Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.

Noble metals in polyoxometalates.

Polyoxometalates containing late transition and noble metal atoms

In situ generated catalysts and preformed catalysts are two practical strategies widely used in cross-coupling methodology that have long been considered to involve the same active species in the catalytic cycle. Recent mechanistic studies have revealed two fundamentally different pictures of catalytic reactions in solution. Preformed catalysts with strongly bound ligands initiate transformations mainly involving single type of metal species. In contrast, in situ generated catalysts give rise to cocktail-type systems with different metal species presented in solution. The role of catalyst precursor, interconversions of catalytic species during reaction, stability and recycling of catalyst, catalysis by autocatalyst exhaust and plausible sources of metal-containing contaminants are the key points discussed in this review.

Catalytic C–C and C–Heteroatom Bond Formation Reactions: In Situ Generated or Preformed Catalysts? Complicated Mechanistic Picture Behind Well-Known Experimental Procedures

Catalytic removal of nitric oxide with hydrogen and carbon monoxide in the presence of excess oxygen

A new preparation method of Co-Mo/γ-Al2O3 HDS catalyst has been developed by using the (NH4)3[CoMo6O24H6]·7H2O Anderson type heteropolyoxomolybdate supported on γ-Al2O3. The system can be considered as an interesting and simplified alternative to the traditional bimetallic catalyst. Diffuse reflectance spectroscopy measurements have been employed to confirm that the planar-arrangement of the heteropolyanion is not substantially altered by the adsorption process. The corresponding adsorption isotherm has been registered at room temperature due to the good solubility of the phase.

In comparison with the traditional HDS catalysts, this new system shows the following relevant aspects: (a) the activity for the HDS of thiophene is similar in both cases, although the Co content is considerably lower than that of the impregnation of the ammonium heptamolybdate and cobalt nitrate hexahydrate solutions ([Co]/([Co]+[Mo])=0.14 in relation to 0.25–0.40 in the conventional system); (b) the phase adsorbs well onto the support; (c) the activity of molbydenum seems to be promoted by the presence of cobalt in the ordered distribution of the heteropolyanion on the surface of γ-Al2O3 (synergy-like effect). The primary structure of supported heteropolyoxomolybdate is clearly preserved; (d) whereas the conventional catalysts can be prepared through a series of steps (two impregnation operations, one for drying and another for the calcination at 550°C), the proposed method only requires one impregnation step and a drying step at 80°C, suppressing the calcination at 550°C.

Anderson type heteropolyoxomolybdates in catalysis : 1. (NH4)3[CoMo6O24H6].7H2O/γ-Al2O3 as alternative of Co-Mo/γ-Al2O3 hydrotreating catalysts

Structures and catalytic activity of Pt$z.sbnd;Mo bimetallic ensembles derived from a new planar 6PtMo6O2498$minus; heteropolyanion supported on Al2O3 and SiO2I. Characterization of the supported 6PtMo69 catalysts

To investigate the effect of alkali impurity in Mo/SiO2 on the MoO
 x
 structure on SiO2 surfaces SiO2-supported Mo oxides were prepared with various amounts of Na ions in a class-1 clean bench with a laminar flow in a class-1000 clean room. The Na concentrations were varied in the range 0-5000 ppm, while the Mo loading on SiO2 was maintained at 0.7 wt%. The Mo-Na/SiO2 samples obtained were characterized by diffuse reflectance UV-visible and Raman spectroscopy. Three types of Mo species were identified: octahedral monooxo Mo monomer species, Na2Mo2O7 and MoO3. At less than 100 ppm Na both octahedral Mo monomers and MoO3 species were formed on SiO2. The MoO3 species was transformed to Na2Mo2O7 at 2000 ppm Na, where the Na ions interact directly with the Mo species on the surface. The octahedral monooxo Mo monomer species seems not to be influenced significantly by Na impurity.

The effect of ppm-level Na impurity on the structure of SiO2-supported Mo catalysts prepared in a clean room

Structures and Catalytic Activity of Pt-Mo Bimetallic Ensembles Derived from a New Planar (PtMo6O24)8- Heteropolyanion Supported on Al2O3 and SiO2. Part 1. Characterization of the Supported (PtMo6) Catalysts.

T. Liu

Papers

Structures and catalytic activity of Pt$z.sbnd;Mo bimetallic ensembles derived from a new planar 6PtMo6O2498$minus; heteropolyanion supported on Al2O3 and SiO2I. Characterization of the supported 6PtMo69 catalysts

The effect of ppm-level Na impurity on the structure of SiO2-supported Mo catalysts prepared in a clean room

Structures and Catalytic Activity of Pt-Mo Bimetallic Ensembles Derived from a New Planar (PtMo6O24)8- Heteropolyanion Supported on Al2O3 and SiO2. Part 1. Characterization of the Supported (PtMo6) Catalysts.