Understanding of NOx storage property of impregnated Ba species after crystallization of mesoporous alumina powders

Utilization of Reactive Nitrogen Compounds for Nitrogen Circular Economy

Nitrogen oxides (NOx) should be purified according to environmental regulations, being restricted increasingly year by year. A wide variety of denitration technologies, such as selective catalytic reduction (SCR) of NOx to nitrogen (N2) and NOx storage reduction (NSR) to N2 by injecting reducing agents like ammonia (NH3), has so far been developed practically. Sophisticated catalytic approaches are perhaps mandatory for the sustainability in energy including complete purification of NOx. As one of the solutions to overcome problems for environment and resource simultaneously, this concept article focuses on the utilization of reactive nitrogen (Nr) compounds, mainly NOx, for encouraging an opening to consider nitrogen circular economy. For the recycling of NOx via NH3, a challenging but rational catalytic technology can be proposed by an alternate switching the inlet gas between NOx containing oxidative gas and H2 containing reductive one without an operation to change the reaction temperature. Considering the reactivity of NOx higher than that of N2, this kind of NOx to NH3 (NTA) process is promising for synthesizing NH3, being valuable not only as fertilizer but also as fuel in near future.

Smart synthesis of highly porous metal oxide powders with the self-assembly of amphiphilic organic compounds

Supramolecular chemistry-mediated synthesis has thus far been employed for the design of ordered mesoporous structures surrounded by various metal oxides that are helpful as nanometer-scaled unique reaction containers with high specific surface area, large pore volume and uniform mesopores useful for the storage and mass transport of large-sized molecules. The evaporation-induced self-assembly (EISA) process is very powerful for fabricating mesoporous metal oxide films with the rapid evaporation of solvents. Although a similar EISA process is also applied to synthesize mesoporous metal oxide powders using the room-temperature drying process with slow evaporation of solvents, the control of the evaporation rate should be quantified for the complete reproduction of high-quality metal oxide powders. In this feature article, I introduce our recent challenge in synthesizing highly porous metal oxides in powder form with the smart optimization of synthetic conditions by combining several EISA processes to eliminate the mismatch of the rate of solvent evaporation, inducing the self-assembly of amphiphilic organic molecules.

Neutralization-mediated extraction of amphiphilic organic molecules for obtaining high-quality mesoporous alumina

A solvent extraction method was improved using organic bases such as triethylamine (Et3N) that neutralize HCl effectively and stabilize sol-gel derivative alumina frameworks as insoluble species, thereby achieving removal of EOnPOmEOn at a rate higher than 90% to obtain high-quality mesoporous alumina.

Modelization and implementation of free adsorption and electrosorption of Cr (VI) from wastewater using Al2O3 nanoparticles: assessment and comparison of the two processes

The objective of this study was to apply the technique of electrosorption in order to assess the capacity of heterogeneous adsorption under an electric field. This was to enhance the adsorption capacity of the nanoparticles, to shorten the adsorption time, and to reduce the cost of the purification of contaminated waters. A final objective of this study was to compare the free adsorption (FA) and the electrosorption (ES) to understand the interface adsorbent/adsorbate at different contact conditions. For these purposes, a potentially efficient, environment-friendly absorbent was synthesized for dechromation purposes. The experimental design method generated optimum conditions as t_c = 123 min, T = 318°K, and C₀ = 100 mg/L. Freundlich's well-fitted modeling proved that the adsorption of chromate (VI) on nano-Al₂O₃ occurred on a homogenous surface. In addition, the adsorption coefficient intensity n did not only confirm monolayer adsorption but also indicated a favorable adsorption process. Thermodynamic studies confirmed the reaction spontaneity and the physisorption of the process. The electrosorption process was also tested using 20mA/cm² as applied current density. Free-adsorption (FA) and electrosorption (ES) processes were compared. The maximum recorded yield was 99% for (EA) against 87% for (FA). EDS analysis recorded 11.3% of chromate adsorbate with free adsorption. The amount of Cr (VI) on nano-Al₂O₃ was 42.5 %. Nevertheless, the Al₂O₃ nanoparticles lost their crystallinity and exploded after the ES process. Mechanisms of both (FA) and (ES) were proposed.

Enhanced γ-phase crystallinity of Al2O3 frameworks at the concave surface of PS-b-PEO templated spherical pores

The crystallinity of inorganic solids like metal oxides after the porosity design is the crucial factor that should be investigated for enhancing their physicochemical properties. In most cases, metal oxide frameworks around mesopores, that are designed through the supramolecular mediated approach, are resulted to be amorphous. Accordingly, a rational guideline has been required for enhancing the crystallinity of frameworks at such concave surfaces. We have so far surveyed a crystallization behavior of alumina (Al2O3) frameworks to its γ-phase around spherical mesopores (∼40 nm) and discussed further transition to the α-phase around much larger pores (∼200 nm). In this paper, we prepared new and helpful Al2O3 powders having PS-b-PEO templated pores (∼25 nm and ∼75 nm) smaller than those of our previous case. After careful discussion of the pore size variation by considering the molecular structure of PS-b-PEO, we explained the crystallization behavior of the Al2O3 frameworks to enhance its γ-crystallinity. This knowledge is quite beneficial for designing highly porous Al2O3 powders with abundant crystallinity for use as catalyst supports, which is very useful for assessing synthetic procedures of other mesoporous metal oxides having high crystallinity.

Efficient abatement of NOx emitted from automotive engines via adsorption on the Ba-CMK-3 adsorbents

The Ba-CMK-3(x) (x was the Ba(NO₃)₂:CMK-3 mass ratio and equals to 5, 10, and 15 wt%) samples were prepared by the incipient impregnation method, which were used for the adsorption of NO + O₂ at room temperature. The samples were characterized by the XRD, BET, TEM, TPD, TG, and DRIFTS techniques. The results showed that the CMK-3 and Ba-CMK-3(x) samples possessed an ordered two-dimensional hexagonal mesoporous structure, and Ba was uniformly dispersed on the surface of CMK-3. After Ba doping, the surface areas and pore size distributions of the Ba-CMK-3(x) samples were altered due to the synergistic effect of partial blocking of the channels by Ba and partial etching of the carbon materials by O₂ produced from Ba(NO₂)₃ decomposition at high temperatures. The sequence in NO adsorption capacity was Ba-CMK-3(10) (108.1 ± 0.55 mg/g) > Ba-CMK-3(15) (106.2 ± 0.72 mg/g) > Ba-CMK-3(5) (102.3 ± 1.33 mg/g) > CMK-3(88.8 ± 1.15 mg/g), with the Ba-CMK-3(10) sample showing the best (NO + O₂) adsorption performance. We proposed the two main adsorption pathways in the process of NO adsorption: (i) NO reacted with O₂ to form NO₂, part of NO₂ were weakly adsorbed on the surface hydroxyl groups, part of NO₂ were adsorbed to form the nitrite and nitrate species, and the left NO₂ was disproportionated to the NO, NO₂^-, and NO₃^- species; and (ii) NO was directly oxidized to the NO₂^- species by the oxygen-containing functional groups in carbon, and then some of the NO₂^- species were transformed to the NO₃^- species directly or via disproportionation. The regeneration efficiencies of the Ba-CMK-3(x) samples were slightly inferior to that of the CMK-3 sample.

A Robust Mesoporous Al2 O3 -Based Nanocomposite Catalyst for Abundant NOx Storage with Rational Design of Pt and Ba Species

The nanostructural design of heterogeneous catalysts has often been demanded for assessing synergetic effects, which should be developed further by using high-surface-area porous metal oxide supports. However, such opportunities have been undermined by the poor stability of ordered mesoporous structures. Herein, rational design is demonstrated to obtain nanocomposite catalysts showing improved NO_x storage properties owing to the presence of Ba species over a well-designed mesoporous alumina (Al₂ O₃ ) support. It is found that Ba species are impregnated successfully only after the stabilization of the mesoporous structure by full crystallization of Al₂ O₃ frameworks to the γ-phase, with the formation of Pt nanoparticles coinciding with complete removal of organic components. All the insights during this synthetic procedure are essential for designing high-performance catalysts to purify and recover NO_x molecules, and are applied for designing a variety of cutting-edge mesoporous nanocomposite catalysts.

Accelerated crystallization of mesoporous Al2O3 powder recovered by spray-drying with a large amount of heated air

Crystallization into α-Al₂O₃ was accelerated with a large amount of heated air during spray-drying to recover mesoporous Al₂O₃ powders.