Topics in Catalysis最新文献

Zeolites are investigated for complete methane oxidation to reduce sintering and deactivation of the active PdO nanoparticles. Pd/H-CHA is shown to have good low-temperature activity and remarkable tolerance to SO₂. After an induction period with loss of activity, the activity is recovered and the catalyst withstands more than 200 h on stream with 1000 ppm methane in the presence of 2 ppm SO₂. The zeolite counter ions play a key role, and the literature indicates that ion exchange with alkali metals provides better water tolerance. Here we show, however, that the alkali ion exchanged Pd-CHA possess inferior sulfur tolerance compared to the parent Pd/H-CHA since the recovery of the catalytic effect is blocked. Deactivation by simultaneous SO₂ and water remains an unsolved challenge for complete methane oxidation catalysts.

Graphical abstract

A Pd/CHA catalyst for methane oxidation is shown to have remarkable resistance towards SO₂ in the feed gas and to lose it upon ion exchange with alkali metal ions.

The Three-Way Catalytic performances of Pd supported on dual-substituted LaFeO₃ catalysts have been studied from temperature-programmed experiments in typical TWC operating conditions. La has been partly substituted by Ca and Fe by Cu. Pd was introduced simply by wet impregnation. Particular attention was paid to the structure and composition of La-substituted by calcium and A-deficient perovskites to stabilize palladium dispersion and oxidation state. Weak interactions between oxidic Pd species and LaFeO₃ lead the prevalence of metallic Pd species which are responsible of the highest metallic Pd dispersion. In contrast, much less reducible oxidic Pd species can be stabilized in defective sites characteristic of La-deficient et Ca-substituted perovskite structures then improving oxygen mobility. The changes in reaction rates, activation energies, and selectivities for oxidation and reduction reactions would solely reflect the participation of Pd as active sites on Pd/LaFeO₃, while the cooperative effect between palladium and surface oxygen species belonging to the perovskite lattice would be responsible for the superior performance of Pd/La_1− xCa_xFe_0.8Cu_0.2O₃. The practical interest of this composition is emphasized through the comparison with a benchmark Pd/Ce_xZr_1−xO₂ catalyst.

Colloidal Gas Aphrons (CGAs) are microbubbles with a stable air core, surrounded by a hydrogen-bonded aqueous shell and surfactant bilayers. They are generated in a specially designed baffled generator using surfactant solutions at high rotational speeds exceeding a critical threshold. While CGAs have diverse applications, including enhanced oil recovery, aerated concrete production, soil and water remediation, and porous material synthesis, limited understanding exists regarding their properties variations when generated in a recycle mode of operation. The present paper systematically explores experimentally both the batch and batch-recirculation modes to evaluate their influence on the CGAs quality, specifically focusing on air holdup and stability. A meticulous examination of the effects of surfactant concentration, disc rotational speed, and CGAs recirculation rate offers valuable insights into the dynamics of formation and overall stability of CGAs. Furthermore, the anticipated distinctions between the outcomes of batch and batch-recirculation modes of operation of a CGAs generator are analyzed and discussed. Batch-recirculation demonstrates negligible influence on the air holdup and volume of CGAs generated over extended durations, yielding results comparable to those observed in batch mode. Nonetheless, a noticeable enhancement in the CGAs build-up occurs during the initial stages of the recirculation mode of operation. While long-term batch-recirculation shows minimal impact on the overall generation of CGAs, reflected in similar air holdup values and volumes as in standard batch mode, it demonstrates a rapid initial formation. After 5 min of CGAs generation in batch and batch-recirculation modes at 4000 RPM, the air holdup was 0.3 and 0.45, respectively, and height of CGAs dispersion was 9.9 cm and 11.2 cm, respectively. This early-stage enhancement during recirculation suggests improved generation kinetics, although the final CGAs yield remains comparable between both modes. This experimental finding may have an important bearing on large-scale batch generation of CGAs and optimization of such production processes in practice.

In the realm of chemical industries, heterogeneous catalysts are pivotal, enabling the molecular transformations that lead to the formation of desired products. Nano-catalysts have attracted significant international attention because of their diminutive size and enhanced surface area, resulting in improved interfacial interactions and expanded functional capabilities. In the realm of green chemistry, nano-catalysis is recognized as an effective technology owing to the distinctive characteristics of nano-particles (NPs), which possess vast exterior area and enhanced efficiency of catalysts. NPs are regarded as versatile catalysts among a large variety of application spanning since energy conversion to chemical production. The applications of nano-catalysis extend into various aspects of daily life, including personal care items, environmental cleanup (such as the extraction of heavy metals and the management of manufacturing devastate), pharmaceuticals, bio-sensors, bio-medical applications, and food processing. Consequently, recent advancements in methodical and scientific research focused on sustainable catalysis have garnered international interest in addressing the challenges posed by industrial pollution. Nano-catalysts are particularly advantageous for green production, as they facilitate rapid chemical transformations, improve yield, and simplify the processes of catalyst separation and recovery. In this review we will give a comprehensive summary of the advancement completed in the green multi-component synthesis of imidazoles, coumarines, dihydro-pyridines, benzoxanthene, pyrazole, naphthopyran, α-aminophosphonates, and β-amino carbonyl derivatives using various heterogenous nano-catalytic systems, we have carefully reviewed ten years' worth of research papers, from 2013 to 2024. We looked for research that skillfully combined numerous catalyst designs employing eco-friendly metals and biodegradable composites, rather than restricting our focus to a single green chemical approach

Solid acids and super-acids have been the subjects of continued interest due to their numerous applications in many chemical and pharmaceutical industries. They are claimed to be responsible for producing more than 1 × 10⁸ metric tons of products per year. In recent times, in particular, inorganic solid acid-catalyzed organic synthesis and transformation reactions have gained more attention due to the proven advantage of heterogeneous catalysts, simplified product isolation, mild reaction conditions, high selectivity, ease in recovery and reuse of the catalysts, and reduction in the generation of wasteful side products. In that context, we were interested in investigating various industrially important organic reactions to replace toxic and corrosive reagents, noxious or expensive solvents, and multistep processes with single-step and solvent-free ones by employing environmentally benign solid acid catalysts. The primary objective of this mini-review is to summarize the recent developments in biomass-based organic synthesis and transformation reactions of commercial significance catalyzed by WO_x/ZrO₂ green solid acid catalysts. The preparation of catalysts and their characterization are briefly discussed, emphasizing the application of these catalysts for a variety of practical reactions.

In this present review paper, the catalytic applications of carbon quantum dots (CQDs) as an efficient heterogeneous catalyst for organic conversion under sustainable and greener protocols have been investigated. The CQDs have carboxylic acid and hydroxyl functional moieties utilized for the modification of the surface of the CQDs. Moreover, CQDs and CQD-based composites have generated C–C, C–N, C–O, etc., bonds that leads to various organic synthesis via straightforward methodology. The following CQDs and decorated CQDs such as magnetic CQDs, CNDs, CQDs-N(CH₂PO₃H₂)₂, CQDs-N(CH₂PO₃H₂)₂/SBA-15, BPEI-CD, CDs/Bi₂MoO₆, Cu(I)-doped CQDs and SCQDs catalyzed one-pot multicomponent reactions are discussed. And also, CQDs and decorated CQDs have ensured excellent stability, recyclable, economically viable, and environmentally friendly, shorter reaction time, and avoid tedious work-up procedures. This review paper highlighted the synthesis of a one-pot multicomponent reaction catalyzed by the CQD catalyst.

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Single atom catalysts (SACs) have attracted significant interest due to their unique properties and potential for enhancing catalytic performance in various chemical reactions. In this study, we atomistically explore adsorption properties and catalytic performance of single Cu atoms anchored at low-index CeO₂ surfaces, focusing on the oxidation of CO and H₂. Utilizing density functional theory (DFT) calculations, we report that Cu adatoms bind favorably on different CeO₂ surfaces, following a stability order of (100) > (110) > (111). The charge transfer from a single adsorbed Cu atom to Ce leads to the reduction of Ce⁴⁺ to Ce³⁺ and the oxidation of Cu⁰ to Cu⁺. This strengthens molecular bonds at Cu sites, particularly for CO, while H₂ shows a by ~ 1 eV weaker adsorption. CO oxidation is energetically more favorable than H₂ oxidation on the Cu/CeO₂(111) surface. The rate-controlling steps for the Mars–van Krevelen mechanism involve the formation of a bent CO₂ intermediate for CO and H₂O for H₂. The lattice oxygen atom at the interface plays a key role for both oxidation processes. Our findings highlight the potential of single atom catalyst, Cu/CeO₂, for selective CO adsorption and its subsequent oxidation in heterogeneous catalysis.

In this work, Ni-Ga oxides in bulk and supported onto alumina were prepared by coprecipitation and impregnation for the evaluation of the oxidative dehydrogenation (ODH) of ethane assisted by CO₂. X-ray diffraction (XRD) results indicate that the enhanced catalytic activity exhibited by the Ni-Ga oxides bulk catalysts could be related to NiO crystallite size (8 nm) in addition to the high dispersion of the active phase observed by scanning electron microscopy (SEM). Diffuse reflectance spectroscopy (UV-Vis DRS) displayed a Ni predominance with octahedral symmetry (O_h) for the catalysts. X-ray photoelectron spectroscopy (XPS) revealed changes in the surface chemical environment for the catalysts related to the gallium promoter effect. Ni 2p_3/2 analysis indicated that the Ni²⁺ and Ni³⁺ ions, Ni²⁺-OH species, or Ni²⁺ vacancies on the surface of the unsupported catalysts have an important role in catalytic activity. In addition, Ga 3d results suggest that the catalytic activity of the unsupported catalysts could be connected to the similar concentration of Ga^y and Ga³⁺ species (ca. 50%), whereas the absence of activity for supported catalysts could be attributed to the Ga³⁺ species concentration higher than 90%. Finally, relationships for ethane conversion and selectivity toward ethylene with the Ox_(nuc)/Ox_(ele) ratio were found. The analysis of the peak areas in O 1s spectra revealed that the higher selectivity toward ethylene of the NiGa-8 catalyst (ca. 95%) could be related to a similar peak area of nucleophilic and electrophilic oxygen species in the surface.

Graphical Abstract

This study aims to develop a sustainable and recyclable SnO–CeO₂ nanocomposite catalyst for efficient one-pot synthesis of 5-amino-1,3-diphenyl-1 H-pyrazole-4-carbonitrile in water under mild conditions. SnO–CeO₂ nanocomposite was synthesized via a simple coprecipitation method and characterized using XRD, SEM, TEM, FTIR, XPS, BET, and UV-Visible spectroscopy. Its catalytic performance was evaluated in one three-component reaction of malononitrile, phenylhydrazine, and substituted aromatic aldehydes, using water as a green solvent. The recyclability of catalyst was assessed over multiple reaction cycles. The nanocomposite exhibited excellent catalytic efficiency, achieving high yields (81–96%) in shorter reaction times compared to conventional methods. Structural integrity and catalytic activity were retained after five cycles, confirming its stability and recyclability. The synthesized compounds were confirmed via ¹H NMR and ¹³C NMR spectral analysis. The synergistic effect between SnO and CeO₂ enhances catalytic performance, making nanocomposite a sustainable and cost-effective alternative to conventional catalysts. Its high efficiency, water-mediated reaction conditions, and reusability reinforce its potential for green and scalable organic synthesis.