Catalytic Decomposition of Organic Molecules by Clays

Abstract

HERE we consider some aspects of the behaviour of clays and other products of rock weathering in the catalytic decomposition of organic molecules. Much of the interest in this topic has centred on the use of clays and oxides as versatile catalysts in industrial processes and on clays as catalysts in petroleum genesis1,2. It is accepted that many clay or oxide catalysed reactions do not entail any obvious rapid changes to the catalyst; however, for some it seems there is a positive correlation between initial catalytic activity and the rate at which carbonization (fouling) of the catalyst occurs, evident as a darkening of the catalyst surface. For example, Shimoyama and Johns3 found a montmorillonite-induced catalytic decarboxylation reaction of n-docasanoic acid was arrested because catalytic sites on the clay were rendered inactive by deposition of carbonaceous material, probably of a kerogen-like nature. Later, Johns and Shimoyama4 refer to sites on the catalyst as having been deactivated by carbon deposition, which is in line with the statement of Fripiat5 regarding the catalysed decomposition of less hydrogenated carbon compounds. Similarly, Walker6 found that macroscopic crystals of vermiculite immersed in boiling glycerol for a few minutes became black. Powdered vermiculites behaved like larger crystals but, according to Walker, smectites failed to blacken in boiling glycerol.