K. Pamin

Novel “ship-in-the-bottle” type catalyst: evidence for encapsulation of 12-tungstophosphoric acid in the supercage of synthetic faujasite

A new type of “ship-in-the-bottle” catalyst has been obtained by encapsulation of heteropolyacid H3PW12O40 in the supercage of faujasite. As shown by XRD and IR, the structure of zeolite Y after encapsulation is retained.31P MAS NMR reveals that the signal at −14.4 ppm, assigned to the Keggin unit, is in the case of the encapsulated catalyst much broader than the line observed for a sample containing the heteropolyacid adsorbed on the zeolite. The broadening is due to interaction between phosphorus and aluminium from zeolite. Highly active catalysts are formed by encapsulation, as exemplified here by strongly increased activity and modified selectivity in isomerization and disproportionation ofm-xylene.

The effect of peripheral substituents in metalloporphyrins on their catalytic activity in Lyons system

Manganese porphyrin catalysts with different number of halogens atoms substituted at the phenyl and pyrrole rings were investigated in the Lyons system in oxidation of cyclooctane with molecular oxygen (as air) to cyclooctanone and cyclooctanol without the use of sacrificial co-reductant. The catalytic activity of metalloporphyrins increases with the increase of the redox potential of metalloporphyrins in the investigated system and shows almost linear relationship with the number of the halogens on porphyrin macrocycle. On the basis of obtained results the new reaction mechanism is discussed and proposed.

Immobilization of dodecatungstophosphoric acid on dealuminated zeolite Y: a physicochemical study

Abstract 12-Tungstophosphoric acid (PW 12 ) has been supported on dealuminated zeolite Y. The catalysts were studied by XRD, DTA/DTG, IR, argon adsorption and MAS NMR spectroscopy. The structure of dealuminated faujasite is retained upon contact with a very strong PW 12 acid, which becomes thermally stabilized. Two types of Keggin anions exist at the surface: those strongly interacting with the OH groups of the support, prevailing at low coverages, and those weakly interacting with the zeolite, prevailing at high coverages. Transformations of m -xylene proceed along three pathways: isomerization, disproportionation and dealkylation. Pure zeolite shows high selectivity to isomerization. Deposition of PW 12 acid dramatically increases the selectivity of disproportionation to toluene and trimethylbenzenes, which rises with the growing acid loading.

Manganese porphyrins as catalysts for oxidation of cyclooctane in Lyons system

Abstract Oxidation of cyclooctane with molecular oxygen (as air) in the presence of first generation manganese porphyrins XMn III (TTP), where X=F − , Cl − , Br − , I − , OH − , CH 3 COO − , as catalysts was investigated in the Lyons system. The catalytic activities of the metalloporphyrins in the oxidation of cyclooctane to cyclooctanone and cyclooctanol are covariant with electronegativity of halides as axial ligands and increase with the decrease of the redox potential of metalloporphyrins. It was concluded that axial ligands are involved in the reaction initiating the reaction by generating the radicals with simultaneous reduction of the manganese porphyrin. Relatively high yields of products were obtained without the use of sacrificial co-reductant.

Molybdenum Complexes as Catalysts for the Oxidation of Cycloalkanes with Molecular Oxygen

A group of new polymolybdates was synthesized and tested in the catalytic oxidation of cycloalkanes. Investigated compounds exhibit broad structural diversity including polymolybdates with isolated anionic clusters (0-dim), polymeric anions (1-dim), Mo–O layers (2-dim) as well as hexagonal and orthorhombic molybdenum oxides (3-dim). All studied molybdenum complexes were found to be active in the reaction conditions yielding ketones and alcohols as main products. In the case of layered compounds (2-dim), dicarboxylic acid was detected in the mixture of reaction products. The structure of investigated molybdenum compounds was shown to have influence on yields and selectivities of the investigated reactions. Anionic layers separation (in 2-dim materials) as well as type and charge of organic cations present in the compounds are prime examples of structural factors influencing the oxidation reactions efficiencies. On the basis of obtained results and literature reports a mechanism for the oxidation of cycloalkanes by polymolybdates has been proposed.Graphical Abstract

Keggin-Type Heteropoly Salts as Bifunctional Catalysts in Aerobic Baeyer-Villiger Oxidation

The cobalt, manganese, and iron salts of tungstophosphoric or molybdophosphoric acid with growing content of metals were applied for the first time as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone with molecular oxygen. The catalysts were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and ethanol decomposition reaction. Introduction of transition metals into the heteropoly structure increases the activity of resulting heteropoly salts in comparison with parent heteropolyacids. It was shown that the most active catalysts are salts of the heteropoly salts with one metal atom introduced and one proton left (HMPX) type, (where M = Co, Fe, Mn, and X = W, Mo) with the metal to proton ratio equal one. Among all of the studied catalysts, the highest catalytic activity was observed for HCoPW. The effect indicates that both the acidic and redox properties are required to achieve the best performance. The Baeyer-Villiger (BV) oxidation mechanism proposed identifies the participation of heteropoly compounds in three steps of the investigated reaction: oxidation of aldehyde to peracid (redox function), activation of carbonyl group (Lewis acidity), and decomposition of the Criegee adduct to ε-caprolactone (Brønsted acidity).

Titanium dioxide doped with vanadium as effective catalyst for selective oxidation of diphenyl sulfide to diphenyl sulfonate

Diphenyl sulfide was oxidized to sulfoxide and sulfone over V-doped TiO2 using a 30% solution of H2O2. The TiO2 samples with different intended content of vanadium (0.02, 0.05, 0.1 and 0.18 mass%) were prepared by incipient wetness impregnation. Physicochemical properties of the V-doped TiO2 were characterized by chemical analysis (ICP-OES), X-ray diffraction (XRD/in situ HT-XRD), UV–Vis diffuse reflectance spectrometry (UV–Vis DRS), N2-sorption measurements, electron paramagnetic resonance and cyclic voltammetry. Both vanadium oxide loading and calcination temperature influenced the structure of the V-TiO2 samples. Vanadium species deposited on TiO2 decreased temperatures required for anatase to rutile phase transformation. The V-TiO2 samples were found to be efficient catalysts for oxidation of sulfides to sulfones. The sample with the lowest vanadium content (0.02VTiO2) presented among the studied catalysts the best catalytic properties with respect to high conversion of diphenyl sulfide to diphenyl sulfonate. An increase in vanadium loading resulted in decrease in catalytic activity of the samples. Also non-modified TiO2 presented significantly lower catalytic activity in comparison with 0.02VTiO2. This interesting effect was related to the formation of highly dispersed vanadium species catalytically active in Ph2S oxidation in the case of the samples with lower V-content. An increase in vanadium loading results in the formation of more aggregated V-species inactive, or less active, in the process of diphenyl sulfide oxidation.

Polymolybdates and Peroxomolybdates: Candidates for Catalysts in Industry

Progress in catalysis depends on a full understanding of the role of the individual components of catalytic materials. Crystallographic studies offer insight into crystal structure, which enables the rational selection of reagents and better planning of the syntheses of novel materials and catalysts. In this paper we have studied the process of the oxidation of hydrocarbons and terpenes with oxygen from the air. Processes of this type are important in so-called “Green Chemistry.” Their application can reduce the amount of environmentally harmful pollutants formed through conventional oxidation based on nitric acid. While investigating the catalytic activity of peroxoand polymolybdates(VI) in the oxidation of cycloalkanes, we found a number of intriguing relationships. To explain them, we designed, synthesized and solved the crystal structures of the family of new peroxomolybdates, tri-, octaand pentamolybdates of amines. Both single crystal and polycrystalline materials were investigated using laboratory as well as synchrotron radiation. Next, we used these compounds as catalysts in certain interesting for industry processes (e.g. oxidation of cyclic hydrocarbons). We have concluded that: − The activity of peroxocompounds is enhanced by the coordination of N-oxide groups to Mo atoms. − The activity of anionic polymeric trimolybdates decreases when ‘surface of polymeric fiber’ is blocked by cations. − The anionic layers of pentamolybdates are separated by cations of variable size. The distance between layers plays a role similar to that of the size of channels in zeolites. Summary: Peroxomolybdates and polyoxomolybdates show great prospects for new industrial uses (besides cracking and desulfurization).

Interaction of metalloporphyrins with lipid bilayers, a calorimetric study

Interaction of metalloporphyrins with lipid bilayers, a calorimetric study The interaction of three metalloporphyrins, containing manganese, iron and cobalt atoms, with lipid bilayers composed of neutral (DPPC) or charged (DMPG) phospholipids were studied by means of scanning differential calorimetry. We found only minute effects exerted by studied compounds on DPPC, while phase transitions of charged DMPG were seriously affected by porphyrins. Analysis of experimental data revealed that due to the electrostatic interactions DMPG bilayers are perturbed not only in the polar head group region. Putative rearrangements of the polar heads packing affects also the acyl chain region of this lipid bilayer. Perturbation of DMPG polar heads induced by porphyrin in complex with manganese atoms is bigger than that induced by other porphyrins.