Search Results (28)

This work investigates the potential of wollastonite-based brushite cement (WBC) for the stabilization and solidification of radioactive waste contaminated by ⁹⁰Sr. This phosphate binder was formed by the reaction of wollastonite (CaSiO₃) with a phosphoric acid solution containing borax and metallic cations (Al³⁺, Zn²⁺). Two cement pastes were investigated: a commercial binder (WBC-C) and an optimized formulation (WBC-O), produced using a zinc-free mixing solution with a higher aluminum content than that of WBC-C. Mineralogical characterizations using XRD, TGA, XRF, SEM-EDX, and Raman spectroscopy showed that both materials mainly contained amorphous hydrated silica and calcium aluminophosphate, along with crystalline brushite, residual wollastonite, and quartz. The stability of WBC-C under γ-irradiation was evaluated up to a dose of 1 MGy. The only observable effect was water radiolysis, leading to dihydrogen production at yields comparable to Portland cement matrices and geopolymers. Strontium leaching, assessed using the ANSI/ANS-16.1-2003 (R2008) procedure, followed a two-stage release mechanism combining surface wash-off and diffusion. The apparent diffusion coefficient D_a of Sr in WBC-C was markedly lower than typical values reported for Portland cement matrices. WBC-O exhibited enhanced Sr retention, possibly due to its higher aluminum content, which refines mesopores and reduces diffusion pathways accessible to Sr. WBC binders therefore appear to be promising candidates for strontium immobilization. Full article

The influence of potassium oxide (K₂O) doping on the hydrodeoxygenation (HDO) performance of trimetallic CoMo–Ni/Al₂O₃ catalysts was systematically investigated using guaiacol as a lignin-derived model compound. Catalysts containing 0, 1, 3, and 5 wt% K₂O were synthesized and characterized by SEM-EDS, N₂ physisorption, XRD, FTIR, and HRTEM. SEM micrographs showed homogeneous morphologies with no significant agglomeration, while EDS analysis confirmed elemental compositions close to nominal values, with K₂O contents increasing proportionally and maintaining uniform surface distribution. Adsorption–desorption isotherms confirmed mesoporous structures with specific surface areas ranging from 258 to 184 m² g⁻¹, decreasing with increasing K₂O loading. XRD revealed γ-Al₂O₃, NiO, (NH₄)₃[CoMo₆O₂₄H₆]·7H₂O, and K₂O phases, with slight peak shifts indicating surface modification rather than lattice incorporation of K⁺. FTIR spectra evidenced characteristic polyoxomolybdate vibrations and metal–oxygen interactions with alumina. HRTEM revealed MoS₂ slab lengths between 1.85 and 2.51 nm, stacking numbers from 2.08 to 3.17, and Mo edge-to-corner ratios (f_e/fc) between 1.39 and 2.43, corresponding to dispersions of 0.45–0.57. Guaiacol conversion remained high (≥95%) for all catalysts, while HDO selectivity strongly depended on K₂O content. At 5 wt% K₂O, cyclohexane selectivity reached 81.3% with an HDO degree of 65%, compared to 52.0% and 31% for the undoped catalyst. Pseudo-first-order kinetic analysis revealed that potassium promotes demethylation and demethoxylation steps while suppressing rearrangement pathways, steering the reaction network toward direct deoxygenation. These results demonstrate that K₂O acts as an efficient structural and electronic promoter, enabling precise control of HDO selectivity without compromising catalytic activity. Full article

Activated alumina is widely used in industry as an adsorbent. Its strong affinity toward water allows for the profound dehydration of gas streams. To optimize such processes, a deeper insight into water interaction with activated alumina is required. This knowledge can be obtained using positron annihilation lifetime spectroscopy, a sensitive tool that unravels previously unknown aspects of adsorption processes. Activated alumina (Compalox^® AN/V-813) was subjected to such a study supported by detailed characterization using scanning electron microscopy, X-ray diffraction, and N₂ adsorption–desorption. A complex porous structure of the material, consisting mainly of boehmite and η-Al₂O₃ or γ-Al₂O₃, was found. It is responsible for significant differences in adsorption and desorption. The course of adsorption is close to the classical layer-by-layer description. However, there are indications of initial water capture at active sites and final water reorganization consisting of filling the smallest free volumes that remain empty. The narrow mesopore inlets that keep water in the pores even at a relative vapor pressure of 0.4 are primarily responsible for the course of the desorption process. During adsorption, water is mainly maintained in the form of small clusters up to the highest pressures, whereas during desorption, it is continuous until narrow pore openings. Full article

Volatile organic compounds (VOCs), particularly aromatic hydrocarbons, pose significant environmental risks due to their toxicity and role in the formation of secondary pollutants. This study explores the potential of catalytic pyrolysis as an innovative strategy for the effective remediation and conversion of aromatic hydrocarbon pollutants. The research investigates the high-efficiency removal and resource recovery of the VOC toluene using a Ni/Al₂O₃ catalyst. The Ni/Al₂O₃ catalyst was synthesized using the impregnation method and thoroughly characterized. Various analytical techniques, including scanning electron microscopy, X-ray diffraction, and N₂ adsorption–desorption isotherms, were employed to characterize the Al₂O₃ support, NiO/Al₂O₃ precursor, Ni/Al₂O₃ catalyst, and the resulting solid carbon. Results indicate that Ni predominantly occupies the pores of γ-Al₂O₃, forming nano/microparticles and creating interstitial pores through aggregation. The catalyst demonstrated high activity in the thermochemical decomposition of toluene into solid carbon materials and CO_x-Free hydrogen, effectively addressing toluene pollution while recovering valuable resources. Optimal conditions were identified, revealing that a moderate temperature of 700 °C is most favorable for the catalytic process. Under optimized conditions, the Ni/Al₂O₃ catalyst removed 1328 mg/g of toluene, generated 915 mg/g of carbon material, and produced 1234 mL/g of hydrogen. The prepared carbon material, characterized by its mesoporous structure and high specific surface area graphite nanofibers, holds potential application value in adsorption, catalysis, and energy storage. This study offers a promising approach for the purification and resource recovery of aromatic volatile organic compounds, contributing to the goals of a circular economy and green chemistry. Full article

This study evaluates the effectiveness of fluidizable VO_x/MgO-γAl₂O₃ catalysts for C₄-olefin production via n-butane oxidative dehydrogenation (BODH). Catalysts were prepared via vacuum incipient wetness impregnation and then characterized by employing several techniques such as BET (Brunauer–Emmett–Teller) method, XRD (X-ray diffraction), LRS (laser Raman spectroscopy), XPS (X-ray photoelectron spectroscopy), TPR/TPO (temperature-programmed reduction/temperature-programmed oxidation), NH₃-TPD (temperature-programmed desorption), NH₃ -desorption kinetics and pyridine-FTIR. The BET analysis showed the prepared catalysts’ mesoporous structure and high surface areas. The XRD, LRS and XPS established the desirable presence of amorphous VO_x phases. The TPR/TPO analyses corroborated catalyst stability over repeated reduction and oxidation cycles. The NH₃-TPD and NH₃ desorption kinetics showed that the catalysts had dominant moderate acidities and weak metal-support interactions. In addition, Pyridine-FTIR showed the critical influence of Lewis acidity. The VO_x/MgO-γAl₂O₃ catalysts were evaluated for BODH using a fluidized CREC Riser Simulator, operated under gas-phase oxygen-free conditions, at 5 to 20 s reaction times, and at 450 °C to 600 °C temperatures. The developed VO_x/MgO-γAl₂O₃ catalysts demonstrated performance stability throughout multiple injections of butane feed. Catalyst regeneration was also conducted after six consecutive BODH runs, and the coke formed was measured using TOC (Total Organic Carbon). Regarding the various BODH catalyst prepared, the 5 wt% V-doped MgO-γAl₂O₃ yielded in a fluidized CREC Riser Simulator the highest selectivity for C₄-olefins, ranging from 82% to 86%, alongside a butane conversion rate of 24% to 27%, at 500 °C and at a 10 s reaction time. Full article

The control of alumina morphology is crucial yet challenging for its various applications. Unfortunately, traditional methods for preparing alumina particles suffer from several limitations such as irregular morphology, poor dispersibility, and restricted application areas. In this study, we develop a novel method for preparing spherical mesoporous alumina using chitin and Pluronic P123 as mixed templates. The effects of reaction temperature, time, and the addition of mixed templates on the phase structure, micromorphology, and optical absorption properties of the samples were investigated. The experimental results indicate that lower temperature and shorter reaction time facilitated the formation of spherical mesoporous alumina with excellent CO₂ adsorption capacity. The periodic density functional theory (DFT) calculations demonstrate that both the (110) and (100) surfaces of γ-Al₂O₃ can strongly adsorb CO₂. The difference in the amount of CO₂ adsorbed by Al₂O₃ is mainly due to the different surface areas, which give different numbers of exposed active sites. This approach introduces a novel strategy for utilizing biological compounds to synthesize spherical alumina and greatly enhances mesoporous alumina’s application efficiency in adsorption fields. Moreover, this study explored the electrochemical performance of the synthesized product using cyclic voltammetry, and improved loading of electrocatalysts and enhanced electrocatalytic activity were discovered. Full article

We introduced a modified sol-gel method using polyvinyl alcohol (PVA) as an additive to improve the permeability of γ-Al₂O₃ membranes by minimizing the thickness of the selective layer and maximizing the porosity. First, the analysis revealed that the thickness of γ-Al₂O₃ decreased as the concentration of PVA increased in the boehmite sol. Second, the properties of the γ-Al₂O₃ mesoporous membranes were greatly influenced by the modified route (method B) compared to the conventional route (method A). The results showed that the porosity and surface area of the γ-Al₂O₃ membrane increased, and the tortuosity decreased considerably using method B. This effect was attributed to the adsorption of PVA molecules on the surface of the boehmite particles, which depended on the synthesis route. The experimentally determined pure water permeability trend and the Hagen–Poiseuille mathematical model confirmed that the modified method improved the performance of the γ-Al₂O₃ membrane. Finally, the γ-Al₂O₃ membrane fabricated via a modified sol-gel method with a pore size of 2.7 nm (MWCO = 5300 Da) exhibited a pure water permeability of over 18 LMH/bar, which is three times higher than that of the γ-Al₂O₃ membrane prepared using the conventional method. Full article

In this study, three solid acid catalysts, namely mesoporous aluminophosphate-supported 12-tungstophosphoric heteropoly acid (HPW/MAP), mesoporous aluminosilicate-supported 12-tungstophosphoric heteropoly acid (HPW/MAS), and gamma alumina-supported 12-tungstophosphoric heteropoly acid (HPW/γ-Al₂O₃) were prepared and characterized. Mesoporous aluminophosphate (MAP) and mesoporous aluminosilicate (MAS) were synthesized via sol-gel and hydrothermal methods, respectively, and 25 wt.% of 12-tungstophosphoric heteropoly acid (HPW) was immobilized on the support materials using the wet impregnation method. The features of the fabricated catalysts were comprehensively investigated using various techniques such as BET, XRD, NH₃-TPD, TGA, and TEM. The surface area of the supported catalysts decreased after HPW impregnation according to BET results, which indicates that HPW loaded on the supports and inside of their pores successfully. The density and strengths of the acid sites of the support materials and the catalysts before reaction and after regeneration were determined by the NH₃-TPD technique. Accordingly, an increase in acidity was observed after HPW immobilization on all the support materials. The catalytic performance of the catalysts was studied through alcoholysis reaction using unrefined green seed canola oil as the feedstock. The maximum biodiesel yield of 82.3% was obtained using 3 wt.% of HPW/MAS, with a methanol to oil molar ratio of 20:1, at 200 °C and 4 MPa over 7 h. The reusability study of HPW/MAS showed that it can maintain 80% of its initial activity after five runs. Full article

Aluminum waste-can management in Malaysia has recently become a serious environmental and public health issue, particularly in metropolitan areas. This has prompted the need to valorize these waste-cans into value-added products using the most economical and environmentally friendly techniques. In this study, the sol–gel technique was used to synthesize high-quality alumina from the aluminum waste-cans collected. From this method, the observed peaks of the synthesized alumina were identified as diaspore (α-AlO(OH)), boehmite (γ-AlO(OH)), aluminum oxide, or gamma-alumina (γ-Al₂O₃) crystalline structure and corundum. The morphological configuration, microstructure, and functional group properties of the synthesized alumina were evaluated. All the synthesized alumina exhibited a non-spherical shape and appeared to have hexagonal-like shape particles. Moreover, the XRD patterns of the synthesized alumina AL-6-30 and AL-12-30 exhibited a small angle (1–10°) with no XRD peak, which indicated a mesoporous pore structure with no long-range order. The overall results of γ-alumina synthesized from the aluminum waste-cans showed an optimal condition in producing a highly structured γ-alumina with excellent surface-area characteristics. The synthesized alumina exhibited stronger and highly crystalline functional characteristics almost comparable with the commercially available brands on the market. Full article

The efficiency of thermochemical heat storage is crucially determined by the performance of the sorbent used, which includes a high sorption capacity and a low regeneration temperature. The thermochemical salt hydrate– γ-alumina composite sorbents are promising materials for this application but lack systematic study of the influence of γ-alumina structural properties on the final storage performance. In this study, mesoporous γ-Al₂O₃ supports were prepared by solvothermal and hydrothermal synthesis containing a block copolymer (F-127) surfactant to design thermochemical CaCl₂ and LiCl composite water sorbents. Altering the solvent in the synthesis has a significant effect on the structural properties of the γ-Al₂O₃ mesostructure, which was monitored by powder XRD, nitrogen physisorption, and SEM. Solvothermal synthesis led to a formation of mesoporous γ-Al₂O₃ with higher specific surface area (213 m²/g) and pore volume (0.542 g/cm³) than hydrothermal synthesis (147 m²/g; 0.414 g/cm³). The highest maximal water sorption capacity (2.87 g/g) and heat storage density (5.17 GJ/m³) was determined for W-46-LiCl containing 15 wt% LiCl for space heating, while the best storage performance in the sense of fast kinetics of sorption, without sorption hysteresis, low desorption temperature, very good cycling stability, and energy storage density of 1.26 GJ/m³ was achieved by W-46-CaCl₂. Full article

KCoMoS₂ was supported on various carbon support materials to study the support effect on synthesis gas conversion. Next to two activated carbons with high micropore volume, a traditional alumina (γ-Al₂O₃) support and its carbon coated form (CCA) were studied for comparison. Coating alumina with carbon increases the selectivity to alcohols, but the AC-supported catalysts show even higher alcohol selectivities and yields, especially at higher temperatures where the conversions over the AC-supported catalysts increase more than those over the γ-Al₂O₃-based catalysts. Increasing acidity leads to decreased CO conversion yield of alcohols. The two activated-carbon-supported catalysts give the highest yield of ethanol at the highest conversion studied, which seems to be due to increased KCoMoS₂ stacking and possibly to the presence of micropores and low amount of mesopores. Full article

This paper reports on a unique reversible reducing and oxidizing (redox) property of Co(III) in Co-doped amorphous SiO₂/γ-Al₂O₃ composites. The Fenton reaction during the H₂O₂-catalyzed sol–gel synthesis utilized in this study lead to the partial formation of Co(III) in addition to Co(II) within the composites. High-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyses for the composite powder sample with a composition of Al:Si:Co = 85:10:5 showed the amorphous state of the Co-doped SiO₂ that modified γ-Al₂O₃ nanocrystalline surfaces. In situ X-ray absorption fine structure (XAFS) spectroscopic analysis suggested reversible redox reactions of Co species in the composite powder sample during heat-treatment under H₂ at 500 °C followed by subsequent cooling to RT under Ar. Further analyses by in situ IR spectroscopy combined with cyclic temperature programmed reduction/desorption (TPR/TPD) measurements and X-ray photoelectron spectroscopic (XPS) analysis revealed that the alternating Co(III)/(II) redox reactions were associated with OH formation (hydrogenation)-deformation (dehydrogenation) of the amorphous aluminosilicate matrix formed in situ at the SiO₂/γ-Al₂O₃ hetero interface, and the redox reactions were governed by the H₂ partial pressure at 250–500 °C. As a result, a supported mesoporous γ-Al₂O₃/Co-doped amorphous SiO₂/mesoporous γ-Al₂O₃ three-layered composite membrane exhibited an H₂-triggered chemical valve property: mesopores under H₂ flow (open) and micropores under He flow (closure) at 300–500 °C. Full article

Mesoporous alumina-based adsorbents consisting of a π-electron acceptor complexing agent (2,7-dinitro-9-fluorenone) were synthesized and characterized. Adsorbents were screened for the removal of sulfur compounds from a model ultra-low-sulfur diesel fuel via a charge transfer complex (CTC) mechanism. The sulfur adsorption isotherms and kinetics were examined. The kinetics of sulfur adsorption followed a pseudo-second-order model with the CTC adsorbents. Among the three adsorbents screened, a commercial γ-Al₂O₃ CTC adsorbent showed the highest desulfurization in a short-run period. The regeneration of spent adsorbent was studied with three different polar solvents, namely chloroform, dichloromethane, and carbon tetrachloride. Dichloromethane was found to be the most suitable solvent for extracting a major portion of sulfur compounds occupied in the pores of the spent adsorbent. γ-Al₂O₃ CTC adsorbent can be reused after regeneration. Thermodynamic parameters such as E_a, ΔG, ΔH, and ΔS provided a better insight into the adsorption process. Full article

Solar hydrogen production via the photoelectrochemical water-splitting reaction is attractive as one of the environmental-friendly approaches for producing H₂. Since the reaction simultaneously generates H₂ and O₂, this method requires immediate H₂ recovery from the syngas including O₂ under high-humidity conditions around 50 °C. In this study, a supported mesoporous γ-Al₂O₃ membrane was modified with allyl-hydrido-polycarbosilane as a preceramic polymer and subsequently heat-treated in Ar to deliver a ternary SiCH organic–inorganic hybrid/γ-Al₂O₃ composite membrane. Relations between the polymer/hybrid conversion temperature, hydrophobicity, and H₂ affinity of the polymer-derived SiCH hybrids were studied to functionalize the composite membranes as H₂-selective under saturated water vapor partial pressure at 50 °C. As a result, the composite membranes synthesized at temperatures as low as 300–500 °C showed a H₂ permeance of 1.0–4.3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with a H₂/N₂ selectivity of 6.0–11.3 under a mixed H₂-N₂ (2:1) feed gas flow. Further modification by the 120 °C-melt impregnation of low molecular weight polycarbosilane successfully improved the H₂-permselectivity of the 500 °C-synthesized composite membrane by maintaining the H₂ permeance combined with improved H₂/N₂ selectivity as 3.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with 36. These results revealed a great potential of the polymer-derived SiCH hybrids as novel hydrophobic membranes for purification of solar hydrogen. Full article

MCM-22, MCM-36, and ITQ-2 zeolites with the intended Si/Al molar ratios of 15, 25, and 50 were synthetized and tested as catalysts for dehydration of methanol to dimethyl ether and dehydration of ethanol to diethyl ether and ethylene. The surface concentration of acid sites was regulated by the synthesis of zeolite precursors with different aluminum content in the zeolite framework, while the influence of porous structure on the overall efficiency of alcohol conversion was analyzed by application of zeolitic materials with different types of porosity—microporous MCM-22 as well as microporous-mesoporous MCM-36 and ITQ-2. The zeolitic samples were characterized with respect to their: chemical composition (ICP-OES), structure (XRD, FT-IR), texture (N₂ sorption), and surface acidity (NH₃-TPD). Comparison of the catalytic activity of the studied zeolitic catalysts with other reported catalytic systems, including zeolites with the similar Si/Al ratio as well as γ-Al₂O₃ (one of the commercial catalysts for methanol dehydration), shows a great potential of MCM-22, MCM-36, and ITQ-2 in the reactions of alcohols dehydration. Full article