Andrea Donato

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.

X-ray photoelectron spectroscopy of Au/Fe2O3 catalysts

Gold catalysts supported on iron oxide have been characterized by X-ray photoelectron spectroscopy (XPS). Depending on the method of preparation and pretreatment, different gold species have been detected on the catalyst surface. In the absence of thermal treatment, the XPS spectra of the impregnated samples show the formation of gold(III) (oxy)chloride species. No metallic gold is formed. Both metallic and oxidized gold species are instead present on the surface of the samples prepared by coprecipitation. Oxidized gold(III) species are predominant on the uncalcinated catalysts. After treatment at high temperature and/or under reaction conditions the amount of metallic gold increases. The XPS data have been correlated with the activity of the investigated catalysts in the oxidation of carbon monoxide at low temperature.

Hydrogenation of Phenol to Cyclohexanone over Palladium and Alkali-Doped Palladium Catalysts

Abstract Palladium catalysts supported on Al2O3 and MgO were prepared and used in the gas-phase hydrogenation of phenol to cyclohexanone. In all range of conditions investigated, selectivity to cyclohexanone was higher on Pd/MgO than on Pd/Al2O3. On Pd/Al2O3 the reaction rates were found to be of first order with respect to the phenol partial pressure and second order with respect to the hydrogen pressure. On Pd/MgO, instead, the order of reaction with respect to phenol was −1 and the order with respect to hydrogen was about 1. Addition of alkali or alkaline earth metals (Ca, K, Cs) to Pd/Al2O3 increased the activity and the selectivity to cyclohexanone without modifying the orders of reaction. On the basis of the results of this study, a reaction mechanism involving adsorption of phenol on the sites of the support at the interface of the palladium metal particles is proposed. The higher selectivity to cyclohexanone found on Pd/MgO compared to Pd/Al2O3, is explained by two different forms of adsorbed phenol.

Catalytic combustion of diesel soot over metal oxide catalysts

Abstract The activity of different metal oxides in the catalytic combustion of a diesel soot having a high amount of adsorbed hydrocarbons has been investigated and tested in a TPO apparatus. Two different steps have been observed. The first is related to the combustion of hydrocarbons adsorbed on soot and the second one to the combustion of the graphitic solid fraction. A high surface area Fe2O3 was found to be the most active catalyst for the oxidation of hydrocarbons, whereas V2O5 was also able to promote the combustion of graphitic carbon. The oxidation of the hydrocarbon fraction has been correlated with the surface area and the strength of the metal-oxygen bond of the metal oxide. The combustion of graphitic carbon is favoured instead on metal oxides having a low melting point. The effect of platinum addition to γ-alumina has been also investigated. Spillover of activated oxygen from Pt to the support has been postulated to take into account the promotion of the oxidation of graphitic carbon.

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.

Influence of Ru precursor, support and solvent in the hydrogenation of citral over ruthenium catalysts

A series of ruthenium supported catalysts were prepared and investigated in the liquid-phase hydrogenation of citral. The mechanism of the reaction was found to be dependent on the Ru precursor, support and solvent used. On the sample prepared from RuCl3 the acetals of citronellal were formed with the subsequent hydrogenation of the isolated C=C double bond. On the samples obtained from precursors which do not contain chloride ions, citronellal was the main reaction product. Hydrogenation of the isolated C=C double bond was negligible. Using cyclohexane as solvent, a large amount of isopulegol was also obtained. The results of the hydrogenation of citral have been correlated to the presence of acid sites and incompletely reduced ruthenium which favour cyclization and acetals formation from citronellal. On the basis of the reported results, a reaction scheme for hydrogenation of citral over ruthenium catalysts is proposed.

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.

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.

Catalytic oxidation of carbon monoxide over Au/Fe2O3 preparations

Low temperature catalytic oxidation of carbon monoxide has been studied over Au/Fe2O3. On the coprecipitated samples the catalytic activity shows a maximum at a gold content of about 5%. Calcination of Au/Fe2O3 decreases the catalytic activity and the stability. The catalytic activity measured is the highest ever reported in the literature on Au/Fe2O3 preparations.

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.