Nitrogen retention by an osmium complex supported on sepiolite

Abstract Magnesian layer lattice silicates such as chrysotile or sepiolite can be transformed into highsurface-area solids covered with groups. Osmium tetroxide can be added to the vinyl CC bond and electron micrographs of the OsSS (“osmium supported on sepiolite”) samples prepared in that way have revealed a rather regular distribution of vinyl groups. It is now shown that upon drying OsSS at 200 °C, the methyl group is oxidized, leading to a surface species with the probable structure Os passing from the eighth to probably the sixth, then finally to the second oxidation state. This structure has interesting properties: (a) at −196 °C it adsorbs H 2 in the ratio of 4H 2 per osmium atom under 400 Torr H 2 ; (b) when treated at 200 °C at the same pressure with H 2 , H 2 is consumed in the ratio of 1 mole H 2 /one osmium atom. It is suggested that during the reduction treatment, the water molecule adsorbed on an osmium atom is replaced by one molecule of hydrogen, less strongly attached. “Reduced” OsSS adsorbs dinitrogen reversibly and under a pressure of 400 Torr N 2 , one N 2 molecule is retained per four osmium atoms at room temperature. It is proposed that N 2 forms -bridged structures.