NO reduction by CO over CuO supported on CeO₂-doped TiO₂: the effect of the amount of a few CeO₂

Abstract

This work is mainly focused on the investigation of the influence of the amount of a few CeO2 on the physicochemical and catalytic properties of CeO2-doped TiO2 catalysts for NO reduction by a CO model reaction. The obtained samples were characterized by means of XRD, N2-physisorption (BET), LRS, UV-vis DRS, XPS, (O2, CO, and NO)-TPD, H2-TPR, in situ FT-IR, and a NO + CO model reaction. These results indicate that a small quantity of CeO2 doping into the TiO2 support will cause an obvious change in the properties of the catalyst and the TC-60 : 1 (the TiO2/CeO2 molar ratio is 60 : 1) support exhibits the most extent of lattice expansion, which indicates that the band lengths of Ce-O-Ti are longer than other TC (the solid solution of TiO2 and CeO2) samples, probably contributing to larger structural distortion and disorder, more defects and oxygen vacancies. Copper oxide species supported on TC supports are much easier to be reduced than those supported on the pure TiO2 and CeO2 surface-modified TiO2 supports. Furthermore, the Cu/TC-60 : 1 catalyst shows the highest activity and selectivity due to more oxygen vacancies, higher mobility of surface and lattice oxygen at lower temperature (which contributes to the regeneration of oxygen vacancies, and the best reducing ability), the most content of Cu(+), and the strongest synergistic effect between Ti(3+), Ce(3+) and Cu(+). On the other hand, the CeO2 doping into TiO2 promotes the formation of a Cu(+)/Cu(0) redox cycle at high temperatures, which has a crucial effect on N2O reduction. Finally, in order to further understand the nature of the catalytic performances of these samples, taking the Cu/TC-60 : 1 catalyst as an example, a possible reaction mechanism is tentatively proposed.

A Study of Low-Temperature CO Oxidation over Mesoporous CuO-TiO2 Nanotube Catalysts

“…The negative shift of both Ti 2p 3/2 and Ti 2p 1/2 is meaningful of two distinguished TiO 2 entities and suggests the change of electronic structure of TiO 2 in CuO-TiO 2 NTs due to the possible formation of Ti 3+ species and oxygen vacancies in the support. The binding energies of the Ti 2p peak at 458.1 and 463.7 eV in CuO-TiO 2 aligns well with values reported for Cu-modified TiO 2 [34][35][36][37]. Moreover, the negative shift of Ti 2p peaks is in agreement with a similar trend observed for Ti 3+ -doped TiO 2 with increased oxygen vacancies [32,37,38].…”

“…For CuO-TiO 2 NTs, the O 1s peak broadens and shifts from 529.6 eV to 529.3 eV. Additionally, a weak shoulder peak is observed at 531.5 eV, which can be attributed to the adsorbed oxygen anions in the (OH-) groups on the surface [35,36] or to the oxygen in CuO [40]. The binding energies of the Cu 2+ XPS peaks are slightly higher for CuO supported on TiO 2 NTs compared to the unsupported CuO nanoparticles, as shown in Figure 5c.…”

“…Figure 6b shows the high resolution XPS spectra of O 1s for the pristine TiO 2 and CuO-TiO 2 NTs catalyst. For TiO 2 NTs, an intense O 1s peak centered at 529.6 eV is observed and is attributed to the lattice O 2− anions bonding to the metal cations in the Ti-O bond [35,36,39]. For CuO-TiO 2 NTs, the O 1s peak broadens and shifts from 529.6 eV to 529.3 eV.…”

“…to 145 cm −1 in CuO-TiO2 NTs can be attributed to the presence of oxygen vacancies [24,45,46]. The CuO modification resulted in changes in the structural and vibrational properties of the TiO2 lattice, which indicates the strong interaction between the CuO and TiO2 NTs support [35,[46][47][48]. The position of the Raman peaks associated with the B1g and A1g vibration modes of TiO2 was influenced by the CuO modification in CuO-TiO2 NTs compared to pristine TiO2 NTs, as can be seen in Figure 7b.…”

Tailoring the reducibility and catalytic activity of CuO nanoparticles for low temperature CO oxidation

“…5a, the Cu 2p XPS results indicate that the binding energies of the Cu 2p in the different CuO nanoparticles are similar and overall align well with values reported in the literature. 42 The peaks centered at 933.4-933.6 eV and 953.4-953.6 eV corresponds to the Cu 2p 3/2 and Cu 2p 1/2 , respectively. These two peaks together with the shake-up peaks present at about 938-945 eV are main XPS features of CuO, indicating the presence of Cu 2+ in all samples.…”