Elisabete M. Assaf

Mechanism of CO Tolerance on Molybdenum-Based Electrocatalysts for PEMFC

In this work, the mechanism of CO tolerance for the hydrogen oxidation reaction (HOR) was investigated on Mo-based carbon dispersed electrocatalysts (Mo/C and PtMo/C). Gas-diffusion electrodes with a diffusion layer formed by Mo/C and a catalyst layer composed by Pt/C, PtRu/C, or PtMo/C, showed enhanced electrocatalytic activity for the HOR in the presence of CO. This phenomenon was associated to a lowering of the CO concentration in the gas channel of the electrodes promoted by a water gas shift (WGS) reaction taking place in the Mo/C layer. The occurrence of this reaction was confirmed by gas chromatographic analyses of the CO content, conducted at the outlet of a Mo/C reactor operating at 100°C and fed with different H 2 O/H 2 /CO/CO 2 mixtures. Experiments made in the presence of CO 2 indicated an additional CO poisoning effect due to the reversing of the WGS reaction, but the Mo-based electrodes still showed a performance superior to that of the standard state-of-the-art PtRu/C.

Preparation and characterization of alumina-supported Co and Ag/Co catalysts

The effect of silver addition as a promoter in alumina supported cobalt oxide catalysts is investigated in this study. The Co/Al2O3 and Ag/Co/Al2O3 catalysts were prepared by incipient wetness impregnation. The catalysts were characterized by inductively-coupled plasma spectrometry, X-ray diffraction (XRD), temperature programmed reduction with hydrogen (TPR-H2), Raman spectroscopy and nitrogen adsorption at 77 K. XDR and Raman Spectroscopy results indicated the presence of Co3O4 species. The peaks observed in the TPR-H2 patterns were attributed to the reduction of Ag2O, Co3O4 crystallites and Co+3, Co+2 species interacting with alumina. It is suggested that silver used as a promoter favors the reduction of cobalt, facilitating the formation of active Co0 sites.

Cu and Ni Catalysts Supported on γ-Al2O3 and SiO2 Assessed in Glycerol Steam Reforming Reaction

Cu and Ni catalysts supported on commercial γ-Al2O3 and SiO2 were tested in the glycerol steam reforming. The catalysts were prepared by the impregnation method and characterized by inductively-coupled plasma atomic emission spectrometry, nitrogen physisorption, temperature programmed reduction with H2 and X-ray diffraction. The characterization indicated several catalytic species in the samples interacting differently with the supports: NiO, CuO and NiAl2O4. The catalytic tests were performed at 600 °C, and the best catalyst was also tested at 500 °C and 700 °C. The results showed that the presence of NiAl2O4 did not favor the deposition of carbon during the reaction, probably due to the greater dispersion of Ni on the catalyst surface. It was also observed that, although NiSi was the most active catalyst for H2 production, it also showed the highest carbon deposit during the reaction.

Catalytic features of Ni supported on CeO2–ZrO2 solid solution in the steam reforming of glycerol for syngas production

Catalysts containing 5 wt% Ni supported on CexZr1−xO2 solid solutions prepared by the Pechini method were tested in steam reforming of glycerol (SRG) reactions. The catalysts were characterized by temperature programmed reduction with H2 (H2-TPR), XANES with H2-TPR, X-ray diffraction (XRD) for fresh and used catalysts, XRD in situ for reduced catalysts, N2-physisorption, oxygen storage capacity (OSC), and scanning electron microscopy (SEM). H2-TPR analysis revealed various degrees of interaction between the NiO phase and the supports, which were confirmed by XANES analysis. XANES data also showed greater reduction of mixed supports, than of pure supports, showing that the presence of Zr4+ promotes CeO2–ZrO2 reduction. XRD confirmed the formation of CeO2–ZrO2 solid solutions, with cubic and tetragonal crystal structures, depending on the composition. N2 physisorption analysis showed a greater surface area on the CeO2–ZrO2 solid solution supports than on the pure supports and this increase may be related to the insertion of ZrO2 in the CeO2 lattice. The SRG reaction was performed at 973 K with molar feed ratios of H2O–glycerol = 3 : 1. All catalysts exhibited catalytic activity for the reaction, but carbon formation was high on the catalysts supported on pure oxide. The 5% Ni50CZ catalyst was the most selective for syngas production in the SRG. In addition to the nickel activity, the experiments revealed the activity of the supports in oxidation reactions, which was assigned to the formation of oxygen vacancies by the interaction of CeO2 with ZrO2.

Produção de hidrogênio a partir da reforma a vapor de etanol utilizando catalisadores Cu/Ni/gama-Al2o3

Cu/Ni/g-Al2O3 catalysts were prepared by an impregnation method with 2.5 or 5% wt of copper and 5 or 15% wt of nickel and applied in ethanol steam reforming. The catalysts were characterized by atomic absorption spectrophotometry, X-ray diffraction, temperature programmed reduction with hydrogen and nitrogen adsorption. The samples showed low crystallinity, with the presence of CuO and NiO, both as crystallites and in dispersed phase, as well as of NiO-Al2O3. The catalytic tests carried out at 400 oC, with a 3:1 water/ethanol molar ratio, indicated the 5Cu/5Ni/Al2O3 catalyst as the most active for hydrogen production, with a hydrogen yield of 77% and ethanol conversion of 98%.

The active phase distribution in Ni/Al2O3 catalysts and mathematical modeling of the impregnation process

Abstract This paper deals with the formation of nickel distribution profiles in NiO/Al 2 O 3 catalysts prepared by dry impregnation of spherical pellets of γ-alumina with nickel nitrate aqueous solutions. The experimental concentration profiles were obtained and a mathematical model for the impregnation process was proposed and used to identify the main process parameters. The partial-differential equations of the model that describe the nickel concentration profiles and the fractional coverage were numerically solved. Backward finite-difference formulas were used to discretize the space variable and the resulting set of ordinary-differential equations was integrated with respect to time using a marching algorithm. The impregnation conditions determine the distribution of the active phase along the pellet. The concentration of the impregnation solution and the time of contact were important in the definition of the profiles, while the effect of the impregnation temperature was less significant. Satisfactory agreement was achieved between model predictions and experimental data, revealing that the simplifications assumed in the model are sound under the experimental conditions studied.

Efeito do teor metálico em catalisadores Co/Al2O3 aplicados à reação de reforma a vapor de etanol

The development of cobalt catalysts to produce hydrogen from ethanol is the goal of this investigation. Co/Al2O3 catalysts were prepared by impregnation and characterized by atomic absorption, nitrogen adsorption, X-ray diffraction, Raman spectroscopy, temperature programmed reduction and carbon analysis. The catalysts contained Co3O4 oxide and Co3+ and Co2+ species interacting with alumina. The cobalt load affects the crystal size and the crystalline structure and higher Co loads influence the reaction mechanism, changing the selectivity of the catalysts, decreasing the amount of CO produced and avoiding the formation of products catalyzed by the support. The ethanol conversion was 50-70% with 10-<1% of CO in the hydrogen.

Óxidos do tipo perovskita para reação de redução de no com CO

In this work, the perovskite-type oxides LaNiO3, LaMnO3, La0,7Sr0,3NiO3 and La0,7Sr0,3MnO3 were prepared by co-precipitation and tested in the NO reduction with CO at 400 and 500 oC for 10 h. The catalysts were characterized by X-ray diffraction, temperature programmed reduction with hydrogen, nitrogen adsorption and chemical analysis. The nonstoichiometric oxygen was quantified by temperature programmed reduction, and the catalytic tests showed that the La0,7Sr0,3MnO3 catalyst presented the higher performance for the reduction reaction of NO with CO. The partial substitution of lanthanum by strontium increased the NO conversion and the N2 yield.

Effects of adding basic oxides of La and/or Ce to SiO2-supported Co catalysts for ethanol steam reforming

In this study, cobalt catalysts supported on La2O3–CeO2–SiO2 were synthesized by the method of impregnation of the support with aqueous solution of the active phase precursor. These materials were tested in ethanol steam reforming (ESR). The catalysts were characterized by in situ X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR), temperature-programmed hydrogen desorption (H2-TPD), temperature-programmed oxidation (O2-TPO), adsorption–desorption of nitrogen (BET) and energy-dispersive X-ray spectroscopy (EDS). After reaction, the spent materials were characterized by XRD, SEM and elemental analysis. The in situ XRD analysis showed the formation of the solid solution CexLa1−xO2−δ and identified cobalt oxide in the spinel structure (Co3O4) and metallic cobalt (Co0). The H2-TPR analysis showed the reduction of cobalt oxide, and it was observed that the peaks of cobalt oxide shifted to lower temperatures as the content of lanthanum increased. The H2-TPD analysis showed that metal surface area and metal dispersion decreased as the percentage of lanthanum oxide in the supports increased. The O2-TPO analysis showed that La2%Ce48%Si50% consumed the most oxygen. The SEM analysis identified filamentous carbon after reaction. The catalysts were active for H2 and CO2 production. The best catalytic performance was shown by Co10%La2%Ce48%Si50%, which gave the highest H2 yield.

Ni/La2O3-SiO2catalysts applied to glycerol steam reforming reaction: effect of the preparation method and reaction temperature

Ni/La2O3-SiO2 catalysts were obtained by different methods of preparation: sequential impregnation, simultaneous impregnation (I-sim), precipitation of support followed by Ni impregnation and co-precipitation. The samples were characterized by energy-dispersive X-ray spectroscopy, nitrogen physisorption, X-ray diffraction (XRD), infrared spectroscopy, temperature programmed reduction (TPR), H2 chemisorption, scanning electron microscopy and thermogravimetric analysis. XRD and TPR results indicated two Ni species in the samples: NiO (I-sim) and La2NiO4 (other samples). Catalytic tests were performed in glycerol steam reforming at 600 oC. The best result was observed with I-sim catalyst, which presented the higher reduction degree, metallic dispersion and metallic area (TPR and TPD). This catalyst was also tested at 500 oC and 700 oC and performed best at 600 oC.