The adsorption of CO at 77 K on zirconia-supported tungsten oxide (ZW) samples prepared by equilibrium adsorption or by impregnation and with tungsten content up to 12.4 W atoms nm-2 was studied with the aim of determining the coverage of ZrO2 surface by the supported tungsten oxospecies. As an essential background for quantitative volumetric measurements, ZW samples were investigated by FT-IR spectroscopy to identify the surface sites responsible for the CO adsorption. FT-IR showed that CO adsorbed selectively and irreversibly on Zr4+cus centres of the support surface, but not on Wcus6+ sites. By volumetric determinations, the coverage of the zirconia surface by tungsten oxospecies was about 50% at maximum, irrespective of the preparation procedure and of the support crystallographic modification (monoclinic or tetragonal). Zirconia coverage remained significantly unchanged after leaching with a NH3 solution that removed tungsten oxospecies not directly interacting with the zirconia surface. This finding indicates that ZrO2 support coverage depends mainly on the tungsten species strongly anchored to the zirconia surface.

WOx/ZrO2 catalysts. Part 3. Surface coverage as investigated by low temperature CO adsorption: FTIR and volumetric studies

MAGNACCA, Giuliana;MORTERRA, Claudio
2003-01-01

Abstract

The adsorption of CO at 77 K on zirconia-supported tungsten oxide (ZW) samples prepared by equilibrium adsorption or by impregnation and with tungsten content up to 12.4 W atoms nm-2 was studied with the aim of determining the coverage of ZrO2 surface by the supported tungsten oxospecies. As an essential background for quantitative volumetric measurements, ZW samples were investigated by FT-IR spectroscopy to identify the surface sites responsible for the CO adsorption. FT-IR showed that CO adsorbed selectively and irreversibly on Zr4+cus centres of the support surface, but not on Wcus6+ sites. By volumetric determinations, the coverage of the zirconia surface by tungsten oxospecies was about 50% at maximum, irrespective of the preparation procedure and of the support crystallographic modification (monoclinic or tetragonal). Zirconia coverage remained significantly unchanged after leaching with a NH3 solution that removed tungsten oxospecies not directly interacting with the zirconia surface. This finding indicates that ZrO2 support coverage depends mainly on the tungsten species strongly anchored to the zirconia surface.
2003
240
119
128
WOx surface coverage; ZrO2; low temperature CO adsorption
G. FERRARIS; S. DE ROSSI; D. GAZZOLI; I. PETTITI; M. VALIGI; G. MAGNACCA; C. MORTERRA
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/38113
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 28
  • ???jsp.display-item.citation.isi??? 25
social impact