Mai He

Characterization of CuO Species and Thermal Solid-Solid Interaction in CuO/CeO2-Al2O3 Catalyst by In-Situ XRD, Raman Spectroscopy and TPR

Abstract Transference of CuO species and thermal solid-solid interaction in CuO/CeO 2 -Al 2 O 3 catalyst prepared by an impregnation method were characterized by in-situ XRD, Raman spectroscopy and H 2 -TPR techniques. For the catalyst calcined at 300 °C, two kinds of CuO species coexist on the surface, that is, highly dispersed and bulk CuO crystalline phase. Four kinds of CuO species are present for the catalyst calcined at 600 °C: (1) highly dispersed CuO, (2) bulk CuO on the surface, (3) bulk CuO in the internal layer of CeO 2 , and (4) CuAl 2 O 4 formed from CuO-Al 2 O 3 interaction. For the catalyst calcined at 800 °C, besides very little highly dispersed and bulk CuO on the surface, most of the CuO has transferred into the internal layer of CeO 2 and the mass of CuAl 2 O 4 are increased. At 900 °C, all of CuO has diffused into the internal layer of CeO 2 and formed CuAl 2 O 4 . The results show that the distribution of CuO species in the catalysts depends on the calcination temperature; the different CuO species can be effectively confirmed by ia-situ XRD, Raman spectroscopy and H 2 -TPR techniques.

Comparative Study of CuO Species on CuO/Al2O3, CuO/CeO2-Al2O3 and CuO/La2O-Al2O3 Catalysts for CO Oxidation

CuO/Al2O3, CuO/CeO2-Al2O3, and CuO/La2O3-Al2O3 (denoted as Cu/Al, Cu/CeAl, and Cu/LaAl) catalysts were prepared by an impregnation method. CuO species and CuO/Al2O3 thermal solid-solid interaction were characterized by in situ XRD, Raman spectroscopy and H2-TPR techniques. For the Cu/Al catalyst, a CuAl2O4 phase exists between the CuO and Al2O3 layer and the CuO phase exists on the surface in both highly dispersed and bulk forms. For the Cu/CeAl catalyst, there is highly dispersed and bulk CuO on the surface, but most of the CuO has transferred into the internal layer of CeO2 as bulk CuO and CuAl2O4. For the Cu/LaAl catalyst, only bulk CuO is present on the surface of the catalyst and no CuAl2O4 is formed. The catalytic activity order for CO oxidation is Cu/CeAl>Cu/Al>Cu/LaAl. The highly dispersed CuO on the catalyst surface may be the active phase for CO oxidation. The results show that the addition of CeO2 not only promotes both the transference of CuO and the formation of CuAl2O4 but also favors the CO oxidation due to the association of highly dispersed CuO with CeO2, while La2O3 hinders the transference of CuO and the formation of CuAl2O4.

CeO2-Y2O3 Washcoat and Supported Pd Catalysts for the Combustion of Volatile Organic Compounds (VOCs)

Abstract A novel CeO 2 -Y 2 O 3 (denoted as CeY) washcoat adhered to the cordierite honeycomb was prepared. The preparation technique, using nano-sized CeO 2 and yttrium citrate as precursors, was friendly to environment because no deleterious products were formed during the operation. The CeY washcoat support and Pd/CeY catalysts were characterized using scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF) spectrometer, and Raman spectroscopy. The results showed that the washcoat had sufficient adhesion and high adsorption efficiency for active species and was suitable for supporting Pd catalysts. For the catalysts, most of Y 2 O 3 entered into the channel of the cordierite honeycomb, whereas CeO 2 and Pd enriched on the surface. Furthermore, model reactions for the catalytic combustion of CO, toluene, and ethyl acetate were carried out to evaluate the performance of the Pd/CeY catalyst. It exhibited fairly good catalytic activity and thermal stability. For those catalysts calcined at 500 °C, the T 99 (the lowest reaction temperature when the conversion is 99%) of CO, toluene, and ethyl acetate was 150, 220, and 310 °C, respectively, whereas for those catalysts calcined at 1050 °C, the T 99 of CO, toluene, and ethyl acetate was 180, 250, and 330 °C, respectively. Catalysts calcined at higher temperature, the crystallite size of active species (PdO) increases, which possibly results in a decline in the catalytic activity.