Nanostructured copper-zirconia composites as catalysts for methanol decomposition

• At low copper loading formation of CuO monolayer on ZrO2 surface occurs.
• Synergistic effect in copper-zirconia interface realizes via different mechanisms.
• Methyl formate could not be intermediate in methanol conversion on ZrO2 and Cu/ZrO2.

Nanostructured mesoporous ZrO2 was obtained by hydrothermal synthesis using surfactant assisted approach. Copper modifications of thus obtained ZrO2 (4–25 wt.% copper) were prepared by incipient wetness impregnation with the corresponding nitrate or acetyl acetonate precursors and further treatment in oxidative or reduction atmosphere. The obtained materials were characterized by N2 physisorption, XRD, UV–vis, FTIR, XPS and temperature programmed reduction with hydrogen and tested as catalysts in methanol decomposition to hydrogen and CO. Selected samples were investigated after partial coverage of the surface with 11C-labeled methanol and 11C-labeled methyl formate. The formation of monolayer of finely dispersed copper oxide species on zirconia at about 4 wt.% copper loading and bulk copper nanoparticles at higher one is observed. It was assumed that zirconia support provides the formation of two types of catalytic sites: the first ones strongly adsorb methanol and exhibit predominantly dehydrogenation activity, while the others, possess acidic function. The modification of zirconia with copper significantly improves the catalytic activity and selectivity in methanol decomposition via (i) creation of additional surface acidic sites which contribute to generation of methoxy intermediates; (ii) stabilization of Cu2+-Cu+ and Cu+-Cu0 redox pairs where the electron transfer is facilitated by zirconia support and (iii) assisting the recombination and release of hydrogen during the transformation of produced on zirconia surface intermediates.

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