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  • 70 Reads
Quantum-chemical study on the role of alkyl chloride Zr,Al-complexes in stereoselective alkene oligomerization

Catalytic reactions of alkene di-, oligo- and polymerization provide a variety of highly demanded products, which structure depends on the type of catalytic system. Currently, a large number of catalytic systems have been proposed, including those based on zirconocenes and organoaluminum compounds. These systems are characterized by high activity and stereoselectivity, in this regard, the establishment of the reaction mechanisms remains an urgent problem.

To identify the factors that determine the stereoselectivity of the alkene oligomerization, catalyzed with Zr complexes, in this work, we performed a series of calculations to determine the thermodynamic and activation parameters of two successive stages of propene insertion into alkyl chloride bimetallic complexes L2ZrМеCl-AlMe3 (where L2 = Cp2, Ind2, Me2SiInd2), which could be considered as catalytically active sites of the reaction. The calculations were carried out using the PBE/3ζ quantum-chemical method (Priroda 6). For comparison, similar reactions were studied with the participation of the [L2ZrR+] cation. In addition, the modeling of the chain termination stage was carried out taking into account the possibility of β-H elimination and the formation of vinylidene oligomers. Comparative analysis of the energy parameters of the reactions made it possible to determine the relationship between the structure of active sites and the properties of the catalytic system

Acknowledgment: The studies were performed with the use of the equipment of Collective Usage Centre “Agidel” of Ufa Research of Russian Academy of Science at the Institute Petrochemistry and Catalysis (АААА-А19-119022290004-8). This work was supported by the Russian Science Foundation, grant 19-73-10122.

  • Open access
  • 135 Reads
A multi-modular family 9 glycoside hydrolase (GH9) enzyme of Clostridium alkalicellulosi

Clostridium alkalicellulosi DSM17461T is a mesophilic bacterium that can grow on different carbohydrates. The draft genome sequence of this microorganism reveals several glucoside hydrolase encoding genes that are important for cellulose degradation. In this study, the gene encoding a multi-modular family 9 glycoside hydrolase (GH9) enzyme was successfully expressed. This enzyme contains GH9 catalytic module, family 3 carbohydrate binding module, and type I dockerin at its C-termini, and we designated this enzyme as CalGH9A. The enzyme actively hydrolyzed carboxymethyl cellulose (CMC) and was able to hydrolyze regenerated amorphous cellulose (RAC) with prolong incubation (3 h) Interestingly, incubation of CalGH9A with beechwood xylan (BWX) for 16 h showed release of reducing sugar. The optimum pH and temperature for CalGH9A to hydrolyze CMC, RAC, BWX were 6.0 and 55 °C. The ability of CalGH9A to generate a series of cello-oligomers (G2-G6), suggesting that the enzyme has an endo-acting capability. The hydrolysis products from regenerated amorphous cellulose (RAC) were cellotriose (a major product), cellobiose, and glucose. CalGH9A showed higher Vmax and lower Km against CMC than those against BWX, suggesting CalGH9A is an endo-glucanase. CalGH9A resisted to several metal ions such as Mn2+, Fe2+, Co2+, Fe3+, Ni2+, Urea, and EDTA; however, Zn2+ and Cu2+ inhibited its activity. CalGH9A showed good tolerance to various concentrations of NaCl and was stable at high NaCl concentrations (10% w/v).

  • Open access
  • 47 Reads
Palladium cyclometallated compounds: evaluation of their catalytic activity in cross-coupling reactions

Catalysts are substances that can increase the speed of a chemical reaction and have been widely used in the chemical industry. Palladium is one of the most popular metals in catalysis, and many palladium complexes have been extensively used, in particular, in cross-coupling reactions with carbon-carbon bond formation. Their possible applications as catalysts, along with their uses in biological assays as anticancer agents makes the palladium family of complexes a very interesting and studied one, where the numerous changes in the ligands allows to greatly modulate their properties.

Herein we report the synthesis of several palladium cyclometallated compounds with thiosemicarbazone ligands and bis(diphenylphosphino)methane (dppm). Also, their catalytic activity in the Suzuki-Miyaura cross-coupling reaction will be evaluated, by using 4−bromoacetophenone and phenylboronic acid as reagents; the reaction being monitored by 1H NMR spectroscopy. A final comparison between the catalytic conversions and the complexes allows to choose the optimal structure.

  • Open access
  • 220 Reads
Fluorine ions in photocatalysts’ synthesis: an obstacle or an ally? The investigation of photocatalysts in Ti-O-F system

Titanium(IV) oxide (TiO2) is one of the most promising photocatalysts, which is expected to be applied in the photocatalytic degradation of xenobiotics. For sustainable development and green chemistry approach recently, much effort has been paid to enhance TiO2 photocatalytic activity in UV-vis light by modifying its structure. The photocatalytic process’s complexity cannot be simply described as electron-hole pairs generations and •OH formation; therefore, the interaction between the surface structure of photocatalyst and reactant molecules needs further investigation. The surface chemistry and morphology of TiO2 are crucial factors that can affect its photocatalytic performance by influencing the selective adsorption and photocatalytic oxidation of substrates.

In this regard, considering the strong complexation between F- and Ti and the high electronegativity of fluorine, the present study focused on Ti-O-F photocatalytic system. An advantage of introducing fluorine compounds inside the reaction system is the stabilization of thermodynamically unfavoured {0 0 1} facets, which are described as more active than other TiO2 facets with defined morphology.

The obtained results for anatase nanosheets with exposed {0 0 1} facets have shown that a higher amount of surface fluorine enhances the photocatalytic degradation of phenol and its mineralization. This observation can be explained by F atoms influencing the surface charge distribution and raising charge separation in the 2D structure of TiO2. Meanwhile, samples with a lower F/Ti ratio on the surface and the presence of Ti3+ exhibited lower photocatalytic activity.

On the other hand, titanium oxyfluoride (TiOF2) used as a precursor for the synthesis of 2D TiO2 had a negative effect on phenol photocatalytic degradation and TOC mineralization. In this case, fluorine ions could induce the surface formation of nonstoichiometric TiO2−x, which decreased photocatalytic activity of TiO2 particles with exposed {0 0 1} facets.


The research was financially supported by the Polish National Science Centre (grant no. NCN 2018/30/E/ST5/00845).

  • Open access
  • 179 Reads
UV LED - based photocatalytic oxidation of selected VOCs
  • We investigated a photocatalytic process to oxidize volatile organic compound (VOC) vapors. The photocatalytic process utilized ultraviolet (λ=365 nm) light emitting diodes (UV-LEDs) as light sources and photocatalytic (TiO2) films coated on the inside surfaces of the reactor. These reactor systems can be applied to mobile and niche applications. UV-LEDs are small, robust light sources that require low direct current (DC) power, which could be provided by a battery. The study results include the design, construction, and demonstration of a lab-scale UV-LED-based photocatalytic system that is capable of reducing or eliminating VOC vapors in air. Test results have demonstrated the sensitivity of the effectiveness of the UV-LED-based photocatalytic system on operating parameters, including flow rate, concentration, type of VOC, humidity, and longevity.
  • Open access
  • 54 Reads
New in the catalytic synthesis of practically important eight- and nine-membered carbocycles by cycloaddition reactions with the participation of 1,3,5-cycloheptatrienes and 1,3,5,7-cyclooctatetraenes

The data obtained by the authors in the field of chemistry of 1,3,5-cycloheptatrienes and 1,3,5,7-cyclooctatetraenes with the participation of complexes of transition metals are summarized. The reactions of cyclocodimerization of 1,3,5-cycloheptatrienes and 1,3,5,7-cyclooctatetraenes with alkenes, dienes and alkynes in the presence of transition metal complexes, carried out by the type of [6π + 2π] - and [4π + 2π] -cycloaddition, are considered. Special attention is paid to the application of these reactions in the synthesis of practically important bi-, tri- and polycyclic strained compounds, as well as in the development of stereoselective methods for the synthesis of natural compounds.

  • Open access
  • 63 Reads
The various types of acetaldehyde adsorption on clean, and on modified Rh(111) surface

The capture, the transformation of CO2 into C1 and into C2 compounds is environmentally and economically important issue. Noble metals, including Rh, are effective catalyst in the synthesis of CO+H2 into C2-oxygenates [1]. Acetaldehyde, (AA) is also important as a hydrogen carrier as it could be an easy H2 storage, carrier compound. In addition, AA has been found as a product also in the decomposition of ethanol on metal surfaces [2]. The interaction of CH3CHO with Rh(111) surface has been investigated by AES, EELS, TDS and work function methods [3]. The chemisorbed acetaldehyde (adsorbed at 100 K ) starts to decompose at 200 K. The main products are adsorbed CO and desorbed CH4 (Tp=260K ). Minor products are adsorbed H and C. A weakly adsorbed CH3CHO desorbs in a sharp peak centered at 150 K. Oligomerised acetaldehyde was also found ( [CH3CHO]n+ , 1<n<5 ) in the gase phase with Tp=225-235 K. In the chemisorbed layer 1-(O)-CH3CHOa and 2-(O,C)-CH3CHOa have been observed. Electronegative and electro positive modifiers may influence the stability of these surface complexes such as i.) surface carbon acts as a simple contaminant and decreases the adsorption of CH3CHO by site blocking mechanism. ii) a direct surface reaction with oxygen led to the formation of acetate. iii) adsorbed potassium increased the thermal stability of acetaldehyde by an extended electronic interaction. The electronic transfer from potassium to the AA orbitals can be suggested as it was obtained in the interaction of K with HCOOH on Rh(111) [4].


[1] A. Kiennemann, R.Breault, J-P. Hinderman, M. Laurin; Chem. Soc. Faraday Trans. 1 1987 83, 2119

[2] Z. Ferencz, A. Erdőhelyi, K. Baán, A. Oszkó, L. Óvári, Z. Kónya, C. Papp, H-P. Steinrück, J. Kiss; ACS Catal. 2014, 4, 1205-1218

[3] I. Kovács, A. P. Farkas, Á. Szitás, Z. Kónya, J. Kiss; Surf. Sci. 2017, 664,

[4] I. Kovács, J. Kiss, Z. Kónya; Catalysts 2020, 10, 675

  • Open access
  • 61 Reads
Cu/ACx catalysts. Effect of the acid functionalization of the support on the metal-support interaction.
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Commercial activated carbon (AC) was subjected to acid functionalization, with a strong acid, HNO3 (AC80 and AC90), and a weak acid, C6H8O7 (ACC). The objective was to modify the surface acid-base characteristics of AC and study its effect on dispersion, metal domain size and metal-support interaction, when copper was added. Cu deposition was carried out by recirculation by impregnation of an alcoholic solution of Cu(NO3)2*3H2O. Supports and catalysts were characterized by XRD, SBET, SEM-EDS, AAS, Isopropanol Decomposition Test, Temperature Programmed Reduction and Dissociative Adsorption of N2O. The functionalized supports showed a higher content of oxygenated functional groups (OFG), of the carboxylic, phenolic and lactonic types, than AC; being higher for AC80 and AC90. The distribution of total acid/base sites showed the same trend. SBET decreased slightly as a consequence of the addition of GFO and/or Cu. The Cu content was higher in the functionalized supports, observing a uniform Cu distribution (elemental mapping). From XRD Cuo and Cu2O for Cu/AC80 and Cu° for Cu/AC90 were identified; while for Cu/ACC no Cu phase was identified. The self-reduction of Cu2+ to Cu+ and Cuo is directly associated with the content and type of OFG present on the surface of the support. Cu/AC80 and Cu/AC90 showed a greater reduction than Cu/ACC, associated with the greater interaction with the surface of the support, in line with the phases identified by XRD. Additionally, these two catalysts presented the smallest metallic domain sizes of Cu (3.3 nm and 4.5 nm), while for Cu/ACC it was 5.8 nm.

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