Alumina nanofibrous structural self-organization in hollow nanotubes caused by hydrogen treatment

Маркова, Е. Б.; Красильникова, О. К.; Serov, Yu. M.; Курилкин, В. В.; Симонов, В. Н.

doi:10.1134/s1995078014040119

Cited by 3 publications

(7 citation statements)

References 8 publications

(11 reference statements)

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“…A plateau for a composite is observed in a narrower temperature range, and after the plateau a sharper increase in heat release occurs, which according to the data of electron microscopy leads to the formation of the denser structure of aggregated tubes than for the initial aluminum oxide. So, while in the Al 2 O 3 TEM image the bundles of the nanotubes that have been formed are clearly seen [7], for the composite the bundles are tightly fused (Fig. 2c).…”

Section: Methodsmentioning

confidence: 91%

“…For the composite this process is more intense than for the initial Al 2 O 3 aerogel [7]. When temperature increases further to 1073 K, the second stage of restructuring of nanofibrous aluminum oxyhydroxide occurs, at which the coils of spiral nanowires interlock and form nanotubes.…”

Section: Methodsmentioning

confidence: 98%

“…Figure 2 shows electron microscope images of TiO 2 /Al 2 O 3 aerogels activated in a hydrogen flux at temperatures from 923 to 1123 K. In this case, Al 2 O 3 nanowires coated with titanium dioxide (Fig. 2a), as well as nanowires of Al 2 O 3 aerogel, curl up and form nanotubes in the process described in [7]. However, the coating of aluminum oxide wires with titanium dioxide has its own peculiarities.…”

Section: Methodsmentioning

confidence: 98%

“…It is clear that the presence of active centers of titanium dioxide on the surface of aluminum oxide nanowires promotes a strong interlocking of wire coils and, respectively, the densification of the structure when compared to Al 2 O 3 [7]. When the temperature of hydrogen treatment increases, the samples of TiO 2 /Al 2 O 3 aerogel change their coloration from light …”

Section: Methodsmentioning

confidence: 99%

“…We have shown earlier [7] that due to high-temperature hydrogen treatment, amorphous nanofibers of an aerogel with a diameter of ~5 nm curl into spirals whose coils interlock and form nanotubes with a diameter of 30 nm, which are associated into bundles due to selforganization of amorphous nanofilaments into nanotubes from nanocrystalline η phase of aluminum oxide occurs, and the resulting aerogels are catalytically active in contrast to other aluminum oxide forms [8].…”

Section: Introductionmentioning

confidence: 99%

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Structural transformation of TiO2/Al2O3 nanowires into nanotubes caused by high-temperature hydrogen treatment

et al. 2016

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It has been shown that the high-temperature hydrogen treatment of aluminum oxide nanowires coated with a monolayer of titanium oxide causes them to curl into nanotubes as a result of self-organization. The physicochemical properties of the nanotubes of a composite aluminum oxide aerogel coated with titanium oxide have been studied using X-ray phase analysis (XRD) and transmission electron microscopy (TEM). As a result of TiO 2 /Al 2 O 3 nanofibrous aerogel treatment with hydrogen, a conversion of amorphous aluminum oxide fibers into tubes of nanocrystalline η-Al 2 O 3 occurs, but in this case the titanium dioxide monolayer does not form a separate phase. A study of the porous structure by the low-temperature adsorption of nitrogen vapors has shown that the aerogels of TiO 2 /Al 2 O 3 nanotubes have a developed mesoporous structure with a small amount of micropores and a specific surface of more than 300 m 2 /g. An increase in the temperature of hydrogen treatment first leads to the growth of an increase in the specific surface to 348 m 2 /g at 923 K, and then to a gradual decrease to 145 m 2 /g at 1123 K. In this case, the diameter of mesopores corresponding to a maximum on a curve of the pore size distribution decreases from 35 nm for a freshly prepared sample to 25 nm at 923 K and to 20 nm at 1123 K. The most homogeneous pores of a 25 nm diameter have the samples activated at 923 K. As a result of the high-temperature hydrogen treatment of the samples, the number of primary adsorption centers of water vapor adsorption decreases about two times. The resulting samples of TiO 2 /Al 2 O 3 aerogels are close in structure to the initial aluminum oxide, whose wires just form nanotubes having a surface coated with titanium dioxide. As a result of the interaction between molecules of titanium dioxide adsorbed on the surface of aluminum oxide tubes, a substantial densification of the composite structure occurs.

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Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structural transformation of TiO2/Al2O3 nanowires into nanotubes caused by high-temperature hydrogen treatment

et al. 2016

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Activating the Growth of High Surface Area Alumina Using a Liquid Galinstan Alloy

et al. 2018

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The growth of high surface area alumina has been investigated with the use of a liquid Galinstan alloy [66.5% (wt %) Ga, 20.5% In and 13.0% Sn] as an activator for aluminum. In this process, the aluminum is slowly dissolved into the gallium–indium–tin alloy, which is then selectively oxidized at ambient temperature and pressure under a humid stream of flowing CO 2 or N 2 to yield amorphous alumina. This preparative route represents a simple and low toxicity approach to obtain amorphous high surface area alumina with very low water content. The as-synthesized high surface area alumina aerogel was a blue-colored solid owing to the Rayleigh scattering by its dendritic fibrous nanostructure consisting of mainly alumina with small amounts of water. Upon annealing at 850 °C, the amorphous product transformed into γ-Al 2 O 3 , as well as θ-Al 2 O 3 upon annealing at 1050 °C. Elemental analysis by energy-dispersive spectroscopy provides further evidence that the high surface area alumina is composed of only aluminum and oxygen. The surface area of the amorphous alumina varied from ∼79 to ∼140 m 2 /g, depending on the initial weight percentage of aluminum used in the alloy. A correlation between the initial concentration of aluminum in the alloy and the surface area of the alumina product was found to peak at ∼30% Al. These results suggest a novel route to the formation of amorphous alumina aerogel-type materials.

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Research into Thermocatalytic Propane-to-Propylene Synthesis Using Iron-Containing Composite Carbon Materials

et al. 2021

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The development of modern thermocatalytic technologies for processing oil and gas raw materials is one of the promising areas for the advancement of chemical production. New highly efficient catalytic systems with the required technical characteristics and long service life play an essential role in solving these issues. The paper focuses on obtaining propylene by selective propane dehydrogenation. In the course of the experiments, composite iron-containing catalysts were synthesized, in which the active component is iron oxide in combination with an inert carbon matrix. FAS activated carbon and carbon nanotubes were used as the matrix. As a result of the synthesis on the catalyst surface it was possible to obtain catalytic centers that transfer electrons by changing the degree of iron oxidation when converting the starting materials into the target reaction products. Findings of research show that the obtained iron-containing catalysts significantly increase the efficiency of the process in comparison with the efficiency of thermal cracking of propane. Thus, the Fe3+/FAS catalyst showed a conversion rate of the initial reagent of 68 % and a propylene selectivity of about 42 %. Further transition to catalytic systems based on singlelayer and double-layer carbon nanotubes modified with iron oxide (Fe3+/CNTI and Fe3+/CNTII) made it possible to obtain propane conversion up to 37--40 % with a decrease in propylene selectivity to 29--30 %. Studies of the service life of the synthesized catalytic systems and the possibility of their regeneration show that, with account for the regeneration, the activity of the catalysts and the main technical characteristics of the propane-to-propylene cracking process remain unchanged for 10 working cycles

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Alumina nanofibrous structural self-organization in hollow nanotubes caused by hydrogen treatment

Cited by 3 publications

References 8 publications

Structural transformation of TiO2/Al2O3 nanowires into nanotubes caused by high-temperature hydrogen treatment

Structural transformation of TiO2/Al2O3 nanowires into nanotubes caused by high-temperature hydrogen treatment

Activating the Growth of High Surface Area Alumina Using a Liquid Galinstan Alloy

Research into Thermocatalytic Propane-to-Propylene Synthesis Using Iron-Containing Composite Carbon Materials

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