Bulgarian Chemical Communications, Volume 50, Special Issue-H, 2018

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Physicochemical properties of monometallic Rh and Ni and bimetallic RhNi catalyst materials supported on unmodified and yttrium-modified alumina
Original Research Article
Pages 3 – 8
R. Palcheva, I. Shtereva, Y. Karakirova, G. Tyuliev, S. Damyanova
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The effect of Y2O3 addition to -alumina carrier on the structure and surface and reductive properties of supported monometallic Rh and Ni bimetallic RhNi materials was studied. Various techniques for physicochemical characterization were used, such as N2 adsorption-desorption isotherms, XRD, UV-vis DRS, XPS, EPR, and TPR. XRD, UV-vis DRS, and XPS results of calcined samples showed the presence of Ni2+ ions in different environment: octahedral and tetrahedral coordination. Well-dispersed yttrium and rhodium oxide species were detected. EPR and TPR data indicated a strong interaction between Ni and yttria, as revealed by higher temperature of reduction of nickel oxide species. Rh promoting effect on the reduction of Ni oxide species was related to hydrogen spillover effect of the noble metal.


Y-doped ceria-supported gold and palladium mono- and bimetallic catalystsfor complete propene oxidation
Original Research Article
Pages 9 – 16
P.Ts. Petrova, G. Pantaleo, A. M. Venezia, L. F. Liotta, Z. Kaszkur, T. T. Tabakova,L.I. Ilieva
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Monometallic Au and Pd as well as bimetallic Pd-Au particles deposited on Y-doped ceria supports were studied in complete propene oxidation (CPO), which was used as a probe reaction for aliphatic hydrocarbons abatement. Y-modified ceria supports (1 wt.% Y2O3) were prepared by impregnation and coprecipitation. Gold (3 wt.% Au) and palladium (1 wt.% Pd) containing samples were prepared by deposition-precipitation method. Bimetallic Pd-Au catalysts were prepared by adding palladium to already deposited gold. Catalyst samples were characterized by BET, XRD, TPR, and XPS techniques. In general, the catalytic activity in CPO did not differ significantly in the presence of Y dopant and because of synthesis method of mixed oxide support. Total propene conversion over gold catalysts was reached at 220 °C. Pd-based catalysts demonstrated a higher oxidation activity in comparison with Au-based samples showing 100% propene conversion at 200 °C. The lowest temperature of total propene oxidation of 180 °C was achieved over the bimetallic Pd-Au catalysts and long-term catalytic performance showed good stability with no loss of catalytic activity.


Silver-based catalysts for preferential CO oxidation in hydrogen-rich gases (PROX)
Original Research Article
Pages 17 – 23
S. Zh. Todorova, H. G. Kolev, M. G. Shopska, G. B. Kadinov, J. P. Holgado, A. Caballero
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Silver samples were prepared by impregnation of different supports (SiO2, CeO2, and MnO2) with aqueous solution of AgNO3. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed desorption of oxygen, high resolution SEM, in situ diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, and tested in the reaction of preferential CO oxidation in H2-rich gases. A 15%Ag/SiO2 sample pretreated in pure oxygen showed the best catalytic performance. It is suggested that oxidative pretreatment leads to the formation of surface and subsurface oxygen species, which rearrange the silver surface thus increasing significantly silver catalyst activity for CO oxidation in hydrogen-rich gases.


Structure and activity of M-Al layered double hydroxides in CO2 methanation reaction as function of the divalent metal
Original Research Article
Pages 24 – 33
M. V. Gabrovska, D. Crişan, D. A. Nikolova, I. Z. Shtereva, L. P. Bilyarska, M. Crişan, R. M. Edreva-Kardjieva
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The effect of divalent metal (Ni or Co) on the structure, phase composition, thermal stability, and reducibility of co-precipitated Al-containing layered double hydroxides (LDHs) as catalyst precursors for CO2 removal by methanation reaction was examined. The catalytic activity was estimated by varying reduction and reaction temperature and space velocity as well. It was observed that the divalent metal in Al-containing LDHs affects the crystallisation degree of the formed layered compounds, their specific surface area, and temperature of LDH decomposition with parallel phase transformation to resultant mixed metal oxides. It was found that Co2+ ions stabilised in CoAl2O4 spinel structure hampered their reduction to metal state, thus leading to deficiency of Co0 active metal surface phase. This phenomenon determined a low activity of Co/Al2O3 catalyst, especially at low reduction temperatures. In contrast, the interaction between Ni2+ and Al3+ ions resulted in generation of readily reducible Ni2+-O species, which favoured a higher activity of Ni/Al2O3 catalyst after reduction at the same temperatures. Spinel-type phases were formed at different temperatures as a function of the divalent metal and determined catalyst activity in the purification of H2-rich streams from traces of CO2 by methanation reaction.


Catalytic behaviour of nanostructured Ce-Mn oxide catalysts in ethyl acetate oxidation
Original Research Article
Pages 34 – 39
R. N. Ivanova, G. S. Issa, M. D. Dimitrov, T. S. Tsoncheva
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Ce-Mn mixed oxide catalysts were prepared by co-precipitation method and used as catalysts for complete oxidation of ethyl acetate. The influence of Ce/Mn ratio was in the focus of the discussion in close relation with their catalytic activity. The obtained materials were characterised by different techniques, such as nitrogen physisorption, XRD, UV-Vis, and temperature-programmed reduction with hydrogen. A higher specific surface area favouring a higher catalytic activity as compared with pure CeO2 and MnOx was established for all binary oxides. A strong effect of sample composition on dispersion and redox behaviour of the binary oxides was also found.


Biogenic iron-containing materials synthesised in modified Lieske medium: composition, porous structure, and catalytic activity in n-hexane oxidation
Original Research Article
Pages 40 – 48
M. Shopska, G. Kadinov, D. Paneva, I. Yordanova, D. Kovacheva, A. Naydenov, S. Todorova, Z. Cherkezova-Zheleva, I. Mitov
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Leptothrix genus bacteria were cultivated in Lieske medium modified by the presence of inorganic material. Two modifiers were used: a fibrous 0.3% Pd/mesoporous silica-alumina catalyst and a one-side anodic oxidised aluminium foil. Obtained biomasses (named LieskeV and LieskeA, respectively) were studied by the methods of infrared and Mössbauer spectroscopy, X-ray diffraction, nitrogen adsorption, and chemical analysis. Examination of fresh samples revealed that LieskeA contained γ-FeOOH, α-FeOOH, and Fe3O4, whereas LieskeV comprised γ-FeOOH, α-FeOOH, and γ-Fe2O3 of various ratios. Elemental analysis indicated 0.003% Pd and proved that some amount of the modifier is incorporated in the LieskeV material. Registered transformations in original (biogenic or chemical) iron oxide/hy-droxide phases after catalytic activity tests confirmed that LieskeV samples contained a larger amount of γ-Fe2O3 obtained from biogenic precursor, and some γ-FeOOH. LieskeV biomass was found to be more active in the reaction of n-hexane oxidation. This material also impeded incomplete oxidation to carbon monoxide. Despite very small amounts of palladium present in LieskeV samples, the latter process is probably assisted since palladium is an active catalyst for CO oxidation. Carbon monoxide oxidation in the case of LieskeV samples was stimulated by two components, which exhibit a certain activity in the studied process. Biogenic γ-Fe2O3 showed some intrinsic activity in CO oxidation and its dominance is a second reason for control of the incomplete hexane oxidation. A third feature of the Pd-modified samples, determining their relatively higher activity, is the presence of slightly larger pores that allow enhanced mass transfer of the reagents inside the catalytic particles.


Modification and characterization of iron-containing biogenic materials as catalysts for the reaction of CO oxidation
Original Research Article
Pages 49 – 55
T. M. Petrova, D. G. Paneva, S. Zh. Todorova, Z. P. Cherkezova-Zheleva, D. G. Filkova, M. G. Shopska, N. I. Velinov, B. N. Kunev, G. B. Kadinov, I. G. Mitov
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The present study is focused on the preparation of modified iron-containing biogenic materials and testing them as catalysts for the reaction of CO oxidation. Modification was performed by impregnation of biogenic material obtained in Lieske cultivation medium. Impregnation was done using solutions of palladium chloride, cobalt nitrate, and manganese nitrate. Samples were characterized by X-ray diffraction, infrared spectroscopy, and Mössbauer spectroscopy. XRD results revealed that the starting biogenic material was X-ray amorphous, however, the presence of mixtures of low-crystalline iron oxyhydroxides, goethite and lepidocrocite, could not be excluded. Heating of Pd- and Co-modified materials led to the formation of oxide phases of Co3O4, γ-Fe2O3, and α-Fe2O3. Infrared spectra confirmed metal oxyhydroxide complete transformation to metal oxides in thermally treated samples. Mössbauer spectra of samples preheated at 300 °C indicated that the formed materials had a low degree of crystallinity, which is a specific feature of highly dispersed oxide materials. Doublet components in the Mössbauer spectra are indicative of nanosized highly dispersed particles demonstrating superparamagnetic behaviour. A ferrite MnFe2O4 phase was formed during synthesis of Mn-modified sample. Mössbauer spectra recorded at the temperature of liquid nitrogen showed a decrease of doublet part, which is typical of iron oxide particles of sizes below 4–10 nm. All the prepared samples were active in the reaction of CO oxidation, most active being manganese-modified catalyst. A synergistic effect was proposed between iron and manganese oxide components. Sample analysis after catalytic tests by means of Mössbauer spectroscopy revealed no changes in phase composition and dispersion.


Levulinic acid esterification on SO3H-modified mesoporous silicas
Original Research Article
Pages 56 – 60
H. I. Lazarova, M. D. Popova, A. Szegedi, B. Likozar, V. Dasireddy, N. Novak-Tusar
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Ordered mesoporous SBA-15 silica and a nanosized KIL-2 material with textural mesoporosity were synthesised and modified with sulphonic groups. Functionalisation with SO3H groups was performed by a two-step procedure, in which mercapto-modified mesoporous silicas were obtained first in reaction with mercaptosilane followed by treatment in H2O2 to result SO3H-modified mesoporous silicas. Initial and SO3H-containing mesoporous materials were char-acterised by X-ray diffraction (XRD), N2 physisorption, TG analysis, and TPD of ammonia. The catalytic performance of the SO3H/SBA-15 and SO3H/KIL-2 catalysts was studied in levulinic acid esterification with ethanol. A sulphonic-functionalised SBA-15 mesoporous material showed a higher conversion of levulinic acid to ethyl levulinate.


Supported palladium containing perovskite catalysts for methane combustion
Original Research Article
Pages 61 –65
S. G. Stanchovska, D. N. Guergova, G. M. Ivanov, R. K. Stoyanova, E. N. Zhecheva, A. I. Naydenov
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Citrate solution method is very suitable for preparation of multielement perovskites in the form of powders and thin layers. In this study, we demonstrate the feasibility of the method for deposition of perovskite-based materials on conventional γ-alumina and industrial metal carriers. A perovskite-based entity of La(Co0.8Ni0.1Fe0.1)0.85Pd0.15O3 composition manifested a high catalytic activity in the methane combustion reaction. Preliminary data on the practical applicability of the perovskite-based material supported on monolithic VDM®Aluchrom Y Hf carrier are reported. Taking into account the high thermal stability of the catalytically active phase it is concluded that the prepared material can serve as a basis for further development of an effective technology for abatement of methane emissions.


Catalytic abatement of CO and VOCs in waste gases over alumina-supported Cu-Mn catalysts modified by cobalt
Original Research Article
Pages 66 – 73
E. N. Kolentsova, D. Y. Dimitrov, D. B. Karashanova, Y. G. Karakirova, P. Ts. Petrova, T. T. Tabakova, G. V. Avdeev, K. I. Ivanov
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Production of formaldehyde by selective oxidation of methanol is an important industrial process. The main by-products in the waste gases are CO and dimethyl ether (DME). Currently, rational design of new catalytic materials with improved efficiency in the removal of air pollutants is a topic of appreciable research. The aim of this study was to combine advantages of both Cu-Mn and Cu-Co catalytic systems by obtaining a new mixed Cu-Mn-Co catalyst of high activity and selectivity in the simultaneous oxidation of CO, methanol, and DME. XRD, TEM, EPR and TPR techniques were used to characterise prepared samples.


Hexane and toluene oxidation on LaCoO3 and YCoO3 perovskite catalysts
Original Research Article
Pages 74 – 79
M. Markova-Velichkova, Ts. Lazarova, G. Ivanov, A. Naydenov, D. Kovacheva
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Solution combustion technique was applied to prepare perovskite-type LaCoO3 and YCoO3 catalysts supported on α-Al2O3. X-ray diffraction and scanning electron microscopy were used for physicochemical and morphological char-acterisation of fresh and worked catalysts. Sample catalytic activity was studied with respect to complete oxidation of hydrocarbons (n-hexane and toluene). It was found that n-hexane is difficult to oxidise as compared to toluene. Reaction kinetics tests and experiments on so-called ‘depletive’ oxidation were conducted to establish reaction mechanism. Experimental results showed that Eley-Rideal and Mars-van Krevelen mechanisms were unlikely. The methods applied indicated that toluene complete oxidation on both catalysts proceeded via Langmuir-Hinshelwood mechanism by dissociative adsorption of oxygen, the reacting hydrocarbon and oxygen being adsorbed on different active sites. The result proved that lanthanum-containing samples exhibited a higher activity than yttrium catalysts. Different A-posi-tioned cations of perovskite catalysts are discussed about their effect on structural, morphological, and catalytic properties.


Nanosized mesoporous titania composites promoted with ceria and zirconia as catalysts for ethyl acetate oxidation: effect of preparation procedure
Original Research Article
Pages 80 – 86
G. S. Issa, M. D. Dimitrov, D. G. Kovacheva, T. S. Tsoncheva
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The aim of the current investigation was to develop a series of titania-based nanosized mesoporous binary materials promoted with Ce and Zr and to test them as catalysts for total oxidation of ethyl acetate. Metal oxide materials were synthesised by template-assisted hydrothermal approach and homogeneous precipitation with urea. The main aspect of the study was to find a relationship between preparation procedure and structure, texture, surface, and catalytic properties of the obtained materials. These materials were characterised by low temperature nitrogen physisorption, XRD, Raman and UV-Vis spectroscopy, and temperature-programmed reduction with hydrogen. The hydrothermal method enabled formation of mesoporous materials of better homogeneity as compared to urea-synthesised counterparts where certain microporosity was registered as well. Doping agents affected preparation procedures. Improved texture parameters of ZrTi binary oxides obtained by the hydrothermal technique facilitated their catalytic activity as compared to urea analogues. Just an opposite effect of preparation was observed for CeTi materials.


Synthesis, structure, and catalytic properties of SrFe12O19 hexaferrite
Original Research Article
Pages 87 – 92
K. V. Koleva, N. I. Velinov, I. G. Genova, T. S. Tsoncheva, V. S. Petkova
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M-type SrFe12O19 hexaferrites were synthesised by means of co-precipitation method followed by annealing at 600 °C and 850 °C. A portion of a sample, treated at 850 °C, was further subjected to high-energy ball milling for 1 and 5 hours. TG-DTG-DTA, X-ray powder diffraction, and 57Fe Mössbauer spectroscopy were used for samples characteri-sation. A well-crystallised SrFe12O19 hexaferrite phase and small amount of secondary hematite (α-Fe2O3) phase were observed after annealing at 850 °C. Changes in the structure and a decrease in crystallite size of SrFe12O19 from 47 nm to 22 nm were observed after one-hour ball-milling treatment. Prolongation of the milling time induced separation of hematite phase and the highest amount was achieved after 5 hours of treatment. All samples exhibited good catalytic activity and CO selectivity in methanol decomposition. Mössbauer study of catalytically tested materials demonstrated stability of the hexaferrite phase under reductive reaction conditions.


Mechanochemically assisted solid state synthesis and catalytic properties of CuWO4
Original Research Article
Pages 93 – 98
M. N. Gancheva, P. M. Konova, G. M. Ivanov, L. I. Aleksandrov, R. S. Iordanova, A. I. Naydenov
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The synthesis and catalytic properties of nanostructured copper tungstate have been investigated in this study. A mixture of CuO and WO3 at a molar ratio of 1:1 was subjected to intensive mechanical treatment in air using a planetary ball mill for different periods of time. Structural and phase transformations were monitored by X-ray diffraction analysis, differential thermal analysis, and infrared spectroscopy. Mechanochemical treatment promoted progressive amorphisation of the initial oxides. Full amorphisation was achieved after 7 h milling time and remained up to 20 h milling time. DTA measurements of amorphous sample showed that the crystallization temperature was 430 °C. A pure nanostructured CuWO4 phase was prepared after thermal treatment of amorphous phase at 400 °C. Nanostructured CuWO4 was tested in the reactions of complete oxidation of C1-C4 hydrocarbons and the highest temperature for 10% conversion (T10) was measured with methane. Repeated addition of one further carbon atom to the methane molecule led to a decrease in T10 by about 70 °C (from methane to propane) and further by 30 °C from propane to n-butane. Calculated apparent activation energies for the reaction of complete oxidation decreased from methane to n-butane, and this effect correlated with diminished strength of the weakest C-H bond of the corresponding hydrocarbon.


Mesoporous nanostructured TixSn1-xO4 mixed oxides as catalysts for methanol decomposition: effect of Ti/Sn ratio
Original Research Article
Pages 99 – 104

I. Genova, T. Tsoncheva, M. Dimitrov, D. Kovacheva
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The aim of the current investigation is to elucidate the impact of the Ti/Sn ratio in TixSn1-xO4 mixed oxides on their textural, structural, redox, and catalytic features. Mesoporous mixed oxides of different Ti/Sn ratio were synthesised by template-assisted hydrothermal technique. The obtained materials were characterised by a complex of physicochemical techniques, such as nitrogen physisorption, XRD, Raman, UV–Vis, FTIR, and TPR with hydrogen. Methanol decomposition to syngas was used as a test reaction. The catalytic activity of the binary materials was affected in a complicated way by their phase composition. The latter was improved due to an increase in material specific surface area and pore volume and strongly suppressed because of significant structural changes.


Synthesis, characterization and photocatalytic performance of brannerite-type LiVMoO6
Original Research Article
Pages 105 – 108
M. K. Milanova, R. S. Iordanova, M. N. Gancheva
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Crystalline LiVMoO6 with brannerite structure was synthesized by mechanochemically assisted solid-state synthesis. A mixture of Li2CO3; V2O5, and MoO3 of oxide 1:1:2 molar ratio was subjected to intense mechanical treatment for 10 min in air using a planetary ball mill (Fritsch-Premium line-Pulversette No 7) and zirconia vials and balls (5 mm in diameter). The mechanically treated mixture of the metal oxides was subsequently heated for 1 hour at 450 °C. XRD, Raman spectroscopy, and SEM investigations were performed to examine phase formation, local structure, and morphology of the obtained product. Preliminary mechanical activation of the reagents led to the formation of highly reactive precursor and annealing of the latter formed submicron-sized particles of LiVMoO6 with irregular shape, which were highly agglomerated. Photocatalytic results showed that adsorption of Маlachite Green dye (MG) on the LiVMoO6 surface is a prerequisite for its photodegradation. Degradation percentage of Маlachite Green in the presence of LiVMoO6 photocatalyst was about 70% after 210 min of UV irradiation time.


Properties of mechanochemically synthesised N-doped Fe2O3-ZnO mixed oxide
Original Research Article
Pages 109 – 119
N. G. Kostova, M. Fabian, E. Dutkova, N. Velinov, Y. Karakirova, M. Balaz
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This work reports synthesis and characterisation of N-doped Fe2O3-ZnO mixed oxide and the ability of this material to decolourise Methyl Orange organic dye in aqueous solution under visible light irradiation. The photocatalytic material was prepared using eco-friendly simple mechanochemical synthesis. The photocatalysts were characterised by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and electron paramagnetic resonance (EPR) methods as well as Mössbauer spectroscopy. XRD analysis showed that employed mechanochemical synthesis promoted changes in crystallite size. A lower band gap was observed. The lower band gap and an improved photocatalytic activity under visible light irradiation of the mechanochemically synthesised nitrogen-doped Fe2O3-ZnO mixed oxide were registered in comparison with ZnO. A lower intensity in the PL spectra of N-Fe2O3-ZnO confirmed better separation and lower electron-hole recombination rate and accordingly higher photodecolourisation performance than initial ZnO.


Mineralization of pharmaceutical drugs by ZnO photocatalysts under UV light illumination
Original Research Article
Pages 116– 121
N. Kaneva, A. Bojinova, K. Papazova, D. Dimitrov
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Zinc oxide films were obtained by simple suspension method through mixing commercial ZnO powder, ethanol, and polyethylene glycol. Samples were deposited with one and five layers by dip coating. Film efficiency was evaluated by decolourisation of the pharmaceutical drugs Paracetamol and Chloramphenicol. Drugs mineralisation kinetics in distilled water upon UV light illumination was studied as a model system for contaminated wastewater. Photocatalytic experiments with commercial ZnO powders (unannealed and annealed) were also investigated. The films and the powders were characterised by SEM, XRD, BET, and UV-vis spectroscopy. The effects of catalysts amount and annealing temperature were examined. ZnO showed higher photocatalytic efficiency in Paracetamol degradation as compared to that of Chloramphenicol.


Characterisation of mechanochemically synthesised N-doped TiO2
Original Research Article
Pages 122 – 129
N. G. Kostova, M. Fabian, E. Dutkova, M. Balaz, M. Shipochka
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N-doped TiO2 photocatalyst (P25-u) was prepared by combined mechanochemical/thermal synthesis. Urea was used as nitrogen source. Wet grinding experiments have been conducted on titanium dioxide P25 Degussa in a high-energy planetary mill. As-milled samples were calcined at 400 °C. The samples were characterised by X-ray diffraction (XRD), N2 adsorption-desorption isotherms, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL) analysis. XRD results showed that art of phase anatase transforms to rutile during wet milling. All XRD peaks were broadened indicating that the crystallite size was within the nanometre range. P25-u samples possessed lower SBET values than the initial P25 Degussa. Milling in the wet environment resulted in deterioration of the porous structure. A lower photoluminescence intensity of mechanochemically synthesised P25-tu samples in comparison with the initial P25 ones indicated a lower recombination rate of photoexcited electrons and holes. Estimated Ebg value for P25-u was 2.36 eV. This result suggests a possibility to apply as-prepared material as a photocatalyst in degradation process with visible light irradiation. Mechanochemically synthesised N-doped TiO2 samples using urea exhibited a higher decolourisation rate of Methyl Orange dye than the commercially available TiO2 Degussa powder under visible light irradiation.


Synthesis and investigation of composite photocatalysts on the base of nickel and zinc oxides
Original Research Article
Pages 130 – 134
K. I. Milenova, K. L. Zaharieva, S. V. Vassilev, S. S. Dimova, I. D. Stambolova, V. N. Blaskov
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Photocatalytic activities of NiO0.8ZnO0.2-ZnO samples obtained by precipitation from various starting materials (chlorides and nitrates) followed by thermal treatment at two different temperatures (450 °C or 650 °C) were compared. Powder X-ray diffraction and FTIR spectroscopy were used to characterize the investigated catalysts. Oxidative photodegradation of Malachite Green dye on NiO0.8ZnO0.2-ZnO catalysts over a period of 2 hours using UV light was studied. Photodegradation degree of the Malachite Green dye using NiO0.8ZnO0.2-ZnO obtained from chlorides and treated at 450 °C or 650 °C, are 89 and 86%, respectively. Samples from nitrate precursors calcined at 450 °C or 650 °C exhibited a higher photocatalytic degradation activity 99 and 94%, respectively.


Photocatalytic behaviour of NiMnO3/Mn2O3 materials for degradation of Malachite Green and Methylene Blue dyes under UV irradiation
Original Research Article
Pages 135 – 139
K. L. Zaharieva, K. I. Milenova, S. V. Vassilev, S. S. Dimova, I. D. Stambolova, V. N. Blaskov
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The present work describes a study of the photocatalytic behaviour of NiMnO3/Mn2O3 materials for degradation of Malachite Green (MG) and Methylene Blue (MB) dyes as model contaminants under UV light irradiation. Samples were prepared by precipitation using nickel and manganese acetates as starting materials and sodium hydroxide precipitant, and then thermally treated at a different temperature – 450 and 650 °C. Powder X-ray diffraction analysis and Fourier-transform infrared spectroscopy were applied to study phase composition and structure of synthesized NiMnO3/Mn2O3 samples. Photocatalytic measurements were carried out using MG or MB aqueous solution with starting concentration of 5 ppm. According to experiments using NiMnO3/Mn2O3 photocatalysts calcined at 450 and 650 °C the degree of degradation of Malachite Green and Methylene Blue dyes after 120 minutes was increased as follows: NiMnO3/Mn2O3, 450 °C, MB (10%) ˂ NiMnO3/Mn2O3, 650 °C, MB (13%) ˂ NiMnO3/Mn2O3, 650 °C, MG (67%) ˂ NiMnO3/Mn2O3, 450 °C, MG (78%). It was established that the NiMnO3/Mn2O3 samples showed a much higher photocatalytic ability for degradation of Malachite Green relative to Methylene Blue dye under UV illumination.


Investigations of abiotic and biotic materials based on iron oxyhydroxides for photocatalytic dеcolourization of dyes in aqueous solutions
Original Research Article
Pages 140 – 143
K. L. Zaharieva, M. G. Shopska, K. I. Milenova, R. Angelova, M. Iliev, G. B. Kadinov
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Photocatalytic ability of abiotic and biotic materials was investigated in the reaction of dеcolourization of Methylene Blue and Malachite Green dyes under UV illumination. Tests were carried out with aqueous solution of studied dyes at a concentration of 5 ppm. Biotic material containing lepidocrocite was synthesized by cultivation of Leptothrix genus of bacteria in a Sphaerotilus-Leptothrix group bacteria isolation medium (ICCL). A reference abiotic sample was prepared in a sterile ICCL not infected by bacteria. Photocatalytic efficiency of examined materials was compared with lepido-crocite synthesized by precipitation. Abiotic, biotic, and synthesized materials were studied by infrared spectroscopy. The biotic material demonstrated a higher photocatalytic activity in Methylene Blue dye dеcolourization than abiotic sample. In contrast, a higher dеcolourization degree for Malachite Green dye (83%) was determined using abiotic mate-rial in comparison with a biotic sample (70%). Synthesized lepidocrocite demonstrated a higher degree of dеcolouri-zation of Malachite Green dye (89%) in comparison with that of Methylene Blue dye for the same period of 120 minutes.


Enhancing the PMS activation ability of Co3O4 by doping with Bi and Mg
Original Research Article
Pages 144 – 150
V. V. Ivanova-Kolcheva, M. K. Stoyanova
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A series of Co-Bi and Co-Mg composite oxides were prepared by co-precipitation method and their catalytic activity for heterogeneous peroxymonosulphate (PMS) activation was investigated through Acid Orange 7 (AO7) degradation in aqueous solutions. The as-prepared catalysts were characterized by XRD, XPS, TEM, and ICP-OES. A significant increase in catalytic activity of Co3O4 by modifying with Bi and Mg oxides was registered. Composites with 50 wt.% Co3O4 content displayed the best catalytic activity by achieving complete removal of 50 mg dm–3 AO7 within 12–15 minutes under the reaction conditions of 0.1 g dm–3 catalyst and PMS/AO7 molar ratio of 6:1. The enhanced PMS activation functionality of the composite catalysts was ascribed to an increased amount of surface hydroxyl groups because of modifying with the basic oxides. Surface hydroxyls favoured the formation of a surface Co(II)-OH intermediate and thus the generation of sulphate radicals (SRs) from PMS was accelerated. АО7 degradation was found to follow first order kinetics. The quenching study clearly indicated that oxidative degradation of AO7 is a radical-involved process with SRs being the dominant radical species. The Co-Bi and Co-Mg composite oxides presented stable performance with minor cobalt leaching even under acidic conditions.


Green seed-assisted fly ash zeolitisation at room temperature
Original Research Article
Pages 151 – 155
B. Z. Barbov, Yu. A. Kalvachev
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Zeolite X has been successfully synthesised from fly ash produced by combustion of lignite coal at Maritsa Iztok 2 thermal power plant using a two-stage process: fusion with sodium hydroxide followed by hydrothermal treatment at room temperature. NaX zeolite crystallisation started later by decreasing NaOH amount. In order to optimise synthesis process a seed-assisted procedure was introduced. Preliminary synthesised zeolite X from pure chemicals was used as a seed material. On the one hand, seed addition affected synthesis direction to the desired zeolite structure (a monophase zeolite X product) and resulted in reduced synthesis time, but also reduced sodium hydroxide amount upon melting. In this way, zeolitisation may increase cost-effectiveness and eco-efficiency.


Preparation and application of nanosized zeolite as a carrier for a lipolytic enzyme
Original Research Article
Pages 156 – 160

M. D. Dimitrov, M. Guncheva, D. G. Kovacheva
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Porous inorganic materials have been extensively applied as enzyme carriers due to their high mechanic stability and high specific surface area, resistance to microbial attack, stability in organic solvents, and stability upon heating. In recent years, enzymes immobilised on nanosized materials have attracted scientist attention with regard to new emerging applications such as biosensing and medical diagnostics. This research aims to investigate the potential of a nanosized and mostly mesoporous zeolite (nano-Zeo) as a suitable carrier for lipase from porcine pancreas (PPL). For comparative purpose, a nanosized MCM-41 silica material with spherical morphology was studied. The latter was used as a starting material to prepare the nanosized zeolite by densification of the initial amorphous MCM-41 silica nanospheres in presence of a diluted solution of tetrapropylammonium hydroxide, the nanospheres being further transformed into MFI-type of zeolite via steam-assisted crystallisation. Both the starting material and the nano-Zeo particles were characterised by means of X-ray diffraction, nitrogen physisorption, and scanning electron microscopy techniques. Loaded protein amount was comparable for the two carriers: 64.0±2.3 and 80.4±3.4 mg/g for MCM-41 and nano-Zeo, respectively. However, nano-Zeo showed over twofold higher specific loading with regard to the mesoporous specific surface area of the studied materials. Besides, monolayer surface distribution and a higher specific lipase activity were estimated for the nano-Zeo-PPL preparation, which is probably due to lipase molecules attached in a proper orientation.


Improved catalyst performance of Ni/SiO2 in vegetable oil hydrogenation: impact of Mg dopant
Original Research Article
Pages 161 – 168
M. V. Gabrovska, D. A. Nikolova, J. B. Krstić, D. R. Loncarević, P. T. Tzvetkov, M. G. Shopska, V. D. Radonjić, M. V. Stanković, D. M. Jovanović, L. Т. Spasov1, D. B. Simeonov
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Mg-doped co-precipitated Ni/SIG precursors were studied as edible sunflower oil hydrogenation catalysts applying two types of commercial silica gels (SIG) as supports of different texture characteristics: a microporous type (SIG-A) and a mesoporous type (SIG-C). It was found that texture parameters of both the silica gels and magnesium addition allow obtaining of catalysts of various hydrogenation activities and fatty acid composition of the products. The results reveal the highest hydrogenation activity of MgNi/SIG-C catalyst because of higher amount and accessibility of metal nickel particles on the catalyst surface generated through reduction procedure. A dominant activity of MgNi/SIG-C catalyst is ascribed to appropriate mesoporosity, which controls diffusion. It was established that Mg-doped Ni/SIG-C possessed a capacity for use as an efficient edible vegetable oil hydrogenation catalyst due to high hydrogenation activity, high saturation level of linoleic acid (C18:2cis), moderate amounts of C18:1trans fatty acids, and C18:0 stearin acid formation in the partially hydrogenated sunflower oil.


Synthesis of polyphenylacetylene by iron(III) chloride catalyzed carbonyl olefin metathesis polymerization of chalcone
Original Research Article
Pages 169 – 173
H. Penchev, S. S. Dimova, K. L. Zaharieva, F. S. Ublekov, Ch. Novakov, V. Sinigersky
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Carbon-carbon bond formation is a fundamental reaction in organic synthesis, one of its most important applications being synthesis of polymers and copolymers. Studies of the olefin metathesis reaction have resulted in extensive knowledge regarding synthesis of molecules applied in agricultural, petroleum, and pharmaceutical industries. The most commonly used catalysts for this purpose are ruthenium, molybdenum, and tungsten-based complexes.
Recently, Ludwig et al. have successfully conducted iron(III)-catalysed carbonyl-olefin metathesis reaction for synthesis of low molecular weight compounds.
In this study, we demonstrate for the first time that the carbonyl-olefin metathesis reaction, catalysed by anhydrous iron(III) chloride, can also be effectively applied in polymerization mode by using a single bifunctional monomer as chalcone. Polymerization was performed in a simple and efficient way under mild reaction conditions in solvents of various polarity, such as 1,2-dichloroethane and toluene. The average molecular mass of the synthesized oligomers reached 5000 g.mol−1, which was higher than reference values so far reported. In situ doping of the as synthesized polyphenylacetylenes with FeCl3 represents another advantage of selected synthetic approach.
Obtained products were characterized by gel permeation chromatography, 1H NMR, and FTIR spectroscopy. The structure of the obtained oligomers was studied by X-ray diffraction analysis..


Adsorption of thiophene and its polyaromatic derivatives from model fuel on pyrolyzed rice husks: kinetics and equilibrium
Original Research Article
Pages 174 – 180
S. A. Uzunova, I. M. Uzunov, I. R. Ivanov, D. B. Angelova
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Kinetics of fuel adsorptive desulphurisation was studied using a model fuel containing thiophene, benzothiophene, and dibenzothiophene of initial total sulphur content (Sin) of 415, 218, and 111 wppm over pyrolyzed rice husks (PRH) under batch mode conditions. Total sulphur content was determined by X-ray fluorescence analysis. Second order kinetics, intraparticle diffusion model, and Elovich equation were used to analyse kinetic data. It was found that a second-order kinetics model adequately described adsorption of the three sulphur compounds on pyrolyzed rice husks. The equation provided the best fit between calculated and experimentally determined values of adsorption capacity. Value differences varied between 1.3% for Sin 111 ppm and 5.9% for Sin 415 ppm. Adsorption affinity of the three sulphur compounds as well as equilibrium adsorption capacity of pyrolyzed rice husks were investigated by deter-mination of adsorption isotherm. Analysis of experimental data was conducted by using the isotherms of Langmuir, Temkin, and Freundlich. Data from multiple linear regression analysis pointed out that Freundlich isotherm described most adequately the adsorption equilibrium of polyaromatic sulphur heterocycles in the system fuel/PRH..


Study of Fe3Mo3N catalyst for ammonia decomposition
Original Research Article
Pages 181 – 188
S. F. Zaman, L. A. Jolaloso, A. A. Al-Zahrani, Y. A. Alhamed, S. Podila, H. Driss, M. A. Daous, L. A. Petrov
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A novel synthesis route, using citric acid as a chelating agent, for the preparation of high surface area γ-Mo2N and Fe3Mo3N bulk samples and their application as catalysts for hydrogen production via NH3 decomposition reaction were investigated. Successful formation of high surface area pure bulk phase of Fe3Mo3N (SBET = 24.9 m2 g‒1) was confirmed by using XRD, XPS, SEM-EDX, and HRTEM techniques. The Fe3Mo3N catalyst showed moderate catalytic activity for ammonia decomposition reaction. It demonstrates 100% conversion of NH3 at 600 °C at 6000 h‒1 GHSV. At lower reaction temperatures the Fe3Mo3N catalyst has higher catalytic activity than γ-Mo2N.


DRIFT study of the mechanism of methanol synthesis from CO2 and H2 on CeO2-supported CaPdZn catalyst
Original Research Article
Pages 189 – 195
A. S. Malik, S. F. Zaman, A. A. Al-Zahrani, M. A. Daous, H. Driss, L. A. Petrov
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This article reports results of mechanistic DRIFTS study of methanol synthesis from CO2 and H2 on CaPdZn/CeO2 catalyst. The catalyst exhibited superior catalytic performance with ~100% selectivity to methanol and 7.7% conversion of CO2 at 30 bar and 220 °C. In situ DRIFTS measurements were carried out under experimental conditions and the presence of various surface reaction intermediate species and their subsequent conversion to methanol were carefully monitored. The catalyst was characterised by BET, CO chemisorption, CO2-TPD, and HRTEM to evaluate the physiochemical properties and structure morphology of fresh and spent samples. DRIFTS investigation confirmed the formation of mono- and bidentate formates, CH2O, and CH3O intermediate species suggesting that the reaction mechanism follows formate pathway for the synthesis of methanol from CO2 hydrogenation over CaPdZn/CeO2.


Ionic gold and catalytic activity of gold catalysts for CO oxidation
Original Research Article
Pages 196 – 200
A. M. Ali
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This study is aimed to investigate the catalytic activity of freshly prepared gold catalysts supported on three metal oxide supports CeO2, ZrO2 and mechanically mixed CeO2+ZrO2 (DOS) for the CO oxidation under atmospheric pressure. The catalytic activity of both Au/CeO2 and Au/DOS were nearly the same and far higher than that of an Au/ZrO2 sample. The higher catalytic activity of both the Au/CeO2 and Au/DOS catalysts is attributed to the presence of Au+1 and Ce+4 ions as well as to enhanced CeO2 oxygen mobility in the presence of ZrO2..


A DFT study of ammonia dissociation over Mo3N2 cluster
Original Research Article
Pages 201 – 208
S. F. Zaman
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Density functional theory (DFT) calculations were performed to generate the potential energy surface of ammonia decomposition over a Mo3N2 cluster by investigating elementary surface reaction steps of the dehydrogenation pathway of NH3. Ontop adsorption of NHx (x = 0‒3) species over an Mo atom was found to be the most favourable adsorption arrangement. The rate limiting step for NH3 dissociation was the abstraction of the 2nd hydrogen according to the following surface elementary reaction (NH2*ad → NH*ad + H*ad) with an activation energy of 41.2 kcal/mol and an endothermic heat of reaction of 28.05 kcal/mol. The Nitrogen dissociation energy 35.19 kcal/mol over the cluster is much higher than over the Ru(0001) surface.


Rapid synthesis of (3-bromopropyl)triphenylphosphonium bromide or iodide
Original Research Article
Pages 209 – 212
S. I. Minkovska, N. T. Burdzhiev, A. A. Alexiev, T. G. Deligeorgiev
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A novel rapid method for the preparation of (3-bromopropyl)triphenylphosphonium bromide was developed. The synthesis was accomplished by microwave irradiation of 1,3-dibromopropane with triphenylphosphine at a ratio of 1:1 for 2 minutes in xylene or toluene or without any solvent. The target compound was isolated in good yield (81−93%) and high purity.