Electron-poor copper nanoparticles over amorphous zirconia-silica as all-in-one catalytic sites for the methanol steam reforming

The addition of a specific amount of silica (10 wt.%) to zirconia was found to significantly influence the morphological and electronic properties of supported copper nanoparticles in a Cu/ZrO2-SiO2 catalyst. The so-developed catalyst was tested in the methanol steam reforming reaction and reached at 3500 h(-1) of space velocity a hydrogen productivity of 370 mmol h(-1) g(cat)(-1), that is four times higher than that obtained with a Cu/ZrO2 catalyst. The reason of such an improved activity was elucidated via a series of in-situ characterization, including synchrotron XRPD, XPS, and FTIR analyses with probe molecules. The results show that the addition of silica inhibits both the crystallization of the support and the copper reduction, leading to particularly small and stable copper nanoparticles ranging 2-3 nm in diameter. Although completely reduced and in the metallic state (neither Cu2+ nor Cu+ were detected), these so-small nanoparticles feature a markedly electron poor surface on which methanol preferentially adsorbs. Since both the dehydrogenation of the intermediates and the subsequent molecular hydrogen formation are performed by the same site, the hydrogen production rate results markedly boosted. The drawback of having a different adsorption site and two distinct Cu-0 and Cu+ sites is thus overcome thanks to this all-in-one catalytic site, and the copper actually participating to all the reaction is maximized.