Iron oxide modified diamond blends containing different amounts of ultradispersed diamond were prepared and characterized by nitrogen physisorption, X-ray diffraction, temperature programmed reduction, Mossbauer and IR spectroscopy. The catalytic behavior of these composite materials in methanol decomposition to hydrogen, carbon monoxide, and methane has been also studied. The initial state and phase transformations of the supported highly dispersed iron oxide particles in various pretreatment media, as well as their reductive and catalytic properties, strongly depend on the ultradispersed diamond content in the diamond blends. (c) 2006 Elsevier Inc. All rights reserved.