Study of the Properties of CuO/VO_x/Ti_0.5Sn_0.5O₂ Catalysts and Their Activities in NO + CO Reaction

Abstract

CuO/VO x /Ti 0.5 Sn 0.5 O 2 catalysts were prepared by an impregnation method and were tested on a NO þ CO model reaction. Both copper oxide and vanadium oxide can be highly dispersed on Ti 0.5 Sn 0.5 O 2 (denoted as TS, hereafter) support. The dispersed oxides form VÀOÀCu species when coexisting in the catalyst system. The formation of VÀOÀCu species renders the dispersed vanadium oxide aggregated and easier to be reduced; in contrast, the reduction temperature of dispersed copper oxide species is evidently higher than that without vanadium oxide (CuO/TS samples). The surface dispersed VÀOÀCu species are mainly the active component for the NO þ CO reaction. The activities of CuO/VO x /TS catalysts are highly dependent on the operating temperature and the amount of VÀOÀCu species. In the reaction atmosphere, NO molecules are adsorbed onto Cu 2þ sites, reduced V xþ (V 4þ or V 3þ ) sites, and even TS support, forming ÀNO and NO 3 À species. Adsorption of CO molecules proceeds only on Cu þ sites. The active species change with varying reaction temperature; hence, the NO þ CO reaction goes through different mechanisms at low and high temperatures over these catalysts.

Surface structure characteristics of CuO/Ti0.5Sn0.5O2 and its activity for CO oxidation

“…While for 02CuTS and 07CuTS catalysts, increasing the temperature to 200 • C results in not only the continuous enhancement of ∼2100 cm −1 peak, but also the appearance of CO 2 (not shown). However, further increasing the temperature leads to the decrease of this peak and remains even at 225 • C, finally disappearance at 350 • C. This observation suggests that copper oxides are reduced in two steps, namely first from Cu 2+ to Cu + and further to Cu 0 [29,35].…”

“…The space group of rutile is D 14 4h (P4 2 /mnm). Three Raman vibration modes appear in TS support, i.e., E g (426 cm −1 ), parallel to the c-axis, as well as B 1g (143 cm −1 ) and A 1g (610 cm −1 ), perpendicular to the caxis [35,36]. The E g and A 1g vibration modes are inserted in Fig.…”

Influence of molar ratio and calcination temperature on the properties of Ti Sn1−O2 supporting copper oxide for CO oxidation

“…Interestingly, calcination leads not only to the chemical shift of Cu 2p 3/2 and Cu 2p 1/2 signals to low BE but also to the decrease in the shake-up peak due to the characteristic Cu 2+ . In addition, except for 5CuT3S1-1200, a shoulder peak appears at 930.3 eV, which is assigned to the reduced state of copper species [50].…”

“…All of them can be divided into three reduction peaks (labeled as H1, H2, and H3). The two peaks at the low-temperature region (H1 and H2) are mainly attributed to the stepwise reduction of surface-dispersed copper oxide species, that is, Cu 2+ → Cu + and Cu + → Cu 0 [42,43,49], whereas the other peak at the high-temperature region (H3) may be mainly assigned to the reduction of the surface Ti 4+ (Sn 4+ ) of supports, crystalline CuO, or the CuO that interacts strongly with the support [50].…”

“…The Cu 2p spectra mostly show Cu 2+ and a small amount of Cu + , located at 933.2 and 930.8 eV, respectively [50]. The oxygen vacancy may result in the generation of Cu + , and the oxygen of CuO occupies the vacancy and forms the Cu O Ti (Sn) band.…”