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.
| A: DRIFT Spectra
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| B:Transmission infrared spectra |
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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
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