Jugoslav Krstić

Alumina/silica supported K2CO3 as a catalyst for biodiesel synthesis from sunflower oil.

The new type of catalyst for fatty acid methyl esters (FAME or biodiesel) synthesis with K(2)CO(3) as active component on alumina/silica support was synthesized using sol-gel method. Corresponding catalyst (xerogel) was prepared by 12h drying the wet gel in air at 300 degrees C, 600 degrees C or 1000 degrees C at atmospheric pressure. The catalysts activity in the methanolysis of sunflower oil was compared to the activity of the pure K(2)CO(3). The effects of various reaction variables on the yield of FAME were investigated. It was found that the temperature of 120 degrees C and methanol to oil molar ratio of 15:1, are optimal conditions for FAME synthesis with synthesized catalyst. Repeated use of same amount of catalyst indicated that effect of potassium leaching obviously existed leading to decrease of catalyst activity.

Kinetics of heterogeneous methanolysis of sunflower oil with CaO∙ZnO catalyst: Influence of different hydrodynamic conditions

The kinetics of heterogeneous methanolysis of sunflower oil was studied at 60°C using mechanochemically synthesized CaO∙ZnO as catalyst. Influence of agitation speed, catalyst amount and methanol to oil molar ratio on the rate of reaction was analyzed. The rate of the process depends on the two resistances - mass transfer of triglycerides to the catalyst surface and chemical reaction on the catalyst surface, which are defined as the values of the overall triglyceride volumetric mass transfer coefficient, kmt,TG, and the effective pseudo first-order reaction rate constant, k, respectively. These kinetic parameters actually determine the value of the apparent reaction rate constant, kapp, whose change with time is defined with the change of triglyceride (TG) conversion. The kinetic model was proposed and the model parameters determined. [Projekat Ministarstva nauke Republike Srbije, br. 45001]

Inorganically modified diatomite as a potential prolonged-release drug carrier

Inorganic modification of diatomite was performed with the precipitation product of partially neutralized aluminum sulfate solution at three different mass ratios. The starting and the modified diatomites were characterized by SEM-EDS, FTIR, thermal analysis and zeta potential measurements and evaluated for drug loading capacity in adsorption batch experiments using diclofenac sodium (DS) as a model drug. In vitro drug release studies were performed in phosphate buffer pH6.8 from comprimates containing: the drug adsorbed onto the selected modified diatomite sample (DAMD), physical mixture of the drug with the selected modified diatomite sample (PMDMD) and physical mixture of the drug with the starting diatomite (PMDD). In vivo acute toxicity testing of the modified diatomite samples was performed on mice. High adsorbent loading of the selected modified diatomite sample (~250mg/g in 2h) enabled the preparation of comprimates containing adsorbed DS in the amount near to its therapeutic dose. Drug release studies demonstrated prolonged release of DS over a period of 8h from both DAMD comprimates (18% after 8h) and PMDMD comprimates (45% after 8h). The release kinetics for DAMD and PMDMD comprimates fitted well with Korsmeyer-Peppas and Bhaskar models, indicating that the release mechanism was a combination of non-Fickian diffusion and ion exchange process.

Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Ni/SiO2 materials with identical composition (SiO2/Ni = 1.0) have been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO2 precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H2-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni2+-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni2+-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of high activity in the vegetable oil hydrogenation.

Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

The state of nickel in the silver modified NiMg/SiO2 vegetable oil hydrogenation catalysts

Two series of silver modified Ni-Mg materials were synthesized by precipitation-deposition on SiO2 support derived from two silica sources: diatomite activated at 800°C (Series a; Mg/Ni = 0.1 and SiO2/Ni = 1.07) and synthetic water glass (Series b; Mg/Ni = 0.1 and SiO2/Ni = 1.15). The modification with silver was made at three molar Ag/Ni ratios, namely 0.0025, 0.025, and 0.1. The effects of the source of the silica support and the silver presence and content on the nickel state in the silver modified reduced-passivated NiMg/SiO2 precursors of the vegetable oil hydrogenation catalyst were established by X-ray diffraction and X-ray photoelectron spectroscopy techniques. The passivation procedure was applied in order to protect the metallic nickel particles from further oxidation. The crystallization of the formed nickel hydrosilicate phases depends on the source of the silica support, more expressed in the diatomite supported samples. It was shown that the silver modification of the NiMg/SiO2 precursors enhances the reduction of the nickel hydrosilicates accompanied by formation of relatively smaller metallic nickel particles, more pronounced in the water glass supported precursors. The increase of the silver content in the water glass deposited samples is responsible for the metallic nickel dispersion increase. The higher content of the Ni0 particles on the surface of the diatomite deposited samples is in accordance with the higher stability of the larger metallic nickel crystallites to oxidation during the passivation step. On contrary, higher dispersed Ni0 particles on the surface of the water glass supported samples are more susceptible to the oxida

A study of the dispersity of iron oxide and iron oxide-noble metal (Me = Pd, Pt) supported systems

Samples of one-(Fe) and two-component (Fe-Pd and Fe-Pt) catalysts were prepared by incipient wetness impregnation of four different supports: TiO2 (anatase), γ-Al2O3, activated carbon, and diatomite. The chosen synthesis conditions resulted in the formation of nanosized supported phases—iron oxide (in the one-component samples), or iron oxide-noble metal (in the two-component ones). Different agglomeration degrees of these phases were obtained as a result of thermal treatment. Ultradisperse size of the supported phase was maintained in some samples, while a process of partial agglomeration occurred in others, giving rise to nearly bidisperse (ultra-and highdisperse) supported particles. The different texture of the used supports and their chemical composition are the reasons for the different stability of the nanosized supported phases. The samples were tested as heterogeneous catalysts in total benzene oxidation reaction.

Temperature dependence of catalytic cyclohexane partial oxidation in a polytetrafluoroethylene reactor

Polymer-supported Co(II) catalyst was prepared and its activity and selectivity in the partial oxidation of cyclohexane was determined at several temperatures in a polytetrafluoroethylene reactor (PTFE). The catalyst was characterized by means of SEM-EDX, FTIR, diffuse reflectance UV-Vis, N2 sorption, and mecury porosimetry. Activation energies were determined under steady state conditions for the net production of cyclohexanone and cyclohexanol and for cyclohexane and oxygen net consumption. Some activation energies were lower than the ones reported for the uncatalyzed process, indicating that the catalyst played an important role in the initiation of the free-radical reaction.

Supported Nickel-Based Catalysts for Partial Hydrogenation of Edible Oils

Nickel-based catalysts, supported on diatomite, silica gel and perlite, with high nickel loadings, have been prepared by precipitation-deposition method. Various nickel precursor salts were used for the preparation of catalyst precursors. In the precursor state, the catalysts were characterized using nitrogen physisorption, mercury porosimetry, infrared, and X-ray diffraction spectroscopy. The reducibility of catalyst precursors was evaluated using hydrogen temperature programmed reduction. Hydrogen chemisorption and X-ray photoelectron spectroscopy measurements were performed with the aim of characterizing the chemical state of the catalyst precursors. This research was focused on the study of some major factors on the state, dispersion and reducibility of a deposited Ni phase by the combined use of mentioned experimental techniques. We have examined the influence of the nature of support and the use of modifiers on activity of nickel-based catalysts in the partial hydrogenation of sunflower and soybean oils. Nitrogen physisorption and mercury porosimetry data showed that synthesis operating conditions and pore structure of supports have a profound effect on the textural properties of catalyst precursors. The analysis of infrared and X-ray diffraction spectra showed the existence of chemical species and phases which indicate the different extent of interaction between the support and the active metal. Temperature programmed reduction study revealed that the reduction features depend on the identity of the nickel precursor salt and its interaction with the support. A stronger interaction of the supported Ni phase with support hinders the reduction of catalyst precursors. Hydrogen chemisorption results showed the presence of nickel crystallites varying from 5 to 47 nm in size. The X-ray photoelectron spectroscopy data confirmed the formation surface species with different strength of interaction and different nickel crystallite sizes. The hydrogenation results showed significant differences, depending on the support and the modifier, as well as structural characteristics of reduced catalyst precursors. The results show the importance of modifiers in the control of the activity and selectivity of the partial hydrogenation

Perlite as a potential support for nickel catalyst in the process of sunflower oil hydrogenation

Investigation was conducted in order to elucidate the possibility of using perlite as support for preparation of nickel based precursor catalyst, potentially applicable in vegetable oil hydrogenation process. On three differently prepared expanded perlite, nickel catalyst precursors with identical Ni/SiO2 = 1.1 and Ni/Mg = 10/1 ratios were synthesized by precipitation-deposition method. Different techniques, SEM micrography, He-pycnometry, calcimetry, Hg-porosimetry, N2-physisorption, H2-chemisorption and temperature programmed reduction, were used for characterization of obtained samples. Determining the precursor texture, morphology and reducibility shows a successfully deposited nickel phase on perlite support with promising properties for vegetable oil hydrogenation. Chosen precursor was reduced and passivated in paraffin oil and the obtained catalyst showed significant catalytic activity in the test of sunflower oil hydrogenation.