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 h ighly dispersed nickel metal (d(av) approximate to 4 nm) was investigated b y FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni-0/SiO2 leads to the formatio n of Ni(CO)(x) (x = 2, 3) subcarbonyls (band at ca. 2090 cm(-1)) and neglig ible amounts of Ni(CO)(4) adsorbed on SiO2 (band at 2048 cm(-1)). Up to thi s temperature CO causes no detectable erosion of the metal surface. Above 1 45 K the rate of interaction between CO and the nickel particles significan tly increases. Until 235 K Ni(CO)(4) mainly remains in the adsorbed state, while at still higher temperatures the equilibrium between adsorbed and gas eous Ni(CO)(4) (band at 2058 cm(-1)) is shifted towards the latter. It is a ssumed that subcarbonyls formed on defect sites of the metal surface are pr ecursors of the nickel tetracarbonyl. Successive adsorption-evacuation cycl es of CO at room temperature result in a decrease in the amount of the Ni(C O)(4) formed, probably due to a reduction of the number of defect metal sit es. On the basis of (CO)-C-12 and (CO)-C-13 coadsorption, an alternative in terpretation of the band at 2048 cm(-1) to species containing isolated Ni(C O)(3) groups is proposed.