Catalysis Today最新文献

In this study, we synthesized MnO_x nanowires via hydrothermal methods and explored the impact of nickel (Ni) doping on their morphology and electrochemical properties. We investigated the structural and chemical changes induced by Ni incorporation by utilizing TEM and XPS analyses. Our results revealed that Ni doping influenced the distribution of manganese oxidation states, with 1.6 wt% Ni-doped nanowires exhibiting the optimized condition. Also, we observed a balance between the Mn³⁺/Mn⁴⁺ ratio with the Ni doping. Electrochemical characterization demonstrated enhanced capacity in Ni-MnO_x nanowires at the 1.6 wt% Ni doping level. Galvanostatic charge-discharge measurements confirmed the superior performance of this level of Ni doping; moreover, the fabrication of asymmetric supercapacitor cells using these nanowires showed improved energy storage capabilities. The main results showed exceptionally high capacity (955.55 and 383.33 mAh g⁻¹ at 1 and 20 A g⁻¹, respectively) and an excellent rate capability. Cycling stability tests over 8500 cycles demonstrated excellent retention of capacity, underscoring the durability of the optimized Ni-MnO_x nanowires, with a retention of 85 % of its initial capacity. Thus, this study emphasizes the significance of Ni doping in MnO_x nanowires for enhancing electrochemical performance when the synthetic process is controlled, offering valuable insights for high-performance energy storage device development.

Olefin hydroformylation is one of the most significant examples of homogeneously catalyzed conversion processes. However, developing chemo/regio-selective and stable solid catalysts has remained a persistent challenge in heterogeneous catalysis. Particularly the design of solid catalysts for the hydroformylation of light, gaseous olefins, such as ethylene and propylene, has been extensively researched, given that the products from these processes are key players in the oxo-chemicals market. Additionally, developing selective, continuous gas-solid C_2–3 olefin hydroformylation processes prospectively offers a reactive separation alternative to conventional and massively energy-intensive cryogenic distillation separation methods. In this review, we first assess the potential of reductive olefin hydroformylation as a cost-effective alternative to conventional cryogenic distillation processes for recovering value from industrial gas mixtures of ethylene and propylene. Taking a conventional ethylene splitter as a reference case, a reactive separation through ethylene reductive hydroformylation to 1-propanol is predicted to provide significant savings in terms of utility costs. Next, major advances in the design and development of solid catalysts for ethylene and propylene hydroformylation are surveyed, with an emphasis on single-atom catalysts (SACs) and supported metal nanoclusters. These catalysts have recently achieved hydroformylation activity and chemo/regio selectivity comparable to, or even surpassing, those traditionally exclusive to free molecular catalysts in solution. Different catalyst design strategies, including the heterogenization of metal coordination complexes in supported ionic liquid phase (SILP) catalysts and porous organic ligands (POLs), as well as the tuning of oxide-supported catalysts via the adjustment of metal-oxide interfacial effects or through nanoconfinement within zeolitic frameworks, are systematically reviewed and compared. Finally, conclusions are provided, alongside a critical perspective on fundamental and practical aspects that require particular attention to ensure rational and systematic progress toward optimized catalysts and reaction settings, ultimately paving the way for the heterogenization of light olefin hydroformylation processes.

This study investigated the effects of Beta zeolite ion exchange with Fe, Zn, and Co on ethanol conversion to hydrocarbons. Various characterization techniques such as X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), magic angle rotation nuclear magnetic resonance spectrometry (MAS NMR) of ²⁹Si and ²⁷Al, scanning electron microscopy (SEM), nitrogen physisorption, ammonia temperature-programmed desorption (NH₃-TPD) and Fourier transform infrared spectroscopy (FTIR) were employed. Catalytic tests were performed at temperatures from 475 to 550 °C under ambient pressure. The metal addition to Beta zeolite reduced micropore area and volume, decreased the concentration of the extra-framework aluminum, and increased total acid site density and Lewis acid sites, except for Fe. For all catalysts, ethylene was identified as the primary product. However, catalysts containing Zn and Co displayed the formation of propylene and C1 to C3 paraffins. The catalyst with Fe exhibited the highest deactivation and a significant decrease in acidity, attributed to the formation of extra-framework aluminum, resulting in exclusive ethylene production.

Nine {ONO} ligands were prepared and treated with ZnEt₂ to form a range of complexes. The resulting complexes were characterised in solution through ¹H and ¹³C{¹H} NMR spectroscopy, and in the solid state through single-crystal XRD and elemental analysis. Moderate reactivity towards lactide polymerisation was demonstrated, with hydroxyl complexes reaching high conversion in 1–2 minutes at 300: 1: 1. All complexes successfully degraded PLA to methyl lactate and the effect of reaction time, temperature and catalyst loading was explored. Zn(4)₂ successfully produced ethyl and n-butyl lactate and was shown to work in ambient conditions, albeit with reduced yield and selectivity. The production of BHET from waste PET was demonstrated with a selection of the most active catalysts. Zn(4)₂ was shown to be capable of sequential PLA/PET degradation and to be tolerant of HDPE/PVC contaminants.

Recently, catalysts based on bulk indium oxide (In₂O₃) have been used in CO₂ valorization; however, several studies correlate crystal phase with performance without considering possible changes during the reaction. In this context, we investigated different crystal phases of bulk In₂O₃ (pure cubic, hexagonal, or mixed-phased) in CO₂ hydrogenation, where we observed variations in catalytic activity associated with phase transitions occurring under reaction conditions. We systematically compared the crystal phase and surface area before and after the reaction, showing that, at 350°C, independent from the initial In₂O₃ structure, there is a tendency to form the cubic phase accompanied by the loss of surface area. To reach these results, we employed various synthetic methods that tailored structural and textural characteristics to achieve desired properties; for the first time, we obtained a cubic major mixed-phase In₂O₃ structure at a 3-hour synthesis time by using a microwave-assisted method. Such material presented the best methanol productivity. Thus, as not previously reported, our results revealed that utilizing bulk hexagonal In₂O₃ may not be interesting under this temperature; also, a higher surface area does not necessarily provide improved conversion rates. XPS, XRD, EPR, MEV, N₂ physisorption, CO₂-TPD, and H₂-TPR were performed and corroborated our investigations.

Layered rare earth hydroxides (LREHs) with unique layer structure and tunable properties have shown attractive potentials as heterogeneous catalyst, but is still challenging in biomass valorization towards valuable chemical production due to the poor catalytic activity. Herein, Mg-modified erbium hydroxides (Mg-LErHs) with well-constructed layered structure have been first fabricated, where the properties and structure of Mg-LErHs significantly depend on the proportion of Mg. The results of catalyst characterizations reveal that Mg introduction increases the interlayer spacing and the content of Er(III)-O. Mg modification also hinders the desorption of crystallized H₂O and dehydroxylation, thereby increasing the degree of crystallinity and promoting the stability of the catalyst. The activity test indicate that Mg modification greatly promotes the production of lactic acid from monosaccharides, where Mg(5.8)-LErHs affords the highest lactic acid yield of 60.9 %. Mg-LErHs also outperform other Mg-LREHs catalysts for the production of lactic acid. The highest catalytic activity of Mg(5.8)-LErHs are possibly attributed to its highest degree of crystallinity, and the increased layer spacing after Mg modification might have an advantage in facilitating the entry of substrate. The increased Er(III)-O content with high Lewis acidity might facilitate the combination with electronic-rich carbonyl oxygen in substrate. This research may provide a novel strategy to design the layered rare earth catalysts with tunable catalytic activity for biomass valorization.

This study focuses on the catalytic synthesis of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF). The influences of temperature, O₂ pressure, initial HMF concentration (i.e., catalytic loading), and NaOH:HMF ratio are studied. A minimum temperature is required to promote oxidation, but it also favors the humins formation. The HMF degradation is identified as the bottleneck of this approach, requiring working with a minimum O₂ pressure and a high catalytic loading to prevent the humins formation. At 80ºC, a NaOH/HMF ratio of 2:1, and 25 bar oxygen pressure, FDCA selectivity reached 87 % after 8 hours, with minimal humins formation. This result represents an improvement in the sustainability of typical conditions proposed in the literature, mainly because of the minimum NaOH excess used. Additionally, the study explored a one-pot process integrating fructose dehydration and HMF oxidation. While promising, challenges arose in preventing HMF degradation during the process. Nonetheless, these findings highlight viable pathways for sustainable FDCA production, emphasizing the importance of optimizing reaction conditions to balance FDCA yield and humins prevention.

A diverse suite of Zn-SAPO-34 catalysts was synthesized employing three distinct methodologies for the incorporation of zinc species: thermal ion exchange, wet impregnation, and physical mixing. The catalysts were characterized using various analytical techniques including XRD, FT-IR, BET, SEM, XRF, XPS, NH₃-TPD, and Py-IR, to elucidate the crystal structure, morphology, surface acidity, and the presence of zinc species within the catalysts. The study showed that the method of zinc introduction markedly impacts the physicochemical properties of the catalysts. Different approaches to introducing zinc species significantly influence the acid strength and type on the catalyst surface, with variations in the existing states of zinc across the catalysts. Specifically, zinc species introduced via thermal ion exchange coexist as ZnOH⁺ and ZnO within the catalyst, whereas those from wet impregnation and physical mixing are individually present as either ZnOH⁺ or ZnO. Furthermore, the study examined the catalytic performance of these Zn-SAPO-34 catalysts in the dehydration of fructose to produce 5-hydroxymethylfurfural (HMF). Catalysts prepared via thermal ion exchange exhinited superior performance, achieving an remarkable HMF yield of 94.6 %. Additionally, in situ infrared technology was used to investigate the effect of zinc species introduction on the fructose dehydration process, indicating suggesting that the introduction of zinc species enhances the transformation of fructose molecules.

The renewable platform chemical furfuryl alcohol (FOL) plays a pivotal role in the development of biorefineries and is manufactured by the catalytic hydrogenation reaction of furfural (FAL) which is, after bioethanol, the 2nd highest demanded biomass downstream product. High catalytic activities (TOF > 20000 h⁻¹) with essentially quantitative selectivities to the desired product FOL (> 99 mol%) have been achieved in the novel hydrogenation of FAL employing water-soluble platinum catalysts modified with the industrially applied benchmark ligand trisulfonated triphenylphoshine (TPPTS) under mild and neutral conditions in the green and sustainable aqueous solvent. The apparent activation energy of the Pt/TPPTS catalyst amounts 4.7 kJ/mol. This usually low value points out the presence of a highly active platinum TPPTS catalytic system to convert efficiently the aldehyde moiety of FAL into an alcohol group to yield selectively FOL in water. Five recovery and recycling experiments of the Pt/TPPTS catalytic system showed that the catalyst possesses some stability and keeps its very high selectivity towards FOL in the aqueous solvent. The work disclosed here is consistent with six of the twelve principles of Green Chemistry which are: i) high atom economy i.e. low E-factor due to the clean incorporation of molecular hydrogen to the substrate FAL to yield selectively FOL, ii) use of innocuous solvents i.e. water, iii) use of renewable biomass-derived FAL, iv) use of catalytic reagents, v) designing safer chemicals because the products are bio-based value added chemicals, and vi) inherent safer chemistry for accident prevention because of the high heat capacity of the aqueous solvent which renders exothermic reactions such as hydrogenation reactions more safe especially in the large industrial scale.

A Periodic Mesoporous Organosilica (PMO) containing the cationic 4,4-bipyridinium group, presenting 0.25 mmol g⁻¹ that corresponds to 11.5 w/w%, was successfully prepared. This material was designed to have the ionic group acting as anchoring agent of PdCl₄^2- anion complex, in a much lower amount than the available cationic sites (3 and 15 molar%). Subsequently, the palladium complex was in situ reduced to obtain stabilized palladium nanoparticles (PdNP). The ensemble of characterization results showed that the PMO material walls have a cylindrical morphology with hexagonal packing, generating well-ordered pores with a narrow size distribution and high surface area, even after being decorated with PdNP. This material is a candidate to be an efficient nanoreactor considering that it contains spatial uniformity in its chemical sites and confined environment. Aiming to evaluate the availability of palladium sites, the material was used as a catalyst in the reduction of p-nitrophenol model reaction. Although the catalyst of the present study has a comparable activity with other already reported systems, it presents the impressive lowest molar palladium/p-nitrophenol ratio found in literature.