Elena V. Murzina

Reaction Products and Transformations of Intermediates in the Aqueous‐Phase Reforming of Sorbitol

Aqueous phase reforming of sorbitol over Pt supported on an alumina catalyst is investigated, in order to identify the intermediates involved in the transformation of the initial feed. Parameters such as the sorbitol feed rate and temperature are studied. To identify the intermediates, an approach based on analysis of the gas and liquid phases as well as the total carbon content was developed. According to analysis by gas chromatography combined with mass spectrometry of volatile substances collected with solid-phase microextraction, over 260 compounds are involved in the transformation of sorbitol. Of these, 50 of the major products are identified with high reliability. It is shown that a great variety of compounds, bearing different functionalities, form part of the reaction network. The formation of the majority of identified compounds is explained and a reaction network for the formation of sorbitol and intermediate molecules transformation is proposed.

Kinetics of lactose and rhamnose oxidation over supported metal catalysts

Several mono- and bimetallic Pd, Pt, Rh and Ru supported on alumina and active carbon catalysts were characterized by CO chemisorption, nitrogen adsorption, XPS and XRD and acidity titrations were performed for active carbon supported catalysts. These catalysts were tested in oxidation of two sugars, namely lactose and rhamnose, at 60 °C and at 70 °C under slightly alkaline conditions (pH 8) with molecular oxygen. The results revealed that there is an optimum metal particle size in a range of 3-10 nm giving the highest initial TOFs for both oxidations. Furthermore, the catalytic activities and conversions were related to other catalyst properties, such as the type and amount of promoters and the presence of different phases. In situ catalyst potential measurements revealed that there is an inverse correlation between the increase of catalyst potential as a function of sugar conversion and the catalyst activity after prolonged reaction times. This method is a valuable tool for in situ characterization of catalysts correlating well with their activities.

Lactose oxidation kinetics with oxygen in catalyst-solution-gas three-phase system with simultaneous electrical potential measurement of supported gold catalyst

Lactose oxidation kinetics was studied on an supported gold catalyst with simultaneous control of catalyst potential. The experimental data were described well by the suggested mechanism and kinetic model of this reaction.

Aldose to ketose interconversion: galactose and arabinose isomerization over heterogeneous catalysts

Isomerization of glucose, galactose and arabinose to corresponding keto-sugars was studied in the present work over a range of heterogeneous catalysts. Magnesium aluminates with different ratios between oxides resulting in materials with a Mg/Al ratio from 0.2 to 0.9 were prepared, characterized and evaluated in terms of their catalytic behavior. The catalyst with a Mg/Al ratio close to hydrotalcites was the most efficient considering activity, selectivity and stability. The sugar structure was shown to have a minor influence on catalytic activity and selectivity.

Novel Nano Catalysts on the Base of Hyper-crosslinked Polystyrene for Carbohydrates Oxidation

The synthesis and catalytic properties of Pd, Pt, Ru nanoparticles in nanostructures of polymers are described. The controlled growth of metal nanoparticles in a polymer matrix was achieved. The catalytic systems have been studied in selective oxidation of monosaccharide. These processes are of particular interest because the products are the intermediates in the synthesis of biology active substances.

Controlled synthesis of PVP-based carbon-supported Ru nanoparticles: synthesis approaches, characterization, capping agent removal and catalytic behavior

Polyvinylpyrrolidone (PVP) stabilized Ru nanoparticles (NPs) with a mean size of ca. 2.4 nm were synthesized and immobilized on mesoporous Sibunit, macroporous carbon nanofibers of platelet structure (CNF-Pl) and micro-/mesoporous TiC carbide-derived carbon (CDC), providing 1.7–2.9 wt% Ru/C catalysts with a mean Ru size of 2.1–2.7 nm. The presence of PVP on the catalyst surface drastically diminished the activity in structure-sensitive hydrogenation of galactose to galactitol. Different PVP removal and support modification methods were tested to elucidate the effect of support hydrophilicity/hydrophobicity, preliminary support functionalization, and additional Ru NPs washing prior to immobilization as well as degree of PVP removal on catalytic behavior. For characterization of the carbon supports and synthesized catalysts TEM, XPS, XRD, XRF, water adsorption/desorption experiments and N2 physisorption were applied. Carbon supports were functionalized before Ru NPs immobilization by treatment with 5 wt% HNO3, conc. HNO3, Ar (700 °C), air (350 °C), and H2 (700 °C) without visible support microstructure alterations. Several protocols for PVP removal were applied such as solvothermal (with water and acetic acid aqueous solutions at 220 °C) and thermal treatment (in air, argon, hydrogen or nitrogen at different temperatures) not resulting in noticeable changes in Ru NPs size. The thermal treatment in air at 180 °C followed by reduction at 250 °C was found to be more effective in the case of Sibunit and CNF-Pl, while solvothermal treatment in water at 220 °C (PN2 25 bar) improved significantly the activity of TiC-CDC-based catalysts. Untreated Sibunit and CNF-Pl carbon supports provided higher activity in galactose hydrogenation with Ru/Sibunit exhibiting the best catalytic activity and being also the most hydrophilic according to water sorption isotherms. The catalytic activity of untreated micro-/mesoporous Ru/TiC-CDC increased noticeably depending on the support pretreatment in the order: untreated < 5% HNO3 < conc. HNO3. Additional TiC-CDC support functionalization was proposed to be required because of a relatively low amount of oxygen-containing groups on the surface compared to Sibunit and CNF.