Characterization of oxide-supported ligand-protected osmium cluster catalysts

Volcano relationships in metal cluster catalysis: An infrared spectroscopic monitor of site character

“…The following findings apply to all systems reported by the authors involving the use of the cluster carbonyls Os3(CO)12 [3][4][5][6], H2Os3(CO)10 [7], H4Os4(CO)12 [6,9], Osr(CO)ls [3][4][5][6], and H2Os~0C(CO)~4 [8,10]. First, infrared and EXAFS spectroscopies show that impregnation of these cluster compounds onto the supports, pretreated as described in reference 3, result in no chemical change and no catalytic activity.. Second, catalytic activation by heating in helium or in vacuum at 10 K nun to 523 K results in the loss or reaction of a minority (typically 10%) of the carbonyl ligands [3], and provides materials which adsorbed CO and Oz at room temperature [4] and which are active catalysts for reactions involving hydrogen [5][6][7][9][10][11].…”

“…First, infrared and EXAFS spectroscopies show that impregnation of these cluster compounds onto the supports, pretreated as described in reference 3, result in no chemical change and no catalytic activity.. Second, catalytic activation by heating in helium or in vacuum at 10 K nun to 523 K results in the loss or reaction of a minority (typically 10%) of the carbonyl ligands [3], and provides materials which adsorbed CO and Oz at room temperature [4] and which are active catalysts for reactions involving hydrogen [5][6][7][9][10][11]. Evidence from uv-visible spectroscopy [3], EXAFS spectroscopy [8][9][10] and high resolution transmission electron microscopy [3] confirm that the clustered state is retained.…”

“…The catalytically active cluster was a complex entity. During thermal activation, not only was a small proportion of the carbonyl ligands lost, evolved as gaseous CO, but a further small proportion underwent reaction generating carbon dioxide and leaving ligand-C associated with the catalyst (Boudouard reaction) [3,6,9,[12][13][14].…”

“…A small degree of cluster growth attends the thermal activation of Os3-Os4-and Os6-clusters, whereas the Osi0-cluster retained its nuclearity. The catalytic activities of these materials ranged over more than three orders of magnitude [5][6][7]9].…”

“…The use of metal cluster compounds provides the possibility of retention of the clustered state of the metal thereby giving additional control over metal particle morphology, and hence over catalyst activity and selectivity. The authors have investigated in detail catalysts obtained by impregnation of a range of osmium and ruthenium carbonyl clusters onto silica, alumina, titania and ceria [3][4][5][6][7][8][9][10][11]. These studies have included careful standardisation of preparative procedures, detailed characterisation of the catalysts obtained, studies of the adsorption of carbon monoxide and of dioxygen, and investigations of the hydrogenation of ethene, of carbon monoxide, and of carbon dioxide, and the hydrogenolysis of ethane.…”