Search Results (59)

The selective conversion of high-molecular-weight paraffins (C₂₀–C₄₀) into linear alpha-olefins is often hindered by severe diffusion limitations and secondary over-cracking. This study addresses these challenges by transforming low-value natural minerals into sophisticated catalytic systems. We present a “top-down” engineering strategy for designing hierarchical catalysts based on natural Kazakhstani clinoptilolite. The multi-stage modification involves synergistic demineralization and precision chelation (EDTA, sulfosalicylic acid) to generate a tailored mesoporous architecture. This framework serves as a host for the sub-nanometric immobilization of Keggin-type heteropolyacids (PW₁₂, PMo₁₂), ensuring optimal active-phase dispersion. The innovative dual-step modification successfully bypassed the “micropore barrier”, creating a high-surface-area hierarchical network that facilitates the transport of bulky paraffinic molecules. Precise localization of heteropolyacid clusters within the created mesopores resulted in the formation of superstrong Lewis acid sites, as confirmed via temperature-programmed ammonia desorption. These sites triggered a highly efficient monomolecular beta-scission mechanism, suppressing undesirable hydrogen transfer reactions. The resulting catalysts achieved a breakthrough in technical paraffin cracking, delivering a 70% liquid product yield with an unprecedented >50% selectivity toward the C₇–C₁₄ α-olefin fraction. This work demonstrates a sustainable pathway for upgrading natural zeolites into high-performance, green catalysts that rival expensive analogs in precision and efficiency. Full article

In this review, the application of microbially induced calcium carbonate precipitation (MICP) for repairing coal mining-induced cracks in loess soils was summarized, and its objectives, main findings, and key challenges were highlighted. First, the formation characteristics and engineering demands of mining-induced loess cracks were analyzed, and the limitations of existing repair methods in terms of durability, adaptability, and environmental impact were emphasized. The advantages of MICP for soil stabilization, crack sealing, and ground improvement were presented, demonstrating its potential for use in the remediation of cracks in loess. Key challenges in practical implementation, including uneven injection, clogging, environmental constraints on microbial activity, ammonia byproduct risks, and insufficient long-term stability assessment, were discussed. Overall, MICP offers a sustainable and effective strategy for loess crack repair, providing a promising approach for ecological restoration and geotechnical reinforcement in mining-affected regions. 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

The compliant discharge of landfill leachate constitutes a pivotal factor for the effective implementation of integrated water resource management. Aged landfill leachate exhibits complex composition and an imbalanced carbon-to-nitrogen ratio. Electrocatalytic oxidation technology, as an efficient advanced oxidation process, demonstrates promising application potential. This study employed Ti/RuO₂–IrO₂ Anodes for the electrocatalytic oxidation treatment of aged landfill leachate. The removal efficiencies and variation patterns of chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen at different current densities and reaction times were systematically investigated, along with an analysis of energy consumption and current efficiency. The degradation and transformation processes of organic matter were elucidated using Three-dimensional Excitation–Emission Matrix (EEM) Spectra. Fresh anodes and those used for 1000 h were characterized by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) to elucidate their failure mechanisms. The results demonstrate that electrocatalytic oxidation achieves efficient pollutant removal. At a current density of 1000 A/m² and a reaction time of 30 min, the effluent concentrations of ammonia nitrogen and total nitrogen satisfied the discharge standards, while COD complied with emission requirements after 60 min. The pollutant removal efficiencies were positively correlated with current density and reaction time. EEM analysis revealed that the electrocatalytic process effectively disrupts the structure of macromolecular organic matter, degrading it into smaller molecules and eventually achieving complete mineralization. Electrode characterization identified titanium substrate corrosion due to coating cracks and coating detachment as the primary causes of electrode failure. This study confirms the effectiveness of electrocatalytic oxidation technology for treating aged landfill leachate, and provides a theoretical foundation and technical support for its practical engineering application. The technology exhibits considerable theoretical significance and promising application potential in the treatment of landfill leachate. Full article

This work numerically examines the premixed combustion of partially cracked ammonia/air in a cavity-stabilized micro-combustor. Effects of the equivalence ratio (Φ) and inlet temperature (T_in) on the combustion features, flame–wall heat transfer and nitrogen-containing emissions are investigated quantitatively at a cracking ratio of 0.6. Results show that increasing Φ from 0.8 to 1.2 shifts the high-temperature region downstream and causes it to elongate axially. This spatial expansion decreases peak temperatures and distributes heat release over a longer distance. Mean wall temperature and overall heat loss are thus decreased due to weakened near-wall thermal interaction. NO formation closely follows the high-temperature and OH-rich zones. However, at Φ = 1.2, oxygen limitation suppresses NO production and redirects fuel-bound nitrogen towards N₂O, enhancing its outlet emissions. As T_in increases from 300 K to 500 K, the improved reactivity of the mixture promotes an upstream shift of the main reaction zone. The reaction zone becomes more concentrated within the cavity. Such structural changes intensify NO formation but simultaneously compress the high-temperature zone, which reduces the wall-averaged temperature and overall heat loss. In the extended downstream post-flame region, lower temperatures and limited radical activity suppress NO₂ formation and N₂O decomposition. As a result, NO₂ emissions decrease monotonically, while N₂O emissions exhibit a gradual increase. These findings provide useful insights into the effects of operating parameters on combustion stability, heat transfer and nitrogenous pollutant evolution in microscale partially cracked ammonia flames. 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

The global transition toward a low-carbon economy has intensified the interest in green hydrogen as a key enabler of industrial decarbonization. In particular, the steel sector, one of the most carbon-intensive industries, offers significant opportunities for emissions reduction through H₂-based technologies. This study presents a techno-economic assessment of alternative green hydrogen supply pathways, namely alkaline electrolysis and ammonia cracking, and evaluates their integration into hydrogen-based direct reduction (HyDR) routes. Process simulations are performed using Aspen Plus^® V14 to quantify the energy consumption, hydrogen demand, and associated CO₂ emissions across multiple configurations and case studies. A comprehensive 3E (energy, economics, and environmental) evaluation framework is applied to compare system performance and assess the suitability of each pathway for large-scale deployment. The results indicate that ammonia cracking represents a technically viable and potentially competitive hydrogen supply option for steel decarbonization under the assumed operating conditions, highlighting its relevance as a transitional pathway toward low-carbon steel production. Full article

Achieving a green transition in the energy structure and reducing reliance on traditional fossil fuels has become a global imperative for addressing climate change and promoting sustainable development. The search for clean energy alternatives to traditional fossil fuels has emerged as a critical challenge in the energy and power sector. Ammonia (NH₃) shows great potential as a zero-carbon fuel in the energy sector, but issues such as its low flame propagation speed, high ignition energy requirements, and elevated NO_x emissions limit its widespread industrial application. To address these issues and enhance ammonia combustion, plasma-assisted combustion technology has gained widespread attention in recent years as an effective solution. The plasma-assisted technology enhances combustion stability and efficiency of ammonia, and effectively suppresses NO_x emissions. Additionally, the high-energy electrons and intense chemical reactions in plasma help to decompose and crack ammonia fuel, increase flame propagation speed, and thus improve ammonia combustion performance. This paper provides a comprehensive review of the latest research advancements in plasma-assisted technology in ammonia combustion. It covers the fundamental principles of plasma generation, the mechanisms of combustion enhancement, industrial application status, and development trends. The aim is to assess the potential of plasma-assisted combustion technology in achieving efficient, stable, and low-carbon ammonia combustion, and to explore its future prospects for industrial application. 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

This study examines the high-temperature degradation of Hastelloy C276, a corrosion-resistant nickel-based alloy, during exposure to combustion products generated by methane and 99% cracked ammonia. Using a high-pressure optical combustor (HPOC) at 4 bar and exhaust temperatures of 815–860 °C, standard tensile specimens were exposed for five hours to fully developed post-flame exhaust gases, simulating real industrial turbine or burner conditions. The surfaces and subsurface regions of the samples were analysed using scanning electron microscopy (SEM; Zeiss Sigma HD FEG-SEM, Carl Zeiss, Oberkochen, Germany) and energy-dispersive X-ray spectroscopy (EDX; Oxford Instruments X-MaxN detectors, Oxford Instruments, Abingdon, United Kingdom), while mechanical properties were evaluated by tensile testing, and the gas-phase compositions were tracked in detail for each fuel blend. Results show that exposure to methane causes moderate oxidation and some grain boundary carburisation, with localised carbon enrichment detected by high-resolution EDX mapping. In contrast, 99% cracked ammonia resulted in much more aggressive selective oxidation, as evidenced by extensive surface roughening, significant chromium depletion, and higher oxygen incorporation, correlating with increased NO_x in the exhaust gas. Tensile testing reveals that methane exposure causes severe embrittlement (yield strength +41%, elongation −53%) through grain boundary carbide precipitation, while cracked ammonia exposure results in moderate degradation (yield strength +4%, elongation −24%) with fully preserved ultimate tensile strength (870 MPa), despite more aggressive surface oxidation. These counterintuitive findings demonstrate that grain boundary integrity is more critical than surface condition for mechanical reliability. These findings underscore the importance of evaluating material compatibility in low-carbon and hydrogen/ammonia-fuelled combustion systems and establish critical microstructural benchmarks for the anticipated mechanical testing in future work. Full article

This study assesses four hydrogen production pathways (electrolysis, ammonia cracking, steam biomethane reforming, and methane pyrolysis) for an inland refinery under European Renewable Energy Directive III (RED III) goals. Using multicriteria decision analysis (MCDA), economic, environmental, technological, and implementation factors were evaluated. The results show that biomethane reforming offers the lowest cost, while electrolysis provides the best environmental and technological performance. Sensitivity analysis highlights electricity price as the key factor. The MCDA model proved to be effective for systematic comparison and informed strategic decision making. However, RED III regulatory requirements may favor ammonia or electrolysis for renewable fuel of non-biological origin production, emphasizing the need for long-term strategic planning to maintain competitiveness. 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

Ammonia (NH₃) is a promising zero-carbon fuel, but it faces critical challenges in combustion utilization, especially NO emission. Intensive previous studies have been carried out to deepen the understanding towards NH₃ combustion and NO emission characteristics but most of them focus on the premixed combustion mode. This work conducts both experiments and large-eddy simulations (LESs) for various NH₃/CH₄ mixtures, from pure methane to pure ammonia, under both premixed and non-premixed combustion modes, to gain a clear insight into the NO emission performance and formation mechanism of the two combustion modes. It is shown that the non-premixed combustion exhibits a stratified flame appearance, mainly due to the different reactivity between CH₄ and NH₃. Accordingly, the non-premixed combustion mode produces the lower NO emission across all NH₃ blending ratios with respect to its premixed counterpart. Further, LES results show that the flame stratification is responsible for the lower NO emission by creating a strong fuel-rich region in the combustor center where a part of NH₃ undergoes thermal cracking into H₂ and N₂. In addition, the performance of several existing NH₃/CH₄ mechanism models is estimated by comparing the predicted NO emissions against the present experimental measurement for both premixed and non-premixed mixing patterns, and the present proposed model shows the lowest error among the candidates. Full article

Cracked ammonia is attracting attention as a carbon-free energy carrier, yet trace residual ammonia after reforming can significantly affect nitrogen oxide (NOx) emissions. This study quantifies how residual ammonia from 0 to 10,000 ppm affects NOx formation using one-dimensional premixed flame simulations under gas turbine-relevant conditions (ϕ = 0.5 and 2.0, 673 K, 20 atm). NO formation is evaluated using integrated rate of production (ROP) analysis, reaction pathway analysis, and A-factor sensitivity analysis (defined as sensitivity to the pre-exponential factor in the Arrhenius rate expression). Under lean conditions (ϕ = 0.5), NO increases approximately linearly with residual ammonia. Even at 100 ppm, the dominant NO formation route shifts rapidly from thermal and N₂O mechanisms to fuel NO chemistry led by HNO. In contrast, under rich conditions (ϕ = 2.0), the final NO level remains below 10 ppm. Under rich conditions, residual ammonia and the higher flame temperature raise gross NO production in the reaction zone, yet strong DeNOx reactions in the post-flame region consume most of it, resulting in low net NO emissions. These mechanistic results inform cracking targets and the design of staged combustion strategies to minimize NOx formation when deploying cracked ammonia in practical gas turbine systems. Full article

Ammonia, widely regarded as the “hydrogen carrier of the future,” offers high hydrogen content, ease of production, and a well-established infrastructure for handling and transportation globally. Meanwhile, ammonia cracking requires a heat supply at high temperatures, and induction heating provides efficient, precise, and rapid heating to conductive materials of different shapes and sizes. Therefore, this work presents a proof of concept for ammonia cracking using induction heating with three different reactor configurations: (1) a 3D metal workpiece; (2) a 3D metal workpiece and Ni/Al₂O₃ catalyst; and (3) only Ni/Al₂O₃ catalyst. The performance of the inductively heated reactor is also compared to an electric furnace. The results showed that the reactor with the workpiece and the catalyst required 97 W to reach 650 °C, being the most efficient in terms of power usage when compared to the workpiece alone and the electric tube furnace, which required 39% and 132% more, respectively; the least efficient configuration is with just the catalyst, needing 138 W to reach just 116 °C. Overall, the introduction of the 3D workpiece allowed for fast and uniform conversion and heating within the reactor, enabling efficient and dynamic process control when applying induction heating to chemical reactors. Full article