Production of supported metal catalysts by the decomposition of metal carbonyls (review)

Abstract

The following text is a review of efforts made to produce highly dispersed metal catalysts via the thermal decomposition of metal carbonyls. It is shown that on hydroxylated supports the decomposition of all metal carbonyls follows a characteristic pattern. Low-temperature (<400 K) heating leads to the formation of partially decarbonylated metallic species (subcarbonyls) which are associated with hydroxyl groups. It is probable that these metallic subcarbonyls are monodispersed. Higher-temperature treatment (the precise temperature is a function of the particular metal carbonyl) leads to the interaction of the subcarbonyls with the oxygen of the hydroxyl groups to form completely decarbonylated, possibly monodispersed, metal oxide species. There is some evidence that these highly dispersed oxide species have unique catalytic properties. Only following high-temperature reduction (ca. 750 K) have stable metallic particles been produced on hydroxylated supports by metal carbonyl decomposition. The metal particles produced in this manner are not of an unusually high dispersion. The nature of the decomposition process on dehydroxylated supports has not been as thoroughly studied as the process on hydroxylated supports. However, preliminary results offer promise that metal carbonyl decomposition on dehydroxylated supports may lead to the formation of very highly dispersed, zero-valent metal particles.