R. Psaro

Carbon tetrachloride hydrodechlorination with organometallics-based platinum and palladium catalysts on MgO

Hydrodechlorination of carbon tetrachloride was performed at atmospheric pressure over Pd and Pt catalysts supported on various inorganic oxides (Al2O3, MgO, CeO2) and obtained from different organometallic precursors (Pd(acac)2, [Pd(C3H5)Cl]2, Pt(acac)2 and Pt(CH3CN)2Cl2. Generally, Pd-based catalysts show low conversion levels and high selectivity to C1–C7+ hydrocarbons with a distribution that fits a typical Schulz–Flory mechanism for alkyl polymerization. On the other hand, Pt catalysts show high and stable activity, the major products are CHCl3 and in lesser extent methane. Catalytic performances depend on the stability, under reaction conditions, of the metal phase, that could be related to the nature of chlorine species pre-adsorbed on catalysts. Owning to their superior catalytic performances, the structural modifications of Pt catalysts under reaction conditions were characterized by EXAFS spectroscopy.

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.

Molecular metal carbonyl clusters and volatile organometallic compounds for tailored mono and bimetallic heterogeneous catalysts

Abstract Specific studies carried in Milan laboratory in the application of metal carbonyl clusters to preparation of supported catalysts are reviewed. Examples are reported of catalysis by heterogeneous organometallic surface species, such as 1-butene isomerisation catalysed by silica-anchored osmium carbonyl species, or of catalysis by very small metal particles produced under catalytic conditions, such as ethylene hydroformylation using silica supported [Rh12(CO)30]2− as precursor. Highly active bimetallic FeIr MgO catalysts for methanol synthesis, have been pr prepared by controlled reductive decomposition of physisorbed [Et4N]2[Fe2Ir4(CO)16] and [Et4N]2[Fe2Ir2(CO)12] clusters. In these examples, evidence of the nature of the catalytic entities is reached by in situ DRIFTS characterisation under catalytic conditions or using EXAFS measurements. Metal particles deposited inside the zeolitic cavities have been obtained by mild reduction conditions of entrapped organometallic compounds introduced by chemical vapour deposition (CVD). In this way, non-acidic Pt KL , Pd NaY catalysts for hydrocarbon reforming have been prepared. Bimetallic Pt Re and Rh Mn particles, entrapped inside a NaY zeolite, have been easily obtained by CVD of M2(CO)10 carbonyls (M  Re, Mn) on pre-reduced metal particles.

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.

Bifunctional copper catalysts. Part II. Stereoselective synthesis of (-)-menthol starting from (+)-citronellal

The one-step transformation of (+)-citronellal into (-)-menthol has been realised with yield ∼90% and stereoselectivity up to 80% under mild conditions in the presence of Cu/SiO2 by exploiting the presence of acidic and hydrogenation sites on the catalyst surface, the unusual reducibility of an olefinic bond under these conditions and the chemoselectivity of the process.

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.

Surface organometallic chemistry: Reductive carbonylation of silica-supported MCl3·3H2O (M=Rh, Ir)

Abstract The reductive carbonylation of silica-supported MCl3·3H2O (M=Rh, Ir) was studied at atmospheric pressure under CO and under a mixture of CO and H2O. It was observed that these salts may be converted respectively into [Ir(CO)3 Cl]n and [Rh(CO)2Cl]2 under CO. At 70 °C, in the presence of CO and H2O, Ir4(CO)12 is selectively obtained. Under the same experimental conditions [Rh(CO)2Cl]2 sublimes, while at 25 °C the liberated HCl inhibits further reduction to rhodium carbonyl clusters. However, Rh6(CO)16 might easily be obtained, working at 25 °C with CO and H2O, using [Rh(CO)2Cl]2 as the starting material instead of RhCl3. The inhibiting effect on the nucleation process of HCl and the role of water are discussed in the comparison with the reductive carbonylation of a chlorine-free rhodium salt, [Rh(O2CCH3)2]2.

A molecular approach to the hydrogen transfer reduction of ketones catalyzed by silica-supported osmium carbonyls

Abstract A study of the catalytic activity of the well-characterized silica surface-grafted cluster [Os 3 (μ-H)(CO) 10 (μ-OSi⩽)] in the hydrogen transfer reduction of saturated and unsaturated ketones is reported. The cluster stability under the reaction conditions is investigated by means of temperature-programmed decomposition (TPDE) and IR spectroscopy. Evidence for a clustercatalyzed reaction is suggested only in the reduction of saturated ketones.

119Sn mössbauer study and catalytic properties of magnesia-supported platinum-tin catalysts prepared by surface organometallic chemistry

Pt-Sn/MgO catalysts prepared by Surface Organometallic Chemistry were investigated by 119 Sn Mossbauer spectroscopy. The results indicate that, on the reduced catalyst, most of the tin forms bimetallic particles with a Sn-rich surface, whereas the remainder is present as Sn(II) and Sn(IV) compounds. Changes of the structure of the particles after a catalytic test and implications on the properties of the catalysts in the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols are discussed.

A molecular approach to heterogeneous catalysis. Ethylene hydroformylation catalysed by silica-supported [Rh12(CO)30]2− cluster anion: influence of the countercations Li+, Na+, K+, Zn2+

Abstract Cluster-derived rhodium catalysts, prepared from salts of the cluster anion [Rh 12 (CO) 30 ] 2− supported on silica, have been studied in ethylene hydroformylation. A catalyst pre-treatment was carried out in Ar at 393 K before the admission of the hydroformylation mixture. The selectivity for propanal formation depends on the alkaline countercation in the following order: K≥Li≥Na. The Zn-promoted catalyst is the most selective. The corresponding value for the unpromoted system, prepared from neutral Rh 4 (CO) 12 , was about 20% lower. In situ infrared studies suggest the oxidative disruption of the metal framework of the physisorbed Rh 12 cluster to take place in isolated Rh I (CO) 2 species. In catalytic conditions a reductive agglomeration of Rh(I) into metallic particles occurred. Remarkable effects on activity and/or selectivity are induced on promoted systems only upon a catalyst pre-treatment in O 2 at 723 K. A simple exposure to the hydroformylation mixture at 393 K was enough to generate the active metallic phase.