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1
Content available Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation
Wiertel M., Surowiec Z., Budzyński M., Gac W.
Nukleonika
|
2015
|
Vol. 60, No. 4, part 1
783--787
EN
In this paper, results of positron annihilation lifetime spectroscopy (PALS) studies of MnFe2O4/MCM- -41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps) annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.
2
Content available Influence of annealing temperature on structural and magnetic properties of MnFe2O4 nanoparticles
Surowiec Z., Wiertel M., Gac W., Budzyński M.
Nukleonika
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2015
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Vol. 60, No. 1
137--141
EN
Nanoparticles of manganese ferrite were obtained by the impregnation of highly ordered mesoporous MCM-41 silica support. The investigated sample contained 20% wt. Fe. The obtained nanocrystallites were strongly dispersed in silica matrix and their size was about 2 nm. The sample annealing at 500°C led to increase of particle size to about 5 nm. The Mössbauer spectroscopy investigations performed at room temperature show on occurrence of MnFe2O4 nanoparticle in superparamagnetic state for the sample annealed in all temperatures. The coexistence of superparamagnetic and ferromagnetic phase was observed at liquid nitrogen temperature. The sample annealed at 400°C and 500 °C has bigger manganese ferrite particle and better crystallized structure. One can assign them the discrete hyperfi ne magnetic field components.
3
Content available Synthesis and characterization of iron - cobalt nanoparticles embedded in mesoporous silica MCM - 41
Surowiec Z., Wiertel M., Budzyński M., Gac W.
Nukleonika
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2013
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Vol. 58, No. 1
87-92
EN
Fe1.xCox/MCM-41 nanocomposite materials were prepared by wet impregnation of the silica mesoporous support with aqueous solution of iron and cobalt salt mixtures. Samples, after calcination, were reduced at 573 K in order to obtain homogeneous distribution of (Fe-Co)3O4 oxide species over the MCM-41 support. Bimetallic systems were achieved through high temperature reduction, carried out at 1073 K. The temperature-programmed reduction studies indicated complex nature of the oxide species. The phase analysis of the obtained samples after low temperature reduction process carried out by means of X-ray diffraction method and using 57Fe Mossbauer spectroscopy revealed the presence of nanostructured magnetite- and maghemite-like phases. The samples with higher cobalt contents (x . 0.2) contained additionally bimetallic phases. The complete transformation of oxide phases to bimetallic Fe-Co systems occurred during reduction process in hydrogen at 1073 K. It was observed that high temperature processing caused partial transformation of highly dispersed iron oxide nanocrystallites into fayalite species embedded in the silica walls.
4
Content available Positron annihilation studies of mesoporous iron modified MCM-41 silica
Wiertel M., Surowiec Z., Budzyński M., Gac W.
Nukleonika
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2013
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Vol. 58, No. 1
245-250
EN
MCM-41 silica materials modified by iron incorporation in the stage of its synthesis were investigated. The aim of the studies was determination of the nature of iron species and the influence of its content on the structural changes of materials and following the changes of their properties. For this purpose, the N2 sorption/desorption method and positron annihilation lifetime spectroscopy (PALS) were used. Disappearance of the longest-lived ortho-positronium (o-Ps) component (tau5) present in the PALS spectra of the initial MCM-41 material in the spectra of Fe-modified MCM-41 measured in vacuum is a result of a strong chemical o-Ps quenching and/or the Ps inhibition mechanism. Filling of pores by air or N2 at ambient pressure causes reappearance of the (tau5) component with lifetime shortened in comparison to that observed in vacuum for pure MCM-41 to the extent which can be explained by usual paramagnetic quenching in air. In contrary to the tendency observed for (tau5) lifetime which is practically independent of Fe content, the relevant intensity I5 monotonically decreases. This fact suggests that only inhibition of Ps formation occurs for the samples in air. Observed anti-quenching effect of air seems to be a result of competition of two processes : neutralization of surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by O2 molecules.
5
Content available An application of Mössbauer spectroscopy in the studies of iron - molybdenum silica mesoporous materials
Surowiec Z., Wiertel M., Marynowska A., Gac W., Zawadzki W.
Nukleonika
|
2013
|
Vol. 58, No. 1
137-141
EN
Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. Four samples with different metal contents relative to silica were investigated. Incorporation of iron and molybdenum ions in the synthesis stage led to structural changes of the MCM-41 support. With an increasing metals content, cylindrical pores of silica initially transformed into bottle-ink type pores, and then into the slit-like ones. Mössbauer spectroscopy investigations indicated that Fe ions were embedded in the silica walls and then formed nanosized crystallites in the pores. Superparamagnetic phase was observed at liquid nitrogen temperature.
6
Content available remote Badania modyfikowanych niklowych katalizatorów reformingu
Borowiecki T., Gac W., Gołębiowski A., Pańczyk M., Ryczkowski J., Stołecki K.
Przemysł Chemiczny
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2011
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T. 90, nr 10
1898-1903
7
Synthesis and Characterization of Bimetallic Ag-Mn-MCM-41 Materials
Deryło-Marczewska A., Gac W., Popivnyak N., Żukociński G., Pasieczna-Patkowska S.
Polish Journal of Chemistry
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2008
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Vol. 82, nr 1-2
263-270
EN
The series of mesoporous, bimetallic Ag-Mn-MCM-41 materials were synthesized by applying direct synthesis and ion-exchange methods. Their surface and structure characteristics were analyzed using nitrogen adsorption/desorption isotherms, XRD data, FT-IR/PA spectrometry, and temperature programmed reduction. The differences between the porous structure and the forms of metallic species formed in the structure and on the silica surface were found for the materials synthesized by direct synthesis and ion-exchange method.
8
Steam Reforming of Methane on the Ni-Re Catalysts
Borowiecki T., Denis A., Pańczyk M., Gac W., Stołecki K.
Polish Journal of Chemistry
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2008
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Vol. 82, nr 9
1733-1742
EN
The influence of rhenium on the properties of a commercial nickel catalyst in the steam reforming of methane was presented. The addition of Re up to 4 wt. % causes the in crease of the amount of chemisorbed hydrogen, dispersion of active phase, catalyst activity as well as its resistance to coking. The investigations show a good agreement be tween the resistance to coking obtained by the temperature-programmed reaction (TPReaction) and by the traditional thermogravimetric method. The obtained results are very interesting particularly concerning the increase in both activity and resistance to coking.
9
Content available remote Katalizatory palladowe na nośniku glinowym modyfikowanym jonami wapnia, lantanu i ceru do całkowitego utleniania metanu
Stasińska B., Gac W., Ioannides T., Machocki A.
Przemysł Chemiczny
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2006
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T. 85, nr 8-9
758-760
PL
Przedstawiono wyniki badań aktywności i stabilności termicznej katalizatorów palladowych w reakcji utleniania metanu. Badano katalizatory palladowe na nośnikach: glinowym i glinowym modyfikowanym jonami wapnia, ceru lub lantanu, otrzymanych metodą zol-żel. Katalizatory zawierające czysty tlenek glinu posiadają wysoko rozwiniętą powierzchnię, a wprowadzone modyfikatory powodują jej obniżenie w stopniu zależnym od metody suszenia prekursora nośnika. Wykazano, że katalizatory z modyfikowanymi nośnikami wymagają wyższych temperatur do całkowitego utlenienia metanu niż katalizatory z czystym nośnikiem glinowym, które okazały się dość stabilne termicznie.
EN
Pure Al2O3 and Ca, La, or Ce-modified Al2O3-supported 1% Pd catalysts were studied in a complete oxidn. of CH4. The supports were prepd. by the sol-gel method to have X/(X+Al) = 0.03 (X= La, Ce) or 0.333 (X = Ca) and impregnated with aq. Pd nitrate. The Ca, La, or Ce oxide added to alumina suppressed the activity of the Pd catalysts. The pure Al2O3-supported catalysts were highly active. CH4 was completely oxidized to CO2 at temps. precluding formation of NOx.
10
Content available remote Why does the activity of Pd/Al2O3 catalysts in the reaction of methane oxidation depend on the dispersion of palladium phase?
Machocki A., Stasińska B., Gac W.
Polish Journal of Chemical Technology
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2006
|
Vol. 8, nr 2
93-96
EN
The characterization of Pd/Al2O3 catalysts with varied dispersio of palladium phase, prepared with a chlorine-free precursor, with similar palladium loading and on the same support has been performed in order to identify the factors responsible for the variation of their activity in the oxidation of methane. The higher dispersion of the palladium phase decreases the temperatures necessary to achieve desired methane conversions. The rate (turnover number) of the reaction is higher on small crystallites up to 350°C, at higher temperatures the opposite relation is observed. Such dependences can result from the changes in the number of Pd-PdO active sites, and the different activity of the single active site may be attributed to the interaction between palladium phase crystallites and Al2O3 support. This interaction causes different redox properties of the small and large palladium phase crystallites, i.e.: (i) easier oxidation of palladium and stronger bonding of oxygen in small palladium oxide crystallites, (ii) easier donation of lattice oxide ions from the support to small palladium phase crystallites and (iii) their stabilization in a more oxidized state.
11
Content available remote The effect of thermal treatment on NiO-MgO-Al2O3 systems
Borowiecki T., Gac W., Grzegorczyk W., Denis A.
Polish Journal of Chemical Technology
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2004
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Vol. 6, nr 2
4-8
EN
The NiO-MgO-Al2O3 systems obtained by the deposition method are good precursors of coking resistant catalysts for natural gas (methane) conversion. The studies of the effect of high-temperature treatment in air or helium on the phase composition of catalysts, NiO reducibility and nickel dispersion are presented.
12
Content available remote Zastosowanie metod temperaturowo programowanych do charakteryzowania perowskitowych katalizatorów manganowo-lantanowych modyfikowanych srebrem i przeznaczonych do bezpłomieniowego spalania metanu
Machocki A., Loannides T., Stasińska B., Gac W., Denis A., Piasieczna S.
Przemysł Chemiczny
|
2003
|
T. 82, nr 3
216-220
13
Content available remote Promotowane katalizatory niklowe w reakcji reformingu parowego węglowodorów
Borowiecki T., Czubryt-Idzik M., Denis A., Gac W., Sikorska Cz., Gołębiewski A., Stołecki K.
Przemysł Chemiczny
|
2003
|
T. 82, nr 8-9
671-674
14
Content available remote Katalizatory Ni/MgO-Al2O3 w reakcji reformingu metanu z parą wodną i /lub ditlenkiem węgla
Pańczyk M., Gac W., Denis A., Sikorska Cz., Czubryt-Idzik M., Gołębiowski A., Stołecki K., Borowiecki T.
Przemysł Chemiczny
|
2003
|
T. 82, nr 8-9
748-751
15
Content available remote Zastosowanie metod temperaturowo-programowanych do badań katalizatorów reformingu parowego węglowodorów
Borowiecki T., Denis A., Gac W., Gryglicki J., Stasińska B.
Zeszyty Naukowe. Chemia / Politechnika Łódzka
|
1999
|
Z. 47
41-59
PL
Przedstawiono wyniki badań katalizatorów nilowych i niklowych promotowanych niewielkimi ilościami molibdenu, przeznaczonych do reformingu parowego węglowodorów, metodami temperaturowo-programowanymi. Zastosowanie TPR oraz TPD wodoru, amoniaku i pary wodnej pozwoliło na stwierdzenie różnic we właściwościach katalizatorów. Wprowadzenie dodatku Mo powoduje utrudnienia redukcji NiO, zwiększa ilość silnie wiązanego wodoru i pary wodnej, natomiast nie zmienia kwasowości nośnika.
EN
The paper presents the results of nickel catalysts without and with a molybdenum promoter used for steam reforming of hydrocarbons. The studies were performed with the temperature-programmed method. The use of TPReduction, TPDesorption of hydrogen, ammonia or steam enabled to find out the differences in the properties of catalysts. The introduction of Mo results in the decreasing of the NiO reduction rate, increasing the amount of strongly bonded hydrogen and steam but it does not change the support acidity.
16
Content available remote Temperaturowo-programowana redukcja katalizatorów FeCu/SiO2
Machocki A., Gac W., Gryglicki J., Czubryt-Idzik M.
Zeszyty Naukowe. Chemia / Politechnika Łódzka
|
1999
|
Z. 47
119-129
PL
W pracy omówiono przebieg redukcji nośnikowych katalizatorów żelazowo-miedziowych suchym i wilgotnym wodorem. Pełna efektywność promotującego działania miedzi zaznacza się już przy małych (5% w stosunku do ilości żelaza) zawartościach miedzi.
EN
Reduction of silica supported iron-copper catalysts is considered. TPR studies show that copper facilitates their reduction. This effect is seen under very low concentration of copper in catalysts.
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