Jingfang Sun

Promotional effect of doping SnO2 into TiO2 over a CeO2/TiO2 catalyst for selective catalytic reduction of NO by NH3

TixSn1−xO2 was prepared by a co-precipitation method, and a series of CeO2/TixSn1−xO2 samples were prepared to investigate the effect of doping SnO2 into TiO2 for selective catalytic reduction of NO by NH3. The results of catalytic tests suggested that the catalyst with the optimal molar ratio (Ti : Sn = 1 : 1) exhibited the best catalytic performance. Moreover, the NO removal efficiency of CeO2/Ti0.5Sn0.5O2 was higher than that of CeO2/TiO2. The obtained samples were characterized by BET, XRD, H2-TPR, XPS, NH3-TPD and in situ DRIFT. The results revealed that the introduction of SnO2 resulted in the formation of rutile-type Ti0.5Sn0.5O2 solid solution with larger specific surface area and better thermal stability. The interactions between CeO2 and the Ti0.5Sn0.5O2 support could improve the redox performance of the catalyst, which was beneficial to the enhancement of catalytic activity at low temperature. Furthermore, doping SnO2 enhanced the surface acid sites and weakened the adsorption of nitrates, which played an important role in the catalytic reaction process. Finally, in situ DRIFT demonstrated that the competition adsorption happened between bridging nitrates and NH3 gas and the selective catalytic reduction of NO by NH3 proceeded mainly via the Eley–Rideal mechanism over Ce/TiO2 and Ce/Ti0.5Sn0.5O2.

Comparative study on the catalytic CO oxidation properties of CuO/CeO2 catalysts prepared by solid state and wet impregnation

A series of CuO/CeO2 catalysts were prepared by solid state impregnation (SSI) and wet impregnation (WI) methods and characterized by X-ray diffraction, H2 temperature-programmed reduction (H2-TPR), laser Raman spectroscopy (LRS), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and X-ray photoelectron spectroscopy (XPS). XPS and H2-TPR results showed that SSI increased the dispersion of the copper species on the catalyst surface, which benefited the reduction of CuO species. LRS results indicated that a higher concentration of oxygen vacancies was obtained by the SSI method unlike the WI method. CO oxidation results showed that at a given CuO loading, the activity of the catalysts prepared by SSI was higher than that of their counterparts prepared by WI. Based on the combined characterization results, it was suggested that the enhanced activity was closely related to the higher concentrations of oxygen vacancies and Cu+-CO species on the catalysts. Last, a possible synergetic mechanism was proposed for CO oxidation over the CuO/CeO2 catalysts.

Engineering the NiO/CeO2 interface to enhance the catalytic performance for CO oxidation

In this work, NiO/CeO2 catalysts were synthesized with tunable CeO2 crystal facets ({110}, {111} and {100} facets) to study the crystal-plane effects on the catalytic properties. Kinetic studies of CO oxidation showed that NiO/CeO2 {110} had the lowest activation energy. Furthermore, the obtained samples were characterized by means of TEM, XRD, Raman, N2-physisorption, UV-Vis DRS, XPS, H2-TPR and in situ DRIFTS technologies. The results demonstrated that the geometric and electronic structures of the nickel species were dependent on the NiO/CeO2 interfaces, which had an influence on the synergetic interaction of absorbed CO and active oxygen species, and then the generation of the formate intermediate played an important role in the catalytic performance. The possible interface structures of nickel species on the CeO2 {110}, {111} and {100} surface were proposed through the incorporation model, suggesting that the advantageous NiO/CeO2 {110} interface facilitated CO adsorption/activation and active oxygen species formation, leading to the best catalytic performance.

Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO

Abstract In order to investigate the influence of MnO 2 modification methods on the catalytic performance of CuO/CeO 2 catalyst for NO reduction by CO, two series of catalysts ( x Cu y Mn/Ce and x Cu/ y Mn/Ce) were prepared by co-impregnation and stepwise-impregnation methods, and characterized by means of X-ray diffraction (XRD), Raman spectra, H 2 -temperature programmed reduction (H 2 -TPR), in situ diffuse reflectance infrared Fourier transform spectra ( in situ DRIFTS) techniques. Furthermore, the catalytic performances of these catalysts were evaluated by NO+CO model reaction. The obtained results indicated that: (1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method, which was beneficial to the improvement of the reduction behavior; (2) The excellent reduction behavior was conducive to the formation of low valence state copper species (Cu + /Cu 0 ) and more oxygen vacancies (especially the surface synergetic oxygen vacancies (SSOV, Cu + –Mn (4– x )+ )) during the reaction process, which were beneficial to the adsorption of CO species and the dissociation of NO species, respectively, and further promoted the enhancement of the catalytic performance. Finally, in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods, a possible reaction mechanism (schematic diagram) was tentatively proposed.

Catalytic performance of highly dispersed WO 3 loaded on CeO 2 in the selective catalytic reduction of NO by NH 3

Abstract The influence of tungsten trioxide (WO3) loading on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia (NH3) over WO3/cerium dioxide (CeO2) was investigated. The NO conversion first rose and then declined with increasing WO3 loading. It was found that the crystalline WO3 in the 1.6WO3/CeO2 sample could be removed in 25 wt% ammonium hydroxide at 70 °C, which improved the catalytic activity of the sample. The obtained samples were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, hydrogen (H2) temperature programmed reduction, NH3 temperature programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The results revealed that the dispersed WO3 promoted the catalytic activity of WO3/CeO2 while the crystalline WO3 inhibited catalytic activity. The oxygen activation of CeO2 was inhibited by the coverage of WO3, which weakened NO oxidation and adsorption of nitrate species over WO3/CeO2. In addition, the NH3 adsorption performance on CeO2 was improved by modification with WO3. NH3 was the most stable adsorbed species under NH3 SCR reaction conditions. In situ DRIFT spectra suggested that the NH3 SCR reaction proceeded via the Eley-Rideal mechanism over WO3/CeO2. Thus, when the loading of WO3 was close to the dispersion capacity, the effects of NH3 adsorption and activation were maximized to promote the reaction via the Eley-Rideal route.