Fabiana M.T. Mendes

The cyclohexanol dehydrogenation on RhCuAl2O3 catalysts Part 1. Characterization of the catalyst

Abstract In this first part, we examined the structure and morphology of RhCu Al 2 O 3 catalysts with low metal contents, which have been used in cyclohexanol dehydrogenation. The catalysts were prepared by successive wet impregnation after intermediate calcination. They were characterized by TPR, DRS, XPS, XRD and CO FT-IR in the oxide form. The results indicate a high degree of reduction and the presence of copper ions located in octahedral sites. The Rh Al 2 O 3 and RhCu Al 2 O 3 catalysts display an enrichment of rhodium at the surface, and the presence of copper allows the restructuring of the surface complexes, as shown by DRS and XPS measurements. The cluster formation during reduction is attributed to the promoting effect of copper. Infrared results show that the interaction of copper with the support prevents the redispersion or oxidation of rhodium crystallites acting as a “sacrificed anode.”

The cyclohexanol dehydrogenation on RhCu/Al2O3 catalysts: 2. Chemisorption and reaction

Abstract Rh Cu supported on alumina were selected for the dehydrogenation of cyclohexanol. Highly dispersed Rh Cu supported on alumina were obtained and characterized after reduction. The metallic surface area was determined by frontal H 2 chemisorption and by N 2 O decomposition followed by TPR. The TPR method for surface oxide reduction after exposing the catalyst to N 2 O decomposition for the determination of the active phase is in good agreement with the frontal H 2 chemisorption method on rhodium, copper and bimetallic catalysts. The temperature and time exposition are important parameters for a complete oxidation of the monolayer, in particular for lower concentration of copper. An exposition time of 20 h is needed to complete a monolayer oxidation. Metallic copper is oxidized to Cu 1+ and Cu 2+ although not all Cu 2+ is reduced to Cu 1+ without oxidation of a sublayer. For the bimetallic catalysts Rh Cu a complete monolayer was attained. The TOF values were calculated based on the total active sites which give correct interpretation of the activity. The activity decreases when copper is added to rhodium which was attributed to an ensemble effect. For lower contents the selectivity of ketone was enhanced, which could be explained by simultaneous geometric and electronic effects. The selectivity on the monometallic catalysts prevails toward cyclohexene formation, indicating strong influence of the acidic sites. However, for the bimetallic catalysts it changed drastically toward dehydrogenation. The second metal affects the surface sites enhancing the metallic or bimetallic formation for dehydrogenation. This phenomena explains the electronic effect on bimetallic Rh Cu systems.

Kinetic Rates of the Fischer Tropsch Synthesis on a Co/Nb2O5 Catalyst

Abstract The kinetics of the Fischer-Tropsch reaction over a Co/Nb 2 O 5 catalyst in a fixed bed reactor was investigated experimentally. Experiments were carried out under isothermal and isobaric conditions ( T =543 K, P =2.1 MPa) and under different conditions of several H 2 /CO feed molar ratio (0.49–4.79), space velocities (0.2–3.8 h −1 ), mass of catalyst (0.3–1.5 g), and CO conversion (10%–29%). Synthesis gas conversion was measured and data were reduced to estimate the kinetic parameters for different Langmuir-Hinshelwood rate expressions. Differential and integral reactor models were used for the nonlinear regression of kinetics parameters. One of the rate equations could well explain the data. The hydrocarbon product distributions that were experimentally determined exhibited an unusual behavior, and a possible explanation was discussed.

The effect of pressure on promoted Ru and Re-Co/Niobia catalysts in the Fischer-Tropsch synthesis

Abstract Co/Nb2O2, Co-Ru/Nb2O5 and Co-Re/Nb2O5 catalysts were prepared and characterized by TPR. The catalysts were investigated on CO hydrogenation under 0.4, 2 and 4Mpa. The total pressure has an important effect on the product distribution. The selectivity toward diesel and C5+ hydrocarbons achieves a maximum at reaction pressure of 2.0Mpa. The catalysts had good stability over 50h on stream at reaction conditions.

Reproduction and structure of the population of the Chaetognath Parasagitta friderici in Guanabara Bay (Brazil) based on short term sampling

The aim of this study was to describe the total density, densities of developmental stages and the reproduction period of Parasagitta friderici. Weekly samples were collected at one station in the channel of Guanabara Bay, Rio de Janeiro, during one year. Three vertical hauls were made for each sample, and P. friderici was separated, the developmental stages were identified, and body length (BL), ovary length (OL) and seminal vesicle width (SVW) were measured. Throughout the year P. friderici was the most abundant chaetognath species occurring in all four developmental stages, the densities of which varied from week to week. Higher densities of adults occurred in the spring, followed by peaks of juveniles in the summer. Although P. friderici seems to reproduce continuously in Guanabara Bay, a reproductive peak was apparent during the spring. The intensification of reproduction during the spring, with juveniles occurring in the summer, seems to be related to the period of higher food supply during the rainy season and intrusions of the South Atlantic Central Water.