Search Results (439)

This study clarifies the catalytic role of chloride ions on the corrosion performance of SS316L alloy immersed in molten LiNaK carbonate salt at 700 °C. Accordingly, isothermal static immersion corrosion tests were systematically conducted under different experimental conditions. Our results revealed that the presence of Cl significantly accelerates the corrosion process: the rate constant of the corroded samples increased from 11.3 × 10⁻² mg/cm² to 13.8 × 10⁻² mg/cm² with the addition of Cl. Continuous migration of Cl₂ and volatile metal chlorides leads to the formation of obvious pores, transverse cracks along grain boundaries, surface wrinkles, and partial spalling of the oxide scale, thereby severely aggravating substrate degradation. Notably, no chlorine-containing compounds or chlorine-rich regions were detected in the corroded samples, confirming that chlorine is not consumed in the corrosion process, rather it acts as an autocatalyst through the cyclic process of “oxidation–diffusion–reaction–regeneration”. Full article

Ammonia has emerged as a strategically advantageous hydrogen carrier; however, its efficient decomposition using conventional solid catalysts remains technically challenging from an industrial standpoint, particularly in terms of long-term stability and large-scale implementation. In this study, we propose a strategy for ammonia cracking by utilizing Sn-based molten metal alloys in a bubble column reactor, which provides a sintering-resistant and thermally efficient catalytic platform. Among various candidate transition metals, the Sn-Co alloy exhibited the most superior catalytic performance, demonstrating a significant reduction in the apparent activation energy to 52.6 kJ/mol. To the best of our knowledge, this study provides the first experimental evidence of the catalytic role of molten metals in the ammonia decomposition process. Structural characterization confirmed that the molten alloy maintains its metallic state without the formation of nitrides, verifying the function of the molten metal as an active catalyst rather than a sacrificial reagent. This work offers a new catalytic approach that addresses the requirements for the commercialization of ammonia cracking through improved scalability and chemical durability. Full article

While temperature and acidity dominate the design of zeolite catalysts for olefin cracking, the role of reaction time as an independent variable governing pathway dynamic remains elusive. This study integrates experimental and simulation methods to unravel the dynamic competition among carbenium ion cracking, thermal cracking and Confined Catalytic Radical (CCR) pathways during 1-pentene cracking on H-ZSM-5 zeolite at 650 °C. Analysis of the optimum performance envelope (OPE) curves for cracking products revealed that, in the initial reaction stage, the CCR mechanism significantly enhances ethylene yield. As the reaction time prolongs, C₅+ olefins in the gas phase undergo further cracking on the zeolite surface, markedly increasing the contribution of the carbenium ion pathway. Molecular simulations indicate that C₅+ olefins exhibit stronger adsorption capacity but lower diffusion coefficients on H-ZSM-5, and this adsorption–diffusion disparity is a key factor influencing the evolution of 1-pentene cracking pathways. Concurrently, thermal cracking reactions are also enhanced with increasing residence time, which is unfavorable for ethylene formation. This work elucidates the time-dependent evolution of 1-pentene cracking pathways and the regulatory role of intraparticle mass transfer, providing a theoretical basis for optimizing light olefin selectivity through the adjustment of reaction time and catalyst structure. Full article

The present study evaluates the electrochemical behaviour of reinforcing steel embedded in an alkali-activated eco-cellular geopolymer concrete designed for applications in environments with high chloride exposure. The material was formulated using a ternary precursor composed of fluid catalytic cracking residue (FCC), Class F fly ash, and ground granulated blast furnace slag (BFS), activated with an alkaline solution and combined with preformed foam to generate a microstructure characterised by predominantly closed porosity and low capillary connectivity. The electrochemical response of the system was assessed through open circuit potential (OCP) measurements, Tafel polarisation curves, electrochemical impedance spectroscopy (EIS), and potentiodynamic tests under accelerated exposure to NaCl solutions. The results demonstrate a markedly improved electrochemical performance, evidenced by shifts in OCP towards more noble values, reductions of 45–65% in corrosion current density (Icorr), and increases of up to fourfold in charge transfer resistance (Rct), together with the development of broader and more stable passive regions. This behaviour is attributed to the synergistic interaction between the formation of dense N-(C)-A-S-H (sodium/calcium–aluminosilicate hydrate) and C-(A)-S-H (calcium–aluminosilicate hydrate) gels, the eco-cellular architecture with low capillary connectivity, and the stable high alkalinity of the activated matrix, which collectively restrict ionic transport and promote the passive stability of the reinforcing steel—defined here by noble OCP values, low Icorr, high Rct, and sustained passive domains in polarisation curves. Overall, the findings position the developed eco-cellular geopolymer concrete as a sustainable, high-performance alternative for infrastructure exposed to chloride-rich environments. Full article

Hydrogen has been widely regarded as a key energy carrier. However, its storage and long-distance transportation are challenging, resulting in the emergence of ammonia as a potential carrier of hydrogen due to its high hydrogen density, ease of liquefaction, and established transport infrastructure. This study presents a techno-economic and environmental impact assessment of two methods of hydrogen production from ammonia: catalytic cracking (ACC) and electrocatalytic (AEC) decomposition, modeled under the specific local economic conditions of Brunei Darussalam. Analysis over a 20-year plant lifetime under local economic conditions indicates that the more technologically established ACC achieves a higher net present value of USD 7.298 million, compared to USD 6.867 million for AEC, primarily due to its significantly lower replacement costs. Sensitivity analysis indicates that AEC becomes economically favorable at production rates above approximately 29.5 kg/h or electricity prices exceeding USD 0.13/kWh. Environmental impact analysis indicates that AEC produces higher lifetime CO₂ emissions of approximately 84.9 million kg, compared to ACC with approximately 44.0 million kg of CO₂ emissions under grid-based electricity supply. This is mainly due to its higher electricity demand. Overall, the study highlights clear economic–environmental trade-offs between ACC and AEC and underscores the importance of integrated techno-economic and environmental evaluation for ammonia-based hydrogen systems in a Bruneian context. Full article

Spent fluid catalytic cracking catalysts (E-cat) are a challenging waste from the petroleum refining industry, enriched with heavy metals such as nickel, vanadium, and iron. This study proposes a circular valorization strategy by incorporating E-cat into a chemically bonded iron phosphate ceramic matrix, known for its excellent waste stabilization properties. Composites were synthesized at room temperature using E-cat, hematite, and phosphoric acid, with E-cat contents from 0% to 35%. Characterization by XRF, XRD, SEM, compressive strength, and water absorption tests identified an optimal formulation containing 16% E-cat, achieving a maximum compressive strength of 16.6 MPa, 35% higher than the control. This improvement can be attributed to the dual function of E-cat, acting both as a micro-aggregate that promotes matrix densification and as a pozzolanic component that enhances mechanical reinforcement. These results demonstrate that iron phosphate ceramics represent a low-energy and sustainable strategy for the immobilization of spent catalysts and the production of durable construction composites. Full article

In this work, the kinetics of the redistribution of oils, resins, and asphaltenes in high-viscosity oil from the Karazhanbas field (Republic of Kazakhstan) were investigated. This was achieved with an ultrasonic treatment (22 kHz, 50 W) in the presence of a zeolite catalyst (1.0 wt%). The parameters of the technological process were established as a temperature range from 30 to 70 °C and an exposure time of 3 to 11 min. This allowed us to increase the oil content by 14.8% and decrease the concentration of resins by 12.2% and asphaltenes by 2.6%. Conversion schemes (“oils ↔ resins” and “resins ↔ asphaltenes”) were developed, which made it possible to determine the main direction of the reaction processes. The most rapid process is the conversion of resins to oils (k₂ = 0.1148–0.1860 min⁻¹). The process of the cracking of asphaltenes with the formation of resins (k₄ = 0.1023–0.1413 min⁻¹) ranks second in rates. Condensation reactions, including the transition of oils to resins (k₁ = 0.0175–0.0252 min⁻¹) and resins to asphaltenes (k₃ = 0.0139–0.0194 min⁻¹), occur significantly more slowly. The calculated activation energies (7.0–10.4 kJ/mol) show that the cavitation treatment of high-viscosity oil in the presence of a catalyst effectuates the processing of heavy oil with minimal energy consumption. A group composition analysis of the light and middle oil fractions demonstrated an increase in paraffinic, naphthenic, benzenic, and olefinic hydrocarbons, with a simultaneous decrease in naphthalenes and heteroatomic compounds. The results obtained confirm the effectiveness of ultrasonic–catalytic treatment for the structural cracking of high-viscosity oil and the formation of lighter hydrocarbon fractions. Full article

The sustainable management of typical petrochemical hazardous wastes, such as oil sludge (OS), spent fluid catalytic cracking catalysts (SFCCs), and petrochemical-contaminated soil (PCS), poses a significant challenge. This study developed a synergistic sintering strategy that utilizes the complementary properties of these materials, with OS serving as an organic source, SFCCs and PCS providing an aluminosilicate framework, and waste glass powder (GP) acting as a fluxing agent to produce an environmentally friendly, high-strength ceramsite (OSPG-Opt). Single-factor experiments were first conducted to investigate the effects of OS content, sintering temperature, and duration. Subsequently, the Box–Behnken design was employed to optimize the process for maximizing aggregate strength. The optimal conditions were determined to be 30.5% OS content, a sintering temperature of 1142 °C, and a sintering time of 32 min. Under these conditions, the resulting ceramsite demonstrated a compressive strength of 23.12 MPa, along with a bulk density of 1012.50 kg/m³ and low water absorption of 1.61%, meeting the requirements of the Chinese standard T/CSTM 00548-2022 for structural materials. Microstructural analysis identified the presence of quartz, anorthite solid solution, hematite, and albite. The remarkable mechanical strength is attributed to an interlocking structure of anorthite solid solution within a glassy matrix, which also contributes to effective heavy metal immobilization, ensuring the excellent environmental performance of the final product. Full article

The increasing energy demand and global dependence on conventional fuels have resulted in severe greenhouse gas (GHG) emissions, necessitating the development of sustainable bioenergy alternatives. Algal is recognized as a promising feedstock for the production of fourth-generation biofuels. This study optimizes catalytic pyrolysis of Arthrospira platensis for bio-oil production via a dual-bed catalyst system of iron-impregnated dolomite (Fe/DM) and a copper-impregnated spent fluid catalytic cracking catalyst (Cu/sFCC). A face-central composite design (FCCD) and response surface methodology (RSM) were used for the delineation of optimal conditions, ensuring that all experimental tests remained within feasible operating conditions of 500–600 °C, a reaction time of 45–75 min, a N₂ flow rate of 50–200 mL/min, and a catalyst loading of 5–20 wt%. The bio-oil yield was maximized at 39.73 ± 2.86 wt% at 500 °C for 45 min, a N₂ flow of 50 mL/min, and 5 wt% catalyst loading to feedstock with a 0.4:0.6 mass ratio of Fe/DM: Cu/sFCC. The dual-catalysts combined Brønsted and Lewis acid sites enhanced the catalytic activity, which promotes the cleavage of carbon–carbon and carbon–hydrogen bonds, including the mechanism of catalytic pathways such as dehydration, decarboxylation, oligomerization, aromatization, and further cracking reactions, and was successful in converting high-molecular-weight molecules into lighter hydrocarbons and significantly improving product selectivity, demonstrating a highly effective pathway for producing high-quality sustainable biofuel. Full article

Catalytic pyrolysis is a crucial technology for lignin valorization, where the catalyst support itself can play a pivotal role in influencing the catalytic process. This study systematically investigates and compares the distinct catalytic effects of two commonly used catalyst supports, HZSM-5 zeolite and activated carbon (AC), during lignin pyrolysis. Macrokinetic analysis was conducted using TGA coupled with the Friedman kinetic model to determine the apparent activation energies (Ea) and coke yields. The evolution of functional groups was analyzed using Py-GC/MS coupled with quantitative functional group indexing. Additionally, the evolution of small-molecule gases during catalytic pyrolysis was monitored using TGA-FTIR. The results demonstrate differences in the catalytic pathways promoted by HZSM-5 and AC. HZSM-5 effectively deoxygenated lignin by removing methoxy and hydroxyl groups, resulting in a reduction in Ea by 83 kJ/mol at 80% conversion and suppression of coke formation. In contrast, AC, exploiting its large specific surface area as a reaction platform, promoted the conversion of methoxy groups into methyl and hydroxyl functional groups, rather than directly removing them. Moreover, the use of AC led to a marked increase in Ea, and the coke yield increased by 2.5%. This study provides valuable insights for the rational design of efficient catalyst systems for biomass conversion. Full article

With rising demand for clean energy and uncertainty surrounding large-scale renewable deployment, ammonia has emerged as a viable carrier for hydrogen storage and transportation. This study conducts a global patent-based analysis of ammonia-to-hydrogen production technologies to determine technological maturity, dominant design pathways, and emerging innovation trends. A statistically robust retrieval, screening, and classification process, based on the PRISMA guidelines, was employed to screen, sort, and analyze 708 relevant patent families systematically. Patent families were categorized according to synthesis processes, catalyst types, and technological fields. The findings indicate that electrochemical, plasma-based, photocatalytic, and hybrid systems are being increasingly investigated as alternatives to low-temperature processes. At the same time, thermal catalytic cracking remains the most established and widely used method. Significant advances in reactor engineering, system integration, and catalyst design have been observed, especially in Asia. While national hydrogen initiatives, such as those in Brunei, highlight the policy importance of ammonia-based hydrogen systems, the findings primarily provide a global overview of technological maturity and innovation trajectories, thereby facilitating long-term transitions to cleaner hydrogen pathways. Full article

The maritime transport sector’s reliance on fossil-based fuels remains a major contributor to global greenhouse gas emissions, underscoring the urgent need for sustainable alternatives such as marine biofuels. Thermochemical pyrolysis of biomass and plastic waste represents a promising route for producing renewable and recycled marine fuel feedstocks. This review provides an integrated analysis of the full production and upgrading chain, encompassing pyrolysis of lignocellulosic biomass and polymer-derived resources, catalytic upgrading, and qualitative evaluation of product distribution and yield trends. Particular emphasis is placed on montmorillonite-based catalysts as naturally abundant, low-cost, and environmentally benign alternatives to conventional zeolites. The review systematically examines the influence of key montmorillonite modification strategies, including acid activation, pillaring, and ion-exchanged, on acidity, textural properties, and catalytic performance in catalytic cracking and hydrodeoxygenation processes. The analysis shows that catalyst modification strongly governs the yield, selectivity, and reproducibility of biofuels. By adopting this integrated perspective, the review extends beyond existing works focused on isolated upgrading steps or zeolitic catalysts. Key research gaps are identified, particularly regarding long-term catalyst stability, deep deoxygenation of real bio-oils, and compliance with marine fuel standards. Full article

Polyethylene is the most used plastic in the world, and over 90% of this plastic is ultimately disposed of in landfills or released into the environment, leading to severe ecological implications. In this research, the technoeconomic feasibility of upcycling low-density polyethylene (LDPE) to produce ethylene is studied. The catalytic conversion of LDPE to ethylene is considered in microwave heating mode and Joule heating mode. Experimental data is obtained under conditions where most of the upcycled products are in the gas phase. A flowsheet is developed that produces industrial quantities of ethylene for both heating modes. A technoeconomic analysis and a life cycle analysis are conducted and compared with the traditional ethane cracking process for producing ethylene. Simulation results indicate that the upcycling system exhibits a lower capital expenditure and a comparable operating expenditure relative to conventional ethane steam cracking while generating additional valuable co-products, such as propylene and aromatic hydrocarbons, leading to a higher net present value potential. Sensitivity analyses reveal that the electricity price has the most significant impact on both the net present value and levelized cost of production, followed by the low-density polyethylene feedstock cost. Life-cycle assessment reveals a substantial reduction in greenhouse-gas emissions in the upcycled process compared to the fossil-based ethane steam-cracking route, primarily due to the use of renewable electricity, the lower reaction temperature that reduces utility demand, and the use of plastic waste as the feedstock. Overall, the proposed process demonstrates strong potential for the sustainable production of ethylene from waste LDPE. Full article

Plastic streams dominated by polyethylene (PE) including PE HD/MD (High Density/Medium Density) and PE LD/LLD (Low Density/Linear Low Density), polypropylene (PP), and polyvinyl chloride (PVC) across Europe demand a design framework that links synthesis with end of life reactivity, supporting circular economic goals and European Union waste management targets. This work integrates polymerization derived chain architecture and depolymerization mechanisms to guide selective valorization of commercial plastic wastes in the European context. Catalytic topologies such as Bronsted or Lewis acidity, framework aluminum siting, micro and mesoporosity, initiators, and strategies for process termination are evaluated under relevant variables including temperature, heating rate, vapor residence time, and pressure as encountered in industrial practice throughout Europe. The analysis demonstrates that polymer chain architecture constrains reaction pathways and attainable product profiles, while additives, catalyst residues, and contaminants in real waste streams can shift radical populations and observed selectivity under otherwise similar operating windows. For example, strong Bronsted acidity and shape selective micropores favor the formation of C₂ to C₄ olefins and Benzene, Toluene, and Xylene (BTX) aromatics, while weaker acidity and hierarchical porosity help preserve chain length, resulting in paraffinic oils and waxes. Increasing mesopore content shortens contact times and limits undesired secondary cracking. The use of suitable initiators lowers the energy threshold and broadens processing options, whereas diffusion management and surface passivation help reduce catalyst deactivation. In the case of PVC, continuous hydrogen chloride removal and the use of basic or redox co catalysts or ionic liquids reduce the dehydrochlorination temperature and improve fraction purity. Staged dechlorination followed by subsequent residue cracking is essential to obtain high quality output and prevent the release of harmful by products within European Union approved processes. Framing process design as a sequence that connects chain architecture, degradation chemistry, and operating windows supports mechanistically informed selection of catalysts, severity, and residence time, while recognizing that reported selectivity varies strongly with reactor configuration and feed heterogeneity and that focused comparative studies are required to validate quantitative structure to selectivity links. In European post consumer sorting chains, PS and PC are frequently handled as separate fractions or appear in residues with distinct processing routes, therefore they are not included in the polymer set analyzed here. Polystyrene and polycarbonate are outside the scope of this review because they are commonly handled as separate fractions and are typically optimized toward different product slates than the gas, oil, and wax focused pathways emphasized here. Full article

Ammonia serves as a critical medium for hydrogen storage and energy transportation, making the development of efficient ammonia cracking technologies essential for advancing hydrogen energy applications. Plasma-assisted ammonia cracking has emerged as a promising approach for clean energy conversion, leveraging non-thermal plasma to effectively decompose ammonia into hydrogen and nitrogen. Compared to conventional thermal catalytic cracking, this method offers several advantages, including rapid startup and response, operational flexibility, and the ability to operate under low-temperature and atmospheric pressure conditions. This study presents a novel high-pressure plasma reactor designed to overcome the high-energy barriers associated with conventional methods. Through systematic optimization of discharge parameters, reactor configuration, and catalyst integration, significant improvements in both ammonia conversion efficiency and energy utilization have been achieved. Experimental results demonstrate that increased discharge power and reduced ammonia flow rate enhance cracking performance. In the absence of a catalyst, conversion efficiency initially increases with pressure but subsequently decreases at higher pressures. However, the incorporation of a catalyst markedly improves overall performance across all tested conditions. These advancements support the practical implementation of ammonia-based systems for distributed hydrogen supply and clean propulsion technologies. Full article