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.

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