Search Results (552)

This work presents a case study of sensitivity analysis applied to the modeling of ethanol steam reforming (SRE) in a catalytic porous medium, with a focus on hydrogen production. Considering the high variability of parameters reported in the literature, the objective is not to propose a universal model, but rather to assess the impact of uncertainties associated with input parameters on the model outcomes. The model was developed under steady-state conditions, coupling flow in porous media, species transport, and heat transfer, with kinetics described as a function of partial pressures. The sensitivity analysis was conducted through the systematic variation of kinetic and physicochemical parameters within ranges associated with their uncertainties. The results indicate that activation energy is the parameter most sensitive to uncertainty variation, exhibiting the greatest impact on hydrogen production. The thermal properties of the medium, particularly thermal conductivity and solid density, also stand out, highlighting the role of thermo-kinetic coupling. In contrast, parameters such as porosity, water reaction order, and particle diameter exhibited low sensitivity under the analyzed conditions. As a main contribution, this work establishes a sensitivity hierarchy associated with parameter uncertainties and provides guidance for other researchers regarding the prioritization of their determination and calibration in hydrogen production models. Full article

The need for a transition to a low-carbon economy has led to the growing demand for hydrogen as a clean energy source. Hence, ethanol steam reforming (ESR) is one of the promising technological pathways for hydrogen production. Ethanol, which is the major feedstock, can be obtained from abundant biomass. However, one of the major drawbacks is catalyst deactivation due to the high temperature requirement to start the reaction. This study therefore focused on employing a response surface approach to optimize the operating conditions (reaction temperature, steam-to-ethanol ratio and catalyst amount) of ethanol steam reforming over an Iridium-promoted Ni/MCM-41 catalyst. The Iridium-promoted Ni/MCM-41 catalyst was synthesized using the sequential wet impregnation method and characterized using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), N₂ physisorption analysis, and X-ray diffraction (XRD). A central composite experiment design (CCD) was employed to study the effect of the variables on the hydrogen production from the ESR. The catalytic efficacy was ascertained by evaluating the H₂ yield under varied experimental conditions provided by the CCD. The characterization of the catalyst revealed well-dispersed Ir and Ni nanoparticles on a mesoporous MCM-41 support. Catalytic evaluations indicate that the H₂ yield was most influenced by the reaction temperature (correlation coefficient of 0.68), followed by the catalyst amount (correlation coefficient of 0.34) and steam-to-ethanol ratio (correlation coefficient of 0.28). A maximum H₂ yield of 5.82 mol/mol ethanol was obtained at 798.11 °C, a steam-to-ethanol ratio of 3.40, and 1.25 g of catalyst. These findings underscore the importance of Ir-promoted Ni/MCM-41 catalyst for efficient H₂ production, highlighting the reaction temperature as a critical parameter for process optimization. Full article

Hydrogen from biogenic sources is central to the transition to a carbon-neutral energy system, offering flexibility for mobility and industrial applications. Decentralized steam reforming of biogas enables on-site hydrogen production but requires precise heat management due to its strongly endothermic nature. In small-scale systems, conventional manufacturing approaches often limit geometric flexibility and thermal integration, whereas additive manufacturing enables highly integrated reactor structures that overcome these constraints. This study presents the development and experimental evaluation of a compact, monolithic reformer additively manufactured from silicon-infiltrated silicon carbide, combining combustion and reforming zones in a single component to enhance heat transfer and compactness. The reactor features an internal U-shaped reforming channel filled with a nickel-based catalyst and was tested under varying loads. CH₄ conversions of 95–99% close to equilibrium were achieved at gas hourly space velocities up to 75,000 h⁻¹. Stable internal heat supply sustained reforming, although combustion results remain preliminary due to manufacturing-related blockages in the combustion channels, as revealed by computed tomography (CT) analysis. Energy assessments indicate that thermal efficiency is primarily limited by external heat losses of up to 46%, resulting from the high operating temperatures and small reactor dimensions. The results demonstrate the feasibility of the integrated reactor concept while highlighting current limitations related to manufacturability and heat losses, providing a basis for future optimization and scale-up. Full article

This study investigates the influence of isomorphous substitution of Aluminum by V, Zr, La, and Ni in Beta zeolite frameworks used as supports for Ni-based dry reforming of methane catalysts. The research focuses on how the nature of the incorporated metal affects catalytic activity and long-term stability. Catalysts were synthesized using both co-impregnation and sequential impregnation strategies. Physicochemical characterization—including gas adsorption, X-ray diffraction, transmission electron microscopy, and H₂ temperature-programmed reduction—revealed distinct structural roles for each metal. Results indicate that V primarily occupies T-vacancy sites within the dealuminated Beta framework, whereas Ni resides as charge-compensating extra-framework species or highly dispersed NiO clusters. Zr and La tend to form highly dispersed oxide species or occupy enlarged silanol nests. Notably, the addition of La₂O₃ was found to significantly enhance the long-term stability of the catalysts during the dry reforming of methane process. V-modified catalysts exhibited the highest activity but suffered from low stability; conversely, Zr incorporation offered the best overall performance, balancing high activity with enhanced stability, achieving 85% CO₂ and 75% CH₄ conversion, with no detectable carbon deposition after 98 h on stream. Full article

Efficient utilization of carbon dioxide (CO₂) is a critical route toward carbon cycling and low-carbon energy systems. Compared with conventional thermocatalysis, photocatalysis, and electrocatalysis, plasma catalysis can activate CO₂ under relatively mild conditions through high-energy electrons, vibrationally excited molecules, radicals, and other reactive species, while catalytic surfaces can redirect reaction pathways and improve selectivity. Rather than only compiling reported performances, this review critically evaluates plasma-catalytic CO₂-to-energy conversion from three perspectives: reliable mechanistic knowledge, unresolved uncertainties in plasma–catalyst synergy, and the practical credibility of reactor–catalyst combinations. The fundamentals of non-thermal plasma, CO₂ activation, key metrics, plasma–catalyst coupling, and catalyst/reactor/operation factors are first clarified. Representative advances in CO₂ splitting, CO₂ hydrogenation, dry reforming, and CO₂–H₂O co-conversion are then compared with attention to energy input, selectivity, power determination, and data comparability. Finally, the key barriers to industrial deployment are discussed, including low energy efficiency, long-term catalyst stability under plasma exposure, uncertain absorbed-power measurement, incomplete carbon/oxygen balances, scale-up of filamentary discharges, and the lack of standardized reporting protocols. This review aims to provide a critical reference for mechanism-guided catalyst design, reactor engineering, and realistic process assessment in plasma-catalytic CO₂ utilization. Full article

Dry reforming of methane (DRM) is a key reaction for syngas production and greenhouse gas utilisation, involving multiple interacting operating variables. In this work, an interpretable machine learning approach based on CatBoost regression coupled with SHapley Additive exPlanations (SHAP) is applied to a previously published DRM dataset to analyse the influence of reaction temperature, CH₄/CO₂ feed ratio, and Ni loading on CH₄ and CO₂ conversions and H₂ and CO yields. The objective of this study is methodological rather than experimental, focusing on the use of interpretable machine learning to extract variable importance hierarchies and conditional interaction effects from data-limited DRM studies. The analysis confirms that reaction temperature is the dominant controlling parameter, while feed ratio and Ni loading exhibit secondary, regime-dependent influences. No new catalytic mechanisms or experimental findings are proposed. The results illustrate how CatBoost–SHAP analysis can complement experimental DRM research by providing transparent, quantitative interpretation of published datasets under realistic data constraints. These findings are consistent with established DRM thermodynamic and kinetic behaviour, where temperature governs endothermic reforming reactions, while feed composition and metal loading influence carbon formation pathways and catalytic activity. Full article

The vision for global net-zero carbon emissions by 2050 has intensified the demand for sustainable and low-carbon energy resources. Within this context, recent discoveries of substantial methane (CH₄) reserves, coupled with the rapidly growing interest in hydrogen (H₂) as a clean energy carrier, have underscored the strategic importance of developing efficient and economically viable technologies for methane conversion. This current review investigates hydrogen production specifically from coalbed methane (CBM), a methane-rich unconventional gas resource embedded in coal seams. Both catalytic and non-catalytic pathways for hydrogen generation are reviewed, including steam methane reforming (SMR), partial oxidation (POX), autothermal reforming (ATR), direct methane decomposition (DMD), and plasma-assisted pyrolysis. Catalytic processes such as SMR remain the most mature and cost-effective, though they emit significant CO₂ unless integrated with carbon capture and storage (CCS) technologies. Non-catalytic routes, including thermal and plasma-based decomposition, offer CO₂-free hydrogen generation while producing solid carbon byproducts with potential commercial value. Hybrid coal–CBM systems are also discussed as integrated approaches for improving energy efficiency and resource utilization. The techno-economic assessment compares hydrogen yield, production cost, and environmental impact across methods, emphasizing the advantages of CBM as a high-purity methane source. Case studies, particularly from China, highlight the practical potential of CBM in supporting hydrogen infrastructure. The paper concludes that catalytic routes such as SMR are the most commercially mature and cost-effective but remain CO₂-intensive unless coupled with carbon capture and storage. Non-catalytic approaches, including direct methane decomposition and plasma pyrolysis, enable CO₂-free hydrogen generation while yielding solid carbon byproducts of potential commercial value, though they are less developed. Hybrid coal–CBM systems offer a balanced pathway to improve efficiency, resource utilization, and sustainability in future hydrogen production strategies. Full article

The rapid expansion of the biodiesel industry has led to a significant surplus of crude glycerol, creating both a challenge and an opportunity for its sustainable valorization. The aim of this review is to provide a comprehensive overview of glycerol upgrading strategies that integrate upstream purification methods with downstream catalytic conversion pathways. Conventional and emerging purification technologies are critically discussed, with particular attention to their efficiency, cost, and compatibility with catalytic processes. Major catalytic routes such as acetalization, oligomerization, carbonation, hydrogenolysis, oxidation, etherification, esterification and steam reforming are systematically analyzed in terms of reaction mechanisms, catalyst design, and process conditions. Although high conversions and selectivities are often achieved under optimized conditions, key limitations such as catalyst deactivation, equilibrium constraints, feedstock impurities, and scalability issues remain significant barriers to industrial implementation. The review highlights the strong interdependence between glycerol purity, catalytic performance, and process design, emphasizing the need for integrated approaches. Recent advances in multifunctional catalysts, reactor engineering, and process intensification are discussed as promising strategies to overcome current challenges. Overall, this work provides a critical perspective on the state of the art and identifies future directions toward the development of efficient, scalable, and sustainable glycerol-based biorefinery processes. Full article

Producing hydrogen from ethanol steam reforming (ESR) is a carbon-neutral and environment-friendly method, which has been expected to reduce the excessive emission of environmental pollution and over-exploitation of fossil resources. Currently, great advances have been made on heterogeneous catalysts, but an in-depth and more comprehensive understanding to further promote this reaction process is still required. Herein, the thermodynamic and kinetic analyses of ESR are firstly highlighted. Then, various reaction pathways of ESR are discussed in detail, respectively combined with experimental studies and density functional theory calculations. On this basis, the key factors affecting the catalytic performance over non-noble and noble metal catalysts are summarized, such as alloying, optimization of the preparation methods, promoter addition and support modification. In addition, the process intensification technologies, including catalytic membrane reactors, adsorption-enhanced reforming and microchannel reactors, are analyzed regarding breaking the thermodynamic limitations and improving the heat and mass transfer efficiency. Finally, the challenges and potential strategies of ESR in the research of dynamic reaction mechanisms, regulation of catalyst stability and integration of intensification technologies are summarized. Full article

To accelerate the transition to sustainable energy, efficient methods for CO₂-free hydrogen production and carbon utilization are needed. This study presents a new, sustainable approach for the simultaneous production of hydrogen, valuable hydrocarbons, and functional carbon materials by converting methane in low-pressure microwave plasma. Compared to traditional methane reforming methods (such as steam reforming), our plasma-based process operates at low temperatures, eliminates direct CO₂ emissions, and enables the conversion of methane into three valuable products: (1) environmentally friendly hydrogen for fuel cells and energy storage systems, (2) a range of valuable organic products (C₂H₂, C₂H₄, C₂H₆), and (3) functional carbon films with self-improving catalytic properties. Optical emission spectroscopy (OES) and the Langmuir double probe method were used for plasma diagnostics, revealing an increase in the concentration of active species (CH, Hα, C₂) and electron temperature upon argon addition. The structure, morphology, and impurity composition of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Gas-phase byproducts were analyzed using gas chromatography–mass spectrometry (GC-MS). Argon addition at an Ar/CH₄ ratio of 1 leads to the formation of carbon films with a more ordered structure, as confirmed by XRD data, and improved surface morphology. It was established that argon, by effectively participating in the excitation and dissociation processes of methane molecules through energy transfer from metastable states and increased electron temperature, optimizes plasma–chemical reactions, promoting the deposition of higher-quality carbon coatings. Full article

The interest in more sustainable energy sources has necessitated research in hydrogen production from various reliable pathways. This study investigates the potential of hydrogen production by ethanol-assisted CO₂ reforming over Al-MCM-41-supported Ni catalysts considering the effect on the catalytic performance and stability. The Ni/Al-MCM-41 catalysts were synthesized via wet impregnation method and characterized using different instruments and techniques. Evidence of the formation of well-crystallized Ni nanoparticles dispersed on the Al-MCM-41 support was confirmed by X-ray diffraction analysis and field emission scanning electron microscopy. The amount of Ni loading, which varied from 5 to 15%, was confirmed using energy-dispersive analysis, while the mesoporous nature of the Ni/Al-MCM-41 was ascertained using N₂ physisorption analysis. The performance of the Ni/Al-MCM-41 catalyst as a function of the ethanol conversion, CO₂ conversion, hydrogen and CO yield is strongly corrected with Ni loading and reaction temperature. The ethanol conversion and hydrogen yield increase with the increase in reaction temperature. At a reaction temperature of 550 °C the lowest ethanol conversion and hydrogen yield of 32.3% and 33.7% were obtained over the 5 wt% Ni/Al-MCM-41 catalyst, while the highest ethanol conversion of 87.4% and hydrogen yield of 75.5% were obtained over the 15% Ni/Al-MCM-41 at 700 °C. The 15 wt% catalyst achieves the most balanced syngas profile at 700 °C, where the H₂ and CO yields are optimized through the synergistic consumption of both ethanol and CO₂. It can be inferred that the reaction follows a bifunctional pathway whereby the Ni active sites are responsible for the ethanol dissociation while the CO₂ adsorption and activation are enhanced by the Al-MCM-41 support. Full article

Dry reforming of methane (DRM) converts the greenhouse gases methane (CH₄) and carbon dioxide (CO₂) into syngas (hydrogen (H₂) and carbon monoxide (CO)). Despite its numerous advantages, DRM has not yet been industrialized due to catalyst deactivation and competing side reactions. While Ni-based catalysts have been widely used, they are prone to increased carbon deposition and sintering, and although bimetallic systems and oxygen-based supports have shown promise, their effects on carbon deposition are yet to be fully understood. In this study, carbon nanotube (CNT)-supported Pt-Ni catalysts incorporating mixed oxides of CeZrO₂ and CeZrLaO₂ were investigated to evaluate the impact of support composition and metal–support interactions in DRM. The catalysts were synthesized and subsequently tested in DRM. Catalysts supported on CNTs displayed higher CH₄ and CO₂ conversions compared to conventional ceria–zirconia, highlighting the beneficial role of the carbon nanotube support in improving dispersion and accessibility of the metal active sites. Addition of Pt was found to promote reverse water–gas shift (RWGS) reaction, whereas the addition of La was found to decrease catalytic activity. Despite the formation of a Ni-Pt alloy, the obtained catalysts favored RWGS over DRM. These findings illustrate key limitations and design considerations for optimization of CNT-supported bimetallic catalysts in DRM. Full article

The rapid accumulation of plastic and biomass waste has emerged as a major environmental and resource management challenge, driven by increasing global consumption, low recycling efficiency, and the long-term persistence of waste in natural ecosystems. Conventional valorization routes such as pyrolysis, gasification, reforming, and fermentation provide promising pathways for converting waste into fuels and chemicals, yet their industrial deployment remains constrained by thermodynamic limitations, tar formation, catalyst deactivation, high energy demand, and complex downstream separation requirements. Despite increasing research activity, a comprehensive review that systematically addresses membrane reactor (MR) mechanisms, configurations, and their specific applications in the valorization of both plastic and biomass waste remains lacking in the current literature. In recent years, MR technology has attracted increasing attention as a platform for process intensification, integrating reaction and selective separation within a single unit. By enabling in situ product removal, MRs shift reaction equilibria toward higher conversion, selectivity improvement, and a reduction in separation severity and overall energy consumption. This critical review provides a unified and systematic assessment of MR technologies for the valorization of plastic and biomass waste. Reactor configurations, membrane materials, transport mechanisms, and catalytic systems are comprehensively examined, with particular emphasis on hydrogen-selective, oxygen-permeable, and water-selective membranes and their roles in reforming, tar mitigation, and syngas upgrading. The techno-economic and environmental implications of MR integration are critically discussed, together with current technology readiness levels (TRLs) and scale-up challenges. Overall, this review highlights MRs as a versatile and enabling platform for next-generation waste-to-value technologies and outlines their potential role in supporting the transition toward circular, low-carbon fuel and chemical production. Full article

Biomass gasification technology is a crucial pathway for obtaining clean syngas and achieving efficient utilization of carbon resources. However, tar is one of the main factors restricting the industrialization of biomass gasification technology. Among various solutions, catalytic steam reforming is regarded as the most promising solution. Currently, natural minerals and Ni-based catalysts have been demonstrated to be effective and economically viable for tar removal, which are widely used in industrial fluidized beds. Therefore, the basic reaction principles of tar steam reforming were briefly introduced. The development of tar steam reforming catalysts, focusing mainly on natural minerals and Ni-based catalysts, have been studied in this review. The catalytic cracking mechanisms of natural minerals such as dolomite and limestone, as well as the steam reforming mechanism of Ni-based catalysts, have been thoroughly summarized. In addition, the active sites of the catalysts, reaction pathways, and the essence of catalyst deactivation are discussed. Based on this, the catalytic effect of these two catalysts for steam reforming of tar in the fluidized bed was summarized. Further, the engineering challenges (such as mass transfer, wear, and continuous regeneration) and the corresponding process optimization measures were comprehensively reviewed, and future perspectives are discussed. Full article

The performance and mechanism of heterogeneous catalytic reactions are fundamentally governed by the formation, stability, and reactivity of transient surface intermediates. These species—such as isocyanates, alkyl groups, carboxylates, formates, carbonates, alkoxy and acyl intermediates—often exist at low concentrations and with short lifetimes, making their identification challenging. This review summarizes the current knowledge on the formation, spectroscopic identification, and thermal behavior of these intermediates on metal single crystals, metal nanoparticles, and oxide-supported catalysts. Emphasis is placed on key reactions including CO and NO oxidation–reduction, CO and CO₂ hydrogenation, Fischer–Tropsch-related pathways, and reforming of ethanol. Advanced surface-sensitive techniques (TDS, XPS, UPS, IR, HREELS) are highlighted for their role in elucidating intermediate structures and reaction pathways. The isocyanate surface complex is an existing intermediate in NO reduction with CO, and NCO is responsible for NH₃ formation. Alkyl groups can be prepared from thermal- or photo-induced dissociation of alkyl halogenide. Oxygen-containing intermediates relevant to CO₂ hydrogenation are addressed, with particular attention to formate, carboxylate, and related species. M/CeO₂ (M = Pt, Rh, Ir, Ru) seems to be the best catalyst for hydrogen production from ethanol reforming. The nature of support may affect hydrogen production. The review also discusses how metal–support interactions, particle size, and surface morphology influence intermediate stability and catalytic selectivity. Overall, the work provides a comprehensive framework for understanding how transient surface complexes control technologically important catalytic transformations. Full article