Anne-Riikka Leino

“Double‐Peak” Catalytic Activity of Nanosized Gold Supported on Titania in Gas‐Phase Selective Oxidation of Ethanol

Recent years have seen a growing amount of fundamental research dealing with selective oxidation of alcohols and polyols using molecular oxygen (air) as a cheap and clean oxidant in the presence of solid catalysts. In this respect, supported gold nanoparticles have attracted great attention owing to their unique catalytic properties under mild conditions. Moreover, gold catalysts are becoming increasingly important for the conversion of biomass-derived alcohols, such as ethanol and glycerol, into other useful chemicals. Bioethanol, in particular, is an example of a promising renewable feedstock to obtain corresponding products of oxidation and concurrent reactions; acetaldehyde, 1,1-diethoxyethane, ethyl acetate and acetic acid, which are normally formed one by one with increase of temperature. As a result, more or less complex mixtures of these products or a predominant individual product can be obtained depending on the reaction conditions and the nature of the catalyst (gold particle size, support, preparation procedure). Notably, exactly the same spectrum of products, for example, aldehydes, acetals, esters and carboxylic acids, is typically produced in the presence of other supported metals (e.g. , Pt, Pd, Ru) or metal oxide catalysts (e.g. , V2O5, NbMoVOx), although generally under harsher conditions. Therefore, it seems quite possible that all reactions indicated above have similar mechanistic aspects. However, no generally accepted mechanism has, to date, been formulated for these reactions (see, however, Refs. [8–11]), as it has been for gold-catalyzed reactions of CO, O2, H2, and other small molecules. [12–13] During our monitoring of a gas-phase oxidation of ethanol, a large variety of solid catalysts, such as supported noble metals, metal oxides, and multicomponent systems have been tested. Among them, about thirty different supported gold catalysts were examined. Herein we report an unusual catalytic behavior of Au/TiO2, which was the only tested catalyst to give rise to a second low-temperature peak of activity. The most active gold catalysts are known to be those that contain small particles of gold (<10 nm in diameter), especially on reducible supports such as titania or ceria. 14] Taking this into account, several samples of 2 wt % Au/TiO2 were prepared according to a direct ion-exchange procedure 15] using ammonia as a washing agent to give an average gold particles size close to 2 nm (Figure 1; see also the Supporting Information). The catalytic performance of Au/TiO2 (d = 1.9 1 nm) sample

Photocatalytic activity of TiO2 nanoparticles : effect of thermal annealing under various gaseous atmospheres

The structure, composition and photocatalytic activity of TiO(2) nanoparticles annealed in various gas atmospheres (N(2), NH(3) and H(2)) were studied in this work. The effect of treatment on crystal structure, particle size, chemical composition and optical absorbance were assessed by means of x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy and diffuse optical reflectance/transmittance measurements, respectively. Photocatalytic properties of the materials were evaluated by three different methods: degradation of methyl orange in water, killing of Staphylococcus aureus bacteria and photogeneration of radicals in the presence of 3-carboxy-2,2,5,5-tetramethyl pyrrolidine-1-oxyl (PCA) marker molecules. The results indicate that the correlation between pretreatment and the photocatalytic performance depends on the photocatalytic processes and cannot be generalized.

Isomerization of α-Pinene Oxide Over Iron-Modified Zeolites

Fe-modified mordenite, ferrierite, Y, ZSM-5, ZSM-12 and beta zeolite catalysts were prepared by solid state ion-exchange and conventional liquid phase ion-exchange methods from aqueous solutions. Sn- modified H-beta-300 zeolite catalyst was prepared by the later method. The characterization of proton form, Fe and Sn modified zeolites was carried out using X-ray powder diffraction, scanning electron microscopy, Mössbauer spectroscopy with magnetic measurements, transmission electron microscopy, nitrogen adsorption, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopy, thermo-gravimetric analysis and FTIR spectroscopy using pyridine as a probe molecule. Isomerization of α-pinene oxide over the Fe and Sn modified zeolite catalysts was carried out in the liquid phase using a batch-wise glass reactor. Formation of campholenic aldehyde and fencholenic aldehyde were observed to be influenced by the structure, acidity of zeolite and contents of Fe and Sn, reaction temperature and the catalysts pretreatment.

On the way to improve cetane number in diesel fuels: Ring opening of decalin over Ir-modified embedded mesoporous materials

Embedded materials prepared from MCM-41 together with BE or TON were synthesized, characterized and tested in the ring opening of decalin in a temperature range of 523–623 K. The characterization results revealed that both microporous and mesoporous phases were present in the catalyst. Ir-modification did not change the phase purity, affecting, however, the acidity due to metal-support interactions. The parameters studied in ring opening of decalin were support structure, presence of Ir and temperature. The detailed analysis of 2D/3D isomers and ring opening products showed that the main ring opening products contained ethyl side chain. The Ir-modified embedded mesoporous catalysts were active and relatively selective in the ring opening of decalin, giving 35% selectivity to the ring opening products at 98% conversion at 573 K and 6 MPa.

Electrical transport through single-wall carbon nanotube–anodic aluminum oxide–aluminum heterostructures

Aluminum foils were anodized in sulfuric acid solution to form thick porous anodic aluminum oxide (AAO) films of thickness approximately 6 microm. Electrodes of carboxyl-functionalized single-wall carbon nanotube (SWCNT) thin films were inkjet printed on the anodic oxide layer and the electrical characteristics of the as-obtained SWCNT-AAO-Al structures were studied. Nonlinear current-voltage transport and strong temperature dependence of conduction through the structure was measured. The microstructure and chemical composition of the anodic oxide layer was analyzed using transmission and scanning electron microscopy as well as x-ray photoelectron spectroscopy. Schottky emission at the SWCNT-AAO and AAO-Al interfaces allowed by impurity states in the anodic aluminum oxide film together with ionic surface conduction on the pore walls of AAO gives a reasonable explanation for the measured electrical conduction. Calcined AAO is proposed as a dielectric material for SWCNT-field effect transistors.

Mechanistic investigations of the reaction network in chemo-bio catalyzed synthesis of R-1-phenylethyl acetate

The kinetics and reaction network of the one-pot synthesis of R-1-phenylethyl acetate was investigated at 70°C in toluene over a combination of three different catalysts: PdZn/Al2O3 as a catalyst for acetophenone hydrogenation, lipase as an enzymatic catalyst for R-1-phenylethanol acylation with ethyl acetate and Ru/Al2O3 as a racemization catalyst for S-1-phenylethanol. In addition to the desired reactions, other reactions, namely hydrogenolysis and dehydration of (R, S)-1-phenylethanol and debenzylation of (R, S)-1-phenylethyl acetate also occurred. The kinetic results revealed that ethylbenzene formation was enhanced with higher amounts of PdZn/Al2O3, whereas lipase did not catalyze ethylbenzene formation. Furthermore, ethylbenzene was formed in the hydrogenolysis of (R, S)-phenylethanol and in the debenzylation of (R, S)-1-phenyl-ethylacetate over Pd/Al2O3 catalyst. The presence of Ru/Al2O3 catalyst, in which Ru was in the oxidation state of 3+, enhanced the formation of R-1-phenylethyl acetate, although no clear racemization of S-1-phenylethanol during the one-pot synthesis of R-1-phenylethyl acetate was observed. Dynamic kinetic resolution of (R, S)-1-phenylethanol in toluene, was, however, demonstrated over Ru/Al2O3 and lipase.