R. Pietropaolo

Hydrogenation of α,β-unsaturated aldehydes over PtSn/Nylon

Abstract Hydrogenation of α,β-unsaturated aldehydes has been carried out over supported Pt and PtSn/ catalysts. Over platinum there is preferential formation of saturated adehydes due to the lower energy of the CC double bond with respect to the CO bond. Addition of tin to Pt/Nylon causes a drastic change in the product distribution. On the PtSn samples the reaction proceeds mainly through the hydrogenation of the CO bond with formation of α,β-unsaturated alcohols. The rate of reaction has been found to increase with the addition of small amounts of tin. However, catalysts having a Sn Pt ratio higher than 1.2–1.3 are inactive. It is suggested that the effect of tin ions is related to their acid properties which enhance the reactivity of the CO bond. At higher tin contents the platinum active sites are unable to activate hydrogen molecules.

HYDROGENATION OF CINNAMALDEHYDE OVER RU/C CATALYSTS : EFFECT OF RU PARTICLE SIZE

Abstract Hydrogenation of cinnamaldehyde has been carried out over Ru catalysts supported on activated carbon at 333 K and atmospheric pressure using ethanol as solvent. The activity and selectivity of Ru/C catalysts have been investigated in order to elucidate the effect of metal particle size on the hydrogenation of unsaturated aldehydes. The specific activity expressed per Ru surface atom remains constant with metal dispersion, indicating that the rate-determining step of the reaction is structure-insensitive. Selectivity to cinnamyl alcohol increases with Ru particle size, reaching a value of about 60% on the less dispersed samples.

Influence of metal particle size in the hydrogenation of citral over Ru/C

Selective hydrogenation of citral has been studied under mild conditions over Ru catalysts supported on activated carbon. Geraniol, nerol, citronellal and isopulegol were the main reaction products. Isopulegol is obtained by isomerization of citronellal. Small amounts of citronellol are formed through the hydrogenation of citronellal. The specific catalytic activity per Ru surface atom as well as the products distribution remains constant with changing metal particle size. A comparison with results obtained on the hydrogenation of cinnamaldehyde on the same Ru/C catalysts is reported.

Hydrogenation of cinnamaldehyde over platinum catalysts: influence of addition of metal chlorides

Abstract The effect of addition of metal chlorides to platinum-supported catalysts has been studied in the hydrogenation of cinnamaldehyde in the liquid phase. FeCl 3 , SnCl 4 and GeCl 4 were found to be the most effective promoters for the selective synthesis of cinnamyl alcohol. The rate of reaction increased by addition of small amounts of metal chlorides and then decreased at higher contents. Selectivity to cinnamyl alcohol was slightly dependent on the concentration of the additives and on the level of conversion. A reaction mechanism for the hydrogenation of cinnamaldehyde over promoted platinum is suggested.

Hydrogenation of citral over Ru-Sn/C

Citral has been hydrogenated over Ru-Sn/C catalysts. The Ru-Sn/C system has been studied as a function of the Ru/Sn ratio. Under the conditions used the carbonyl group and the conjugated double bond are hydrogenated. No products obtained from the hydrogenation of the isolated double bond are formed. Addition of tin on the Ru/C decreases the number of Ru active sites on the surface with a corresponding increase in the specific catalytic activity. A higher selectivity (>80%) to geraniol + nerol is observed on the samples with the highest Sn/Ru ratio. The higher selectivity and higher specific activity are attributed to an activation of the C≐O bond by tin ions.

Selective transfer hydrogenolysis of glycerol promoted by palladium catalysts in absence of hydrogen

Selective conversion of glycerol into 1,2-propanediol in the presence of a Pd/Fe2O3catalyst, under inert atmosphere, is reported for the first time; the hydrogen necessary for the hydrogenolysis reaction derives from the dehydrogenation of the solvent (2-propanol or ethanol), promoted by supported palladium, itself reduced “in situ” by alcohols.

Liquid phase hydrogenations over platinum-tin catalysts

Abstract Hydrocinnamaldehyde and phenylacetylene have been hydrogenated over Pt and Pt-Sn catalysts. The Pt-Sn system has been studied as a function of the Pt/Sn ratio. In the hydrogenation of the CC triple bond, addition of tin to platinum causes a sharp decrease in the rate of reaction. In the hydrogenation of the CO group, an increase is instead observed at lower tin contents with a subsequent decrease at the higher Sn/Pt ratios. These results are discussed in terms of: (a) an interaction between tin and platinum which deactivates the active metal sites and (b) an interaction between hydrocinnamaldehyde and tin ions which enhances the reactivity of the CO group.

Glycerol hydrogenolysis promoted by supported palladium catalysts.

Catalytic hydrogenolysis, with high conversion and selectivity, promoted by supported palladium substrates in isopropanol and dioxane at a low H(2) pressure (0.5 MPa), is reported for the first time. The catalysts, characterized by using BET isotherms, transmission electron microscopy (TEM), temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were obtained by coprecipitation and impregnation techniques. The coprecipitation method allows catalysts with a metal-metal or a metal-support interaction to be obtained, which enhances the catalytic performance for both the conversion of glycerol and the selectivity to 1,2-propanediol. Analogous reactions carried out with catalysts prepared by using impregnation are less efficient. A study of the solvent and temperature effect is also presented. The obtained results allow the hydrogenolysis mechanism to be inferred; this involves both the direct replacement of the carbon-bonded OH group by an incoming hydrogen or the formation of hydroxyacetone as an intermediate, which subsequently undergoes a hydrogenation process to give 1,2-propanediol. Finally, catalytic tests on a large-scale reaction at a higher H(2) pressure and recycling of the samples were carried out with the better performing catalysts (Pd/CoO and Pd/Fe(2)O(3) prepared by using coprecipitation) to verify possible industrial achievements.

Hydrogenation of citral and cinnamaldehyde over bimetallic Ru-Me/Al2O3 catalysts

Abstract Hydrogenations of citral and cinnamaldehyde have been investigated over Ru-Me/Al 2 O 3 (Me = Ge, Sn, Pb). Two series of catalysts have been prepared by using the controlled surface reaction (CSR) technique (RuEC series) and the more conventional co-impregnation method (RuNI series). Addition of Ge increases the catalytic activity on the RuEC series whereas no modifications are found on the samples prepared by co-impregnation. The selectivity to unsaturated alcohols is not influenced by the presence of Ge. Addition of tin increases both the activity and the selectivity regardless of the preparation method. The presence of lead does not modify the selectivity and a slight decrease in the catalytic activity is observed on the sample of the RuNI series. On the basis of the characterization data available on the investigated catalysts, it is suggested that Ru and Ge interacts when the samples are obtained through the CSR technique. Such an interaction increases the catalytic activity likely through a decrease of the strength of adsorption of one of the reaction components. The positive effect of tin on the catalytic activity and selectivity is discussed.

Hydrogenation of C=C and C=O groups on ruthenium-tin catalysts

The effect of addition of tin on the catalytic activity of Ru/C catalysts has been investigated in the liquid phase hydrogenation of β-methylstyrene and hydrocinnamaldehyde. On increasing the Sn content, the amount of CO chemisorbed decreases, indicating a decrease in the number of Ru surface atoms. In the hydrogenation of β-methylstyrene the specific activity of Ru (calculated per Ru surface atom) remains constant regardless of the Sn/Ru ratio. An increase of specific activity is however observed in the hydrogenation of hydrocinnamaldehyde. It is suggested that tin, present mainly as Sn ions, enhances the reactivity of the C=O group.