Topics in Catalysis最新文献

Nickel-promoted molybdenum carbide (Mo₂C) catalysts supported on γ-Al₂O₃ were synthesized via incipient wetness impregnation and evaluated for dry methane reforming (DMR). Comprehensive physicochemical characterizations including XRD, SEM-EDS, H₂-TPR, XPS, TPSR, and TG-DSC were conducted to elucidate structure-performance relationships. Non-promoted Mo₂C exhibited poor catalytic stability due to oxidation during DMR. The incorporation of nickel significantly enhanced catalytic activity and stability by promoting the in-situ re-carburization of oxidized Mo species and facilitating methane activation. The optimized Ni/Mo molar ratio of 1:1 led to the formation of a stable Ni-Mo synergistic phase, which exhibited superior resistance to sintering and deactivation.

This study employed machine learning (ML) to predict nitrogen dioxide (NO₂) pollution in Marylebone Road, London a high-traffic urban corridor using historical data from 2015 to 2022 to forecast concentrations for the period January 2023 to January 2025. Four ML models were developed and evaluated: Linear Regression, Random Forest, LightGBM, and an Ensemble Stacking model. These models incorporated meteorological and pollutant data and were assessed using Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and R-squared (R²). The Ensemble Stacking model outperformed the others, achieving an R² of 0.9723, MAE of 3.91 µg/m³, and RMSE of 6.25 µg/m³. In comparison, the Linear Regression model showed the lowest performance (R² = 0.8307, MAE = 11.55, RMSE = 15.45), while Random Forest (R² = 0.9232) and LightGBM (R² = 0.9719) demonstrated intermediate accuracy. The best-performing ensemble model was further used to simulate NO₂ trends with and without titanium dioxide (TiO₂) catalyst intervention, assuming a 28% NO₂ reduction. Temporal analysis revealed that NO, NO₂, and NOₓ concentrations peaked during colder months (November–January) and weekdays. Correlation analysis showed a weak negative relationship between NO₂ and ozone (O₃) (R² = 0.26), moderate positive correlations with black carbon (BC) (R² = 0.597) and sulfur dioxide (SO₂) (R² = 0.654), and a very weak positive correlation with particulate matter (PM2.5) (R² = 0.143). The study concludes that ensemble stacked ML models are effective for predicting NO₂ concentrations and that TiO₂ nanocatalyst interventions hold promise for reducing NO₂, BC, and SO₂ levels in urban environments.

Amides, which contain both oxygen and nitrogen, are present in many potential feedstocks for renewable fuels. There is a consequent need to study the hydrodenitrogenation (HDN) and hydrodeoxygenation (HDO) of amides. This work studies the HDN and HDO of hexadecanamide with sulfided NiMo/(gamma )-(hbox {Al}_2hbox {O}_3) and NiMo/(hbox {TiO}_2) catalysts. The experiments are conducted in a batch reactor, with decalin as a solvent. Hexadecanamide is found to easily undergo either dehydration into hexadecanenitrile or deammonization into palmitic acid. Hydrotreating of hexadecanamide consequently occurs either through an initial HDO step (dehydration) into hexadecanonitrile, followed by reduction and HDN of the resulting hexadecylamine, or through an initial HDN step (deammonization) followed by HDO of the resulting palmitic acid. On both NiMo/(gamma )-(hbox {Al}_2hbox {O}_3) and NiMo/(hbox {TiO}_2), HDN of the amide is slower than HDO. The secondary amine, dihexadecylamine, is a major intermediate, formed through condensation reactions between hexadecylamine and palmitic acid or by the self-condensation of hexadecylamine. Thus, after the initial dehydration or deammonization step, hydrotreating of the primary amide follows the pathways associated with the HDN of primary amines and the HDO of primary carboxylic acids. NiMo/(hbox {TiO}_2) is a more active amide hydrotreating catalyst than NiMo/(gamma )-(hbox {Al}_2hbox {O}_3). This is attributed to (hbox {TiO}_2) catalyzing the initial dehydration (HDO) step, as well as to more complete sulfidation of Mo and the better incorporation of the Ni promoter in the (hbox {MoS}_2) phase on (hbox {TiO}_2).

Ni supported on SiO₂ with various morphologies such as nanocubes, nanorods, nanospheres and dendritic mesoporous silica (DMS) are prepared and employed for zero emission hydrogen production (Turquoise hydrogen). The fresh calcined catalysts possessed NiO (200) planes predominantly while in the reduced samples Ni⁰ (111) planes are majorly exposed irrespective of SiO₂ morphology. Among these the Ni-DMS demonstrated a higher rate of H₂ production while, the Ni/nanorods showed inferior activity. Formation of Ni silicate was found only in case of Ni/nanorods. Ionic Ni reduced below 600 °C seems to exhibit better CH₄ cracking rate, as was depicted from H₂-TPR results. Variation in graphitic carbon was found due to difference in SiO₂ morphology as well as the reducibility of nickel interacted with SiO₂.

Using an annular structured reactor the oxidation of CO and H₂ over silver was studied at temperatures employed during the industrial partial oxidation of methanol to formaldehyde. Silver tubes were systematically exposed to different atmospheres and imaged at regular intervals using scanning electron microscopy to gain insight into both reaction activity and catalyst restructuring. The reactant feed has a profound effect on restructuring, and a “dynamic steady-state morphology” is identified for each gas mixture. The exposed catalysts show clear signs of stepped surface faceting, grain growth and formation of small pinholes (< 1 μm). H₂ oxidation conditions promote the formation of numerous angular surface cavities (> 3 μm). Addition of steam to the feed, however, inhibits the formation of stepped facets. Silver is active towards both CO and H₂ oxidation, and co-feeding both reactants has a synergistic effect. Addition of steam leaves the H₂ oxidation activity unaffected but completely inhibits the formation of CO₂ via CO oxidation. The results clearly show that the effects of H₂O formation are very different from those of H₂O addition and that CO is not a precursor towards CO₂ in the silver-catalysed methanol to formaldehyde system, in which steam is usually co-fed. The systematic approach taken here allows the effects of temperature and gas composition to be decoupled, and the results can be used in future studies to ascribe restructuring features to various reactants.

The selection of appropriate catalysts is critical for the efficient operation of hydrotreaters, due to the diverse types of reactions inherent to the process. In this study, various Type I and Type II sulfided NiMo/γ-Al₂O₃ hydrotreating catalysts were prepared using chelating agents and support modification, and the apparent activity differences were evaluated using step response experiments. The experiments were conducted in a trickle bed reactor at 300 °C and 120 barg using phenanthrene and carbazole as model compounds while the apparent activities were elucidated using dynamic reactor modelling. It was found that the addition of citric acid to the impregnation solution to chelate the Ni leads to an average 30% increase in the active site density for hydrogenation (HDA) and hydrodenitrogenation (HDN), without significantly affecting the reaction rate coefficients suggesting similar activity per active site. Phosphorus modification of the support, however, results in larger reaction rate coefficients for both hydrogenation of phenanthrene as well as adsorption and reaction coefficients for carbazole, resulting in more active catalysts both for HDA and HDN. This enhanced activity is accompanied by increased selectivity to HDN suggesting that catalysts exhibiting higher activity for HDA reactions are more susceptible to inhibition by organonitrogen compounds. In addition, dynamic activity testing indicated that catalysts with superior HDN activity attain their new steady state in the shortest time. Thus, the selection of catalysts for efficient hydrotreater operation necessitates activity testing under dynamic conditions to account for competing and inhibitory reactions, rather than relying solely on steady-state activity. Such an approach, allows for the elucidation of the differences in HDA and HDN activity, providing valuable insights to support the catalyst selection process.

The urgent demand for high-performance and sustainable energy storage solutions necessitates the development of advanced electrolytes with superior electrochemical properties. Hybrid lithium electrolytes, which integrate the advantages of inorganic and organic ionic conductors, have emerged as promising candidates for next-generation energy storage devices. This review presents a comprehensive bibliometric analysis of 1569 research articles from 2019 to 2024, sourced from Scopus and Web of Science (WOS) databases, highlighting the rising research focus on hybrid electrolytes. Key material properties such as wide electrochemical windows, thermal and chemical stability, low toxicity, and reduced volatility are critical for enhancing battery performance. The discussion encompasses recent advancements in solid-state, polymer, and hybrid electrolytes, emphasizing their role in improving energy density, cycling stability, and safety. Furthermore, this study examines the challenges associated with hybrid electrolytes, including ionic conductivity limitations, interfacial compatibility, and scalability for industrial applications. The integration of novel materials such as NASICON-type ceramics, perovskites, sulfides, and garnet-based electrolytes is explored for their potential to revolutionize lithium-ion battery technologies. By bridging the gap between fundamental research and practical implementation, this review provides insights into the future directions of hybrid electrolytes, paving the way for more efficient and sustainable energy storage systems.

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Single-atom catalysts (SACs) offer a promise of providing unique properties, superior selectivity, and maximum atomic efficiency compared to traditional nanoparticle catalysts. However, their stability under reaction conditions remains a critical challenge. This study examines the reactivity and structural evolution of a thermally stable (~ 700 K) model Rh/Fe₃O₄(001) SAC, where Rh is substituted into the surface layer. Previously, we demonstrated that water formation via the Mars-van Krevelen mechanism during formic acid conversion destabilizes in-surface octahedral Rh, yielding active Rh adatoms and clusters that dynamically re-incorporate into the Fe₃O₄ lattice at 700 K. Here, we follow the evolution of the catalyst structure and changes in the CO and CO₂ formation kinetics during multiple formic acid conversion cycles. Temperature-programmed reaction spectroscopy (TPRS) cycles to 700 K reveal that small Rh clusters formed during the first several cycles can re-incorporate into the Fe₃O₄(001) lattice. Over subsequent cycles, larger nanoparticles eventually form and persist. These effects are further accelerated when annealing is limited to only 550 K. Changes in the CO₂ formation/desorption temperature in TPRS reveal that the activity for formic acid dehydrogenation increases progressively from single atoms to clusters and nanoparticles. This study provides fundamental insights into the dynamic behavior and performance of SACs during catalytic reactions.