Capturing CO by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO capture. Two commercial cerias and two home-prepared samples, CeO and CeO-ZrO (75% CeO) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N-adsorption, XPS, H-TPR, Raman and FTIR spectroscopy. Static and dynamic CO adsorption experiments were applied to assess the CO capture performance. The type of surface species formed and their thermal stability were evaluated by FTIR spectroscopy and CO-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO adsorption and, consequently, demonstrated almost identical CO capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO diffusion resistance. Having the same surface area as the synthesized CeO, the mixed CeO-ZrO oxide exhibited the highest CO capture capacity of 136 μmol g under dynamic conditions. This was related to the highest concentration of CO adsorption sites (including defects) on this sample. The CeO-ZrO system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.