Anton V. Tokarev

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.

Aqueous-phase reforming of xylitol over Pt/C and Pt/TiC-CDC catalysts: catalyst characterization and catalytic performance

The aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM. The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF.

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.

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.

Sibunit-Supported Mono- and Bimetallic Catalysts Used in Aqueous-Phase Reforming of Xylitol

Carbon-supported mono- and bimetallic catalysts prepared via incipient wetness impregnation were systematically studied in aqueous-phase reforming (APR) of xylitol aiming at hydrogen production from biomass. The catalytic performance of several VIII group metals and their combinations, such as Pt, Ni, Pt–Ni, Re, Pt–Re, Ru, Pt–Ru, and Pt–Co, was compared for xylitol APR in a fixed-bed reactor at 225 °C and 29.7 bar (N2). Ni/C, Ru/C, and Re/C catalysts displayed significantly lower activity compared to others. Activity and selectivity to H2 of bimetallic Pt–Ni/C, Pt–Co/C, and Pt–Ru/C catalysts were close to that of Pt/C. Pt–Re/C catalyst showed an outstanding performance which was accompanied by a shift of the reaction pathways to the alkane formation and thereby lower hydrogen selectivity. Addition of the second metal to Pt was not found to be beneficial for hydrogen production, thus leaving Pt/C as the optimum carbon-supported catalyst.

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.