C. Crisafulli

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.

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.

Pt catalysts supported on H-type zeolites for the catalytic combustion of chlorobenzene

The deep oxidation of chlorobenzene was investigated over Pt catalysts supported on H-type zeolites (H-ZSM5 and H-beta). Pt/zeolite catalysts showed a higher activity compared to Pt/γ-Al2O3 samples which were tested for comparison. Within each class of zeolite, the activity of Pt/zeolite catalysts was found to be higher on the samples with lower SiO2/Al2O3 ratio. Amounts of polychlorinated benzenes (PhClx) were produced in the order Pt/H-ZSM5<Pt/H-beta<Pt/γ-Al2O3 and were found to be roughly independent of the SiO2/Al2O3 ratio of the zeolitic support. The trend in the PhClx formation observed on Pt/zeolite samples, both in terms of total amount and relative distribution, was explained on the basis of a product shape selectivity effect induced by the zeolite, a lower size of zeolite channels hindering the further chlorination of PhCl to PhClx.

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.

Ni–Ru bimetallic catalysts for the CO2 reforming of methane

This paper reports the study on the effect of addition of various amounts of Ru to supported Ni catalysts towards the CO2 reforming of methane. Catalytic activity results have shown that in the case of silica supported samples addition of Ru strongly enhances the catalytic performance of the Ni sample, both in terms of activity and stability. The influence of Ru addition is instead much less remarkable on H-ZSM5 zeolite supported samples. On the basis of FT-IR spectra of adsorbed CO, H2 and O2 chemisorption and temperature-programmed reduction measurements, it has been proposed that the different trend observed on the two series of catalysts is related to different metal–metal and metal-support interactions occurring on the catalysts. In particular, the strong improvement in the activity and stability observed on silica supported Ni–Ru bimetallic samples has been attributed to an increase in the metallic dispersion of Ni as a consequence of the formation of Ni–Ru clusters with the surface mainly covered by Ni.

Selective hydrogenation of phenol to cyclohexanone over supported Pd and Pd-Ca catalysts: an investigation on the influence of different supports and Pd precursors

The gas-phase selective hydrogenation of phenol to cyclohexanone has been investigated over supported Pd catalysts in order to clarify the role of the support, the Pd precursor and the addition of Ca in controlling activity, selectivity and stability of the catalytic system. The catalytic results showed that over monometallic Pd catalysts prepared by PdCl2 as precursor the order of activity and selectivity to cyclohexanone was the following: Pd/La2O3>Pd/CeO2>Pd/Al2O3. The same order of activity was observed over ex-Pd(CH3COO)2 catalysts. However, over these latter samples the selectivity to cyclohexanone was very high regardless of the support used. Addition of calcium strongly improved the catalytic performance of both ex-chloride and ex-acetate Pd catalysts supported on alumina, whereas no significant improvement was observed on Pd catalysts supported on CeO2 and La2O3. On the basis of characterization data (CO chemisorption, TPD and FT-IR) reported in this paper it has been suggested that the acid–base properties of supported Pd catalysts strongly influence the adsorption–desorption equilibrium of the reactant and products, being responsible for directing the selectivity to the reaction products. The catalytic activity of the system appears to be, instead, mainly controlled by the palladium sites on which hydrogen is activated.

Influence of the support on CO2 methanation over Ru catalysts : An FT-IR study

The hydrogenation of CO2 to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO2. Ru/ZSM-5 was more selective to methane than Ru/SiO2. On the basis of FT-IR spectra of CO and CO2 adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane.

FT-IR characterization of alkali-doped Pd catalysts for the selective hydrogenation of phenol to cyclohexanone

A detailed FT-IR investigation of CO, phenol and cyclohexanone adsorbed on alkali-doped Pd catalysts has been carried out in order to get information on the influence of the support and of the addition of promoters (alkali or alkaline earth metals) on the catalytic performance of Pd-supported catalysts in the selective hydrogenation of phenol. The obtained results are consistent with a mechanism that involves the reaction of phenol, adsorbed on the support as a phenolate species, located nearby Pd sites on which hydrogen is activated. The basicity of the support plays an important role in the adsorption of the phenol. Promoters have been found to modify the electronic properties of the palladium sites.

Au–Ag/CeO2 and Au–Cu/CeO2 Catalysts for Volatile Organic Compounds Oxidation and CO Preferential Oxidation

Oxidation of volatile organic compounds (VOC) and preferential oxidation of CO in the excess of H2 (CO-PROX) were investigated over mono and bimetallic Au–Ag/CeO2 and Au–Cu/CeO2 catalysts. For the oxidation of VOC (2-propanol, ethanol and toluene) Au/CeO2 was the most active catalyst for the combustion of alcohols to CO2, Ag/CeO2 gave the best performance in the toluene total oxidation, Au–Ag/CeO2 and Au–Cu/CeO2 showed the highest selectivity to partial oxidation products. For CO-PROX Au–Ag/CeO2 and Au–Cu/CeO2 samples exhibited higher CO2 yield at low temperature than monometallic ones. The improved performance of bimetallic catalysts were accounted for an enhancement of surface ceria oxygens mobility caused by the addition of Ag or Cu to Au/CeO2 and involved in both investigated reactions. This effect was more evident on Au–Ag/CeO2 where a strong Au–Ag interaction occurred with formation of Au–Ag alloy or linked monometallic nanoparticles.Graphical Abstract