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Nanopartículas de Pt suportadas em Al2O3 e CeO2-Al2O3: síntese e caracterização de catalisadores aplicados à reação de deslocamento gás-água
(Universidade Federal de São Carlos, 2011-04-28) Ribeiro, Renata Uema; Bueno, José Maria Corrêa; https://lattes.cnpq.br/0157452280626031; https://lattes.cnpq.br/9202692096525582
Colloidal Pt nanoparticles were synthesized according to an adapted procedure from Song and co-workers [1], which it was based on the reduction of dihydrogen hexachloroplatinate by ethylene glycol in a basic solution, but using two PVP/Pt = 0,2 and 10 ratio. Both the ratio lead to monodisperse platinum nanoparticles with similar sizes (2.0 and 2.8 nm). Colloidal Pt nanoparticles solutions were incorporated into alumina during sol-gel synthesis and showed different stabilities when submitted to thermal treatment in synthetic air, He and H2 atmospheres. PVP/Pt ratio added to nanoparticles after synthesis was the main parameter considered to the stability of the particles on the support. Using a minor PVP/Pt ratio lead to particles agglomerates during calcinations step in synthetic air. On the other hand, when an excess of PVP was used stable and disperse particles were obtained during a severe thermal treatment. The anchoring of particles into support during incorporation stage could be the most plausible explanation for this. Platinum nanocatalysts supported on alumina and ceriaalumina showed catalytic activity for the water gas shift reaction. CO conversion data indicated that the increasing of CeO2 loading of 12 to 20% lead to an improvement in the catalytic activity. XPS measurements after pre-treatment in H2 confirmed the presence of Pt+on the catalyst surface containing ceria, suggesting some metal-support interaction. In situ characterization techniques allowed to a better understanding of species involved into water gas shift reaction mechanism. Through X-ray absorption near edge structure in the Pt edge measurements showed reduced Pt during reaction for all catalysts, suggesting that similar electronic density of sites was present. This was also observed in CO adsorbed DRIFTS measurements. Nevertheless, XANES spectra in the Ce edge showed some changes in oxidation state of Ce during the reaction, indicating the occurrence of redox mechanism, mediated by ceria. In situ DRIFTS experiments showed little concentrations of formates and carbonates species on the catalyst surface during the reaction, suggesting that more than one mechanism may occur simultaneously.
Ação das enzimas extracelulares na dinâmica da decomposição de macrófitas aquáticas
(Universidade Federal de São Carlos, 2011-04-28) Sciessere, Luciana; Bianchini Júnior, Irineu; https://lattes.cnpq.br/0659731944736389; https://lattes.cnpq.br/0782646321102015
Given the importance of mineralization processes to the knowledge of biogeochemical cycles in aquatic environments and aiming to detail these processes through enzymatic activities of microorganisms which act on aquatic macrophytes detritus, this study had as main goals to determine the dynamics of five enzymes activities which act on degradation of lignocellulosic wastes (endoglucanase (EC 3.2.1.4 and EC 3.2.1.91), β- xylanase (EC 3.2.1.8), β-1,4-glucosidase (EC 3.2.1.21) peroxidase (EC 1.11.1.7) and polyphenol oxidase (EC 1.10.3.2)) and the annual succession and efficiency of these enzymes during aquatic macrophytes decomposition, according to intrinsic (fiber content and chemical quality) and extrinsicconditions (temperature, pH, condition of oxygenation and proximity of sediment) in two aquatic systems. The experiments were conducted in the ecological station of Jataí (Luiz Antonio SP). For each experiment 216 litter bags (20 × 20 cm; ф pore = 0.4 mm) were prepared with fragments of Salvinia molesta (10 g (DW)), Eichhornia azurea (15 g (DW)), Cyperus giganteus (Exp. I) and Eleocharis sp. (Exp. II) (15 g (DW)) previously dried. The litter bags were incubated in 3 different sites in two depths: surface (≈ 0.2 m) and sediment-water interface (≈ 3.0 m) at Lagoa do Óleo (oxbow lagoon) in January 2008 and Represa do Beija-Flor (reservoir) in January 2009. Each sampling day (1, 3, 5, 30, 60, 90, 120, 150, 200, 250, 300 and 350) three litter bags of each depth were collected and taken to the laboratory for remaining particulate matter analysis. Taking into account the similarity observed between the systems, it was considered that those detritus were decomposed into acid environment with low nutrient availability (at least part of the year) and, mostly, aerobic (anaerobic periods could have occurred in s-w interface). The chemical quality, characterized by C:N ratio, exercised greatest influence on POMR mass loss and decay coefficients. Enzyme activity on the studied detritus was initiated at the same time of leaching process, intensively. After this period, a decrease in this activity was observed, occurring intermediate peaks. Until the 350th day of decomposition there was a predominance of hydrolytic enzymes activity in relation to oxidative enzymes. There was a direct relationship between mass loss and enzyme activity, related mainly to xylanase activity.