In comparison with the separate components, the combination on the same support material of dispersed palladium nanoparticles and grafted molecular rhodium complexes has provided evidence of improved activity in the hydrogenation of arenes.[1] It was proposed that the catalytic efficiency is a consequence of a hydrogen-spillover process that would enhance specifically the hydrogenation activity of the molecular catalyst.[1] A recent study of the hydrogenation of arenes with a catalyst obtained by silica sol-gel coentrapment of metallic palladium and [Rh(cod)(m-Cl)] 2 disagrees with the hydrogen-spillover hypothesis and suggests that the action of both metals is caused by a synergistic effect; [2] however, no explanation of the nature of this effect has been forthcoming. Herein, we provide a rationale for this synergistic effect, and show that the grafted rhodium complex speeds up the hydrogenation of arenes to cyclic dienes.Three different heterogeneous catalysts were tested in the hydrogenation of some arenes in n-pentane at relatively low temperature (40-60 8C) and 30 bar H 2 . A highly dispersed palladium metallic phase and the Rh I complex [Rh(cod)(sulphos)] (cod = cyclooctadiene; sulphos = À O 3 S(C 6 H 4 )CH 2 -C(CH 2 PPh 2 ) 3 ) were separately supported on high-surfacearea porous silica . A calcination/reduction procedure of silica-supported PdCl 2 was employed to prepare Pd 0 /SiO 2 , 1, with a metal content of about 10 wt %, while the Rh I complex was grafted by using a known procedure involving hydrogen bonds between silanols of the support and sulfonate groups from the sulphos ligand.[3] The single-site catalyst, [Rh(cod)-(sulphos)]/SiO 2 , 2 (Figure 1 A) with a metal content of about 0.5 wt %, was previously employed to catalyze the hydrogenation and hydroformylation of olefins in either gas-solid or liquid-solid phase.[3a] Upon hydrogenation, the cod ligand

Cathodoluminescence spectroscopy is profitably exploited to study energy transfer mechanisms in Au and Pt/black TiO2 heterostructures. While Pt nanoparticles absorb light in the UV region, Au nanoparticles absorb light by surface plasmon resonance and interband transitions, both of them occurring in the visible region. The intra-bandgap states (oxygen vacancies) of black TiO2 play a key role in promoting both hot electron transfer and plasmonic resonant energy transfer from Au nanoparticles to the TiO2 semiconductor with a consequent photocatalytic H2 production increase. An innovative criterion is introduced for the design of plasmonic composites with increased efficiency under visible light.

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The Ru(II) complex [(sulphos)Ru(NCMe) 3 ](OSO 2 CF 3 ) (1) has been immobilized on partially dehydroxylated high-surface-area silica via hydrogen-bonding interactions between the silanol groups of the support and the SO 3groups from both the sulphos ligand and the triflate counteranion (sulphos ) -O 3 S(C 6 H 4 )CH 2 C(CH 2 PPh 2 ) 3 ). Compound 1 has been authenticated in the solid state by a single-crystal X-ray analysis and in solution by NMR spectroscopy, while its silica-grafted form [(sulphos)Ru(NCMe) 3 ](OSO 2 CF 3 )/SiO 2 (1/SiO 2 ) has been characterized by DRIFT and CP MAS 31 P NMR studies. The supported hydrogen-bonded (SHB) complex 1/SiO 2 is an effective and selective catalyst for the hydrogenation of benzylideneacetone to benzylacetone and of benzonitrile to benzylidenebenzylamine in n-octane. No appreciable ruthenium leaching into the hydrocarbon phase was observed in either case. Analogous hydrogenation reactions catalyzed by either the aqueous-biphase catalyst 1 in water/n-octane or the homogeneous analogue [(triphos)Ru(NCMe) 3 ](OSO 2 CF 3 ) 2 in THF have been carried out (triphos ) MeC(CH 2 PPh 2 ) 3 ). The silica-supported catalyst is slightly less active but much more selective and recyclable than the soluble congeners. In an attempt to rationalize the selectivity exhibited by the SHB catalyst, various model studies have been performed in different phase variation systems. Incorporation of the results obtained led to the conclusion that, in contrast to fluid solution reactions, no heterolytic splitting of H 2 at ruthenium occurs in the heterogeneous phase.