S. Galvagno

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.

FT-IR study of Au/Fe2O3 catalysts for CO oxidation at low temperature

Coprecipitated Au/Fe2O3 catalysts used for low-temperature catalytic oxidation of carbon monoxide have been studied by FT-IR spectroscopy of adsorbed CO. The FT-IR results have shown that after preparation and exposure to a CO/O2 mixture gold is present on the surface mainly as Au1+ and Au0 species. It has been found that in the CO oxidation Au1+ is more active and less stable than Au0.

Influence of catalyst pretreatments on volatile organic compounds oxidation over gold/iron oxide

Abstract This paper reports a study on the influence of calcination pretreatments on the catalytic behaviour of the Au/iron oxide system towards the combustion of some representative volatile organic compounds (2-propanol, ethanol, methanol, acetone and toluene). The catalytic activity of Au/Fe 2 O 3 samples towards the total oxidation to CO 2 has been found to be strongly dependent on the catalyst pretreatment, decreasing on increasing the calcination temperature. On the basis of characterisation data (XPS, FT-IR, XRD, BET surface area) it has been proposed that the catalytic behaviour is related to the gold state and/or the iron oxide phase. It appears plausible to suggest that the gold oxidation state and/or the particle size play a key role in the catalytic combustion of volatile organic compounds.

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.

CO2 reforming of methane over Ni–Ru and Ni–Pd bimetallic catalysts

This paper reports the effect of noble metal addition (Ru, Pd) to supported Ni catalysts towards the reaction of CO2 reforming of methane. On the basis of FT-IR spectra of adsorbed CO, H2 chemisorption and TPR measurements it has been proposed that the different behaviour of the Ni-based bimetallic catalysts can be related to different metal–metal interactions occurring on the catalysts. In particular, the strong improvement in the activity and stability observed in the case of ex-nitrate Ni–Ru catalysts has been attributed to an enrichment of the catalyst surface in nickel due to the formation of Ni–Ru clusters with the surface mainly covered by Ni. This leads to an increase in the metallic dispersion of Ni and favours the formation of more reactive intermediate carbonaceous species.

CO and NO2 sensing properties of doped-Fe2O3 thin films prepared by LPD

Abstract The CO and NO2 sensing properties of iron oxide thin films doped with Au and Zn and prepared by a liquid-phase deposition method (LPD) have been investigated. The undoped Fe2O3 sensor was found to be sensitive to NO2 but not to CO. The addition of Zn increases the sensitivity at low temperature towards NO2 and decreases strongly the intrinsic resistance of the iron oxide film. The addition of gold was necessary to obtain a detectable response to CO, the Au-doped ZnO sensor was found the most sensitive to CO. By operating at an appropriate temperature, these sensors could be able to detect selectively CO and NO2, with negligible humidity cross-sensitivity.

Catalytic combustion of volatile organic compounds over group IB metal catalysts on Fe2O3

Abstract Catalytic combustion of methanol, 2-propanol, and toluene was investigated on co-precipitated Au/Fe2O3, Ag/Fe2O3 and Cu/Fe2O3 catalysts in the presence of excess of oxygen. In the range of temperature investigated (40–400 ° C ) the activity towards the oxidation of volatile organic compounds (VOCs) has been found to be in the order: Au/Fe2O3≫Ag/Fe2O3>Cu/Fe2O3>Fe2O3. This trend of activity has been explained on the basis of the capacity of the IB metal to weaken the Fe–O bond thus increasing the mobility of the lattice oxygen which is involved in the VOCs oxidation through a Mars–van Krevelen reaction mechanism.

Particle size effect in the catalytic hydrogenation of 2,4-dinitrotoluene over Pd/C catalysts

Abstract The liquid phase hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to 2,4-diaminotoluene (2,4-DAT) has been studied over palladium supported on carbon. Catalytic activity and selectivity to the intermediate products were found to depend on the metal particle size. The larger metal particles were the most active and selective towards the formation of the 2,4-nitrohydroxyaminotoluene isomers. The catalysts have been characterized by TPR, XRD, TEM and CO chemisorption. TPR analysis has shown that no formation of a palladium β-hydride phase occurs on these systems irrespectively of the metal particle size. This apparently anomalous behavior has been attributed to the contamination of the Pd metal particles by impurities and/or C atoms migrating from the support. On the basis of the reported results the relationships between the catalytic activity and the metal particle size in the hydrogenation of 2,4-DNT is discussed.

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.