A. Fusi

Homogeneous catalysis by transition metal complexes: IV. The use of mixed catalysts in the oxidation of cyclohexene

Abstract The catalyzed oxidation of cyclohexene in benzene solution has been studied at 65 °C using a mixture of two different homogeneous metal catalysts. In order to obtain a reasonable selective formation of equimolecular amounts of cyclohexene oxide and 2-cyclohexen-1-ol, two types of catalysts have been mixed: catalysts A are catalysts of autoxidation (transition metal phosphine complexes or transition metal acetylacetonates), and catalysts B are catalysts of epoxidation (molybdenum complexes). The conditions necessary to obtain reasonably good activities and selectivities are reported and discussed.

Homogeneous catalysis by transition metal complexes. Part V: Hydroformylation of 1-octene catalysed by [η5-C5H5M(CO)2]2 SPECIES (MFe,Ru)

Abstract The hydroformylation of 1-octene catalysed by [η5-C5H5M(CO)2]2 (MFe,Ru) has been studied under 100 atm of a one to one H2-CO mixture in the temperature range 120 – 175°C. Effects such as the total pressure, the H2 to CO molar ratio, and the catalyst concentration have also been investigated in the case of the ruthenium complex.

Fast transient infrared studies in material science: development of a novel low dead-volume, high temperature DRIFTS cell.

A prototype DRIFTS flow reaction chamber was designed and developed in order to find analytical application in the study of heterogeneous catalysts operating at high temperatures under fast transient gas feed conditions. Minimisation of dead-volumes allows gas replacement in 8-10s at 10mLmin(-1) total flow. To overcome problems related to the reactivity of the cell walls under alternating oxidizing/reducing gases, the cell was built with Inconel 600trade mark, which was tested to be very inert even at high temperatures. The sample holder, which was developed to closely resemble a micro plug-flow reactor, poses some problems in terms of heat transfer to the outer body of the cell (limiting then the maximum reachable temperature) and of the correct measurement of the actual sample temperature. These problems were solved with a careful re-design of the upper part of the cell. The second prototype thus derived is able to reach temperatures up to 803K and allows gas replacement in less than 4s at 10mLmin(-1). The cell is inserted in a MCT-FT-IR, which allows to collect high quality spectra with a 1s time-resolution. The downstream flow can be analysed by a quadrupole mass spectrometer equipped with an enclosed source and by a commercial GC. The performances of this prototype cell are presented showing some tests carried out with ceria-zirconia (Ce(x)Zr(1-x)O(2)) catalysts for CO abatement under real operando conditions.

Diastereoselective epoxidation of hydroxy-containing unsaturated terpenes on heterogeneous titanium-catalyst

The diastereoselective epoxidation of substrates of interest as fine chemicals is here reported and the role of the OH-function in this reaction was studied particularly on non-allylic unsaturated terpenes. A heterogeneous system obtained grafting a titanocene precursor onto a commercial silica was used as catalyst.

On the role of carbonaceous material in the reduction of Cu2+ to Cu+ in Cu-ZSM-5 catalysts

Abstract A multi-technique analytical approach has been used to show that carbonaceous material entrapped in the channels system of Cu- ZSM-5 catalysts may contribute to maintain the copper ions in the oxidation state +1. This suggests that the reduction of Cu 2+ to Cu + does not only occur via water elimination from CuOH + species or via oxygen evolution from [Cu–O–Cu] 2+ species, but also via oxidation of the carbonaceous materials to give CO and CO 2 . This mechanism occurs under high temperature (>300°C) treatments in vacuo or He of Cu-ZSM-5 catalysts containing carbonaceous species and strongly adsorbed water molecules in the first coordination shell of the Cu 2+ . Our results may support the hypothesis about the roles of O 2 and hydrocarbons in the SCR of NO x ; O 2 maintains together with hydrocarbons the optimal valence state of copper (Cu + ) necessary to have the maximum conversion of NO x and hydrocarbons into N 2 and CO 2 .

Homogeneous catalysis with transition metal complexes. Part VII: Heteronuclear platinum clusters as hydrogenation catalysts of carbon—carbon multiple bonds☆

Abstract The hydrogenation of olefins and diolefins and of terminal and internal acetylenes is investigated using a series of heteronuclear platinum clusters as catalysts. Only Pt2Co2(CO)8(PPh3)2 and Pt(C6H11NC)2[Mo(CO)3−(η5-C5H5)]2 show rather poor catalytic properties for olefin hydrogenation, whilst they are good catalysts of low selectivity for the hydrogenation of terminal acetylenes. Pt2Co2(CO)8(PPh3)2 is also a good catalyst for selective hydrogenation of diphenylacetylene. The molecular rearrangements of the clusters under the different catalytic reaction conditions are investigated and discussed.

DRIFT study of CO chemisorption on organometallics-derived Pd/MgO catalysts : the effect of chlorine

Magnesia-supported palladium catalysts were prepared from chemical vapour deposition (CVD) of [Pd(C3H5)(C5H5)] and incipient wetness impregnation of [Pd(C3H5)Cl]2 and [Pd(acac)2]. DRIFT spectroscopy of adsorbed CO on prereduced catalysts indicates that the electronic state of metal particles depends on the preparation methodology and markedly on the organometallic precursor. Inn-heptane reforming at 500°C, the highest activity and selectivity were shown by the CVD-based system. Chloride ions deriving from the impregnation solvent exchange with surface hydroxyls. Acidic Mg-Cl sites are thus formed, which induce a beneficial effect on the catalytic properties. The reforming activity collapsed when a chlorine-containing precursor was used, due to a partial coverage of the palladium surface with chemisorbed chlorine atoms.

Homogeneous catalysis by transition metal complexes. Part VI: Hydroformylation of 1-octene catalysed by [η5-C5R5M(CO)2X] and [η5-C5R5M(CO)2]2 species (R = H, CH3, C6H5; M = Fe, Ru; X = Cl, Br, I)

Abstract The hydroformylation of 1-octene catalysed by the title compounds has been examined at 135 °C under an atmosphere of H2 and CO at a pressure of 85 atm. The influence on the activity and selectivity of various parameters such as the nature of the metal, the nuclearity of the original complex and the electronic and steric effects induced by the substituents on the cyclopentadienyl ligand has been investigated and discussed.

FTIR, XPS and TPD studies on the thermal decomposition of Os3(CO)12/silica: a multitechnique approach to the resolution of some controversial problems

Abstract The preparation of silica-supported osmium catalysts obtained by thermal decomposition of physisorbed Os 3 (CO) 12 has been studied in situ by FTIR, XPS and TPD. Under our experimental conditions, the formation of oxidised Os(II) surface species has been confirmed, either in Ar or in O 2 atmosphere. The occurrence of high nuclearity clusters under thermal treatment has been ruled out also by the study of the surface reactivity of adsorbed [Os 10 (CO) 24 C] 2− . The original Os 3 framework is restored from the Os(II) surface species by prolonged treatments at 523 K under CO.

A molecular approach to heterogeneous catalysis: Part 2. 1-butene isomerization catalyzed by silica-anchored osmium carbonyls

The title reaction has been investigated at 115{degree}C using HOs{sub 3}(CO){sub 10}(OSi chemical bond) as catalyst or catalyst precursor. By FTIR and XP spectroscopy and by TPDE, evidence exists for the in situ formation of molecular oxidized osmium moieties, covalently anchored to the surface, which are the active catalytic species. The intermediate formation of an olefin adduct during the in situ decomposition of the cluster precursors is supported by chemical extraction of the surface species and further FTIR and {sup 1}H NMR characterization. The reversible poisoning effect of CO and the beneficial influence of H{sub 2} on the catalytic activity and selectivity are also reported and discussed. The catalytic behavior of preformed oxidized osmium surface species has been found to be markedly dependent on the preparation method. The highest activity was obtained when they are formed in situ in the presence of 1-butene. Silica-supported metallic osmium catalysts displayed different activity and selectivity, thus confirming the molecular nature of the catalytic process.