Topics in Catalysis最新文献

In this study, Fe₂O₃/TiO₂ nanocomposite was synthesized via a hydrothermal method and evaluated for its dual functionality in visible-light-driven photocatalytic dye degradation and electrochemical nitrite sensing. Structural, optical, and morphological characterizations confirmed the formation of a well-defined heterojunction with improved charge separation and visible light absorption. The nanocomposite demonstrated enhanced photocatalytic performance, achieving 100% degradation of methylene blue (MB) within 120 minutes under visible light. Kinetic studies confirmed pseudo-first-order behavior with an increased rate constant compared to individual TiO₂ and Fe₂O₃ components. Furthermore, the Fe₂O₃/TiO₂ modified glassy carbon electrode exhibited excellent electrocatalytic activity for nitrite detection, achieving a low detection limit of 1.4 µM with a linear response over a wide concentration range. These findings highlight the potential of Fe₂O₃/TiO₂ nanocomposites as multifunctional materials for environmental remediation and chemical sensing applications.

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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.

Series of nickel catalysts, supported on γ-alumina and promoted with different Ce loading (1–5%), have been studied in conventional and sorption-enhanced CO₂ methanation reaction. In addition, a detailed kinetic water adsorption study has been performed on commercial zeolite (13X, 4 A, 3 A). The decrease in adsorption capacity is observed for all zeolites with increasing temperature. The highest water adsorption capacity is observed for the 13X zeolite for all investigated temperatures (100–350 °C). However, the 13X zeolite showed loss of 50% of its capacity after 100 adsorption/desorption cycles while the 4 A and 3 A zeolites are almost unchanged. The catalyst characterization results indicate that upon addition of a small amount of ceria, dispersion of the Ni catalyst is improved as well as CO₂ conversion in conventional methanation. The catalyst that showed best performance was further tested for sorption-enhanced methanation, where water sorbents (13X, 4 A, 3 A) are mixed with catalysts. All the tests performed in presence of zeolites showed an increase in CO₂ conversion compared to those carried out in their absence. In addition, a 34% increase in CO₂ conversion was observed when increasing the H₂/CO₂ ratio to 8 for the system with 13X zeolite. This indicates the enhancement effect when water is removed from the reaction.

Water availability and quality are worldwide issues due to limited resources and contamination stemming from human activities. Different contaminants, including organic and inorganic compounds and microorganisms, threaten surface and groundwater resources. Organic pollutants include pesticides, detergents, pharmaceuticals, cosmetics, organic dyes, etc. Among the organic pollutants, synthetic dyes are one of the serious environmental threats to human and aquatic life. Methyl orange (MO) is a widely used artificial dye in different applications, including paper, leather, textiles, gasoline, food additives, and the pharmaceutical industry. Therefore, monitoring MO in environmental samples like wastewater, groundwater, and food products is crucial. Here, Prussian blue (PB) thin-layer modified ITO electrodes were fabricated and utilized to monitor MO in wastewater samples. SEM and XRD were used to characterize the morphology of the fabricated electrodes. The effect of the PB layer was investigated, and it was found that the use of PB/ITO deposited at 20 cycles depicts the highest current response. Effects of MO concentration, scan rate, and pH on the electrochemical response were investigated. The modified electrode was very sensitive, detecting as little as 5.7 nmol L⁻¹ while working effectively with concentrations from 100 to 10 µmol L⁻¹. The modified electrode showed the capability to monitor MO in groundwater samples.

Investigation of methane bi-reforming over Ni-impregnated La₂O₃-ZrO₂ mixed oxide catalysts to produce hydrogen-rich syngas. A series of supports with varying molar ratios of La-Zr were synthesized using the co-precipitation method, and the metal addition was carried out using the impregnation method. The properties of the materials are characterized by different characterization techniques such as BET, XRD, H₂-TPR, and CO₂-TPD analyses. The overall characterization illustrated that the change in the mole ratio of La₂O₃-ZrO₂ support improves catalyst performance by enhancing CO₂ adsorption and metal-support interactions and reducing carbon deposition. 12 wt% Ni loading catalyst with La₂O₃-ZrO₂ molar ratio of 3:1 showed optimal performance, yielding high methane and CO₂ conversion rates (90% and 75%, respectively) and achieving H₂ yield of 82%. Further, the catalyst demonstrated stability over a 100 h reaction time, ascribed to the strong metal-support interaction along with the change in the basicity with change in the La₂O₃, which improves the overall bi-reforming methane reactivity and enhances syngas production.

A series of CeO_x–CrO_x catalysts were synthesized via the sol-gel method for the oxidation of toluene. A comprehensive set of characterization techniques, including XRD, N₂ adsorption, Raman spectroscopy, HRTEM, H₂-TPR, O₂-TPD, XPS, and in situ DRIFTS, was employed to investigate the structure-performance relationships of the catalysts. Among the catalysts, the one with a Ce/Cr molar ratio of 1:3 exhibited the best performance in toluene oxidation, with the activation energy for toluene degradation decreasing from 54.5 kJ mol⁻¹ for CeO_x to 31.3 kJ mol⁻¹ for the CeO_x–CrO_x (1:3) and CO₂ selectivity reaching 100% at temperatures above 250 °C. This enhancement was primarily attributed to an increased specific surface area, an elevated concentration of highly active Cr⁶⁺ species, and improved reducibility and mobility of surface oxygen species. During the reaction, toluene was rapidly adsorbed and converted into benzoate intermediates, which were subsequently oxidized to form the final products, CO₂ and H₂O.

This work reports the successful synthesis of a highly stable and durable non-PGM catalyst Co₃O₄/Co_xCe_1−xO_2−δ/C via a simple solvothermal process. The electrocatalytic ability of Co₃O₄/C, CeO₂/C and Co₃O₄/Co_xCe_1−xO_2−δ/C are tested for oxygen reduction and oxygen evolution reaction (ORR, OER). Under identical conditions, the electrochemical studies of the catalysts reveal enhanced performance of the Co₃O₄/Co_xCe_1−xO_2−δ/C. It shows the highest geometric current density (j_geo = ̶ 4.1 mAcm⁻² ) at 0.33 V vs. RHE. Moreover, Co₃O₄/Co_xCe_1−xO_2−δ/C has the earliest onset for OER with a bifunctionality index of ΔE = 1.05 V and has the highest turnover frequency. The catalyst was compared with benchmarks like 20 wt% Pt/C for ORR and RuO₂ for OER. Chronoamperometry studies (CA) reveals superior performance of Co₃O₄/Co_xCe_1−xO_2−δ/C over Pt/C for ORR and accelerated durability test (ADT) shows no observable shift of half-wave potential (E_1/2). This enhancement of electrocatalytic ability of Co₃O₄/Co_xCe_1−xO_2−δ/C are attributed to (1) higher degree of Co²⁺:Co³⁺ ratio (3.6) in Co₃O₄/Co_xCe_1−xO_2−δ/C than in Co₃O₄/C (0.8) as revealed from XPS. This is a result of doping of cobalt into CeO₂, and (2) presence of crystalline-amorphous interfaces as observed from HRTEM.

The influence of the type of carbon support on the catalytic activity of Ru/graphitized carbon systems in carbon dioxide methanation was evaluated. Four partly graphitized carbons with varying surface areas (from 50 to 1417 m²/g) were used as supports. The prepared samples were characterized by N₂ physisorption, TG-MS studies, H₂-TPR, CO₂-TPD, XRD, XAS, TEM/STEM, Raman spectroscopy and CO chemisorption. Both the mode of particle size distribution and the dispersion of the active phase clearly depend on the carbon texture; dispersion changes from 27% to almost 90% with increasing carbon support surface area. The degree of support graphitization affects its resistance to undesired methanation under reaction conditions. The activity tests conducted in a model H₂–rich stream with very low CO₂ concentration (1 vol% CO₂) show that the catalysts exhibit good activity, achieving a 20% conversion of CO₂ at a temperature of 270 °C. The increase of the average Ru particle size leads to about sevenfold increase in the CO₂ conversion and a nearly 20-fold increase in TOF values. The catalytic activity or Ru/carbon catalysts is also associated with the presence of basic sites on their surface.

Employing lemon as a green fuel, zinc copper ferrites were synthesized in the current study utilizing the traditional solution combustion technique. The zinc copper ferrites nanoparticles have an average crystallite size of (:sim)23 nm that are confirmed by X-Ray Diffraction (XRD) analysis. UV-diffuse reflectance spectra (DRS) analysis exhibits the bandgap of 2.75 eV and Scanning electron microscopy (SEM) & Energy Dispersive X-ray Analysis (EDAX) analysis reveals the agglomerated particles morphology and homogenous distribution of copper, zinc and iron within the crystal lattice. It is possible to discover that zinc copper ferrites nanoparticles exhibit superior activity when used as an effective material for electrochemical research by using carbon paste electrode and screen-printing electrode. The research findings are validated by their potential applications using cyclic voltammetry (CV) and amperometric (I-t) sensing techniques for the detection of biomolecules like ascorbic acid, creatinine, glucose, lactose, maltose and G-protein and heavy metals like mercury, cobalt as environmental components in 1 to 5 mM concentration. Further, simultaneous detection of two different biomolecules (maltose and G-protein) and heavy metal ions (mercury and cobalt) were carried out. The limit of detection (LOD) and limit of quantification (LOQ) have been determined for sensing of biomolecules and heavy metal ions. The results indicates that, zinc copper ferrites nanoparticles modified carbon paste electrode exhibit superior electrochemical sensing performance.