Topics in Catalysis最新文献

Crystalline MoVTe(Sb)NbO oxide catalysts have been shown to exhibit high oxidation catalytic performance in propane ammoxidation. However, the roles of individual elements remain unclear. In order to elucidate these elemental roles, Nb and Te were introduced into the orthorhombic Mo₃VO_x oxide (Orth-MoVO) through post-hydrothermal treatment. Structural analysis revealed that Nb covers the surface of the Orth-MoVO crystal particles, while Te is accommodated within the hexagonal channel of the orthorhombic structure. Physicochemical characterization demonstrated that Nb enhance the structural stability of the orthorhombic phase, and the introduction of Te into amorphous Mo₃VO_x oxide through post-hydrothermal treatment facilitated crystallization from the amorphous phase to the orthorhombic structure during heat treatment. These findings provide novel insights into the roles of individual elements in Mo-V-Te(Sb)-Nb oxide catalysts.

This work employed a novel, easy, and environmentally friendly method for synthesizing platinum nanoparticles over a multi-walled carbon nanotubes (CNT_f) surface, employing thiophene (TH) as a reducing agent and stabilizer. The nanoparticle size depends on Pt concentration and TH to be employed as counter electrodes in the I⁻/I₃⁻ reduction reaction and compared with the traditional Pt counter electrode. The fabricated counter electrodes were evaluated in dye-sensitized solar cells (DSSCs). The results indicate Pt₂/CNT_f hybrid material counter electrode presents a charge transfer resistance (R_CT) of 4.20 Ω, and the photovoltaic parameters of the cell were Jsc = 11.23 (mA/cm²); V_OC = 0.781 V, and FF = 60.6, with an efficiency of 5.32%. The traditional Pt counter electrode shows an (R_CT) of 8.65 Ω, and the photovoltaic parameters of the cell were Jsc = 11.37 (mA/cm); V_OC = 0.769 V and FF = 64.5, with an efficiency of 5.94%. The Pt₂/CNT_f hybrid material performs similarly to traditional Pt counter electrodes, but the Pt₂/CNT_f hybrid presents five times less Pt concentration.

This study reports the hydrothermal synthesis, comprehensive characterization, and catalytic evaluation of zirconia nanoparticles with various phases for chemoselective reduction of α-keto esters & amides. These nanoparticles exhibited remarkable catalytic activity in highly chemoselective reduction reactions in which monoclinic zirconia NP’s show excellent efficiency, particularly in the reduction of α-keto esters and amides utilizing NaBH₄ as the reductant and methanol/ethanol as environmentally benign solvents. A significant advancement is demonstrated through the achievement of 83–99% conversions for α-hydroxy esters and α-hydroxy amides in a remarkably short time frame of 20–25 min. Furthermore, the ZrO₂ nano-catalyst demonstrates remarkable reusability, maintaining catalytic activity through five consecutive cycles without significant decline. A combination of FE-SEM, XRD, EDX-elemental mapping, FTIR, BET analysis, and Ammonia TPD techniques was employed to investigate the morphology, thermal stability, crystal structure, and surface acidity of fresh ZrO₂ NP’s. The TPD results reveal that M-ZrO₂ exhibits superior acidic properties compared to T-ZrO₂.

Graphical Abstract

While the temperature-programmed desorption of ammonia (NH₃-TPD) is widely used to analyze the combined Lewis and Brønsted acidity of heterogeneous catalysts, the temperature-programmed desorption of isopropylamine (IPAm-TPD) can be used for the selective analysis of Brønsted acidity. This work compared NH₃-TPD and IPAm-TPD as analysis methods for the acidity of zeolitic samples, including H-ZSM-5-23, H-ZSM-5-50, H-ZSM-5-280, a Zn-modified H-ZSM-5-50 sample, and a γ-Al₂O₃ reference sample. For the unmodified H-ZSM-5-23, H-ZSM-5-50, and H-ZSM-5-280, the total acidity determined with NH₃-TPD remained higher and the Brønsted acidity determined with IPAm-TPD lower than the theoretical acidity estimated with the Al content of the materials. When the NH₃-TPD saturation temperature was varied for H-ZSM-5-50 to examine the trends observed in the analyses, the temperature change affected primarily the low temperature peak of the TPD traces. The Zn-modified Zn/H-ZSM-5-50 sample yielded a multi-peak IPAm-TPD trace, though only a single peak trace was expected. Additionally, the value of Brønsted acidity showed no change from the unmodified zeolite.

Various compositions of silica-supported manganese-copper mixed oxide catalysts were explored for the aerobic oxidation of cyclohexane with molecular oxygen as the oxidant. The investigated SiO₂–MnO_x–CuO catalysts with varying weight ratios were prepared by the wet-impregnation method. The prepared catalysts were characterized by various techniques such as XRD, XPS, N₂-physisorption, SEM, and HR-TEM. Among the prepared catalysts, the SiO₂-MnO_x–CuO (SMC964) combination catalyst showed superior catalytic activity with 96% conversion and 96% allylic selectivity (85% selectivity to 2-cyclohexene-1-one and 11% selectivity to 2-cyclohexene-1-ol). Compared to pure metal oxides, the silica-supported mixed metal oxide catalysts demonstrated superior catalytic performance due to high surface area, mixed metal oxide nanoparticles forming on the support, and synergetic interaction between the metal oxides and the support. The influence of different reaction parameters, including the effect of solvent, temperature, reaction time, and catalyst amount, was systematically studied to optimize the reaction conditions. Furthermore, reusability tests over five cycles revealed excellent catalyst stability with negligible loss in activity.

Graphical Abstract

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

The developments of an eco-friendly electrochemical poly l-Met layered carbon paste electrode (l-MN/LCPE) for the analysis of diclofenac (DFN) with the appearance of dopamine (DA) using 0.2 M phosphate buffered solution (PBS) with 7.0 pH at a 0.1 V/s scan rate. The electrochemical behaviour of the DFN was studied using various techniques, including cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Electrochemical impedance spectroscopy (EIS), and Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDX) were used to characterize the external surface structure of the bare carbon paste electrode (BCPE) and l-MN/LCPE. The l-MN/LCPE shows superior electrochemical responses and a greater surface area related to the CPE. Thees’s study explored the effect of pH, and variation of scan rate from 0.025 to 0.300 V/s, showing an adsorption-controlled reaction. The DFN concentration varied from 20 to 250 µM (DPV) and 10 to 160 µM (CV) at the surface of l-MN/LCPE, with a limit of detection (LOD) of 1.71 µM (DPV) 2.48 µM (CV) and a lower limit of quantification (LOQ) of 5.71 µM and 8.28 µM. The modification in the electrode is responsible for enhancement in electrochemical behavior through the formation of film during the electrochemical performance, with improved current response, conductivity, electroactive sites, and superior rapid electron-proton transfer during redox reactions toward the analyte. The l-MN/LCPE fabricated electrode confirms the outstanding repeatability, reproducibility, selectivity, sensitivity, and stability. The work offers a promising and remarkable approach to enhancing the performance of the electrochemical sensors for DFN analysis in pharmaceutical samples containing DFN. These results indicate that the l-MN/LCPE offers a promising platform for monitoring pharmaceutical applications.