Intercalation of copper metal clusters in montmorillonite

Abstract

EXPANDABLE layer silicates such as montmorillonite can be converted to efficient heterogeneous catalysts by introducing catalytically active sites or guest species between the layers or on the external surfaces. Attempts to produce intercalated zero-valent transition-metal particles in layer silicates, by hydrogen reduction for example, have, however, failed: the layers tend to collapse¹, sometimes followed by deposition of metal particles on the external surfaces^2–4. Here we describe the successful intercalation of copper metal clusters of 4–5 Å in montmorillonite by in situ reduction of Cu²⁺ ions using ethylene glycol. These metal-cluster intercalates were stable up to at least 500 °C. The clusters prop the silicate layers apart, much as metal oxides do in pillared clays⁵, and may thus be able to introduce unique catalytic product selectivity through a molecular sieving effect similar to that in cluster-loaded zeolites. As metal clusters of these dimensions behave very differently from the bulk metal⁶, intercalates of this sort may prove to be versatile catalysts.