Effect of Gold on the HDS Activity of Supported Palladium Catalysts

Abstract The effect of gold on palladium catalysts supported on amorphous aluminosilicate was investigated in the hydrodesulfurization of thiophene. A series of bimetallic AuxPdy catalysts was prepared by the slow deposition–precipitation method with decomposition of urea. The structural and surface properties of the samples were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy techniques at different stages of the catalyst life. After calcination at 673 K, gold-enriched solid solutions of approximately Au90Pd10 and Au80Pd20 composition were formed for all samples of different Au/Pd ratios, along with free palladium phases. Au80Pd20 was the prevailing phase. Hydrogen treat…

Metal-support and preparation influence on the structural and electronic properties of gold catalysts

Abstract Nanostructured gold catalysts supported on CeO2 and SiO2 were prepared by the deposition–precipitation (DP) and the solvated metal atom dispersion (SMAD) techniques. The structural and electronic properties of the catalysts were investigated by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Gold was found as small metal nanoparticles (cluster size ∼2 nm) in the SMAD-prepared samples and in ionic state in the DP catalysts. The catalytic activity of the samples was tested in the reaction of low temperature CO oxidation. Gold nanosized particles in a pure metallic state exhibited a worse catalytic performance, both on ceria and…

X-ray Photoelectron-spectroscopy Investigation of Pumice-supported Nickel-catalysts

Pumice-supported nickel catalysts, prepared by the method of slow homogeneous precipitation with urea, were analysed by x-ray photoelectron spectroscopy (XPS). By comparison with similarly prepared silica- and alumina-supported nickel catalysts, a preferential interaction of Ni2+ with Al3+ of the support has been determined. A quantitative XPS analysis indicated large segregation of nickel to the surface. The treatment with H2 at 673 K and 1073 K produced a partial reduction of Ni+2 to Ni0. The extent of the reduction was largest at 1073 K and in this case the reduced Ni in the metallic phase was detectable by x-ray diffraction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in the…

Nanostructured gold catalysts for low temperature CO oxidation

Liquid phase selective oxidation of benzyl alcohol over Pd–Ag catalysts supported on pumice

Abstract Selective oxidation of benzyl alcohol to benzaldehyde was carried out over pumice supported bimetallic and monometallic Pd and Ag catalysts. Preliminary kinetic studies were performed at 333 K in autoclave, at pressure of 2 atm in pure oxygen. Under these conditions, small amounts of benzoic acid were detected with the monometallic Pd pumice being the most active catalyst. The reaction was also carried out under flowing oxygen at atmospheric pressure and at 348 K. Under these conditions, the selectivity to benzaldehyde was 100%. The catalytic activity of the catalysts was measured after different oxidation and reduction treatments at high temperature. In addition, two mechanical mi…

Chemical effect on the XPS spectra of the valence band and on O KLL and Pd MNN Auger spectra in pumice-supported catalysts

X-ray photoelectron spectra of the valence band and X-ray-excited O KLL Auger transition of pumice-supported Pd and Pt catalysts have been obtained and compared to the corresponding spectra of pumice (a naturally occurring amorphous aluminosilicate). The changes observed indicate interaction between metal and support. The valence region of the catalysts consists of three large peaks: one due to the d band of the metals and the other to the O 2p non-bonding orbitals and bonding-type orbitals formed by a mixing of the atomic orbitals (O 2p, Si 3s and Si 3p) of oxygen and silicon from the support. The intensity decrease of the component due to the bonding orbitals, observed in the catalyst spe…

Influence of platinum on catalytic activity of polycrystalline WO3 employed for phenol photodegradation in aqueous suspension

Abstract A series of polycrystalline WO3 solids loaded with platinum (0.5; 1.0; 2.0 and 3.0 wt%) were prepared and characterised by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, specific surface areas determination, X-ray photoelectron spectroscopy. XPS and X-ray results indicate that the samples loaded with Pt up to 1 wt% contained on the surface mainly Pt(2+) species, while those loaded with higher amounts contained Pt(0). Moreover, the samples were employed for a probe reaction, i.e. phenol photooxidation in aqueous suspension, and their photoactivity was compared with that of two TiO2 commercial samples, mainly in the anatase phase. All the Pt–WO3 sa…

Model Pumices Supported Metal Catalysts

The catalyzed, selective hydrogenation, in liquid phase, of 1,3-cyclooctadiene was studied on a series of Pd catalysts supported on natural pumice, model pumices (with variable content of alkali metal ions), silica, and sodium-doped silica. At constant pressure of H2(1 atm.) the reaction follows a zero-order kinetic for all the Pd catalysts. At low metal dispersion (Dx < 20%), Pd/pumice catalysts exhibit higher activity as compared to Pd/silica catalysts; the turnover frequency is maintained even at high metal dispersion in Pd/pumice but Pd/silica and Pd/model pumices without alkali ions show a decrease in activity. At increasingDx, the binding energy shift of Pd 3dlevel is negative in Pd/p…

Pumice-Supported Nickel Catalysts

A series of nickel catalysts supported on pumice was prepared by precipitation and impregnation techniques. The influence of the calcination and reduction temperatures on the structural properties such as lattice parameters and particle dimensions of the oxide precursors and of the reduced catalysts was investigated by X-ray diffraction measurements. The effect of structural changes on the catalytic activity in the hydrogenation of carbon monoxide has been evaluated. The turnover frequencies, as well as product distributions, are discussed in terms of the influence of the support properties and of its interaction with the metal. Changes of the C2+yield over CH4yield ratio versus nickel disp…

The structure of pumice: An XPS and27Al MAS NMR study

In order to investigate the surface structure of pumice, an amorphous aluminosilicate, samples of pumice and of standards of silica and alumina have been studied by x-ray photoelectron spectroscopy (XPS). The effect of a mild acid leaching was also considered. The analysis of the Si 2p, Al 2p and O 1s photoelectron peaks and the Si KLL and O KLL Auger peaks indicated that pumice is formed by tetrahedral silica with some units being replaced by aluminate, AlO2−. The acid treatment decreases the alkali and the aluminate ions. X-ray photoelectron spectra of the valence band of pumices and of standards of Al2O3 and SiO2 agree with the core-level results. To support the conclusions from the XPS …

The thin and medium filters of the EPIC camera on-board XMM-Newton: measured performance after more than 15 years of operation

After more than 15 years of operation of the EPIC camera on board the XMM-Newton X-ray observatory, we have reviewed the status of its Thin and Medium filters. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, Raman scattering, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Furthermore, we have investigated the status of the EPIC flight filters by performing an analysis of the optical loading in the PN offset maps to gauge variations in the optical and UV transmission. We both investigated repea…

XPS study of supported gold catalysts:the role of Au0 and Au+? species as active sites.

Gold nanoparticles supported on different oxides (SiO2, CeO2 and TiO2) were prepared by the SMAD (solvated metal atom dispersion) and deposition–precipitation (DP) techniques. The physical and chemical characterization of the catalysts was performed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the catalytic activity was tested during the reaction of low temperature CO oxidation. The structural and surface analyses evidenced the presence of small gold crystallites (cluster size ∼2–5 nm) in all the SMAD-prepared samples and oxidized gold species in the case of the DP catalysts. A different surface distribution of ionic gold species was found on the different suppo…

Relationship between structure and CO oxidation activity of ceria supported gold catalysts

Gold catalysts supported on cerium oxide were prepared by solvated metal atom dispersion (SMAD), by deposition-precipitation (DP), and by coprecipitation (CP) methods and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was tested in the CO oxidation reaction. The structural and surface analyses evidenced the presence of a modified ceria phase in the case of the DP sample and the presence of pure ceria and gold metal crystallites in the case of the SMAD and CP samples. The DP sample, after a mild treatment in air at 393 K, exhibited only ionic gold, and it was very active below 273 K. By…

XPS study of pumice-supported palladium and platinum catalysts

An XPS study has been performed on samples of monometallic of palladium and platinum and on bimetallic Pd-Pt catalysts supported on pumice. A negative shift of about 0.5 eV in the Pd 3d and Pt 4f binding energies of the catalysis relative to the energies of the same levels in the pure metals suggested an increase in the electron density in both metals. A quantitative XPS analysis indicated that the supported metals did not modify the surface atomic composition of pumice

Structural Changes of Titanium Oxide Induced by Chromium Addition as Determined by an X-Ray Diffraction Study

Abstract An X-ray diffraction study has been carried out on a series of polycrystalline TiO 2 (anatase) catalysts containing Cr(III) at different atomic concentrations (0.2-5.0 at. %), prepared by a co-precipitation method. Analysis of the variation of the unit cell parameters of chromium-doped anatase with respect to pure anatase has allowed us to estimate the solubility limit for the system at around 1.4 at. %. There is no evidence for the existence of a separate crystalline chromium oxide phase. Temperature effects on the cell parameter and on the anatase-rutile transformation rate were also analyzed. An increase in temperature produced release of the chromium from the solid solution. At…

Preparation characterization and photocatalytic activity of polycrystalline ZnO/TiO2 systems. 1. Surface and bulk characterization

Polycrystalline ZnO/TiO2 solids have been prepared with four different methods using home prepared TiO2 (anatase) or TiO2 (rutile) as supports and Zn(NO3)2·6H2O or Zn(CH3COO)2·2H2O as precursors for ZnO. The bulk and surface properties of the samples were investigated by means of TG-DTA, XRD, TEM, SEM-EDAX, XPS, BET surface area determination, and porosity measurements. XRD and TEM results indicate that no significant defect structures exist in any of the samples. The ZnO crystallinity and its enrichment on the surface of TiO2 particles were dependent on the preparation method. The surface areas generally decrease by increasing the amount of ZnO except when ZnO from Zn(CH3COO)2·2H2O was sup…

SYNTHESIS, CHARACTERIZATION AND CATALYTIC PROPERTIES OF GOLD NANOPARTICLES SUPPORTED ON CERIA

Pumice-supported Cu-Pd catalysts: Influence of copper on the activity and selectivity of palladium in the hydrogenation of phenylacetylene and but-1-ene

Abstract Pumice-supported copper–palladium catalysts prepared from organometallic precursor have been tested in the hydrogenation of phenylacetylene and in the hydrogenation/isomerization of the but-1-ene. The structure and catalytic behaviour of the bimetallic catalysts depended on the different temperatures of reduction. The presence of CuO or Cu metal in an alloyed state with Pd influenced the two reactions. The system containing CuO is the most active and selective towards the formation of the monoalkene in the hydrogenation of the highly unsaturated hydrocarbon. The system containing Cu partially alloyed with Pd is more active and selective towards the isomerization of the but-1-ene. T…

Catalytic reduction of nitrates and nitrites in water solution on pumice-supported Pd–Cu catalysts

Abstract Two series of pumice-supported palladium and palladium–copper catalysts, prepared by impregnation with different palladium and copper precursors, were tested for the hydrogenation of aqueous nitrate and nitrite solutions. Measurements were performed in a stirred tank reactor, operating in batch conditions, in buffered water solution at atmospheric pressure and at 293 K. The activities of the catalysts were calculated in terms of nitrate and/or nitrite removal. With the monometallic Pd/pumice, the reduction of nitrite is highly selective; only 0.2% of the initial nitrite content is converted to ammonium ions. The activity in terms of turn over frequency (TOF) is higher as compared t…

Fluorescent nitrogen-rich carbon nanodots with an unexpected β-C3N4nanocrystalline structure

Carbon nanodots are a class of nanoparticles with variable structures and compositions which exhibit a range of useful optical and photochemical properties. Since nitrogen doping is commonly used to enhance the fluorescence properties of carbon nanodots, understanding how nitrogen affects their structure, electronic properties and fluorescence mechanism is important to fully unravel their potential. Here we use a multi-technique approach to study heavily nitrogen-doped carbon dots synthesized by a simple bottom-up approach and capable of bright and color-tunable fluorescence in the visible region. These experiments reveal a new variant of optically active carbonaceous dots, that is a nanocr…

Status of the EPIC thin and medium filters on-board XMM-Newton after more than 10 years of operation I: laboratory measurements on back-up filters

After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton, we have reviewed the status of its Thin and Medium filters by performing both laboratory measurements on back-up filters, and analysis of data collected in-flight. We have selected a set of Thin and Medium back-up filters among those still available in the EPIC consortium, and have started a program to investigate their status by different laboratory measurements including: UV/VIS transmission, X-ray transmission, RAMAN IR spectroscopy, X-Ray Photoelectron Spectroscopy, and Atomic Force Microscopy. We report the results of the measurements conducted up to now, and point out some lessons lear…

Chemical Evolution of Interstellar Methanol Ice Analogs upon Ultraviolet Irradiation: The Role of the Substrate

An important issue in the chemistry of interstellar ices is the role of dust materials. In this work, we study the effect of an amorphous water-rich magnesium silicate deposited onto ZnSe windows on the chemical evolution of ultraviolet-irradiated methanol ices. For comparison, we also irradiate similar ices deposited onto bare ZnSe windows. Silicates are produced at relatively low temperatures exploiting a sol-gel technique. The chemical composition of the synthesized material reflects the forsterite stoichiometry. Si-OH groups and magnesium carbonates are incorporated during the process. The results show that the substrate material does affect the chemical evolution of the ice. In particu…