Reducibility Studies of Ceria, Ce0.85Zr0.15O2 (CZ) and Au/CZ Catalysts after Alkali Ion Doping: Impact on Activity in Oxidation of NO and CO

Abstract

The aim of these studies was to perform thorough research on the influence of alkali metal ions (Li, Na, K and Cs) on the properties of nanogold catalysts supported on ceria–zirconia. The addition of alkali metal ions onto CeO2 further affected the reducibility, which was not noted for the Zr-doped support (Ce0.85Zr0.15O2). Despite the substantial impact of alkali metal ions on the reducibility of ceria, the activity in CO oxidation did not change much. In contrast, they do not have a large effect on the reducibility of Au/CZ but suppressed the activity of this system in CO oxidation. The results show that for CO oxidation, the negative effect of potassium ions is greater than that of sodium, which corresponds to the shift in the Tmax of the reduction peak towards higher temperatures. The negative effect of Li+ and Cs+ spans 50% CO conversion. The negative effect was visible for CO oxidation in both the model stream and the complex stream, which also contained hydrocarbons and NO. In the case of NO oxidation to NO2, two temperature regimes were observed for Au + 0.3 at% K/CZ, namely in the temperature range below 350 °C; the effect of potassium ions was beneficial for NO oxidation, whereas at higher temperatures, the undoped gold catalyst produced more NO2.

Catalytic Transfer Hydrogenation Performance of Magnesium-Doped ZrO2 Solid Solutions

“…They might be responsible for the fracture of these materials, but more studies are needed to confirm or disprove this hypothesis. The texture of the samples (Figure 5) is very similar to that of the previously published solid solutions prepared by us using a similar procedure, such as zirconium-doped ceria [43] and cerium-doped zirconia [44]. However, unlike for pure zirconia (Figure 5a) or zirconia doped with 5% Ce ions (Figure 5d), which fracture in large, irregular chunks using a mortar and pestle, both Zr 0.97 Mg 0.03 O x (Figure 5b) and Zr 0.95 Mg 0.05 O x (Figure 5c) show elongated structures with unusual fracture.…”

Beneficial effect of cerium excess on in situ grown Sr0.86Ce0.14FeO3–CeO2 thermocatalysts for the degradation of bisphenol A

“…Based on the chemical composition, the mmol g −1 of Fe, and considering the hydrogen consumption of the rst peak (Table 2), the percentage of Fe 4+ reduced to Fe 3+ was calculated and corresponds to 44.5%. Assuming that in the region 550-700 °C only reduction of Ce 4+ occurs as suggested in literature, 50 the percentage of Ce 4+ reduced to Ce 3+ was found to be 88%. Finally, supposing that no Fe 2+ is present in the starting perovskite, Ce0, and attributing the reduction peak above ∼750 °C only to the reduction of Fe 3+ to Fe 2+ , the extent of reduction Fe 3+ to Fe 2+ was estimated as 83.9%.…”

Anomalous behaviour of silver catalyst for soot oxidation explained: state of silver when operating and the influence of potassium ions

“…The zirconium-doped ceria and cerium-doped zirconia supports chosen for further testing were selected based on the results of our previous studies, which have shown that the Ce 0.85 Zr 0.15 O 2 and Zr 0.93 Ce 0.07 O 2 supports contain only one phase, the fluoritetype cubic ceria structure and tetragonal zirconia structure, respectively, and have the most beneficial properties. 25,26 As in the case of all of the silver catalysts for soot combustion in the literature cited in the Introduction section, the XRD studies have shown that the silver deposited onto Zr 0.93 Ce 0.07 O 2 is present in the metallic form (Fig. 1), even in the sample which The values of the specific surface area of the cerium-doped zirconia (ZC) and zirconium-doped ceria supports are 63 and 77 m 2 g −1 , respectively (Fig.…”

“…The term "ceria-zirconia" or "ceria-zirconia mixed oxide" is often found in the literature, but is not precise, and the material itself does not contain both oxides as separate phases, but is rather a solid solution of one type of ions incorporated into the matrix of the oxide of the major component. 25,26 When the Ce/(Ce + Zr) ratio is large, the structure of pure ceria is kept intact, i.e., the fluorite-type, cubic structure, but the zirconium ions do influence the lattice parameter of the oxide due to ionic radius mismatch. In this study, such oxides are referred to as "zirconiumdoped ceria".…”