Elizabete Jordão

Effect of metal-support interaction during selective hydrogenation of cinnamaldehyde to cinnamyl alcohol on platinum based bimetallic catalysts

Abstract The ethylenic unsaturation of α-β ethylenic aldehydes is much more reactive to catalytic hydrogen addition than the carbon-oxygen double bond, giving saturated aldehydes in a first step. Fortunately, in a liquid phase hydrogenation, the selectivity to the unsaturated alcohols may be improved by the choice of appropriate solvents and bimetallic catalysts. In this work much attention has been brought to the factors that allow to achieve the best possible selectivity to cinnamyl alcohol. An oxide known to give special metal-support interaction, namely TiO2, was chosen as our support. A careful study of the precursor reduction by TPR was a valuable guide to establish the final preparation for the active phase. The catalyst precursor was dried and reduced in an electric furnace under a flow of gas at atmospheric pressure. Compared to Pt, Pt-Sn and Pt-Fe on carbon, a monometallic Pt/TiO2 catalyst gives an excellent selectivity but a rather poor activity. Finally a selectivity to cinnamyl alcohol as high as 97% and a high activity are reached by using a bimetallic Pt-Fe/TiO2. This good selectivity has been attributed to the metal support interaction.

Hydrogenation of oleic acid over ruthenium catalysts

Abstract The performance of ruthenium-tin catalysts for the liquid phase selective hydrogenation of oleic acid to unsaturated alcohols has been investigated. Titania-supported ruthenium and ruthenium-tin catalysts prepared by conventional impregnation as well as alumina-supported sol–gel ruthenium and ruthenium-tin catalysts have been used. The hydrogenation over the monometallic ruthenium catalysts leads primarily to the saturated stearic acid, which is then consecutively hydrogenated to the saturated stearyl alcohol. The titania-supported monometallic ruthenium catalyst shows a greater activity than the alumina-supported sol–gel one for the hydrogenation of oleic acid to the saturated stearyl alcohol. The hydrogenation over the bimetallic ruthenium-tin catalysts is characterized by the near total suppression of the hydrogenation of the olefine bond in favor of the activation of the hydrogenation of the carboxylic bond, thus leading to the selective formation of unsaturated alcohols. Besides, these catalysts are active for the cis–trans isomerization reaction of the oleic acid to elaidic acid, in competition with the hydrogenation of the carboxylic group. The impregnated titania-supported ruthenium-tin catalyst shows a better performance than the alumina-supported sol–gel ruthenium-tin catalyst for the selective hydrogenation of oleic acid to unsaturated alcohols.

Hydrogenation of citral over ruthenium-tin catalysts

Citral was chosen to probe the kinetic behavior of the hydrogenation of ,-unsaturated aldehydes over HTR and LTR titania-supported Ru-Sn catalysts. The catalysts were prepared by coimpregnation with ethanolic solutions of RuCl 3 and SnCl2 and characterized using temperature-programmed reduction (TPR). The reaction was studied in a liquid phase semi-batch reactor at 399 K and a hydrogen pressure of 5 MPa. The global activity for the citral hydrogenation of HTR Ru-Sn/TiO2 catalysts as well as the selectivity to the unsaturated alcohols of both LTR and HTR Ru-Sn/TiO2 increased with the Sn/Ru atomic ratio, reaching a maximum at a value of Sn/Ru ∼ 0.2. This suggested a promotion of the CO bond hydrogenation by particular bimetallic Sn-Ru ensembles. Besides, while for Sn/Ru ≤ 0.1 the support effect of titania dominated, for higher values of the atomic ratio the performance of the catalysts was controlled by the promoter effect of tin. A combined effect of the support titania with the promoter tin was clearly detected.

Examination of the surface chemistry of activated carbon on enantioselective hydrogenation of methyl pyruvate over Pt/C catalysts

Pt/C catalysts were prepared on oxidized activated carbons. Different oxidation treatments were used both in liquid and gas phase using HNO3 and 5% O2/N2 as the respective oxidizing agents. Thus, different surface chemical properties were achieved. The enantioselective hydrogenation of methyl pyruvate with (−)-cinchonidine as modifier revealed that the catalytic activity is dependent on the concentration of the surface oxygen remaining after activation as measured by XPS. It is suggested that it is a result of the increase in the carbon hydrophilicity that would enable the reactants to go through the catalyst. It is also suggested that the active sites created by the decomposition of the functional groups would allow hydrogen chemisorption and, therefore, the C=O polarization via hydrogen bond interaction. The chemical nature of the surface functional groups did not seem to influence either the catalytic activity or enantioselectivity.

Partitioning optimization of proteins from Zea mays malt in ATPS PEG 6000/CaCl2

This work aimed to establish the relationship between the compositions and pH of ATPS PEG 6000/CaCl2 and the proteins partition from maize malt and also to simplify the process optimization in ATPS for a statistical model, established by response surface methodology (RSM). Results showed that these were no influence of pH on the phase diagrams and on the composition of tie line length of PEG 6000/CaCl2 ATPS. SRM analyses showed that elevated pH and larger tie line length were the best conditions for recovering of maize malt proteins. The maximum partition coefficient by PEG 6000/CaCl2 ATPS was about 4.2 and was achieved in ATPS in a single purification step. The theoretical maximum partition coefficient was between 4.1-4.3. The process was very suitable for continuous aqueous two-phase purification due to the stability of proteins (e.g. and -amylases) and could increase their content into middle.

Técnica para seleção de variáveis aplicada à separação de gases

This paper describes an experimental design technique, known as variables search, developed to expose the critical variables and screen out the irrelevant ones. It is easy to learn and use and clearly dissociates the main and interactions effects from each other. An example of air separation process by pressure swing adsorption was used to demonstrate how the variables search technique works. The phases of identification of the critical variables is shown, step by step,.