Nano-laminate vs. direct deposition of high permittivity gadolinium scandate on silicon by high pressure sputtering

In this work we use the high pressure sputtering technique to deposit the high permittivity dielectric gadolinium scandate on silicon substrates. This nonconventional deposition technique prevents substrate damage and allows for growth of ternary compounds with controlled composition. Two different approaches were assessed: the first one consists in depositing the material directly from a stoichiometric GdScO_(3) target; in the second one, we anneal a nano-laminate of <0.5 nm thick Gd_(2)O_(3) and Sc_(2)O_(3) films in order to control the composition of the scandate. Metal-insulator-semiconductor capacitors were fabricated with platinum gates for electrical characterization. Accordingly, we grow a Gd-rich Gd_(2-x)Sc_(x)O_(3) film that, in spite of higher leakage currents, presents a better effective relative permittivity of 21 and lower density of defects

Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 1. Effect of nickel loading and preparation conditions on catalyst properties

Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, Ni/HZSM-5 catalysts were synthesized via deposition-precipitation (DP) and characterized. The effect of synthesis parameters; including nickel loading, DP time (synthesis contact time), and calcination temperature, on catalyst properties were studied. N2 and CO2 adsorption techniques were used to look at textural properties and confirmed the existence of lamellar species generated from DP. X-ray diffraction (XRD) confirmed that nickel metal was present on the support after reduction and passivation of the catalyst. Temperature programmed reduction showed that all the catalyst preparations were reducible at 733 K after 4 h, and that the DP method formed a mixture of Ni2+ species on the support. Transmission electron microscopy, XRD, and H2 chemisorption were used to determine approximate particle size and dispersion of nickel metal. From all the preparations, the 15 wt% Ni/HZSM-5 catalyst with long DP time (16 h) and low calcination temperature (673 K), exhibited the most favorable particle size (~5 nm) and dispersion (7%)

Oxidation of o-xylene to phthalic anhydride on Sb-V/ZrO2 catalysts

Zirconia-supported and bulk-mixed vanadium-antimonium catalysts were used for the oxidation of o-xylene to phthalic anhydride. Vanadium promoted the transition of tetragonal to monoclinic zirconia. The simultaneous presence of antimony and vanadium on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents, the formation of SbVO4 took place. Sb-V-ZrO2 catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO2 catalysts. However, their selectivity to phthalic anhydride was poor compared to V/TiO2 commercial catalysts. The improved selectivity of the Sb-containing catalysts was attributed to the blocking of non-effective surface sites of ZrO2, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto de Catálisis y Petroleoquímica; EspañaFil: del Val, S.. Instituto de Catálisis y Petroleoquímica; EspañaFil: López Granados, M.. Instituto de Catálisis y Petroleoquímica; EspañaFil: Bañares, M.A.. Instituto de Catálisis y Petroleoquímica; EspañaFil: Fierro, J.L.G.. Instituto de Catálisis y Petroleoquímica; Españ

A simple approach to synthesize g-C3N4 with high visible light photoactivity for hydrogen production

Se-modified g-C3N4 was synthesized from sonicated aqueous suspensions of melamine cyanurate and SeO2. The different thermal condensation temperatures in the 500–650 °C range were found to influence the photophysical properties and hydrogen evolution rates. H2 evolution increased dramatically by two orders of magnitude when Pt co-catalyst (1 wt.%) was incorporated, reaching an HER of 75 µmol H2/h

Crotonaldehyde hydrogenation on Rh/TiO2 catalysts. In situ DRIFTS studies

The surface and catalytic properties in the vapor-phase hydrogenation of crotonaldehyde on Rh/TiO2 has been studied. It was found that a partial reduction of the support produces a surface decoration of the metal component. Thus, interfacial sites are created, which are responsible of an increase in the selectivity to crotyl alcohol, via enhancement of the polarization of the C=O bond. Photoelectron spectra revelead that rhodium is in different oxidation states, with a contribution of ca. 20 % Rhd + and 80 % Rhº species for LTR catalyst and only a slight increase of Rhd + for HTR catalyst. TEM studies revelead that Rh has metal particle size close 3 nm with small increases in the catalyst reduced at high temperature. DRIFTS essayed carried out under reaction conditions allowed to identify crotonaldehyde species strongly adsorbed through the C=C bond and weakly coordinated through both the C=C and C=O bonds. After reduction at 723 K an increase in the peak at 1660 cm-1 ascribed to an interaction between the carbonyl group and the surface, was observed. This peak seems to be stabilized at interfacial Rh/TiOx sites The deactivation in crotyl alcohol formation can be ascribed to the generation of strongly chemisorbed asymmetric carboxylate species detected by band at 1740 cm-1. This band grows at expense of crotonaldehyde O s - bonded intermediate chemisorbed on coordinatively unsaturated sites (Lewis acid sites) responsible of the crotyl alcohol obtaintion (detected by a band at 1653 cm-1). Additionally, a small band at 2068 cm-1 assigned to CO adsorbed on transition metals, which increases with time on-stream may explain the deactivation of the catalysts in flow systems

Synthesis of palladium nanoparticles on carbon nanotubes and graphene for the chemoselective hydrogenation of para-chloronitrobenzene

We have studied the synthesis of palladium nanoparticles over carbon nanotubes (Pd/CNT) and graphene (Pd/G) and we have tested their catalytic performance in the liquid phase chemoselective hydrogenation of para-chloronitrobenzene at room temperature. The catalysts were characterized by N2 adsorption/desorption isotherms, TEM, X-ray diffraction, infrared and X-ray photoelectron spectroscopy and ICP-OES. The palladium particle size on Pd/G (3.4 nm) and Pd/CNT (2.8 nm) was similar though the deposition was higher on Pd/G. Pd/CNT was more active which can be ascribed to the different surface area and electronic properties of the Pd nanoparticles over CNT, while the selectivity was 100% to the corresponding haloaniline over both catalysts and they were quite stable upon recycling.Financial support for the present study was received from CONICYT Chile, project 3130483 (Postdoctoral), Generalitat Valenciana, Spain (PROMETEOII/2014/004) is also gratefully acknowledged

Synthesis of palladium nanoparticles over graphite oxide and carbon nanotubes by reduction in ethylene glycol and their catalytic performance on the chemoselective hydrogenation of para-chloronitrobenzene

Pd nanoparticles have been synthesized over carbon nanotubes (CNT) and graphite oxide (GO) by reduction with ethylene glycol and by conventional impregnation method. The catalysts were tested on the chemoselective hydrogenation of p-chloronitrobenzene and the effect of the synthesis method and surface chemistry on their catalytic performance was evaluated. The catalysts were characterized by N2 adsorption/desorption isotherms at 77 K, TEM, powder X-ray diffraction, thermogravimetry, infrared and X-ray photoelectron spectroscopy and ICP-OES. It was observed that the synthesis of Pd nanoparticles employing ethylene glycol resulted in metallic palladium particles of smaller size compared to those prepared by the impregnation method and similar for both supports. The presence of oxygen groups on the support surface favored the activity and diminished the selectivity. It seems that ethylene glycol reacted with the surface groups of GO, this favoring the selectivity. The activity was higher over the CNT-based catalysts and both catalysts prepared by reduction in ethylene glycol were quite stable upon recycling.Financial support for the present study was received from CON-ICYT Chile, project 3130483 (Postdoctoral), Generalitat Valenciana, Spain (PROMETEOII/2014/004) is also gratefully acknowledged