Синтез та каталітична активність дисперсних оксидів мангану(ІV) в реакції розкладання озону
Вантажиться...
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