 2010, 110, 6009–6048 6009