Redox dynamics of 2D crystalline vanadium oxide phases on high-index anatase facets.

Vanadium oxides exist in a multitude of phases with varying structure and stoichiometry. This abundance of phases can be extended through the use of other oxides as supports, and through redox treatments. However, the combined effects of different supports and redox treatments can be difficult to identify, particularly when present as different terminating facets on nanoparticles.

Probing surface-sensitive redox properties of VO/TiO catalyst nanoparticles.

Redox processes of oxide materials are fundamental in catalysis. These processes depend on the surface structure and stoichiometry of the oxide and are therefore expected to vary between surface facets. However, there is a lack of direct measurements of redox properties on the nanoscale for analysing the importance of such faceting effects in technical materials.

Desorption products during linear heating of copper zeolites with pre-adsorbed methanol.

Desorption products from zeolites with medium (MFI) and small (CHA) pores and with and without ion-exchanged copper were studied during linear heating after the pre-adsorption of methanol using a chemical flow reactor with a gas phase Fourier transform infrared spectrometer. The methanol desorption profiles were deconvoluted and compared with those predicted from first-principles calculations. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to study the samples during methanol desorption following a step-wise increase of the sample temperature.

Local anisotropy in single crystals of zeotypes with the MFI framework structure evidenced by polarised Raman spectroscopy.

Polarised Raman spectroscopy is used to characterise the local structure in single crystals of zeotypes, namely silicalite-1 and ZSM-5, which share the MFI framework structure. Attributes favourable for applying polarised Raman spectroscopy are the orthogonal axes of these single crystals and their size, i.e.

Methane adsorption and methanol desorption of copper modified boron silicate.

Boron silicate (BS) with a chabazite framework structure was synthesised using a direct route and rigorously characterized before it was ion-exchanged with copper to form Cu-BS. Employing infrared spectroscopy, we show that Cu-BS is capable of oxidising methane to methoxy species and methanol interacts with the boron sites without deprotonation.

Catalytically Active Pd-Ag Alloy Nanoparticles Synthesized in Microemulsion Template.

This work investigates the possibility to form catalytically active bimetallic Pd-Ag nanoparticles synthesized in the water pools of a reversed microemulsion using methanol, a more environmental- and user-friendly reductant compared to hydrazine or sodium borohydride, which are commonly used for this type of synthesis. The nanoparticles were characterized with regards to crystallinity and size by X-ray diffraction and transmission electron microscopy. CO chemisorption and oxidation followed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used for investigating the elemental composition of the surface and catalytic activity, respectively.

Nanofabricated Catalyst Particles for the Investigation of Catalytic Carbon Oxidation by Oxygen Spillover.

The catalytic oxidation of carbon by molecular oxygen was studied using C/Pt, Pt/C, Pt/AlO/C, Pt/CeO/C, AlO/C, and CeO/C model samples prepared by hole-mask colloidal lithography. By this technique, the degree of contact between platinum and carbon was controlled with high precision. The oxidation of carbon was monitored using atomic force microscopy and scanning electron microscopy.

SO adsorption on silica supported iridium.

The interaction of SO with Ir/SiO was studied by simultaneous in situ diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry, exposing the sample to different SO concentrations ranging from 10 to 50 ppm in the temperature interval 200-400 °C. Evidences of adsorption of sulfur species in both absence and presence of oxygen are found. For a pre-reduced sample in the absence of oxygen, SO disproportionates such that the iridium surface is rapidly saturated with adsorbed S while minor amounts of formed SO may adsorb on SiO.

The structure-function relationship for alumina supported platinum during the formation of ammonia from nitrogen oxide and hydrogen in the presence of oxygen.

We study the structure-function relationship of alumina supported platinum during the formation of ammonia from nitrogen oxide and dihydrogen by employing in situ X-ray absorption and Fourier transform infrared spectroscopy. Particular focus has been directed towards the effect of oxygen on the reaction as a model system for emerging technologies for passive selective catalytic reduction of nitrogen oxides. The suppressed formation of ammonia observed as the feed becomes net-oxidizing is accompanied by a considerable increase in the oxidation state of platinum as well as the formation of surface nitrates and the loss of NH-containing surface species.

Revealing local variations in nanoparticle size distributions in supported catalysts: a generic TEM specimen preparation method.

The specimen preparation method is crucial for how much information can be gained from transmission electron microscopy (TEM) studies of supported nanoparticle catalysts. The aim of this work is to develop a method that allows for observation of size and location of nanoparticles deposited on a porous oxide support material. A bimetallic Pt-Pd/Al(2)O(3) catalyst in powder form was embedded in acrylic resin and lift-out specimens were extracted using combined focused ion beam/scanning electron microscopy (FIB/SEM).

Mechanisms behind sulfur promoted oxidation of methane.

The promoting effect of SO2 on the activity for methane oxidation over platinum supported on silica, alumina and ceria has been studied using a flow-reactor, in situ infrared spectroscopy and in situ high-energy X-ray diffraction experiments under transient reaction conditions. The catalytic activity is clearly dependent on the support material and its interaction with the noble metal both in the absence and presence of sulfur. On platinum, the competitive reactant adsorption favors oxygen dissociation such that oxygen self-poisoning is observed for Pt/silica and Pt/alumina.

Direct observations of oxygen-induced platinum nanoparticle ripening studied by in situ TEM.

This study addresses the sintering mechanism of Pt nanoparticles dispersed on a planar, amorphous Al(2)O(3) support as a model system for a catalyst for automotive exhaust abatement. By means of in situ transmission electron microscopy (TEM), the model catalyst was monitored during the exposure to 10 mbar air at 650 degrees C. Time-resolved image series unequivocally reveal that the sintering of Pt nanoparticles was mediated by an Ostwald ripening process.

Mechanistic aspects of HC-SCR over HZSM-5: hydrocarbon activation and role of carbon-nitrogen intermediates.

This study focuses on the mechanism of lean NO(2) reduction by hydrocarbons (propane, propene, and isobutane) over HZSM-5. In-situ FTIR measurements indicate a close correlation between formation of isocyanate species, consumption of water (formed in the reaction), and formation of amine species. The results in this investigation confirm our previously suggested reaction mechanism, which involves reaction of NO(+) species and hydrocarbon-derived species over Brønsted acid sites, forming isocyanate species.

Vibrational analysis of H2 and D2 adsorption on Pt/SiO2.

Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)3SiOSi(OH)3.

Self-sustained kinetic oscillations in CO oxidation over silica-supported Pt.

Isothermal self-sustained kinetic oscillations in CO oxidation over silica-supported Pt at near-atmospheric pressure were studied by combined in situ Fourier transform infrared spectroscopy and mass spectrometry. The use of a specially designed reactor and careful choice of the physical properties of the catalyst and reaction conditions made it possible to eliminate diffusion limitations, to determine the maximum CO oxidation rate per Pt site in the purely kinetic regime and to clarify the mechanism of the oscillations. Specifically, our results indicate that during the high reactive periods the reaction mainly occurs on the oxide surface.

Kinetics of the Formation of Nano-Sized Platinum Particles in Water-in-Oil Microemulsions.

The effect of surfactant type and temperature on the kinetics of the formation of platinum nanoparticles in water-in-oil microemulsions by chemical reduction of PtCl(6)(2-) were examined with time-resolved UV-vis absorption spectroscopy. The surfactants used were poly(ethylene glycol)monododecyl ethers (C(12)E(4), C(12)E(5), C(12)E(6)), sodium bis(2-ethylhexyl)sulphosuccinate (AOT), and mixtures of the alcohol ethoxylates and AOT. The oil domain was n-heptane.