Hydrogen Interaction with a Ceria−Zirconia Supported Gold Catalyst. Influence of CO Co-adsorption and Pretreatment Conditions

Abstract

This work reports on the hydrogen interaction with a 3 wt % Au/Ce 0.62 Zr 0.38 O 2 (Au/CZ) catalyst prepared by deposition-precipitation. As deduced from X-ray powder diffraction, electron microscopy (scanning transmission electron microscopy-high-angle angular dark field and high-resolution electron microscopy), and CO volumetric/Fourier transform IR (FTIR) adsorption studies, the investigated catalyst shows a good metal dispersion. By combining FTIR spectroscopy and volumetric chemisorption studies, it is shown that upon treating the Au/CZ catalyst with 40 Torr of H 2 at room temperature a fast and very intense spillover effect occurs. As determined from the recorded isotherm, very high values of the apparent H/Au ratio (>8.0) and of the atomic hydrogen surface density (>11.0 H/nm 2 ) are reached. In parallel with this observation, the onset of a characteristic IR band at 2133 cm -1 shows the occurrence of significant support reduction with inherent appearance of Ce 3+ species. Moreover, the simultaneous growth of the IR band at 1630 cm -1 due to molecular water strongly suggests that even at room temperature oxygen vacancies are also formed. Additional FTIR spectroscopy studies have shown that the hydrogen spillover is strongly inhibited by either co-adsorption of CO or a reducing pretreatment with flowing 5% H 2 /Ar at 673 K. These deactivation effects, however, may be reverted by very mild regeneration treatments at room temperature.

Recent Progress in Chemical Characterization of Supported Gold Catalysts: CO Adsorption on Au/Ceria–Zirconia

“…As revealed by the FTIR studies, 33 at 298 K under P(CO) ranging from 0 to 300 Torr, three major components contribute to the CO adsorption on Au/CZ catalysts. The first one due to CO adsorbed on Au(0) nanoparticles is characterized by a¯-CO stretching band typically occurring at about 2110 cm ¹1 .…”

“…33 Details of the preparation and activation routines are given in ref 33. The comparison of the spectra recorded at 298 K under P(CO) = 100 Torr and after 30 min evacuation at 298 K showed that the weak adsorbed forms, i.e., those corresponding to COAu and CO interacting with the surface Ce 4+ and Zr…”

“…33 If so, a volumetric adsorption routine consisting of two consecutive isotherms at 308 K separated by a 30 min evacuation at the same temperature would allow us to determine the specific contributions of the strong and weak adsorbed forms. Actually, the second isotherm would measure the joint contribution of the two weakly adsorbed forms, whereas the difference between the first and second isotherms would account for the strong, irreversible CO adsorption on the support.…”

Ceria-zirconia supported gold catalysts

“…Thus, the ceria supported gold systems attracted a lot of attention as the catalysts for low-temperature water gas-shift, carbon monoxide oxidation and PROX reactions. In the last 5 years several tens of relevant papers have been published, most of which being quoted in the papers [7,8]. However, pure ceria is relatively resistant to reduction.…”

“…Such unique properties of ceria-zirconia systems seem to make them ideally suited for an application as supports to gold catalysts. Surprisingly, only a few papers concerning Au/Ce x Zr 1-x O 2 catalysts [7,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], tested mainly in the water-gas shift reaction [9][10][11][12][13][14][15][16] and low-temperature CO oxidation [10,[17][18][19][20][21][22][23] have been published so far. In this paper the most important achievements and conclusions coming from these contributions have been reviewed.…”