Search Results (163)

Industrial catalysts are accelerating the global transition toward renewable energy, serving as enablers for innovative technologies that enhance efficiency, lower costs, and improve environmental sustainability. This review explores the pivotal roles of industrial catalysts in hydrogen production, biofuel generation, and biomass conversion, highlighting their transformative impact on renewable energy systems. Precious-metal-based electrocatalysts such as ruthenium (Ru), iridium (Ir), and platinum (Pt) demonstrate high efficiency but face challenges due to their cost and stability. Alternatives like nickel-cobalt oxide (NiCo₂O₄) and Ti₃C₂ MXene materials show promise in addressing these limitations, enabling cost-effective and scalable hydrogen production. Additionally, nickel-based catalysts supported on alumina optimize SMR, reducing coke formation and improving efficiency. In biofuel production, heterogeneous catalysts play a crucial role in converting biomass into valuable fuels. Co-based bimetallic catalysts enhance hydrodeoxygenation (HDO) processes, improving the yield of biofuels like dimethylfuran (DMF) and γ-valerolactone (GVL). Innovative materials such as biochar, red mud, and metal–organic frameworks (MOFs) facilitate sustainable waste-to-fuel conversion and biodiesel production, offering environmental and economic benefits. Power-to-X technologies, which convert renewable electricity into chemical energy carriers like hydrogen and synthetic fuels, rely on advanced catalysts to improve reaction rates, selectivity, and energy efficiency. Innovations in non-precious metal catalysts, nanostructured materials, and defect-engineered catalysts provide solutions for sustainable energy systems. These advancements promise to enhance efficiency, reduce environmental footprints, and ensure the viability of renewable energy technologies. Full article

Waste biomass gasification can contribute to the production of alternative and environmentally sustainable green fuels. Research at the CREC–UWO (Chemical Reactor Engineering Center–University of Western Ontario) considers an integrated gasification process where both electrical power, biochar, and tar-free syngas suitable for alcohol synthesis are produced. In particular, the present review addresses the issues concerning tar removal from the syngas produced in a waste biomass gasifier via a catalytic post-gasification (CPG) downer unit. Various questions concerning CPG, such as reaction conditions, thermodynamics, a Tar Conversion Catalyst (TCC), and tar surrogate chemical species that can be employed for catalyst performance evaluations are reported. Catalyst performance-reported results were obtained in a fluidizable CREC Riser Simulator invented at CREC–UWO. The present review shows the suitability of the developed fluidizable Ni–Ceria γ-alumina catalyst, given the high level of tar removal it provides, the minimum coke that is formed with its use, and the adequate reforming of the syngas exiting the biomass waste gasifier, suitable for alcohol synthesis. Full article

The pulp and paper industry is one of the leading waste-generating industries globally. With the rich energy content of these wastes and many of these mills not paying attention/implementing efficient waste disposal methods, it has become imperative that research efforts on pulp and paper waste valorization be performed; hence this paper. Hydrothermal liquefaction (HTL) technology was adopted due to its ability to transform wet biomass into biocrude. The research studied the effects of reaction parameters such as temperature, residence time, feed concentration, and catalysts on the yield of biocrude. While central composite design (CCD) was used in the design of the experiments, response surface methodology (RSM) was utilized for their optimization. The optimum parametric conditions obtained were the following: temperature: 340 °C; residence time: 56min; and feed concentration: 5%. Zeolite (HZSM-5), gamma-alumina (γ-Al₂O₃), and activated carbon were utilized as catalysts, and their performances with respect to biocrude yield improvement were evaluated. The order of catalytic effect on the biocrude yield was γ-Al₂O₃ (25.65%) > HZSM-5 (23.18%) > activated carbon (21.94%). Catalyst characterization was performed on the fresh and spent catalysts to study their properties and to make informed inferences on their impacts on biocrude yield. Based on the findings from this research, necessary conclusions and recommendations for future work are presented. Full article

The thermal decomposition of hydrogen peroxide (H₂O₂) as a promising green propellant was performed over free-noble metallic-based catalysts deposited on abundant supports. A 30% (w/w) H₂O₂ liquid was decomposed over 1 wt.% of copper-based catalysts deposited on three different supports: γ-alumina, graphite and monocrystal clay. In this research work, the catalytic performance of the thermal decomposition of H₂O₂ was carried out by measuring the differential pressure (ΔP) versus time at initial constant temperatures and, for the first time, by the DTA-TG technique and by the DIP-MS technique at atmospheric pressure. The obtained preliminary results showed that copper deposited on alumina and on graphite are promising catalysts for the decomposition of the H₂O₂ liquid propellant. Moreover, the natural clay can be valorized on the thermal decomposition of H₂O₂ due to its high resistivity and high surface area. The N₂-physisorption technique and scanning electron microscopy technique were used to characterize the effect of the texture properties on the decomposition and to understand the morphological characteristics of the catalyst. Full article

Environmental legislation has focused its attention on improving air quality. In this context, the presence of sulfur compounds in fuels, such as diesel and gasoline, is undesirable. When sulfur is combusted, compounds are emitted as SO_x (SO₂ and SO₃) into the atmosphere, causing acid rain and respiratory diseases. For this reason, environmental norms have been established to reduce the sulfur content of fuels. Sulfur (mainly as alkylbenzothiophenes, dibenzothiophenes and alkyldibenzothiophenes) is removed in refineries through a process called hydrodesulfurization (HDS). HDS is performed at an industrial level with the use of NiMo, CoMo or NiW catalysts supported on alumina. Unsupported MoS₂ (bulk) catalysts have recently attracted attention due to their high activity and selectivity in HDS. In this study, bulk NiMo catalyst precursors were synthesized using solvothermal methods with varying pH and solvothermal synthesis time. The precursors and catalysts were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS) microanalysis, X-ray diffraction (XRD), textural properties using liquid nitrogen physisorption at 77 K, Raman spectroscopy and high-resolution transmission electron microscopy (HTREM). The results indicate that the morphology of the NiMoO₄ precursors synthesized in an ethanol/water mixture varies, forming “grains,” “flakes” or “rods,” depending on the dwell time and synthesis conditions. The catalytic activity results show that the bulk NiMo catalyst synthesized at 2 h presented higher selectivity and catalytic activity in the HDS of 4,6-DMDBT when compared to a supported reference catalyst (NiMo/γ-Al₂O₃). Full article

The indiscriminate disposal of empty aluminum beverage cans poses a major environmental pollution problem. The last decade has witnessed coordinated research targeted at finding cost-effective and practical solutions to minimize and utilize solid waste, which has become a major global environmental concern. This research is focused on the use of readily available waste aluminum (Al) cans for the synthesis of gamma-alumina. This work aims to synthesize γ-alumina from scrap Al cans using the sol-gel method, as well as their characterization. This study further explores the impact of reaction temperature on alumina synthesis at a fixed aging time of a half day. Characterization of γ-alumina was performed via FTIR, XRD, BET, and SEM–EDX analyses. The experimental results revealed the possibility of γ-alumina synthesis from waste Al cans, which can serve as catalysts/supports for various processes. A reaction temperature of 70 °C was found to be optimal for alumina synthesis from Al waste, as evidenced by our FTIR and XRD results, whereas alumina at room temperature recorded the highest surface area, at around 139 m²/g. Also, the results show that all the alumina synthesized at 70 °C recorded the highest weight and atomic percentage, at 9%, 8%, 27%, and 22%. Full article

The sensing properties of adsorption/combustion-type microsensors using 5 wt% Pt-loaded aluminas, which consist of two kinds of alumina (α-Al₂O₃ and γ-Al₂O₃), as sensing (catalytic) materials for ethanol and toluene, were investigated in air, and the mixing effects of α-Al₂O₃ with γ-Al₂O₃ on the dynamic and static responses of the sensors were discussed in this study. The mixing of 50 wt% α-Al₂O₃ with γ-Al₂O₃ was the most effective in enhancing the dynamic responses to ethanol, which originated from the flash combustion behavior of ethanol and/or their partially decomposed products adsorbed on the sensing films from 150 °C to 450 °C, while further mixing of α-Al₂O₃ with γ-Al₂O₃ tended to increase the dynamic responses to toluene. On the other hand, the static responses to both ethanol and toluene, which arise from their catalytic combustion at elevated temperatures (450 °C), mainly increased with an increase in the addition of α-Al₂O₃ in the 5 wt% Pt-loaded aluminas. These results indicate that the synergistic effects of the catalytic activity and the thermal conductivity of the 5 wt% Pt-loaded aluminas are the most important for the sensing properties of these sensors to ethanol and toluene. Full article

Plasma electrolytic oxidation (PEO) has emerged as a promising surface coating technique producing high-quality ceramic coating for light metals like Al, Mg, Ti, and their alloys. AA7075 is one of the commonly used Al alloys for aircraft structures, gears and shafts, and automotives as it provides high yield and tensile strength. However, Al and its alloys have drawbacks that limit their further application. Thus, surface treatments are proposed to improve the metal and its alloy’s properties. In this study, the PEO of AA7075 was carried out with an AC power source under a pulsed unipolar potentiostatic mode at varying voltages of 425 and 450 V in 1000 Hz and at 80% duty cycles of 30 m. The effect of varying voltages on the morphology, coating thickness, and corrosion resistance of the PEO-coated samples was investigated. Surface morphology, elemental distribution, and phase composition were characterized using SEM, EDX, and XRD. A porous structure with a pancake-like shape, a crater, and nodular structures were observed with coating thickness ranges from 12.1 to 55.3 ± 4.67 µm. Al, α-alumina, and γ-alumina were detected in all surface coatings. The PEO-coated sample at 450 V exhibited higher corrosion resistance evaluated via potentiodynamic polarization and EIS. Full article

Nanocrystalline mullite was synthetized by annealing a highly porous 3D structure consisting of nanofibrous aluminum oxyhydroxides treated with ethoxysilanes. The chemical, structural, and phase transformations in the aluminosilicate nanosystem were studied in the temperature range between 100 and 1600 °C. The features of the solid-phase synthesis of mullite at the interface of crystalline alumina with a liquid silica layer are discussed. It was established that chemical modification of the alumina surface with ethoxysilanes significantly limits the interphase mass transport and delays the phase transformation of the amorphous oxide into γ-Al₂O₃, which begins at temperatures above 1000 °C, while the basic structural nanofibrils are already crystallized at ~850 °C. The formation of mullite was completed at temperatures ≥ 1200 °C, where the fraction of γ-Al₂O₃ sharply decreased. Full article

γ-Alumina is often used as a support for hydrodesulfurization catalysts due to its excellent performance. During the catalytic reaction, the strong surface acidity of γ-alumina can induce a strong interaction between the active phase and the support. The reaction activity of the catalyst can be affected by changing the present mode of the active phase on the surface of the support. The (110) crystal plane, acting as the strongest acidity plane of γ-alumina, was selected for modification. The supports modified with boron and phosphorus were successfully constructed, and the acid strengths were quantified by simulating the adsorption of the relevant probe molecules: pyridine in correlation with surface electronic properties via density functional theory. The surface adsorption energy calculation shows that the boron-modified surface is able to moderately reduce the adsorption capacity of alumina, while that of the surface modified by phosphorus is found to be enhanced over the sites of a tetrahedral coordination structure; however, at the other unsaturated Al sites, this is obviously reduced. The results of introducing electric fields imply that applying horizontal electric fields changes the surface acidity of alumina under the premise of a stable structure. With the enhancement of the horizontal electric fields, the adsorption capacity of tetra-coordination sites on the original surface gradually decreases, while those of the others gradually increases. However, for the boron-modified surface, introducing horizontal electric fields can reduce the adsorption capacity of all sites. Hence, microwave-electric-field-assisted modification of B further reduces the surface acidity of alumina, making it beneficial for deep hydrodesulfurization reactions. Full article

The present study investigates hybrid nanofluid (HNF) behavior at the stagnation point near a stretching/shrinking sheet using the Tiwari and Das model. The governing equations were transformed into a boundary layer flow model and simulated using COMSOL Multiphysics 6.0. This research examines flow characteristics, temperature profiles, and distributions by varying parameters: stretching/shrinking ($\lambda$, −2 to 2), slip flow ($\delta$, 0 to 1 m), suction ($\gamma$, 0 to 1), and similarity variables ($\eta$, 0 to 5). The HNF comprised equal ratios of copper and alumina with total concentrations ranging from 0.01 to 0.1. The results showed that velocity profiles increased with distance from the stagnation point, escalated in shrinking cases, and decayed in stretching cases. Increased suction consistently reduced velocity profiles. Temperature distribution was slightly slower in shrinking compared to stretching cases, with expansion along the sheet directly proportional to $\eta$ estimates but controllable through suction adjustments. The findings were applied to enhance photovoltaic thermal (PV/T) system performance. Stretching sheets proved crucial for improving electricity production efficiency. Non-slip wall conditions and increased copper volume fractions in the presence of suction effects led to notable improvements in electrical efficiency. The maximum average efficiency was achieved when $\gamma$ = 0.4, $\lambda$ = 2, $\delta$ = 0.7, and ${\varphi }_2$ = 0.01, which was of about 10%. The present numerical work also aligned well with the experimental results when evaluating the thermal efficiency of conventional fluids. These insights contribute to optimizing PV/T system parameters and advancing solar energy conversion technology, with potential implications for broader applications in the field. Full article

Al₂O₃, Al₂O₃-graphite and Al₂O₃-ZrO₂ coatings were formed on the C45 steel rolls using atmospheric plasma spraying. The influence of graphite and zirconia addition on the surface morphology, phase composition and tribological properties under dry sliding conditions using 30 N load were analyzed. It was found that the addition of graphite or ZrO₂ slightly affected the fraction of the α-Al₂O₃ and γ-Al₂O₃ phases in the alumina coatings. The highest mass loss rate (~8.84 × 10⁻⁴ g/s) was obtained for the friction pair of C45 steel roll and steel plate. The friction coefficient of the Al₂O₃-graphite coating was slightly lower (up to 7%) compared to the coating of Al₂O₃-ZrO₂. However, the friction pair of Al₂O₃-ZrO₂ coating and steel plate demonstrated the highest wear resistance under dry sliding conditions. The increase in the wear resistance of the Al₂O₃-graphite and Al₂O₃-ZrO₂ coatings is due to the formation of tribofilm in the sliding contact zone. Full article

Porous α-Al₂O₃ ceramics are a highly sought-after material with a multitude of applications; for example, they are used as filters, substrates, biomedicine materials, etc. Despite the availability of raw materials, a challenge associated with this technology is the high energy budget caused by sintering above 1500 °C. For the cold sintering processing (CSP) of ceramics, lowering the α-Al₂O₃ sintering temperature is one of the most urgent challenges in the background of its rapid development. This paper is the first to demonstrate a solution to this problem using the CSP of α-alumina ceramics in the presence of pure water as a transient liquid. The manufactured materials were examined using XRD analysis; the evolution of their microstructures during CSP was revealed by SEM; and the porosity was evaluated using the Archimedes method. Ceramics with an open porosity up to 36% were produced at 380–450 °C and 220 MPa in 30 min. An increase in the pressure was found to impede α-Al₂O₃ formation from γ-AlOOH. The development of the microstructure was discussed within the framework of the dissolution–precipitation model and homogenous nucleation. The results of the SEM study pointed to the coalescence of γ-AlOOH grains during CSP. Full article

Effects of Nb on the creep resistance and hot corrosion behavior of the Fe-25Cr-35Ni-2.5Al-xNb (x = 0, 0.6, 1.2) Alumina-Forming Austenitic stainless steels (AFA steels) at 700 °C were investigated. The addition of Nb promoted the precipitation of both nanoscale NbC and γ′-Ni₃(Al, Nb) phases, which exhibited very low coarsening rate constants. The nanoscale NbC and γ′-Ni₃(Al, Nb) phases effectively impeded the migration of dislocations and led to an improvement in creep performance of the Nb-addition AFA steel. The corrosion of AFA steels in Na₂SO₄-25%K₂SO₄ at 700 °C was primarily driven by an “oxidation-sulfidation” mechanism. The addition of Nb, serving as a third element, facilitated the formation of protective Cr₂O₃ and Al₂O₃ films, which improved the hot corrosion resistance performance. However, the formation Nb₂O₅ was found to compromise the compactness of the oxide film, which adversely affected the corrosion resistance. Full article

Tetrahydrofurfuryl alcohol, a cost-effective biomass derivative, offers a sustainable path for synthesizing 1,5-pentanediol through hydrogenolysis. To develop the efficient production of 1,5-pentanediol from this alcohol, we have prepared a series of MgAl₂O₄-modified Pt/WO_x/γ-Al₂O₃ catalysts with varying compositions via impregnation–calcination methods. The physicochemical properties of these catalysts were subsequently characterized using diverse techniques. Characterization revealed that magnesia–alumina spinel modification enhanced Pt particle dispersion, CO adsorption on Pt/WO_x/γ-Al₂O₃, reduced Pt particle reduction temperature, diminished the acid content in the catalysts, and increased the surface oxygen vacancy concentration. These alterations appear to influence the catalyst performance, though other factors cannot be ruled out. Catalytic activity tests demonstrated that magnesia–alumina spinel modification improved tetrahydrofurfuryl alcohol hydrogenolysis activity and the 1,5-pentanediol selectivity of Pt/WO_x/γ-Al₂O₃. Optimal performance was achieved at 12% magnesia–alumina spinel loading, with a tetrahydrofurfuryl alcohol conversion of 47.3% and 1,5-pentanediol selectivity of 88.4%. Full article