Mario de Jesus Mendes

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.

Palladium catalysts in the selective hydrogenation of hexa-1,5-diene and hexa-1,3-diene in the liquid phase. Effect of tin and silver addition Part 1. Preparation and characterization: from the precursor species to the final phases

Palladium, palladium–tin and palladium–silver catalysts, supported on two alumina samples with different acidity, have been prepared by diffusional impregnation for use in the selective hydrogenation of hexa-1,5-diene and hexa-1,3-diene in the liquid phase. UV–VIS–NIR (transmission and diffuse reflectance) studies of the palladium starting solutions and of the solids obtained during all preparation stages (impregnation, drying, calcination) show that the nature of the supported precursor species depends on the acidity of the alumina. Palladium tetrachloropalladate (strongly bound anionic species) are predominant on the more acidic alumina while the more basic one favours the formation of weakly bound neutral complexes through exchange of chloride ligands with hydroxy groups and water. The nature of these species influences not only the particle size of monometallic Pd samples (the stronger the interaction, the smaller the metal particle size), but also the nature of the final bimetallic Pd–Ag catalysts; a Pd–Ag solid solution is observed on the bimetallic catalyst prepared by interaction of a cationic Ag precursor withsupported PdCl42-, whereas interaction with neutral Pd species leads to separate metal phases. The interaction of Sn precursor solutions with supported PdII species induces the formation of heteronuclear species which decompose upon drying; Pd2Sn or Pd3Sn phases are detected on the final catalysts, depending on the initial Pd/Sn ratio and on the nature of the Sn precursor solvent (using ethanol favours the formation of Pd3Sn).

Hydrogenation of oleic acid over sol-gel ruthernium catalysts

The hydrogenation of oleic acid to oleyl alcohol over Ru-alumina and Ru−Sn-alumina sol-gel catalysts has been studied. It was found that, besides its hydrogenation activity, the Ru−Sn-alumina catalyst promotes thecis-trans isomerization of the unsaturated acid. This effect is used to explain some kinetic features of the system, like the high induction time observed in the formation of alcohols, and to re-examine the role of tin.

Kinetic evaluation of hydrogenation of sucrose over ruthenium containing Y zeolites

Hydrogenation of sucrose over Ru/NaY, Ru/USY and Ru/CaY catalysts was carried out in a slurry reactor at 135°C and 12 atm. The catalysts were prepared by ion exchange followed by calcination and reduction. These were characterised as AA, TPR, DTA/TGA, H2/Chemisorption, CO-FTIR, XRD and t-plot. To describe kinetic product distribution, the 4th order Runge-Kutta method was used for determining the kinetic parameters.

Mössbauer Study of 119Sn-Pd Catalysts for Selective Hydrogenation of Hexa-1,5-Diene

The addition of tin to palladium-alumina catalysts induces significant modifications of the catalytic properties of palladium in the hydrogenation of hexa-1,5-diene. The influence of the support, of the metal loading and of the preparation method on the chemical state of tin in Pd-Sn/Al2O3 catalysts are studied by Mössbauer spectroscopy. In reduced catalysts, about 60% of tin is present as Sn(0), which forms different Pd-Sn compounds, that are responsible for the changes in the catalytic performances.