Rinaldo Psaro

Effect of Nature and Location of Defects on Bandgap Narrowing in Black TiO2 Nanoparticles

The increasing need for new materials capable of solar fuel generation is central in the development of a green energy economy. In this contribution, we demonstrate that black TiO(2) nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption. The electronic structure of black TiO(2) nanoparticles is determined by the unique crystalline and defective core/disordered shell morphology. We introduce new insights that will be useful for the design of nanostructured photocatalysts for energy applications.

Surface-supported metal cluster carbonyls. Chemisorption, decomposition and reactivity of Os3(CO)12, H2Os3(CO)10 and Os6(CO)18 supported on silica and alumina and the investigation of the fischer-tropsch catalysis with these systems

Abstract On silica and alumina, Os 3 (CO) 12 , H 2 Os 3 (CO) 10 and Os 6 (CO) 18 are physisorbed (or weakly adsorbed) at room temperature. When the physisorbed cluster Os 3 (CO) 12 is thermally decomposed at ca. 150°C, there is an oxidative addition of a surface MOH group (M  Al???, Si???) to the OsOs bond of Os 3 (CO) 12 with formation of the surface species Os 3 (H)(CO) 10 (OM) (M  Al???, Si???) in which the cluster is covalently bonded to the surface by MOOs 3 bonds.Such a grafted cluster was also obtained was also obtained by bringing Os 3 (CO) 10 (CH 3 CN) 2 or H 2 Os 3 (CO) 10 into reaction with the surface of silica and alumina. On silica the grafted cluster, when treated with CO + H 2 O, can regenerate the starting Os 3 (CO) 12 cluster. The structure of the covalently bonded cluster was also confirmed by the synthesis of the model compound Os 3 (H)(CO) 10 (OSi(Ph) 3 ). Such covalent attachment of a cluster to a surface can be regarded as a model for the metal—support interaction which is frequently involved in heterogeneous catalysis. When the physisorbed clusters Os 3 (CO) 12 , H 2 Os 3 (CO) 10 , Os 6 (CO) 18 or the chemisorbed cluster Os 3 (H)(CO) 10 (OM), (M  Al???, Si???), are heated at about 200°C, there is a breakdown of the cluster cage with simultaneous oxidation of the osmium to two osmium(II) carbonyl species by the surface proton with simultaneous release of hydrogen. The [Os II (CO) 3 X 2 ] 2 and [Os II (CO) 2 X 2 ] n surface species in which X is a surface oxygen atom can be interconverted by a reversible carbonylation-decarbonylation process at 200°C. These two species can be also obtained by decomposition of [Os(CO) 3 X 2 ] 2 , (X  Cl, Br) onto silica or alumina surface or by CO reduction at 200°C of OsX 3 adsorbed on silica or alumina. The structure of one these surface compounds was confirmed by synthesis of the model compound [Os(CO) 3 (OSiPh 3 ) 2 ] m . These surface osmium carbonyl species exhibit a rather high thermal and chemical stability. They appear to be reduced by H 2 to metallic osmium only at 400°C. The thermal decomposition of the supported clusters is followed by a stoichiometric water gas shift reaction as well as a stoichiometric formation of methane. Under CO + H 2 , a Fischer-Tropsch catalyst, which exhibits a high selectivity for methane, is obtained. From the range of temperatures over which those stoichiometric and catalytic reactions are observed it seems reasonable to assume that they involve the Os II carbonyl species rather than metallic osmium.

Modern Surface Organometallic Chemistry

Preface ON THE ORIGINS AND DEVELOPMENT OF ?SURFACE ORGANOMETALLIC CHEMISTRY? The Basic Concept Use of Probe Molecules on Metallic Surfaces as Evidence of Coordination and Organometallic Chemistry at Metal Surfaces Chemical and Structural Analogy between Molecular Clusters and Small Metallic Particles Analogy between Supported Molecular Clusters and Small Supported Catalytic Particles Foundation of Surface Organometallic Chemistry From Organometallic Surface Chemistry to the Elementary Steps Occurring on Surfaces and Stabilization by the Surface of Rather Unstable Molecular Species From Surface Organometallic Chemistry on Oxides to Surface Organometallic Chemistry on Metals From Surface Organometallic Chemistry to Surface-Mediated Organometallic Synthesis Single Metal Site Heterogeneous Catalysts and the Design of New Catalysts PREPARATION OF SINGLE SITE CATALYSTS ON OXIDES AND METALS PREPARED VIA SURFACE ORGANOMETALLIC CHEMISTRY Introduction Surface Organometallic Chemistry on Oxides Reaction of Organometallic Compounds with Supported or Unsupported Group VIII Metals Particles Conclusion CATALYTIC PROPERTIES OF SINGLE SITE CATALYSTS PREPARED VIA SURFACE ORGANOMETALIC CHEMISTRY ON OXIDES AND ON METALS Introduction Stoichiometric Activation of Alkane C-H Bonds Alkane C-C Bond Activation by Tantalum Hydrides. Low Temperature Catalytic Hydrogenolysis of Alkanes Metathesis of Acyclic Alkanes Cross-Metathesis Reactions of Alkanes Homologation of Alkanes Polystyrene Modification and Hydrogenolysis of Linear Alkanes and Polyethylene by a Supported Zirconium Hydride Olefin Metathesis Olefin Epoxidation Deperoxidation of Cyclohexyl Hydroperoxide Some Applications of Supported Nanoparticles Modified by Organometallics Conclusion BUILDING BLOCK APPROACHES TO NANOSTRUCTURED, SINGLE SITE, HETEROGENEOUS CATALYSTS Introduction Current Challenges in Catalysis What is a Nanostructured Catalyst? Benefits of Nanostructuring Catalysts Current Approaches to Nanostructured Catalysts Building Block Approaches to Nanostructured Materials and Catalysis Nanostructured Catalysts via a Non-Aqueous Building Block Methodology A Model for the Growth of Building Block Matrices and a Nanostructuring Strategy A General Procedure for Preparing Nanostructured Catalysts in Silicate Matrices Atomically Dispersed Titanium and Vanadium, Single Site Catalysts Bridge between Nanostructuring and Catalysis Summary TRANSITION METAL SINGLE SITE CATALYSTS ? FROM HOMOGENEOUS TO IMMOBILIZED SYSTEMS Introduction Covalently Anchored Organometallic Complexes on Unmodified Silica Anchoring of Organometallic Complexes via the Metal Center Organometallic Complexes Anchored via a Covalent Linkage to a Ligand Noncovalently Anchored Organometallic Complexes Encapsulated Organometallic Complexes Conclusions CONTROLLED PREPARATION OF HETEROGENEOUS CATALYSTS FOR CHEMO- AND ENANTIOSELECTIVE HYDROGENATION REACTIONS Introduction Catalyst Preparation and Characterization Hydrogenation of Alpha,Beta-Unsaturated Aldehydes Hydrogenation of Aromatic Ketones Enantioselective Hydrogenation Reactions Conclusions WELL-DEFINED SURFACE RHODIUM SILOXIDE COMPLEXES AND THEIR APPLICATION TO CATALYSIS Molecular versus Immobilized Transition Metal Siloxide Complexes in Catalysis Synthesis, Characterization and Catalytic Activity of Well-Defined Surface Rhodium Siloxide Complexes Solid-State NMR Method in Catalysis by Surface Organometallics Mechanism of Hydrosilylation Catalyzed by Surface versus Soluble Rhodium Siloxide Complexes CARBONYL COMPOUNDS AS METALLIC PRECURSORS OF TAILORED SUPPORTED CATALYSTS Introduction Catalysts Prepared from Metal Carbonyls of Groups 6, 7, 10 and Gold Catalysts Prepared from Metal Carbonyls of Group 8: Iron, Ruthenium and Osmium Catalysts Prepared from Metal Carbonyls of Group 9: Cobalt, Rhodium and Iridium Concluding Remarks EXPLOITING SURFACE CHEMISTRY TO PREPARE METAL-SUPPORTED CATALYSTS BY ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION Introduction Surface Organometallic Chemistry Strategies to Avoid the Contamination of Metal Deposits How to Manage the Nucleation and Growth Steps Concluding Remarks ADVANCED DESIGN OF CATALYST SURFACES WITH METAL COMPLEXES FOR SELECTIVE CATALYSIS Introduction Isolation and Epoxidation Activity of a Coordinatively Unsaturated Ru Complex at a SiO2 Surface Chiral Self-Dimerization of V Complexes on a SiO2 Surface for Asymmetric Catalysis Molecular Imprinting Rh-Dimer and Rh-Monomer Catalysts Re Clusters in HZSM-5 Pores for Direct Phenol Synthesis Conclusion SURFACE ORGANOMETALLIC CHEMSITRY OF D(0) METAL COMPLEXES Introduction Ligands Susceptible to React with Hydroxyl Groups of an Inorganic Oxide Ligands Susceptible to Reaction with Lewis Acid Sites of Inorganic Oxides Reactivity of Hydrocarbyl-Metal Complexes and the Metal Atom Inorganic Oxides as Supports for Organometallic Species Models for Surface Organometallic Species Tuning the Catalytic Activity of Surface Organometallic Species Relevant Aspects of the Full Characterization of Some Selected Species Concluding Remarks SURFACE ORGANOLANTHANIDE AND ?ACTINIDE CHEMISTRY Introduction Surface Organolanthanide Chemistry SOLnC Surface Organoactinide Chemistry, SOAnC Catalytic Applications of SOLnC and SOAnC Conclusions and Perspectives ISOCYANIDE BINDING MODES ON METAL SURFACES AND IN METAL COMPLEXES Introduction Modes of Isocyanide Coordination in Transition Metal Complexes Adsorption of Isocyanides (C=N-R) on Metal Surfaces Conclusions MOLECULAR INSIGHT FOR SILICA-SUPPORTED ORGANOMETALLIC CHEMISTRY THROUGH TRANSITION METAL SILESQUIOXANES Introduction Organometallic POSS Derivatives Conclusions SURFACE-MEDIATED NANOSCALE FABRICATION OF METAL PARTICLES AND WIRES USING MESOPOROUS SILICA TEMPLATES AND THEIR SHAPE/SIZE DEPENDENCY IN CATALYSIS Introduction Surface-Mediated Synthesis of Metal/Alloy Nanowires Using Mesoporous Templates Characterization of Nanowires and Nanoparticles in FSM-16 and HMM-1 Mechanism for Formation of Pt Nanowires in Mesoporous Silica Templates Isolation and Characterization of Metal/Alloy Nanowires Free from the Silica Supports Novel Surface-Mediated Fabrication of Rh and RhPt Nanoparticles Using Mesoporous Templates in Supercritical Carbon Dioxide Other Surface-Mediated Synthesis of Metal Nanowires on Porous Membrane and Graphite Steps Shape/Size Dependency in Catalysis of Metal/Alloy Nanowires and Particles in Mesoporous Silica Templates Synthesis of Pt and Au Nanoparticle Arrays in Mesoporous Silica Films and their Electric/Magnetic Properties in Terms of the Quantum-Size Effect Conclusion SURFACE-MEDIATED ORGANOMETALLIC SYNTHESES Introduction Group 7: Rhenium Group 8 Group 9 Group 10 Conclusion

Surface supported metal cluster carbonyls. Chemisorption decomposition and reactivity of Rh4(CO)12 supported on silica and alumina

Abstract Chemisorption of Rh 4 (CO) 12 on to a highly divided silica (Aerosil “0” from Degussa), Leads to the transformation: 3 Rh 4 (CO) 12 → 2 Rh 6 (CO) 16 + 4 CO. Such an easy rearrangement of the cluster cage implies mobility of zerovalent rhodium carbonyl fragments on the surface. Carbon monoxide is a very efficient inhibitor of this reaction, and Rh 4 (CO) 12 is stable as such on silica under a CO atmosphere. Both Rh 4 (CO) 12 and Rh 6 (CO) 16 are easily decomposed to small metal particles of higher nuclearity under a water atmosphere and to rhodium(I) dicarbonyl species under oxygen. From the Rh I (CO) 2 species it is possible to regenate first Rh 4 (CO) 12 and then Rh 6 (CO) 16 by treatment with CO ( P co ⩾ 200 mm Hg) and H 2 O ( P H 2 O ⩾ 18 mm Hg). The reduction of Rh I (CO) 2 surface species by water requires a nucleophilic attack to produce an hypothetical [Rh(CO) n ] m species which can polymerize to small Rh 4 or Rh 6 clusters in the presence of CO but which in the absence of CO lead to metal particles of higher nuclearity. Similar results are obtained on alumina.

Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel-Zinc Materials

Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium through redox transmetalation with Pd(IV) salts. The materials obtained, Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a variety of techniques. The analytical and spectroscopic data show that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small, highly dispersed, and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from Ni--O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl(2)/HCl with ethylene glycol in the presence of Vulcan XC-72. In Pd/C, the Pd particles are larger, less dispersed, and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, containing very low Pd loadings (22-25 microg cm(-2)), were studied for the oxidation of ethanol in alkaline media in half cells and provided excellent results in terms of both specific current (as high as 3600 A g(Pd)(-1) at room temperature) and onset potential (as low as -0.6 V vs Ag/AgCl/KCl(sat)).

Epoxidation on titanium-containing silicates: do structural features really affect the catalytic performance?

Five titanium-containing silicates, with different structural features, were compared: Ti–MCM-41, ordered titanium-grafted mesoporous silica, Ti–SiO2 Davison, nonordered titanium-grafted porous silica, Ti–SiO2 Aerosil, nonporous pyrogenic titanium-grafted silica, MST, nonordered in-framework mesoporous material, and TiO2–SiO2 Grace, commercial amorphous porous mixed oxide. They were tested in the liquid-phase epoxidation reaction on six unsaturated cyclic terpenes. Good performances were obtained on the commercial mixed oxide and also on the three grafted silicates. The in-framework MST showed the worst activity results. Under these conditions, the porosity features do not affect the catalytic performances noticeably and the use of an ordered mesoporous material is not strictly required. Likewise, a very high surface area is not mandatory in order to have an efficient titanium-grafted catalyst in the epoxidation of these substrates.

Bimetallic Au–Pt/TiO2 photocatalysts active under UV-A and simulated sunlight for H2 production from ethanol

A new class of bimetallic Au–Pt/TiO2 photocatalysts were developed and employed in H2 photoassisted production using ethanol as a sacrificial reagent both under UV-A and simulated sunlight irradiation. Remarkably, preliminary experiments show promising hydrogen evolution under visible light using Au0.5–Pt0.5/TiO2 with methanol. The presence of bimetallic Au–Pt nanoparticles and the TiO2 visible light absorption, induced by the presence of oxygen vacancies and/or Ti3+, are the two parameters accounting for the difference in activity.

H2 Production by Renewables Photoreforming on Pt–Au/TiO2 Catalysts Activated by Reduction

Bimetallic Pt-Au nanoparticles supported on reduced anatase nanocrystals represent a new class of promising photocatalysts with high activity in hydrogen production by photoreforming of aqueous solution of renewable feedstock, such as ethanol and glycerol. The catalysts are easily obtained by metal impregnation of commercial TiO₂, followed by a reductive treatment. Remarkably, deeper catalyst pre-reduction results in enhanced photoactivity. When ethanol is used as sacrificial agent, under both UV-A or simulated sunlight irradiation, H₂ is the most abundant product in the gas stream whereas, in the case of glycerol, significant amounts of CO₂ have also been detected, indicating a more efficient oxidation of the organic sacrificial agent. The presence of bimetallic Pt-Au nanoparticles and of Ti³⁺ sites/O²⁻ vacancies in the bulk structure of titania are two key parameters to maximize light absorption and feedstock activation, finally resulting in good photocatalytic performances.

A comparison between silica-immobilized ruthenium(II) single sites and silica-supported ruthenium nanoparticles in the catalytic hydrogenation of model hetero- and polyaromatics contained in raw oil materials

A comparative study of the hydrogenation of various heterocycles, model compounds in raw oil materials, by either Ru(II) complex immobilized on mesoporous silica or Ru(0) nanoparticles deposited on the same support has been performed. The single-site catalyst contains the molecular precursor [Ru(NCMe)3(sulphos)](OSO2CF3) tethered to partially dehydroxylated high-surface-area silica through hydrogen bonds between silanol groups of the support and SO3− groups from both the sulphos ligand [−O3S(C6H4)CH2C(CH2PPh2)3] and the triflate counter anion. Highly dispersed ruthenium nanoparticles were prepared by calcination/reduction of silica-supported Ru3(CO)12. The heterocycles (benzo[b]thiophene, quinoline, indole, acridine) are hydrogenated to cyclic thioethers or amines. The Ru(II) single-site catalyst is active for both benzo[b]thiophene and the N-heterocycles, while the Ru(0) catalyst does not hydrogenate the S-heterocycle, yet is efficient for the reduction of the N-heterocycles and simple aromatic hydrocarbons. The surface silanols promote the hydrogenation of indole via NH⋯ O(H)Si hydrogen bonds and can interact with the π-electron density of all substrates.

Heterogeneous catalytic epoxidation of fatty acid methyl esters on titanium-grafted silicas

Three different titanium-grafted silicates, with different morphological features were compared in the epoxidation, using tert-butylhydroperoxide as oxidant, of methyl oleate, methyl elaidate and of a mixture of methyl esters, obtained from high-oleic sunflower oil. Ti-MCM-41, a well-ordered mesoporous catalyst, showed very high conversions and excellent selectivity on all the substrates. The fatty acid methyl esters derived from renewable raw material were epoxidised selectively with very high yields in a reaction medium completely free from organic acidic compounds. The influence of the pore order of the catalysts on the catalytic performance was also examined. The interactions between the organic substrate and the ordered array of mesopores in Ti-MCM-41 were evidenced.