Control of surface acidity and catalytic activity of γ-Al2O3 by adjusting the nanocrystalline contact interface

Nanoporous Metatitanic acid on γ-Al2O3 aerogel for higher CO2 adsorption capacity and lower energy consumption

Carbon dioxide capture has become an important issue in reducing atmospheric heat these days. In this study, adsorption of carbon dioxide by aerogel Gamma Alumina-Metatitanic Acid has been investigated and optimized. Morphological and structural analyses such as BET, FESEM, FT-IR, and XRD have also been conducted. In addition, Response surface methodology has been applied in order to achieve the optimal conditions, using a five-level Central composite design. The highest amount of adsorption, 12.874 (mmol/g), was recorded at a temperature of 20 (°C), pressure of 7 (bar), and 25 (%wt) of Metatitanic Acid. This was approximately 11.46% and 4.84% higher than those of mesoporous MgO and 4Azeolite, respectively. Regeneration of the adsorbent was also studied at different temperatures and process durations. Metatitanic acid, as a catalyst, reduces the temperature and regeneration time of the adsorbent by creating active sites and surface hydroxyl groups. It also lowers the required activation energy and enhances the thermal conductivity of the composite material. The optimal result was achieved at a temperature of 100 (°C) and a duration of 30 (min). Finally, isothermal and thermodynamic experiments were conducted to establish the most accurate predictive model and conditions, including Enthalpy, Entropy, and Gibbs free energy. The results indicate that the Freundlich model aligned well with the laboratory findings. Additionally, the negative values of Enthalpy, Entropy, and Gibbs free energy suggested that the adsorption process was physical, exothermic, and spontaneous.

Salt-assisted surface charge driven synthesis of large pores alumina as carbon tolerance support for propane dehydrogenation

Porous alumina has been widely used as catalytic support for industrial processes. Under carbon emission constraints, developing a low-carbon porous aluminum oxide synthesis method is a long-standing challenge for low-carbon technology. Herein, we report a method involving the only use of elements of the aluminum-containing reactants (e.g. sodium aluminate and aluminum chloride), sodium chloride was introduced as the coagulation electrolyte to adjust the precipitation process. Noticeably, the adjustment of the dosages of NaCl would allow us to tailor the textural properties and surface acidity with a volcanic-type change of the assembled alumina coiled plates. As a result, porous alumina with a specific surface area of 412 m²/g, large pore volume of 1.96 cm³/g, and concentrated pore size distribution at 30 nm was obtained. The function of salt on boehmite colloidal nanoparticles was proven by colloid model calculation, dynamic light scattering, and scanning/transmission electron microscopy. Afterward, the synthesized alumina was loaded with PtSn to prepare catalysts for the propane dehydrogenation reaction. The obtained catalysts were active but showed different deactivation behavior that was related to the coke resistance capability of the support. We figure out the correlation between pore structure and the activity of the PtSn catalysts associated with the maximum conversion of 53 % and minimum deactivation constant occurring at the pore diameter around 30 nm of the porous alumina. This work offers new insight into the synthesis of porous alumina.

Reaction mechanism for fluorination reactions with hydroxylated alumina sites: Pathways promoting aluminum combustion

Density functional theory calculations were used to reveal the mechanism for the fluorination reaction of active Lewis acid sites on alumina structures, which is important in understanding the pyrophoric processes involving Al particles. In this reaction, hydroxyl groups of active sites are replaced by fluorine anions. Alumina structures were represented by three aluminum aqua hydroxo clusters (labeled AlOOH), in which the Al atom had different coordination spheres, particularly four, five, or six. The F-bearing molecules HF, CH₃F, and CF₄ were taken as reactants for the fluorination reactions. The overall reaction was represented by four reaction steps as follows: (i) formation of the reaction complex, (ii) activation of the transition state (TS), (iii) deactivation of the TS with a formation of the product complex, and (iv) its decomplexation to individual products. The active reaction center of the TS structure is four-membered, in which two bonds break heterolytically and two form. The lowest reaction barriers were observed for the HF molecule, while the two other molecules had significantly higher reaction barriers. Similarly, the largest overall reaction energies (in absolute value) were found for HF, especially for the five- and six-coordinated Al centers. While the positive charge on the Al center remained almost constant throughout the reaction steps, large charge changes were observed for carbon bearing molecules with a formation of the carbenium cations in the TS step. Realizing the important role of HF in promoting exothermic reactions will enable new molecular design strategies for transforming energy release properties of aluminum powder fuels.

Alumina grafted SBA-15 sustainable bifunctional catalysts for direct cross-coupling of benzylic alcohols to diarylmethanes

AlSBA-15 catalysts possessing Brønsted acid and Lewis acid–base bifunctionalities catalyze the direct arylation of benzyl alcohols to diarylmethanes with an 85% product yield through C–O bond activation.

Temperature sensitive synthesis of γ-Al2O3support with different morphologies for CoMo/γ-Al2O3catalysts for hydrodesulfurization of thiophene and 4,6-dimethyldibenzothiophene

Two different kinds of γ-Al₂O₃precursors: stick-like ammonium aluminum carbonate hydroxide and willow leaf-like boehmite could be selectively synthesizedviaa facile hydrothermal method by just adjusting reaction temperature.

Octahedron-based gallium borates (Ga-PKU-1) with an open framework: acidity, catalytic dehydration and structure–activity relationship

The octahedron-based Ga-PKU-1 catalyst with an open framework acted as an efficient solid acid catalyst for isopropanol decomposition.

Metathesis of 1-Butene to Propene over Mo/Al2O3@SBA-15: Influence of Alumina Introduction Methods on Catalytic Performance

A series of Mo-based catalysts for 1-butene metathesis to propene were prepared by supporting Mo species on SBA-15 premodified with alumina. The effects of the method of introduction of the alumina guest to the host SBA-15 on the location of the Mo species and the corresponding metathesis activity were studied. As revealed by N2 adsorption isotherms and TEM results, well-dispersed alumina was formed on the pore walls of SBA-15 if the ammonia/water vapor induced hydrolysis (NIH) method was employed. The Mo species preferentially interacted with alumina instead of SBA-15, as evidenced by X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectrometry, and IR spectroscopy of adsorbed pyridine. Furthermore, new Brønsted acid sites favorable for the dispersion of the Mo species and low-temperature metathesis activity were generated as a result of the effective synergy between the alumina and SBA-15. The Mo/Al2O3@SBA-15 catalyst prepared by the NIH method showed higher metathesis activity and stability under the conditions of 120 °C, 0.1 MPa, and 1.5 h(-1) than catalysts prepared by other methods.

Selective hydrodeoxygenation of bio-oil derived products: ketones to olefins

A catalytic system designed for mild hydrodeoxygenation of ketones to olefins was investigated. Hydrogenation of ketones to alcohols was accomplished over metal catalysts and the alcohol produced was then dehydrated over acidic catalysts.