Supported molecular cluster catalysts

Basset J-M, Lefebvre F, Santini C (1998) Surface organometallic chemistry Some fundamental features including the coordination effects of the support. Coord Chem Rev 178-180 1703 Gates BC (2000) Supported metal cluster catalysts. J Mol Catal A Chem 163 55 Fierro-Gonzalez JC, Kuba S, Hao Y, Gates BC (2006) Oxide- and zeoUte-supported molecular metal complexes and clusters Physical characterization and determination of structure, bonding, and metal oxidation state. J Phys Chem B 110 13326... 

Figure A. Transformations observed between supported molecular cluster and active catalyst for 053(00)J2/Si02 in the presence of carbon monoxide and hydrogen.

Hi ly dispersed supported bimetallic catalysts with bimetallic contributions have been prepared from molecular cluster precursors containing preformed bimetallic bond [1-2]. For examples, extremely high dispersion Pt-Ru/y-AUOa could be prepared successfully by adsorption of Pt2Ru4(CO)ison alumina [2]. By similar method, Pt-Ru cluster with carbonyl and hydride ligands, Pt3Ru6(CO)2i(p3-H)(p-H)3 (A) was used in this work to adsorb on MgO support. The ligands were expectedly removable from the metal framework at mild conditions without breaking the cluster metal core. 

The final probe of molecular clusters is that of selected chemical reactions. The use of probe reactions to study supported cluster catalysts is well established, and we are attempting the development of similar probes of unsupported clusters. The first steps in this direction are the design of a pulsed chemical reactor to go with the pulsed cluster source and the development of criteria for reactions. It is important to recall that at present... 

The literature of metal-support interactions includes httle about the possible chemical bonding of metal clusters or particles to supports. Supported molecular metal clusters with carbonyl ligands removed have afforded opportunities to understand the metal-support interface in some detail, and the results provide insights into the bonding of clusters to supports that appear to be generalizable beyond the small clusters to the larger particles of conventional supported metal catalysts [6]. 

Molecular Clusters as Precursors to Supported Metal Catalysts... 

J. Guzman and B. C. Gates, Supported molecular catalysts metal complexes and clusters on oxides and zeolites, Dalton Trans. 17, 3303—3318 (2003). 

B. D. Chandler, A. B. Schabel, C. F. Blanford, and L. H. Pignolet, The preparation and characterization of supported bimetallic Pt-Au particle catalysts from molecular cluster and chloride salt precursors, J. Catal. 367-383 (1999). 

Synthesis of Supported Bimetallic Catalysts from Molecular Cluster Precursors... 

Supported bimetallic catalysts can be made by adsorption of a bimetallic precursor such as molecular cluster compounds, colloidal particles or dendrimer-stabilised particles. In several cases, homogeneous bimetallic particles have been found where the compositions lie within the miscibility gap of the bulk alloy (e.g. with PtAu particles). This suggests that when the particles are small enough and do not possess metallic properties, the normal rules do not apply. 

Structures and reactivities of supported metal clusters have been investigated mostly by spectroscopic and chemical methods, and the available data generally show that the supported species display chemistry that is comparable to that of precursor clusters in solution. These supported molecular catalysts provide information on the surface intermediates that is complementary to information on conventional metal catalysts. 

The supported clusters described in this chapter have strong connections to industrial supported metal catalysts, although the clusters or particles in industrial catalysts are much less uniform and less susceptible to incisive structural characterization than those considered here. Development and further investigation of structurally simple oxide- and zeolite-supported molecular catalysts will provide fundamental understanding of structure-activity relationships that will direct design of novel and improved industrial supported metal catalysts. 

One of the more active and growing areas of research into the study of condensed matter is the investigation of the properties of atomic and molecular clusters. A detailed understanding of clusters is vital to the study of such diverse phenomena as condensation, the dispersion of supported catalysts, cloud formation, molecular generation on interstellar grains, - and the thermodynamic properties of powders. In addition, the study of clusters is of fundamental importance to the understanding of the transition from finite to bulk behavior. 

Zeolite-supported metal clusters are a new class of catalyst made possible by syntheses involving organometallic chemistry and by precisely controlled treatment of metal complexes in zeolite cages. Elucidation of the preparation chemistry would not have been possible without the guidance of EXAFS spectroscopy. Clusters such as Ir4, Ir, and Pt (where n is about 6) are small enough to be considered quasi molecular rather than metallic. Their catalytic properties are distinct from those of metallic particles, even for structure-insensitive reactions. The zeolite pores seem to confer some properties on the clusters that are not yet well understood. 

The contemporary interest in metal organophosphonate coordination chemistry has received considerable impetus from the applications of such materials as sorbents, catalysts and catalyst supports. The structural chemistry of the metal organophosphonate system is extremely rich " and is represented by mononuclear coordination complexes, molecular clusters, " one-dimensional materials, and layered phases. Extensive investigations have been reported on layered phosphonates of divalent, " trivalent, tetravalent, " and recently hexavalent elements. Several examples of three dimensional metal organophosphonate frameworks have also been described since the first report by Bujoli. " ... 

---