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 (dav≈4 nm) was investigated by FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni0/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 12CO and 13CO coadsorption, an alternative interpretation of the band at 2048 cm−1 to species containing isolated Ni(CO)3 groups is proposed.