Свойства на-несенных на θ-Al2O3 гетерополисоединений в процессе улав-ливания NOх по данным ИК- спектроскопии in situ

It was shown that carrying a small (up to 1%) amount of a heteropoly compound increases the adsorption of NOx as compared to the original carrier. The increase in adsorption is due to the oxidation of NO to NO2 on the carried heteropoly compound. The main adsorption factors are nitrite and nitrate complexes. Their place of localization is the carrier. As temperature increases, the complexes change to nitrates. The presence of ions of varying valencies in the composition of the Kegin anion reduces the strength of the bond of the nitrate complexes with the surface. The ions that are not in the Kegin anion increase the bond strength. The change in the strength of the bond of nitrates with the surface of the carrier is owned to the carrier modification, which results from disintegration of a part of the carried heteropoly compound.С использованием ИК-спектроскопии in situ в режиме термодесорбции проведено исследование механизма активации оксидов азота на массивных гетерополисоединениях, а также состава адсорбционных комплексов, места их локализации, стабильности, механизма взаимных превращений на нанесенных на θ-Al2O3 гетерополисоединениях. Показано, что нанесение небольшого (до 1%) количества гетерополисоединения увеличивает адсорбцию NOх по сравнению с чистым носителем. Увеличение адсорбции связано с окислением NO до NO2 на нанесенном гетерополисоединении. Основными формами адсорбции являются нитритные и нитратные комплексы, которые локализуются на носителе. С повышением температуры нитритные комплексы превращаются в нитратные. Присутствие ионов переменной валентности в составе аниона Кегина уменьшает прочность связи нитратных комплексов с поверхностью; ионы, не входящие в состав аниона Кегина, увеличивают прочность связи. Изменение прочности связи нитратов с поверхностью носителя происходит в результате модифицирования носителя за счет деструкции части нанесенного гетерополисоединения

Properties of heteropoly compounds carried on θ-Al₂O₃ in the capturing of NOx using infra red spectroscopy (in situ)

It was shown that carrying a small (up to 1%) amount of a heteropoly compound increases the adsorption of NOx as compared to the original carrier. The increase in adsorption is due to the oxidation of NO to NO2 on the carried heteropoly compound. The main adsorption factors are nitrite and nitrate complexes. Their place of localization is the carrier. As temperature increases, the complexes change to nitrates. The presence of ions of varying valencies in the composition of the Kegin anion reduces the strength of the bond of the nitrate complexes with the surface. The ions that are not in the Kegin anion increase the bond strength. The change in the strength of the bond of nitrates with the surface of the carrier is owned to the carrier modification, which results from disintegration of a part of the carried heteropoly compound

Axial Changes of Catalyst Structure and Temperature in a Fixed-Bed Microreactor During Noble Metal Catalysed Partial Oxidation of Methane

The catalytic partial oxidation of methane (CPO) over flame-made 2.5%Rh–2.5%Pt/Al2O3 and 2.5%Rh/Al$_2$O$_3$ in 6%CH$_4$3%O$_2$/He shows the potential of in situ studies using miniaturized fixed-bed reactors, the importance of spatially resolved studies and its combination with infrared thermography and on-line mass spectrometry. This experimental strategy allowed collecting data on the structure of the noble metal (oxidation state) and the temperature along the catalyst bed. The reaction was investigated in a fixed-bed quartz microreactor (1–1.5 mm diameter) following the catalytic performance by on-line gas mass spectrometry (MS). Above the ignition temperature of the catalytic partial oxidation of methane (310–330 °C), a zone with oxidized noble metals was observed in the inlet region of the catalyst bed, accompanied by a characteristic hot spot (over-temperature up to 150 °C), while reduced noble metal species became dominant towards the outlet of the bed. The position of both the gradient in oxidation state and the hot spot were strongly dependent on the furnace temperature and the gas flow (residence time). Heating as well as a higher flow rate caused a migration of the transition zone of the oxidation state/maximum in temperature towards the inlet. At the same time the hydrogen concentration in the reactor effluent increased. In contrast, at low temperatures a movement of the transition zone towards the outlet was observed at increasing flux, except if the self-heating by the exothermic methane oxidation was too strong. The results indicate that in the oxidized zone mainly combustion of methane occurs, whereas in the reduced part direct partial oxidation and reforming reactions prevail. The results demonstrate how spatially resolved spectroscopy can help in understanding catalytic reactions involving different reaction zones and gradients even in micro scale fixed-bed reactors