Showing papers by "José Maria C. Bueno published in 2003"

Effect of CeO2 loading on the surface and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts

Abstract: Pt catalysts supported on mixed CeO2-Al2O3 carriers with different CeO2 loading (0.5–10.3 wt.%) were prepared by wetness impregnation method. The catalysts were characterized by SBET, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and thermogravimetric analysis (TG). It was shown that pretreatment temperature and the concentration of CeO2 in the support influences significantly on the morphology of Pt. XRD showed the formation of nanocrystallites of Pt on the surface of alumina and low-loaded CeO2 (≤6 wt.%) samples at higher temperature of calcination (1073 K). Amorphous Pt was observed in all reduced samples. XPS spectra showed the presence of interaction between Pt and Ce, which leads to easy surface reduction of both, ceria and platinum, as revealed by TPR patterns. The effect of CeO2 loading on the catalytic behavior of supported Pt catalysts in the reaction of CO2 reforming of CH4 was determined. Addition of cerium oxide results in improvement of catalytic performance for the reforming of methane with CO2. Pt catalyst with 1 wt.% of CeO2 exhibited the highest specific activity and stability, due to the increase in the metal–support interface area, caused by the higher Pt dispersion.

CO2 reforming of CH4 over Ru/zeolite catalysts modified with Ti

Abstract: Ru/NaY and Ru/USY catalysts were prepared by ion exchange from an aqueous solution of [Ru(NH 3 ) 6 ]Cl 3 . The effect of titanium on the structure of Ru/zeolite introduced by ion exchange or impregnation method from aqueous solution of (NH 4 ) 2 TiO(C 2 O 4 ) 2 ·H 2 O was investigated. The samples were characterized by different techniques, using X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), temperature-programmed desorption of hydrogen (TPD-H 2 ), Fourier transform infrared spectroscopy (FTIR) of CO adsorption and transmission electron microscopy (TEM). Introduction of titanium into Ru/NaY zeolite by ion exchange caused a significant structural collapse of the zeolite framework. Contrary to that, TEM data showed that Ti incorporated into Ru/USY by ion exchange was well distributed within the zeolite cavities. The crystallinity of the USY zeolite decreased significantly after introduction of Ti by impregnation method and a separate phase of titania was formed. The effect of Ti content on the catalytic behavior of zeolite-supported Ru catalysts in the reaction of CO 2 reforming of CH 4 was elucidated. The higher specific activity of Ti-containing catalysts related to CO formation was caused by the both factors, the acceleration of CH x O decomposition (precursor for CO formation) on metal-support interface and participation of the reverse of water gas shift reaction.