Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

© 2014 Pleiades Publishing, Ltd. Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes

Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

© 2014 Pleiades Publishing, Ltd. Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes

Deactivation of industrial alumina catalyst for the skeletal isomerization of n-butenes

The reasons for deactivation of alumina catalyst during the skeletal isomerization of n-butenes, reducing conversion from 31 to 26%, are investigated. It is shown that contamination with metal Fe and Mg microimpurities lowers n-butene conversion in total by approximately 2.5%. The catalyst's activity can be restored by washing out metal microimpurities. Water vapor and feedstock pipelines turn out to be the source of metal impurities. The δ-modification of alumina accumulates during catalyst operation, reducing n-butene conversion by ̃3 abs % and creating an irreversible type of deactivation. The drop in the tempera-ture of phase transition in the presence of Fe and Mg microimpurities is one possible reason for the partial phase transition at a temperature lower than 600°C. It is shown that the accumulation of microimpurities and the alumina δ-phase reduces the number of acid sites and thus the efficiency of alumina catalytic conversion. To prolong the catalyst's operational life, it is recommended that metal impurities be captured from the vapor-feedstock flow by installing a protective layer of a macroporous material with a developed surface inert to the butane fraction upstream of the catalyst. © Pleiades Publishing, Ltd., 2014

Quantitative Analysis of Lewis Acid Centers of γ-Alumina by Using EPR of the Adsorbed Anthraquinone as a Probe Molecule: Comparison with the Pyridine, Carbon Monoxide IR, and TPD of Ammonia

© 2015 American Chemical Society. Quantitative electron paramagnetic resonance (EPR) measurements were done on the alumina oxide surface by using 9,10-anthraquinone probe (AQ) with the AQ amount in the range of (0.5-20) wt %. The nature of three paramagnetic centers observed simultaneously is ascribed to the strong, medium, and weak Al Lewis acid sites on the basis of combined EPR study/infrared (IR) spectroscopy of the adsorbed CO and pyridine/temperature-programmed desorption (TPD) of ammonia. It is shown how the optimal concentration of AQ probe molecule for the exhaustive quantitative examination of alumina surface can be determined directly from EPR. A possibility to characterize the surface distribution of Lewis acid centers by AQ molecules is discussed

Influence of hydrothermal treatment conditions on the structure and catalytic activity of alumina during the skeletal isomerization of n-butenes

In order to obtain an efficient alumina catalyst for skeleton isomerization of n-butenes with a high catalytic activity, we study the influence of hydrothermal treatment (HTT) of alumina systems at 150- 200°C on the parameters of the crystalline and pore structure, and acid-base properties of industrial ?- Al 2O 3. It is shown that the HTT of aluminum hydroxide increases the sizes of microcrystallites and reduces the alumina's specific surface area and the number of acid-base centers. This reduces the activity in the reaction of skeletal isomerization of n-butenes. HTT of the two-phase alumina-aluminum hydroxide sys- tem produces smaller crystallites of γ-Al 2O 3 and raises the acidity of the alumina obtained after calcination at 550°C; as a result, the catalytic activity increases. This method can be used to enhance the activity of industrial samples of alumina in the reaction of skeletal isomerization of n-butenes. © Pleiades Publishing, Ltd., 2012

Electron paramagnetic resonance and electron nuclear double resonance study of the paramagnetic complexes of anthraquinone on the surface of γ-Al2O3

Progress in the synthesis and applications of nanomaterials including nanocatalysts demands a use of precise analytical tools for their surface characterization. Continuous wave (cw) and pulsed electron paramagnetic resonance (EPR) techniques, including electron-nuclear double resonance (ENDOR) have been applied to study paramagnetic complexes formed by adsorption of 9,10-anthraquinone (AQ) as probe molecule by the surface of γ-Al 2O3. Up to three different paramagnetic complexes (11-line pattern and two single EPR lines) could be separated in our experiments. Their spectroscopic characteristics are extracted. It is shown that at very high concentration (ca. 10 wt %) of AQ, the obtained EPR signal is close to the single line and can be incorrectly interpreted as due to the EPR signal of AQ itself or due to the lower catalytic activity of the investigated surface. That fact should be taken into account by using AQ as a probe of the surface catalytic activity. Mims and Davies ENDOR experiments confirm the redistribution of the electron spin density between the ring protons of AQ, aluminum nuclei in AQ-Al2O3 complexes, and remote proton and aluminum nuclei with AQ concentration. The corresponding electron-nuclear distances are extracted. The presented results can be used to expand the application of AQ as a sensitive probe for the catalysts surface characterization. © 2014 American Chemical Society

SYNTHESIS OF MAGHEMITE BY THERMAL ANNEALING

The paper considers the preparation of a nanostructured maghemite powder as a result of thermal magnetite (Fe3O4) treatment. Methods of scanning electron microscopy, energy dispersive analysis, and X-ray analysis were used to analyze the obtained results. X-ray diffraction analysis has showed that as a result of the thermal treatment of the initial powder, γ-Fe2O3 phase (the space group P4132), as well as the phase transition of the crystal structure from Fe3O4 to γ-Fe2O3 with a preferential crystallite orientation for the γ-Fe2O3 phase from the texture plane with Miller indexes (220) are noticed.Данная работа выполнена в рамках реализации научного гранта «Разработка технологии получения нанопорошков железа методом поверхностной оксидации нелегированной стали» финансируемого Комитетом науки Министерства образования и науки Республики Казахстан согласно договору №45 от 12 февраля 2015 года

Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

© 2014 Pleiades Publishing, Ltd. Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes

Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

© 2014 Pleiades Publishing, Ltd. Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes

Effect of hydrothermal treatment on the structure and acid properties of the surface of molded gamma-aluminum oxide

© 2014 Pleiades Publishing, Ltd. Mechanism of the hydrothermal modification of gamma-aluminum oxide was studied. A set of physicochemical methods demonstrated that boehmite crystals are formed in macropores (>500 nm) by the dissolution/precipitation mechanism, whereas in mesopores (<20 nm), rehydration of primary blocks of aluminum oxide occurs from the surface into the bulk. As a result of the phase transition, aggregates of primary oxide blocks are dispersed, which leads, at a certain treatment duration, to an increase in the specific surface area. In this case, the content of acid centers also increases according to the results of a temperature-programmed desorption of ammonia, as also does the catalytic activity in the reaction of skeletal isomerization of n-butenes