On the mechanisms and the selectivity determining steps in syngas conversion over supported metal catalysts: An IR study

An IR study of syngas and methanol conversion has been performed over Cu-ZnO-Al2O3 methanol synthesis catalyst, Ni-Al2O3 methanation catalyst and Co-Al2O3 Fischer Tropsch catalyst. The data, obtained at low pressure, provide unequivocal evidence of the existence of a way via oxygenated intermediates (formates, possibly dioxymethylene, methoxy groups) in the three cases. In the selectivity determining step, methoxy groups desorb associatively as methanol on Cu-ZnO-Al2O3. Methoxy groups are selectively hydrogenolyzed to methane over Ni-Al2O3. Over Co-Al2O3 oxygenated surface species may be involved in the chain growth to give C2+ compounds. It is possible that this mechanism coexists with the via-carbide all-metallic catalysis reported for methanation and FT synthesis, on the basis of studies performed on pure metals. (c) 2006 Elsevier B.V. All rights reserved.