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Several ternary oxides CuCeZrOy(CCZ) were synthesized by a facile grinding method followed by calcination at high temperatures, and used as catalysts for CO oxidation at low temperatures. The influences of calcination temperature (400–600 °C) on the physicochemical properties of the as-synthesized ternary oxides were investigated by thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, inductively coupled plasma-optical emission spectrometry (ICP-OES), N2adsorption, H2-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) characterizations. The results show that the increase in calcination temperature from 400 to 500 °C is conducive to the high dispersion of CuOxon catalyst surface and the incorporation of Cu species into the support to form the Cu–Ce–Zr–O solid solution. Further raising of calcination temperature from 500 to 600 °C, however, leads to the segregation of Cu species from the solid solution to aggregate on support surface and growth of highly dispersed CuOxnanoparticles. The highest catalytic activity is acquired over the CCZ calcined at 500 °C, which can be ascribed to the largest contents of Cu+species and oxygen vacancies owing to the formation of the maximum amount of Cu–Ce–Zr–O solid solution.

In this paper, the CuO–CeO2catalyst was prepared by a direct solvothermal method. The effects of different copper salt precursors (copper nitrate, copper acetate, copper sulfate) on the catalytic performance of the prepared catalyst for CO oxidation were investigated. The physical and chemical properties of the prepared catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2physical adsorption, inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption analysis of CO (CO-TPD), in-situdiffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), and temperature-programmed reduction with H2(H2-TPR). The results show that the CuO–CeO2catalyst prepared with copper acetate as precursor (CC-A) exhibits the best catalytic activity for CO oxidation at low temperatures, with T50and T90values of 62 and 78 °C respectively, which is mainly attributed to its large specific surface area, pore volume, CO adsorption capacity, and large amount and strong reactivity of surface oxygen. However, the CuO–CeO2catalyst prepared with copper nitrate as precursor (CC–N) displays better stability and resistance to water or CO2poisoning than CC-A.

Two different Mn–Ce-Ox/TiO2catalysts were prepared by ordinary impregnation (denoted as MCT) and citric acid assisted impregnation (denoted as MCT-CA) methods, respectively. Excellent NOxremoval is achieved over MCT-CA for selective catalytic reduction with NH3(NH3-SCR), and 100% NOxconversion is obtained at 125 °C under weight hour space velocity (WHSV) of 80000 mL/(gcat·h). Particularly, 100% NOxis converted on MCT-CA in the presence of 10 vol% H2O at 175 °C. As H2O and SO2coexist in the reaction system for 9 h, NOxconversion can still be maintained >90%, much higher than that (22%) of MCT. A series of characterization results indicates that MCT-CA exhibits a larger BET specific surface area, pore volume, and pore size, which enhances the dispersion of Mn and Ce oxides and promotes the rapid adsorption of reactants and desorption of products. Additionally, MCT-CA possesses more Mn4+, Ce3+, chemisorbed oxygen species, and stronger reducibility, facilitating the conversion of NO to NO2. Specially, the amount of active NH3species and active nitrate species on MCT-CA is much more than that over MCT. The combined effect of the aforementioned factors devotes to the excellent low-temperature SCR performance and tolerance to H2O/SO2over MCT-CA.

A modified CuO/CeO2catalyst was prepared by surfactant-assisted impregnation method and showed better catalytic activity for low temperature CO oxidation than that from conventional impregnation method. The physicochemical properties of different CuO/CeO2catalysts were characterized by thermogravimetric and differential scanning calorimetric measurements (TG-DSC), X-ray diffraction (XRD), N2adsorption-desorption, Raman spectroscopy, H2temperature-programmed reduction (H2-TPR), temperature-programmed desorption of O2(O2-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results suggested that the addition of hexadecyl trimethyl ammonium bromide (CTAB) into the impregnation solution could improve the dispersion of CuO species, which could facilitate Cu2+incorporating into CeO2lattice and strengthened the synergistic effects between CuO and CeO2, making the lattice oxygen more active, and eventually resulting in enhanced activity for CO oxidation.

CeO2-ZrO2mixed oxide (Ce0.6Zr0.4O2) prepared by microwave-assisted heating co-precipitation was used as a support to prepare a series of CuO/Ce0.6Zr0.4O2catalysts with various CuO contents (0 wt.%–15 wt.%) via the method of incipient-wetness impregnation. The obtained CuO/Ce0.6Zr0.4O2samples were characterized by N2adsorption, XRD, Raman, TEM and H2-TPR technologies, and their catalytic activities for CO oxidation were investigated. The results showed that the activity of CuO/Ce0.6Zr0.4O2catalyst was strongly influenced by the content of CuO, and the catalyst with 10 wt.% CuO exhibited the best catalytic activity in CO oxidation, which could be attributed to the high dispersion and reducibility of CuO, and high oxygen vacancy concentration in the catalyst.

A series of TiO2–Al2O3composites with Al/Ti molar ratios of 0.1, 0.2, and 0.4 were synthesized by a co-precipitation method and used as supports to prepare supported MnCeOxcatalysts by an impregnation method. The physico-chemical properties of the samples were extensively characterized by N2physisorption, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy element mapping, X-ray photoelectron spectroscopy,H2-temperature programmed reduction, ammonia temperature programmed desorption, and in-situdiffuse reflectance infrared fourier transform spectroscopy. The catalytic activity and resistance to water vapor and SO2of the as-prepared catalysts for the SCR of NOxwith NH3were evaluated at 50–250 °C and GHSV of 80000 mL/(gcat∙h). The results reveal that MnCeOx/TiO2–Al2O3exhibits higher activity and better SO2tolerance than MnCeOx/TiO2. Combining with the characterization results, the enhanced activity and SO2tolerance of MnCeOx/TiO2–Al2O3can be mainly attributed to higher relative concentrations of Mn4+and chemisorbed oxygen species, stronger reducibility, and larger adsorption capacity for NH3and NO, which originate from the larger specific surface area and pore volume, higher dispersion of Mn and Ce species compared with MnCeOx/TiO2. Moreover, in situDRIFTS was used to investigate the reaction mechanism, and the results indicate that the NH3-SCR reaction over MnCeOx/TiO2and MnCeOx/TiO2–Al2O3takes place by both the E–R and L–H mechanisms.