Irina L. Simakova

Catalysis in biomass processing

Biomass has in recent years been considered as a raw material for the production of fuels and chemicals. This work discusses the reasons for the increased interest in mainly lignocellulosic biomass. Gasification, pyrolysis, and depolymerization by hydrolysis are analyzed as key biomass technology. We also discuss which of the sugars obtained via depolymerization by hydrolysis can be processed into fuel or key intermediates of the chemical industry. Lignocellulosic biomass contains such extractants as fatty acids and terpenes, and we therefore describe the catalytic reactions of these substances for the synthesis of fuels and chemicals. Some typical reactions of biomass processing (oxidation, hydrogenation, cracking, etc.) are conceptually close to the process widely known in the refining and chemical industries. There are, however, other considerations due to, e.g., the large number of functional (hydroxyl and other) groups, and the processing of biomass components therefore requires dehydration, aldol condensation, ketonization, decarboxylation, etc. We cover the fundamentals of the approaches to selecting catalysts for these reactions.

Overview of catalytic methods for production of next generation biodiesel from natural oils and fats

Production of biodiesel from natural oils and fats can be achieved using various technologies briefly discussed in this review. A particular appealing concept for production of green diesel is selective catalytic deoxygenation of renewables leading to diesel fuel products. This reaction can be performed over Pd on active carbon supports with saturated and unsaturated fatty acids and their derivatives.

On quantitative description of metal particles size effect in catalytic kinetics

Quantitative description for turnover frequency dependence on the metal cluster size for a two-step catalytic cycle was performed based on a thermodynamic approach, which accounts for changes of the chemical potential upon adsorption depending on the metal cluster size. Such analysis revealed a possibility for turnover frequency to exhibit a maximum. A very good correspondence between calculated and experimental data in hydrogenation and decarboxylation reactions over palladium was achieved.

Improved synthesis and hydrothermal stability of Pt/C catalysts based on size-controlled nanoparticles

A novel method for the preparation of stable Pt/C catalysts with size-controlled nanoparticles has been developed. The method is based on in situ synthesis of the nanoparticles (reduction with NaBH4 in the presence of a support and PVP). Compared to the conventional ex situ route (colloidal synthesis followed by impregnation), this in situ route yields smaller nanoparticles (2.5–3.9 nm) of narrower size distribution. The catalysts prepared by the in situ synthesis showed a higher stability in water at 80 °C, indicating a stronger interaction between the support and the metallic phase. Hydrothermal stability tests were also conducted under conditions equivalent to those of aqueous phase reforming (200 °C, 17 bar and water and diluted acetic acid). Hydrothermal treatment proved to be an excellent method to improve the resistance to leaching of the catalysts. Metal loss was negligible while PVP was almost completely removed from the catalyst; hence, most of the porosity was recovered and the dispersion measured by CO chemisorption increased from 5 to 34–75%. Water at 200 °C was more effective than diluted acetic acid for the removal of PVP. TEM images confirmed that the Pt nanoparticles did not undergo significant changes either in size or morphology upon the hydrothermal treatment, and XPS analysis showed a homogeneous distribution of Pt nanoparticles within the catalyst granules.

Continuous mode linoleic acid hydrogenation on Pd/sibunit catalyst

Catalytic hydrogenation of linoleic acid and oleic acid to stearic acid over palladium on mesoporous carbon sibunit (Pd/sibunit) catalyst was studied in a continuous trickle-bed reactor with the weight hourly space velocity 5.4 h−1 at 120°C and 30 bar using tall oil fatty acid (TOFA) as reactor feed. Stearic acid preparation using TOFA as a raw material is of industrial importance. Pd/sibunit catalysts with spherical particle shape of the size 1.62 mm were synthesized with the palladium loadings 0.5, 1, and 2 wt %. The metal dispersion (%), metal particle size (nm), as well as metallic surface area (m2/g metal) of the three synthesized Pd/Sibunit samples were measured by CO chemisorption. The Pd/C catalysts were tested in linoleic acid hydrogenation, showing promising behavior in terms of activity, selectivity and stability to be used in fixed bed applications. The product stream from the fixed bed reactor was saved and analyzed by X-ray fluorescence (XRF) and direct current plasma (DCP) spectroscopy. The catalyst activity increased with the Pd loading. The lowest metal loading of 0.5 wt % gave the least prone to initial deactivation and thus the most stable catalyst. This catalyst can be recommended for farther pilot testing.

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.

Hydrogenation of Pentanoic Acid into Pentanol Over Ir and Ir-Re Catalysts: Effect of Support and Ir Dispersion

Liquid phase pentanoic acid hydrogenation in decane as a solvent (180 oC, hydrogen pressure 25 bar) was studied over monometallic Ir and bimetallic Ir-Re catalysts supported on alumina, ceria and zirconia, as well as carbon support Sibunit. Before catalytic test all catalysts were preliminary treated in Н2 at 415 oC during 5 h. An XPS study revealed predominant metallic state for Ir in studied catalysts while Re was partially oxidized. Conversion of pentanoic acid changed in the row Ir/CeO2 < Ir/ZrO2 < IrRe/ZrO2 < IrRe/Al2O3 ~ IrRe/C. Selectivity to pentanol was elevated over bimetallic catalysts in the sequence Ir/Al2O3 < Ir/CeO2 ~ Ir/ZrO2 < IrRe/ZrO2 < IrRe/Al2O3 ~ IrRe/C. It was shown that doping of Ir with Re gives a rise of pentanoic acid conversion and selectivity to pentanol in the absence of byside decarboxylation reaction. A series of the most active catalyst IrRe/Al2O3 was prepared varying Ir particle size from 0.8 to 1.7 nm as verified by TEM. Both pentanoic acid conversion and selectivity to pentanol over IrRe/Al2O3 catalyst increased with an increase of mean Ir particle size.

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.

Selectivity Analysis for Networks Comprising Consecutive Reactions of Second and First Order

Abstract Coupling of second and first order reactions in one pot fashion through a cascade process is an often encountered process. Consecutive reactions of this type are considered and selectivity analysis is performed demonstrating dependence of selectivity pattern on reaction parameters.

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.