Formation of Ni(CO)(4) during the interaction between CO and silica-supported nickel catalyst: an FTIR spectroscopic study

The formation of Ni(CO)(4) during interaction of CO with silica-supported highly dispersed nickel metal (d(av) approximate to 4 nm) was investigated by FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni-0/SiO2 leads to the formation of Ni(CO)(x) (x = 2, 3) subcarbonyls (band at ca. 2090 cm(-1)) and negligible amounts of Ni(CO)(4) adsorbed on SiO2 (band at 2048 cm(-1)). Up to this temperature CO causes no detectable erosion of the metal surface. Above 145 K the rate of interaction between CO and the nickel particles significantly increases. Until 235 K Ni(CO)(4) mainly remains in the adsorbed state, while at still higher temperatures the equilibrium between adsorbed and gaseous Ni(CO)(4) (band at 2058 cm(-1)) is shifted towards the latter. It is assumed that subcarbonyls formed on defect sites of the metal surface are precursors of the nickel tetracarbonyl. Successive adsorption-evacuation cycles of CO at room temperature result in a decrease in the amount of the Ni(CO)(4) formed, probably due to a reduction of the number of defect metal sites. On the basis of (CO)-C-12 and (CO)-C-13 coadsorption, an alternative interpretation of the band at 2048 cm(-1) to species containing isolated Ni(CO)(3) groups is proposed.