Surface and bulk characterization of Rh/ZrO₂ prepared by absorption of Rh₄(CO)₁₂ clusters on ZrO₂ powder

Abstract

Rh nanoparticles supported on ZrO2 powder were prepared by adsorbing Rh4(CO)12 clusters from hexane solution under Ar atmosphere. Four samples with Rh content ranging from 0.25 Rh wt.% up to 4.10 Rh wt.% were studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), and time of flight secondary ion mass spectroscopy (ToF-SIMS). TEM measurements show, for all the samples, Rh particles with a size of about 50 Å. The 4.10 Rh wt.% sample also shows some agglomerates of Rh nanoparticles and only for this sample Rh metallic phase was detected by XRD. The profile analysis of the XRD lines indicates an average size of the Rh crystallites of about 60 Å. XPS studies show only a single spectral component for the Zr3d5/2 core line at 182.2 eV. Instead, at least, two components at 307.2 eV and 308.5 eV are detected for the Rh3d5/2 core line. These results suggest that Zr is present only as oxidized state, whereas nonoxidized and oxidized Rh are both observed. A nonoxidized Rh state is also suggested by the XPS valence band electron removal spectrum which exhibits a significant emission within the ZrO2 band gap assigned to Rh 4d bands. A further support to this finding arises from scanning Auger maps of OKVV and RH where nonoxidized Rh is observed. Finally scanning Auger maps using the OKVV and the Zr emissions show surface regions where only the Zr Auger lines are detected, whereas on pure ZrO2 powder this effect is not observed. Since it is possible to rule out from the XPS Zr3d core line spectra, the presence of metallic zirconium hydrogen spillover mechanisms is invoked to explain this result.

First-principles study of the surfaces of zirconia

“…A great deal of experimental data for zirconia surfaces, including Auger, photoelectron, and vibrational spectroscopies as well as electron microscopies and x-ray diffraction, have been reported. [7][8][9][10][11][12][13][14][15] However, these data only provide indirect and incomplete information about the detailed surface atomic structure. Also the interpretation of many experimental studies are often complicated by finite-size effects because samples have granular, often polymorphic, fine structure and the presence of dopants like Y 2 O 3 , which is known to segregate to the surface.…”

Hydrogen adsorption on the tetragonal ZrO2(101) surface: a theoretical study of an important catalytic reactantElectronic supplementary information (ESI) available: data for geometrical and charge differences in detail. See http://www.rsc.org/suppdata/cp/b2/b202330j/

“…The experimental data, including Auger, photoelectron, and vibrational spectroscopy as well as electron microscopy and X-ray diffraction mostly provide indirect and incomplete information about the detailed surface atomic structure. [12][13][14][15][16] The bulk properties on the other hand have been studied by several ab initio [17][18][19] and semiempirical methods. 20,21 Just recently a systematic DFT study of various defects in monoclinic zirconia has been published.…”