Прегледај по Аутор "Obrenović, Zoran"
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- СтавкаDobijanje prelaznih faza aluminijum-oksida polazeći od natrijum-aluminata primenom Bajerovog postupka(Association of the Chemical Engineers of Serbia, 2011) Obrenović, Zoran; Filipović, Radislav; Milanović, Marija; Stijepović, Ivan; Nikolić, Ljubica M.Polazni aluminijum-hidroksidni i aluminijum-oksihidroksidni prahovi za dobijanje prelaznih faza Al2O3 su dobijeni u postupku neutralizacije natrijum-aluminata, dobijenog u klasičnom Bajerovom postupku, 1 M rastvorom sumporne kiseline. U zavisnosti od koncentracije polazog rastvora, trajanja reakcije neutralizacije i pH rastvora, sintetisani su prahovi različitog faznog sastava, uglavnom višefazni, ali sa dominantnom fazom gibsita, bajerita ili bemita. Pored toga, različiti uslovi sinteze uticali su na dobijanje prahova različite morfologije i specifične površine. Posle termičke obrade prahova na 500 oC u trajanju od 30 min, u zavisnosti od njihovog polaznog sastava i morfoloških karakteristika dobijene su prelazne faze aluminijum-oksida i to η- i γ-Al2O3, specifične površine od 264 do 373 m2/g. Pri tome je pokazano da se zagrevanjem bajerit i pseudobemit transformišu u η-fazu, a gibsit u γ-fazu, zadržavajući morfologiju polaznog praha.
- СтавкаFlower-like boehmite nanopowders obtained at low temperature from Bayer liquor(University of Novi Sad, Serbia, 2020) Milanović, Marija; Obrenović, Zoran; Stijepović, Ivan; Nikolić, Ljubica M.Boehmite nanocrystalline powders were obtained by neutralization of Bayer liquor at 70 °C with addition of glucose. Temperature of the neutralization induced formation of the flower-like morphology of the nanopowders. XRD and FTIR results confirmed that the single phase boehmite is formed without any other impurities. Calcination at 500 °C led to the formation of transition y-alumina with the retention of the flower-like morphology. Both as-synthesised and calcined powders possessed high specific surface area with mesopores between 3–6 nm in diameter. Relatively low temperature of neutralization as well as the use of low cost and ecologically friendly glucose as a surfactant are very promising for the possible application in the industrial production of alumina nanopowders.
- СтавкаIon exchange of sodium with hydrochloric acid in ZSM-5 zeolite(Centre for Evaluation in Education and Science (CEON/CEES), 2021) Škrba, Milomirka; Obrenović, Zoran; Došić, Aleksandar; Gligorić, Miladin; Đurić, Biljana; Savić, IvanZSM-5 zeolites are highly silicate materials that have significant application in catalytic processes in petrochemistry, especially due to their high selectivity. Most reactions in the petrochemical industry are acid-catalyzed. The acidic properties of zeolite depend on the number of acid centers, i.e. the presence of hydrogen ions, and therefore, in this paper the possibility of reducing the sodium content in the pores of high silicate zeolite ZSM-5 with the modulus (SiO2 / Al2O3 = 1000) will be investigated, by applying ion exchange with hydrochloric acid. Chemical analysis of samples before and after ion exchange, and application of instrumental methods of X-Ray diffraction, FT-IR spectroscopy, and SEM analysis monitored the influence of the quantity of hydrogen ions on the chemical composition and the structure of ZSM-5 zeolite at different acid concentrations and at different exchange times. It has been shown that the application of ion exchange with hydrochloric acid can reduce the sodium content in zeolite. Even with the application of 5% HCl for 6 hours, the content of sodium in the zeolite is reduced by over 98%. A similar effect is achieved by applying more concentrated hydrochloric acid solutions for a shorter ion exchange time. By prolonging the ion exchange time, there are no significant changes in terms of the final ion exchange. On the other hand, the application of HCl solutions of higher concentrations leads to a slight decrease in the aluminum content in the zeolite, which may partially affect the structural stability of the zeolite. The results obtained by FT-IR and SEM analysis and X-Ray diffraction confirm the possibility of ion exchange with hydrochloric acid, without significant changes in the crystal structure of the zeolite.
- СтавкаNanocrystalline boehmite obtained at room temperature(Elsevier, 2018) Milanović, Marija; Obrenović, Zoran; Stijepović, Ivan; Nikolić, Ljubica M.The single phase nanocrystalline boehmite is obtained for the first time at room temperature by a facile hydrolysis of Bayer liquor. Mesoporosity in boehmite powders was constructed using the glucose as a template. As-synthesized boehmite powders have high surface area (above 350 m2/g) and the average crystallite size less than 5 nm. Through the thermal dehydratation at 500 °C, boehmite isomorphously transforms to γ-alumina retaining the lamellar morphology and mesoporosity of the parent phase.
- СтавкаThe effect of glucose on the formation of the nanocrystalline transition alumina phases(Elsevier, 2011) Obrenović, Zoran; Milanović, Marija; Djenadić, Ružica R.; Stijepović, Ivan; Giannakopoulos, Konstantinos P.; Perušić, Mitar; Nikolić, Ljubica M.Series of alumina powders were synthesized starting from sodium aluminate solution prepared from Bayer liquor. The neutralisation of sodium aluminate solution was performed with the use of sulphuric acid. The influence of glucose as a non-surfactant additive on the structure of alumina powders at moderate pH was investigated. The results show that the properties of the powders are influenced by the initial pH value of the solution, as well as the duration of the neutralisation step. High pHs lead to the formation of powders with heterogeneous structure with bayerite as a dominant phase, which during calcinations converts to h-alumina with high surface area. Addition of glucose to the starting aluminate solution leads to the formation of nanocrystalline boehmite with estimated average crystallite size less than 3 nm and high surface area (above 300 m2/g). After calcinations, boehmite transforms to g-alumina. The results have shown that during the heat treatment, structural transformations proceeded simultaneously with the significant changes in the textural properties of the obtained mesoporous g- and h-alumina powders
- СтавкаUticaj procesnih parametara na morfologiju i adsorpcione osobine nanokristalnog bemita(Association of the Chemical Engineers of Serbia, 2014) Obrenović, Zoran; Nikolić, Ljubica M.; Filipović, Radislav; Milanović, Marija; Stijepović, IvanDobijanje različitih prelaznih faza Al2O3 dobrih adsorpcionih osobina poslednjih decenija privlači veliku pažnju istraživača kako sa aspekta istraživanja tako i sa aspekta primene ovih materijala. Prelazne Al2O3 faze predstavljaju metastabilne polimorfne oblike alumine koje nastaju pri dehidrataciji aluminijum-hidroksidnih (gibsita i bajerita) ili aluminijum-oksihidroksidnih prahova (bemita). U ovom radu sintetisan je nanokristalni bemit polazeći od rastvora natrijum-aluminata, dobijenog u Bajerovom postupku. U procesu neutralizacije sumpornom kiselinom, podešavanjem procesnih parametara i dodatkom glukoze, dobijen je nanokristalni bemit, prosečne veličine kristalita ispod 5 nm i specifične površine iznad 360 m2/g. Za analizu faznog sastava, strukture i morfologije dobijenih prahova primenjene su sledeće metode: rentgenska difrakcija, XRD, Furije transformisana infracrvena spektroskopija, FT-IR, skenirajuća elektronska mikroskopija, SEM i niskotemperaturna adsorpcija azota. Rezultati su pokazali da je, bez obzira na uslove sinteze, a uz korišćenje glukoze, moguće dobiti nanokristalni bemitni prah, na relativno niskoj temperaturi. Pri tome je pokazano da karakteristike praha (struktura i morfologija) zavise od pH vrednosti polaznog rastvora kao i od vremena trajanja reakcije neutralizacije.