ALCOHOL SYNTHESIS FROM SYNGAS OVER NICKEL-CATALYSTS - EFFECT OF COPPER AND LITHIUM ADDITION

Carbon monoxide hydrogenation at 5 MPa was investigated on silica-supported Ni, Ni-Cu, Ni-Li and Ni-Cu Li catalysts, with special focus on C2+OH formation. Copper addition does not result in formation of higher alcohols while lithium does. Over Ni-Cu Li/SiO2, selectivities towards alcohols as high as 85% are observed and higher alcohols such as ethanol and propanol were effectively produced. Addition of copper to nickel results in a remarkable stabilization of the catalytic activity while lithium promotion increases aging of the catalyst significantly. Infrared spectroscopy of adsorbed carbon monoxide shows that copper addition inhibits subcarbonyl formation (Ni(CO)x, x = 2 or 3) and increases the relative abundance of linear species. When lithium promoter is added to Ni/SiO2, some is deposited on the silica support whilst the remaining decorates the metal particles. Subcarbonyl species are stabilized by lithium addition. The spectra obtained over Ni-Cu-Li/SiO2 are practically composed of only two bands, subcarbonyl and linear. By comparing catalytic pattern and infrared data it is concluded that the presence of subcarbonyl species is related to catalyst aging and that active sites for C2 + OH formation are, either isolated nickel atoms associated with Li+, or linked to subcarbonyl formation.