(582co) Comparative Study of CO Adsorption on Zirconia Polymorphs with DRIFT and Transmission FT-IR Spectroscopy

A great deal of work
has been devoted to study the surface properties of zirconia over many years,
mostly due to its excellent catalytic behavior in dehydration, hydrogenation,
and hydrogen exchange reactions as both a catalyst and a support. In this study
the interactions of CO with amorphous zirconia(am-ZrO₂),
monoclinic zirconia(ZrO₂), and tetragonal zirconia(t-ZrO₂)
were investigated by diffuse reflectance FT-IR spectroscopy and transmission
FT-IR to determine the role of hydroxyl on CO adsorption and conversion. The CO
bands and surface intermediates detected by DRIFT were compared with
transmission FT-IR at different temperature and dehydroxylation degree.
Moreover, the effect of different zirconia polymorphs on CO adsorption was
discussed.

The results showed various CO bands and
surface intermediates were observed on three zirconia polymorphs. In DRIFT
spectra, formate and/or bicarbonate species formed by CO reacting with
hydroxyls at high temperature were detected on am-ZrO₂, m-ZrO₂
and t-ZrO₂ and then the active sites for CO adsorption were produced
by consumption of hydroxyls. While in the case of transmission FT-IR spectra, three
different CO bands, bicarbonate and carbonate species were observed on am-ZrO₂
and m-ZrO₂ at room temperature. Only carbonate was formed on t-ZrO₂
and no CO band was detected. Note that active sites for CO adsorption could be
produced by thermal dehydroxylation in vacuum or CO reaction with hydroxyls at
high temperature for am-ZrO₂ and m-ZrO₂. While in the
case of t-ZrO₂, active site for CO adsorption was only created by
the formation of bicarbonate species at high temperature.

Fig. 1  FT-IR of CO adsorption on ZrO₂
polymorphs.

References

1.           
 Kouva S K Honkala, L Lefferts J Kanervoa
(2015) Review: monoclinic zirconia, its surface sites and their interaction with carbon monoxide. Catal. Sci.
Technol. 5:
3473-3490

2.           
Köck
EM, Kogler M, Bielz T, Klötzer B  Penner S (2013)
In Situ FT-IR Spectroscopic Study of CO₂ and CO Adsorption on Y₂O₃,
ZrO₂, and Yttria-Stabilized ZrO₂. J. Phys. Chem. C, 117: 17666-17673

3.           
Pokrovski
K, Jung K T, Bell A T (2001) Investigation of CO and CO₂ Adsorption
on Tetragonal and Monoclinic Zirconia. Langmuir 17:4297-4303

4.           
Kondo J, Abe
H, Sakata Y, Maruya K I, Domen K Onishi T (1995) Infrared
studies of adsorbed species of H₂, CO and CO₂ over ZrO₂,
Chem. Soc. Faraday Trans. 91: 125-132

5.           
Jung K T, Bell
A T (2000) The
effects of synthesis and pretreatment conditions on the bulk structure and
surface properties of zirconia.
J. Mol. Catal. 163: 27-42