Understanding the role of promoters in catalysis: operando XAFS/DRIFTS study of CeO_x/Pt/Al₂O₃ during CO oxidation

A combined operando XAFS/DRIFTS study on CeOx/Pt/Al2O3 catalysts has been performed during CO oxidation and provides insights into the changes in nanoparticle structure and adsorbed species during the reaction profile. The onset of CO2 formation is shown to be concurrent with a rapid re-oxidation of the Pt nanoparticles, evidenced by XAFS spectroscopy, and the loss of bridge bonded CO adsorbed on Pt, as shown by simultaneous DRIFTS acquisition. The continued appearance of linear bound CO on the catalyst surface is shown to remain long after catalytic light off. The interaction of Pt and CeOx is evidenced by the improved performance towards CO oxidation, compared to the non-CeOx modified Pt/Al2O3, and changes in the CO adsorption properties on Pt previously linked to Pt-CeO2 interfaces

VOx/Fe2O3 Shell-Core Catalysts for the selective oxidation of methanol to formaldehyde

Efficient oxidation catalysts are important in many current industrial processes, including the selective oxidation of methanol to formaldehyde. Vanadium-containing catalysts have been shown to be effective selective oxidation catalysts for certain reactions, and research continues to examine their applicability to other reactions of interest. Several VOx/Fe2O3 shell–core catalysts with varying VOx coverage have been produced to investigate the stability of VOx monolayers and their selectivity for methanol oxidation. Catalyst formation proceeds via a clear progression of distinct surface species produced during catalyst calcination. At 300 °C the selective VOx overlayer has formed; by 500 °C a sandwich layer of FeVO4 arises between the VOx shell and the Fe2O3 core, inhibiting iron cation participation in the catalysis and enhancing catalyst selectivity. The resulting catalysts, comprising a shell–subshell–core system of VOx/FeVO4/Fe2O3, possess good catalytic activity and selectivity to formaldehyde

Tailoring Gold Nanoparticle Characteristics and the Impact on Aqueous-Phase Oxidation of Glycerol

Poly(vinyl alcohol) (PVA)-stabilized Au nanoparticles (NPs) were synthesized by colloidal methods in which temperature variations (−75 to 75 °C) and mixed H2O/EtOH solvent ratios (0, 50, and 100 vol/vol) were used. The resulting Au NPs were immobilized on TiO2 (P25), and their catalytic performance was investigated for the liquid phase oxidation of glycerol. For each unique solvent system, there was a systematic increase in the average Au particle diameter as the temperature of the colloidal preparation increased. Generation of the Au NPs in H2O at 1 °C resulted in a high observed activity compared with current Au/TiO2 catalysts (turnover frequency = 915 h–1). Interestingly, Au catalysts with similar average particle sizes but prepared under different conditions had contrasting catalytic performance. For the most active catalyst, aberration-corrected high angle annular dark field scanning transmission electron microscopy analysis identified the presence of isolated Au clusters (from 1 to 5 atoms) for the first time using a modified colloidal method, which was supported by experimental and computational CO adsorption studies. It is proposed that the variations in the populations of these species, in combination with other solvent/PVA effects, is responsible for the contrasting catalytic properties

Photo-induced pyridine substitution in cis-[Ru(bpy)(2)(py)(2)]Cl-2 : a snapshot by time-resolved X-ray solution scattering

Determination of transient structures in light-induced processes is a challenging goal for time-resolved techniques. Such techniques are becoming successful in detecting ultrafast structural changes in molecules and do not require the presence of probe-like groups. Here, we demonstrate that TR-WAXS (Time-Resolved Wide Angle X-ray Scattering) can be successfully employed to study the photochemistry of cis-[Ru(bpy)(2)(py)(2)]Cl-2, a mononuclear ruthenium complex of interest in the field of photoactivatable anticancer agents. TR-WAXS is able to detect the release of a pyridine ligand and the coordination of a solvent molecule on a faster timescale than 800 ns of laser excitation. The direct measurement of the photodissociation of pyridine is a major advance in the field of time-resolved techniques allowing detection, for the first time, of the release of a multiatomic ligand formed by low Z atoms. These data demonstrate that TR-WAXS is a powerful technique for studying rapid ligand substitution processes involving photoactive metal complexes of biological interest

High kinetic inertness of a bis-hydrated Gd-complex with a constrained AAZTA-like ligand

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Insights into the Structure of Dot@Rod and Dot@Octapod CdSe@CdS Heterostructures

CdSe@CdS dot@rods with diameter around 6 nm and length of either 20, 27, or 30 nm and dot@octapods with pod diameters of ?15 nm and lengths of ?50 nm were investigated by X-ray absorption spectroscopy. These heterostructures are prepared by seed-mediated routes, where the structure, composition, and morphology of the CdSe nanocrystals used as a seed play key roles in directing the growth of the second semiconducting domain. The local structural environment of all the elements in the CdSe@CdS heterostructures was investigated at the Cd, S, and Se K-edges by taking advantage of the selectivity of X-ray absorption spectroscopy, and was compared to pure reference compounds. We found that the structural features of dot@rods are independent of the size of the rods. These structures can be described as made of a CdSe dot and a CdS rod, both in the wurtzite phase with a high crystallinity of both the core and the rod. This result supports the effectiveness of high temperature colloidal synthesis in promoting the formation of core@shell nanocrystals with very low defectivity. On the other hand, data on the CdSe@CdS with octapod morphology suggest the occurrence of a core composed of a CdSe cubic sphalerite phase with eight pods made of CdS wurtzite phase. Our findings are compared to current models proposed for the design of functional heterostructures with controlled nanoarchitecture

Polymerized mixed aggregates containing gadolinium complex and CCK8 peptide.

Two novel amphiphilic unimers contg. an aliph. hydrophobic chain (PDA) with two C C triple bonds and hydrophilic heads presenting the chelating agent DTPAGlu and the CCK8 bioactive peptide, resp., have been prepd. by solid phase synthesis. Aggregates obtained by mixing together PDA-DTPAGlu, or its Gd(III) complex, and PDA-L2-CCK8 in 70/30 molar ratio before and after a polymn. process carried out by UV irradn. have been structurally characterized by means of small angle neutron scattering. The relaxivity properties of aggregates contg. Gadolinium complexes have also been investigated. Elongated mixed micelles have been obsd., in which the relaxivity value r1p for each Gadolinium complex, measured at 20 MHz and 298 K, is around 12 mM-1s-1

Nanostructures based on monoolein or diolein and amphiphilic gadolinium complexes as MRI contrast agents

Highly ordered two or three dimensional mesophases in aqueous solution could be usefully obtained by using monoolein (MO) or diolein (DO) monomers. Nanostructures (also indicated as nanoparticles, NPs) of MO or DO containing different amounts (1%, 5%, 10% and 20%) of the synthetic amphiphilic gadolinium complex (C18)2DTPA(Gd) have been prepared and characterized for their relaxometric and structural behaviors. The nanostructure is found in the 110–200 nm range for all investigated systems, while the presence of the gadolinium containing monomer produces a partial loss of the cubic symmetry, as shown by Cryo-TEM images of NPs doped with 10% w/w of (C18)2DTPA(Gd). Gadolinium containing nanostructures display high relaxivity values (in the 10–15 mM1 s1 range at 25 and 20 MHz, with a further increase at 37°C for DO based NPs), and interesting relaxometric properties for their possible use as MRI contrast agents. NPs containing 10% w/w of (C18)2DTPA(Gd) (MO3-NPs and DO3-NPs) have been also derivatized by introducing 3% wt of (C18)2–Peg3000–FA to obtain targeted aggregates (MO3-NP–FA, DO3-NP–FA). A preferential uptake efficiency of DO3-NP–FA in IGROV-1 cells with respect to DO-NPs without folic acid is observed, specially when cells are incubated with low concentrations of nanostructures or at short incubation times, thus indicating its potential use as a target-selective delivery system for MRI contrast agents on tumor cells overexpressing the folate receptor

Breadboard model of the LISA phasemeter

An elegant breadboard model of the LISA phasemeter is currently under development by a Danish-German consortium. The breadboard is build in the frame of an ESA technology development activity to demonstrate the feasibility and readiness of the LISA metrology baseline architecture. This article gives an overview about the breadboard design and its components, including the distribution of key functionalities.Comment: 5 pages, 3 figures, published in ASP Conference Series, Vol. 467, 9th LISA Symposium (2012), pp 271-27