Reducibility of nano-sized cobalt oxides for catalytic applications

Co3O4, pure or supported, is an active catalyst for important industrial processes involving hydrogen such as Fischer-Tropsch Reaction, Water Gas Shift, Steam Reforming, Oxidative Dehydrogenation. The activation of cobalt catalyst in these reactions requires the formation of metallic cobalt and it has been shown that the catalyst performances can be influenced by the reduction procedures. The Co3O4 reduction proceeds in two steps Co3O4CoOCo and the particles size is a determining factor in both reduction processes and activity. The ethanol Steam Reforming Reaction (SRR), CH3CH2OH+3H2O6H2+2CO2 has been investigated by us, on pure and supported Co3O4. Pure Co3O4 exhibits good performances with 100% ethanol conversion, 70% H2 selectivity and 7% CO selectivity at 450°C[1]. Cobalt reduction can be obtained in reaction conditions or in a pre-reduction in pure H2. The reduction in reaction conditions gave higher catalytic activity, because of a lesser sintering of Co with respect to H2 pre-reduction[1]. An investigation on the preparation and characterization of Co3O4 nano-sized[2], allowed us to infer that the different reducibility of nano Co3O4 with respect of micro Co3O4, may influence the Steam Reforming activity. Therefore results on reducibility and catalytic activity of nano Co3O4 are reported and discussed in terms of reduction parameters and of stream stability. Crystalline Co3O4, a cubic spinel structure, with different particle dimensions, was prepared by different methods[2]. The surface area, the average particle dimensions and the morphology were evaluated by BET, XRD and TEM[2], and the cobalt reducibility by H2-Temperature-Programmed-Reduction. The catalytic activity was tested with [EtOH] 5.8x10-5 M, H2O/EtOH=4, GHSV=59000 h-1.