Синтез та каталітична активність дисперсних оксидів мангану(ІV) в реакції розкладання озону
Альтернативна назва
Синтез и каталитическая активность дисперсних оксидов марганца(ІV) в реакции разложения озона
Synthesis and catalytic activity of dispersed manganese(IV) oxides in the reaction of ozone decomposition
Synthesis and catalytic activity of dispersed manganese(IV) oxides in the reaction of ozone decomposition
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Файли
Дата
2017
Науковий керівник
Укладач
Редактор
Назва журналу
ISSN
E-ISSN
Назва тому
Видавець
Одеський національний університет імені І. І. Мечникова
Анотація
У роботі досліджено вплив способу отримання діоксиду мангану на його склад та каталітичну
активність в реакції розкладання озону. Методом рентгенофазового аналізу
встановлено, що зразки IS-Mn(1), IS-Mn(2) і ІІS-Mn напіваморфні, а зразок IІІS-Mn –
кристалічний та відповідає фазі криптомелану KMn8
O16. Каталітична активність оксидних форм мангану в реакції розкладання озону визначається фазовим складом і
збільшується в ряду: IS-Mn(1) < IIS-Mn < IIIS-Mn.
В работе исследовано влияние способа получения диоксида марганца на его состав и каталитическую активность в реакции разложения озона. Методом рентгенофазового анализа установлено, что образцы IS-Mn(1), IS-Mn(2) и ІІS-Mn полуаморфные, а образец IIIS-Mn – кристаллический и соответствует фазе криптомелана KMn8 O16. Каталитическая активность оксидных форм марганца в реакции разложения озона определяется фазовым составом и увеличивается в ряду: IS-Mn(1) < IIS-Mn < IIIS-Mn.
MnO2 samples were prepared via different procedures: (i) permanganate ion reducing with formic acid followed by the precipitate washing with cold (IS-Mn(1)) or hot (IS-Mn(2)) water, (ii) permanganate ion reducing with Mn2+ ion (IIS-Mn), and (iii) KNO3 and MnSO4 melting together (IІІS-Mn). It has been found by X-ray diffraction (XRD) method that, among Mn(IV) samples synthesized via above procedures, IS-Mn(1), IS-Mn(2), and ІІSMn are semiamorphous and only IIS-Mn contains ε-MnO2 and g-MnO2 phases. IІІS-Mn is crystalline and positions and intensities of its reflections in XRD patterns can be attributed to the cryptomelane, KMn8 O16, phase having a tunnel (2´2) structure with potassium ions in its channels. Using a Rietveld refinement, it has been determined that a size of cryptomelane crystallites is several times as much as sizes of the semiamorphous ε-MnO2 and g-MnO2 crystallites. As a result of testing the IS-Mn(1), IIS-Mn, and IІІS-Mn samples in the reaction of ozone decomposition at Cin O3 = 100 mg/m3 , it has been found that the reaction kinetics depends on the nature of the samples and their weights. Varying catalyst weight we draw a conclusion that an effective residence time, t¢, and a specific volume flow (wsp) of ozone-air mixture (OAM) also change. At the invariant linear velocity of OAM, the residence time increases because a height of the catalyst bed increases. Moreover, increasing the catalyst weight, we obtain a decrease in wsp. The increase in τ¢ leads to the increase in kinetic and stoichiometric parameters of the reaction for all samples under study. In the case of IIS-Mn and IІІS-Mn at the sample weight of 0.5 g, we failed to achieve the half-conversion of ozone, i.e. ozone concentration at the reactor outlet, Cf O3 , didn’t become equal to 0.5 Cin O3 , therefore, we stopped the experiments when Cin O3 attained 5 mg/m3 for IIS-Mn and 0.28 mg/m3 for IIISMn. Moreover, these samples have protective abilities: a time of protective action was 180 min for IIS-Mn and 1020 min for IIIS-Mn. Thus, the catalytic activity of manganese oxide forms in the reaction of ozone decomposition depends on their phase composition and crystallinity. Cryptomelane having a tunnel structure (2 × 2) shows the highest activity.
В работе исследовано влияние способа получения диоксида марганца на его состав и каталитическую активность в реакции разложения озона. Методом рентгенофазового анализа установлено, что образцы IS-Mn(1), IS-Mn(2) и ІІS-Mn полуаморфные, а образец IIIS-Mn – кристаллический и соответствует фазе криптомелана KMn8 O16. Каталитическая активность оксидных форм марганца в реакции разложения озона определяется фазовым составом и увеличивается в ряду: IS-Mn(1) < IIS-Mn < IIIS-Mn.
MnO2 samples were prepared via different procedures: (i) permanganate ion reducing with formic acid followed by the precipitate washing with cold (IS-Mn(1)) or hot (IS-Mn(2)) water, (ii) permanganate ion reducing with Mn2+ ion (IIS-Mn), and (iii) KNO3 and MnSO4 melting together (IІІS-Mn). It has been found by X-ray diffraction (XRD) method that, among Mn(IV) samples synthesized via above procedures, IS-Mn(1), IS-Mn(2), and ІІSMn are semiamorphous and only IIS-Mn contains ε-MnO2 and g-MnO2 phases. IІІS-Mn is crystalline and positions and intensities of its reflections in XRD patterns can be attributed to the cryptomelane, KMn8 O16, phase having a tunnel (2´2) structure with potassium ions in its channels. Using a Rietveld refinement, it has been determined that a size of cryptomelane crystallites is several times as much as sizes of the semiamorphous ε-MnO2 and g-MnO2 crystallites. As a result of testing the IS-Mn(1), IIS-Mn, and IІІS-Mn samples in the reaction of ozone decomposition at Cin O3 = 100 mg/m3 , it has been found that the reaction kinetics depends on the nature of the samples and their weights. Varying catalyst weight we draw a conclusion that an effective residence time, t¢, and a specific volume flow (wsp) of ozone-air mixture (OAM) also change. At the invariant linear velocity of OAM, the residence time increases because a height of the catalyst bed increases. Moreover, increasing the catalyst weight, we obtain a decrease in wsp. The increase in τ¢ leads to the increase in kinetic and stoichiometric parameters of the reaction for all samples under study. In the case of IIS-Mn and IІІS-Mn at the sample weight of 0.5 g, we failed to achieve the half-conversion of ozone, i.e. ozone concentration at the reactor outlet, Cf O3 , didn’t become equal to 0.5 Cin O3 , therefore, we stopped the experiments when Cin O3 attained 5 mg/m3 for IIS-Mn and 0.28 mg/m3 for IIISMn. Moreover, these samples have protective abilities: a time of protective action was 180 min for IIS-Mn and 1020 min for IIIS-Mn. Thus, the catalytic activity of manganese oxide forms in the reaction of ozone decomposition depends on their phase composition and crystallinity. Cryptomelane having a tunnel structure (2 × 2) shows the highest activity.
Опис
Ключові слова
оксид мангану(IV), рентгенофазовий аналіз, розкладання озону, оксид марганца(IV), рентгенофазовый анализ, разложение озона, manganese(IV) oxide, X-ray diffraction analysis, ozone decomposition
Бібліографічний опис
Вісник Одеського національного університету = Odesa National University Herald