Search Results (843)

Methanol is the simplest C1 oxygenated compound possessing the highest hydrogen-to-carbon ratio and can therefore be used as an effective hydrogen carrier. Furthermore, it can be easily transported by land and sea because it is liquid at room temperature and atmospheric pressure. Methanol can be converted into hydrogen via methanol steam reforming (MSR), aqueous-phase reforming of methanol (APRM), or aqueous methanol dehydrogenation (AMDH). In this review, various catalysts for MSR, APRM, and AMDH are summarized. Highly active and stable catalysts that can operate under low steam-to-methanol ratios are needed to increase the economics of the MSR process. Compared with the MSR process, the APRM process is rather simple because the water–gas shift reaction can occur simultaneously; however, more constraints exist in the selection of active metals and supports to ensure high activity and stability under APRM conditions. The inherently low reaction rate compared to MSR and the structural vulnerability of the catalyst under severe hydrothermal conditions are obstacles that the APRM catalysts must overcome. The low intrinsic catalytic activity and the high cost of homogeneous catalysts represent fundamental limitations inherent to AMDH catalysts. Based on a literature survey of MSR, APRM, and AMDH catalysts, some future research directions are also discussed. Full article

The Temporal Analysis of Products (TAP) pulse response technique provides valuable insights into catalytic function and reaction kinetics. However, complex fragmentation patterns in the TAP mass spectrometry signals can complicate precise quantification, particularly when analyzing transient gas flux data typical of TAP experiments. This work demonstrates a standard defragmentation method that deconvolves transient TAP signals while maintaining the temporal resolution of the experiment. First, the integrals of calibration gas fluxes are used to determine the fingerprint fragmentation pattern and construct a fragmentation matrix. This matrix is then used to defragment experimental flux data at each recorded time point via a non-negative least squares regression. The effectiveness of this method is demonstrated using virtual data and control experiments with a TAP reactor system. The defragmentation is then applied to the more complex propane dehydrogenation reaction on a chromia/alumina catalyst, which can contain up to ten significant gas species in the reactor outlet. Initial propane pulsing reveals an induction period during which propane is fully oxidized to CO_2, followed by partial reduction to CO. Afterwards, there is a transition in chemistries towards coking and propylene production. Our example illustrates a practical method for the accurate determination of the time-dependent reactant/product concentrations and rates for a thorough analysis of the propane dehydrogenation kinetics. This approach can be broadly applied to any transient mass spectrometry experiment for a better understanding of catalyst-reaction dynamics. Full article

Based on the acid-sensitive characteristics of SBA-15 during synthesis, this study varied the acid types, pH values, and mixed acid ratios during SBA-15 preparation to enhance the performance of CaO/Cr-SBA-15 dual-functional materials (DFMs) in integrated CO₂ capture and utilization for oxidative dehydrogenation of ethane (ICCU-ODHE). It was found that the SBA-15 support synthesized in an H₂SO₄ environment exhibited a high specific surface area and abundant surface silanol groups, which facilitated the dispersion of Cr and increased the proportion of Cr⁶⁺ active sites, thereby achieving the highest ethane conversion. In contrast, the moderate surface acidity of the HCl-prepared support facilitated the selective dehydrogenation of ethane over Cr active sites, effectively inhibiting side reactions and maximizing ethylene selectivity. Further investigations into the effects of pH and mixed acids revealed that pH 1 is optimal for SBA-15 preparation. At this value, the support reached its maximum mesoporous ordering and specific surface area, allowing for optimal Cr dispersion. Consequently, the ethane conversion, ethylene selectivity, and DFM yield all reached their peak values. Any deviation from this pH led to degradation of the support structure and reduced Cr dispersion, resulting in a significant decline in catalytic performance. Among the tested materials, the CaO/Cr-SBA-15-Cl-S DFM synthesized with an HCl-H₂SO₄ mixed acid demonstrated the superior reactivity, achieving an ethylene yield of 33.95%. Long-term cycling tests indicated that the material possesses good stability, with its performance attenuation primarily attributed to coking and adsorbent sintering. Full article

Cobalt-based catalysts are promising for propane dehydrogenation (PDH), but their practical application is hindered by limited propylene yields, rapid deactivation, and an incomplete understanding of the catalytically relevant Co species. Here, alkaline treatment was used to increase the density of silanol defects on Silicalite-1, thereby creating abundant anchoring sites for highly dispersed Co species. The resulting Co/Silicalite-1 catalyst achieved 45% propane conversion, 96% propylene selectivity, and stable operation over 60 h on stream (k_d = 0.005 h⁻¹). Combined characterization indicates that silanol defects stabilize highly dispersed, defect-anchored Co species that are responsible for the superior PDH performance. By contrast, supports with lower silanol defect densities favor aggregated CoO_x/Co₃O₄-like species, which are less selective for PDH, more susceptible to reduction to metallic Co under reducing conditions, and more prone to cracking and coke formation. These findings reveal a strong correlation between silanol defect density, Co speciation, and catalytic performance, offering mechanistic insights and design principles for the development of efficient PDH catalysts. Full article

Short-chain acyl-CoA dehydrogenase (SCAD) is a critical enzyme in mitochondrial fatty acid β-oxidation, catalyzing the initial dehydrogenation of short-chain acyl-CoAs. Mutations in the ACADS gene cause SCAD deficiency (SCADD), a disorder with remarkably heterogeneous clinical presentation. However, the molecular mechanisms underlying substrate specificity and the pathogenicity of most ACADS variants remain poorly understood. Here, we present high-resolution cryo-EM structures of human SCAD in complex with its physiological substrate butyryl-CoA (C₄) and the longer substrate hexanoyl-CoA (C₆). The butyryl-CoA-bound structure at 2.1 Å resolution details a pre-catalytic geometry ideal for hydride transfer, with Glu392 positioned as the catalytic base. We systematically characterized nineteen disease-associated mutations, which we classify into three functional categories: those disrupting FAD binding, those impairing substrate binding, and those compromising protein folding and stability. In addition, using the W177R mutant as a representative model, we demonstrate that folding-defective mutations provoke protein aggregation, leading to proteotoxicity, oxidative stress, and apoptosis, revealing a pathogenic mechanism beyond mere catalytic loss. In brief, our integrated findings elucidate the structural determinants of substrate specificity and catalytic mechanism in SCAD, and provide mechanistic insights into the functional impairments caused by mutations linked to SCADD. Full article

Zirconium hydride is susceptible to dehydrogenation at elevated temperatures. In this study, zirconium hydride was oxidized by in situ oxidation in a CO₂ atmosphere at temperatures ranging from 550 to 700 °C for 10 h. The morphology, elemental distribution, phase structure, and hydrogen barrier performance of the resulting oxide films were systematically characterized using SEM, EDS, XRD, film adhesion and microhardness tests, and dehydrogenation experiments. At 550–600 °C, the formed oxide films are thin and non-uniform, containing numerous micropores and cracks, which results in limited hydrogen barrier performance. When the oxidation temperature is increased to 650 °C, a better balance between the oxidation reaction and diffusion processes is achieved. This leads to the formation of a dense, continuous, and uniform ZrO₂ film with strong adhesion to the substrate. As a result, the initial dehydrogenation temperature increases to 660 °C, while both the dehydrogenation rate and cumulative hydrogen release are significantly reduced, indicating the best overall hydrogen resistance. However, further increasing the oxidation temperature to 700 °C causes an excessively high oxidation rate, which introduces large growth and thermal stresses. These stresses promote the formation of microcracks in the oxide film, weaken the interfacial bonding strength, and consequently reduce the hydrogen barrier performance. The results demonstrate that the hydrogen permeation resistance of the oxide film is mainly governed by film compactness, defect evolution, and interfacial integrity. Based on these findings, 650 °C is identified as the optimal processing temperature for producing a high-quality hydrogen-resistant ZrO₂ film on zirconium hydride under a CO₂ atmosphere. Full article

Traditional oxidative dehydrogenation of n-butene has typically required relatively high operating temperatures (400–500 °C), which has driven increasing interest in the development of catalysts capable of delivering high activity at lower temperatures. In this study, zinc ferrite (ZnFe₂O₄-ST) was successfully synthesized via hydrothermal hydrolysis of Zn–Fe oleate and demonstrated remarkable catalytic performance for the oxidative dehydrogenation of n-butene under mild conditions. At 300 °C, ZnFe₂O₄-ST achieved a conversion of 72.9% with 92.1% selectivity toward 1,3-butadiene, a result that, to the best of our knowledge, ranks among the best reported in the literature. By contrast, ZnFe₂O₄ prepared by conventional coprecipitation (17.2% conversion with 91.3% selectivity) and sol-gel (10.1% conversion with 86.4% selectivity) methods showed much lower activities, highlighting the critical influence of synthesis strategy on catalytic performance. To better understand the origin of these differences, a detailed structural and physicochemical characterization was undertaken using X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (H₂-TPR), temperature-programmed re-oxidation (TPRO), and NH₃-temperature-programmed desorption (NH₃-TPD). These analyses revealed that the as-synthesized ZnFe₂O₄-ST possessed a significantly smaller average particle size, a larger specific surface area, and superior reducibility compared with the other samples. These properties are believed to be the key factors underpinning its outstanding catalytic behavior and provide important insights into the design of efficient low-temperature catalysts for selective oxidative dehydrogenation. Full article

Fluopyram is a widely used nematicide with a growing number of varieties registered both domestically and overseas. However, its absorption, transportation, and metabolism behaviors in plants have not been fully elucidated, thus hindering comprehensive assessment of the risks associated with its use. This study investigated the plant uptake, distribution, and metabolic behavior of fluopyram through 168 h hydroponic experiments. Fluopyram was easily absorbed by the roots of the tested crops, and almost 90.5% and 70.9% of fluopyram was transformed in cucumber and tomato, respectively, leading to the tentative identification of 16 metabolites using Quadrupole Time-of-Flight mass spectrometry. The metabolic reactions involved were hydroxylation, hydroxylation–dechlorination, dehydrogenation, dechlorination, and glucuronidation conjugation. Most metabolites were detected in leaves, suggesting that they have considerable potential to accumulate in the upper parts, even the edible parts. Model prediction indicated that fluopyram and high-toxicity metabolites (M430A, M412C) pose significant risks to aquatic ecosystems across trophic levels, while M574A and M574B showed reduced toxicity due to glucuronidation conjugation. These findings deepen our understanding of the behavioral characteristics of fluopyram within plants, and serve as an important reference for comprehensively assessing its risks. Full article

The purity of titanium sponge is crucial for determining the performance of final titanium alloys, underscoring the importance of impurity control in its precursor, TiCl₄. Among these impurities, VOCl₃ is particularly challenging to remove due to its similar boiling point and complete miscibility with TiCl₄. Although organic reagents are widely employed for vanadium removal, their complex compositions complicate the identification of key active components. This study systematically compares the vanadium removal efficiency of six organic compounds bearing different functional groups. Results demonstrate that 1-dodecene exhibits superior performance, achieving a VOCl₃ removal efficiency of 93.35%. Mechanistic studies reveal that 1-dodecene initially undergoes cyclization to form cyclododecane, followed by aromatization and subsequent carbonization through stacking, dehydrogenation, and coking, ultimately yielding partially graphitized amorphous carbon. In this process, VOCl₃ interacts not only with the incompletely carbonized organic precursor but also directly with the alkenes. These findings elucidate the reaction pathway and central role of linear α-alkenes in vanadium removal, providing a theoretical foundation for developing efficient and stable vanadium removal agents. Full article

The reaction of CO₂ hydrogenation into CH₄ provides an industrial-scale pathway for CO₂ recycling. The controllable design of catalysts with highly active and stable performance is challenging, and investigation of the reaction mechanism is of great significance. In this paper, the reasonable regulation scheme on designing excellent performance catalysts is proposed, and all the reaction paths on the surface of catalysts are also analyzed in detail. It emphasized the fundamental factors influencing the activity of catalysts, and it proposed some practical strategies to effectively improve the performance of the catalysts in combination with the structure–activity relationship. This work has great significance for the optimal performance catalysts of heterogeneous catalytic systems. Furthermore, it provided a rationalized approach to designing catalysts with specific nanostructures and surface properties, such as catalytic reforming, dehydrogenation, hydrogenation, electric catalysis, and many other reactions. In addition, a critical perspective on the future challenges and opportunities in designing high performance catalysts is provided. Full article

To achieve the safe reuse of oil-based drill cuttings, this study employs thermogravimetric analysis and pyrolysis-gas chromatography/mass spectrometry to investigate the formation patterns and kinetic characteristics of pyrolysis products in oil-based drill cuttings. The study included a broad temperature range of 100–980 °C and heating rates of 10, 15, and 20 K/min. Employing the Frazer–Suzuki approach from a multi-step-over-single-step perspective, six pseudo-processes (P1–P6) are isolated for the overall pyrolysis reaction of oil-based drill cuttings. Differences in contributions and activation energies were quantified for each stage. The activation energies for the six pseudo-processes are determined to be 60.81, −59.77, 421.10, 231.64, 225.96, and 349.04 kJ/mol, respectively. With increasing temperature, long-chain aliphatic hydrocarbons in products from oil-based drill cuttings pyrolysis tend to convert into short-chain hydrocarbons and form unsaturated hydrocarbons through dehydrogenation. The oil-based drill cuttings pyrolysis process does not follow a single mechanism but is primarily nucleation-controlled, incorporating multiple reaction mechanisms including geometric contraction, diffusion, and power-law effects. Full article

Although olefin aromatization reactions offer a potential route for the high-value utilization of Fischer–Tropsch naphtha, their industrial implementation is hindered by challenges such as coke-induced deactivation and the formation of large amounts of low-value alkane by-products. In this work, a series of Ga(x%)-EATP-550 catalysts were prepared via equal-volume impregnation of Ga onto an acid-etched attapulgite (EATP) support, followed by calcination at 550 °C. The catalysts were evaluated for the aromatization of olefins. The results show that the reaction proceeds mainly through direct dehydrogenative aromatization, yielding approximately 65% aromatics, while generating short-chain olefins (about 20% yield) as the main by-products. This system effectively suppresses the formation of long-chain aromatics and low-value alkanes, presenting a promising technical pathway for upgrading Fischer–Tropsch naphtha. Full article

This study reports on the performance of alumina-supported copper-based catalysts in the oxidative dehydrogenation of propane, with copper dispersed on two distinct commercial aluminium oxide supports made of micro- and nanosized alumina, respectively. The activity and selectivity of the two catalysts was investigated at temperatures between 250 and 550 °C. At a propane-to-O₂ ratio of 1:1, Cu/nanoAl₂O₃ achieves propylene selectivity of 35–48% at low temperatures (250–300 °C), while Cu/Al₂O₃ only exhibits activity starting at 350 °C with about 40% propylene selectivity. Altering the propylene-to-oxygen ratio to 3:1 enhances selectivity towards propylene in both catalysts, up to about 64% on Cu/Al₂O₃ at temperatures of 250–350 °C. The switch to the mild oxidant CO₂ boosts propylene selectivity to 100%. In case of Cu/nanoAl₂O₃, the rate of propylene formation doubles that of the obtained with O₂ used as oxidant. While with CO₂ the Cu/nanoAl₂O₃ catalyst retains 100% propylene selectivity up to 500 °C, on the less active Cu/Al₂O₃ cracking sets off already at 400 °C. The different size of copper particles in the two catalysts is seen as a primary factor determining the observed differences in the performance of the studied catalysts. Full article

For Co-N-C materials prepared under high-temperature calcination conditions, the formation of Co nanoparticles occurs when the metal loading exceeds 2%. Typically, CoNx is regarded as the primary active site of the catalyst, while Co nanoparticles are considered to possess limited catalytic activity. Consequently, within Co-N-C materials, Co nanoparticles are often likened to ‘ballast stone’ in a catalyst. In the model reaction of formic acid dehydrogenation, we incorporated boron into the precursor, thereby enhancing the electronic metal-support interactions (EMSI) between Co nanoparticles and carbon carriers. Consequently, this modification resulted in a catalytic performance of Co nanoparticles that was comparable to that of Co single-atom catalysts (SACs). Full article

Propylene (C₃H₆) is a vital building block in the chemical industry as it serves as a key raw material for producing plastics, synthetic fibers and numerous daily-use chemicals. However, the current production routes of C₃H₆ are energy-intensive and face sustainability challenges, prompting the scientific community to explore alternative technologies for its production. The oxidative dehydrogenation of propane (ODHP) using CO₂ as a soft oxidant offers a safe and sustainable pathway for C₃H₆ production, where CO₂ can act as a hydrogen scavenger, coke suppressor and site re-activator. Gallium- and chromium-based catalysts are among the most studied systems for CO₂-assisted ODHP, yet they operate by distinct mechanisms: Ga catalysts follow pathways where both acidic and basic sites are involved, while Cr catalysts rely on redox cycles involving variations in the oxidation state of chromium. In addition to performance and reaction mechanism, Ga- and Cr-based catalysts differ markedly in terms of sustainability, with Cr systems facing environmental and regulatory challenges associated with Cr⁶⁺ species toxicity, while Ga systems, although less toxic, are constrained by gallium scarcity and cost. This review compares Ga- and Cr-based catalysts side by side, emphasizing how support effects, addition of promoters and mechanistic insights fine tune their performance. The aim is to highlight the advantages, the limitations as well as the sustainability implications of these materials and finally to outline future directions for designing more efficient and environmentally friendly catalysts for propylene production. Full article