Catalysis Today最新文献

A bimetallic pillared-layered MOF based on Ni and Zn with improved catalytic activity was synthesized and applied in the ethylene oligomerization reaction. According to the XANES spectra, the MOF possesses Ni in the 2+ oxidation state, a well-known active catalytic precursor in oligomerization systems. In addition, Ni and Zn oxide or metallic species were not identified, indicating the absence of impurity phases. µ-XRF and SEM-EDS techniques showed the homogeneous distribution of Ni and Zn species across the SBUs of the bimetallic MOF. Ni/Zn-MOF was applied in the ethylene oligomerization reaction using EASC as the co-catalyst, and the results were compared to its monometallic counterpart Ni-MOF. The bimetallic material Ni/Zn-MOF obtained a TOF corresponding to 135 ×10³ h⁻¹, which accounts for a 60 % increase in the catalytic activity achieved by Ni-MOF (85 ×10³ h⁻¹) under 15 bar of ethylene in a Parr reactor. Moreover, the results obtained in this work are remarkable compared to literature reports for Ni-based MOFs, demonstrating that the co-catalyst employed plays an important role in the catalytic activity. However, Ni/Zn-MOF showed a lower selectivity to α-C₄ oligomers (36 %) against 58 % obtained by Ni-MOF. According to the reuse tests conducted, the bimetallic MOF can be reused for up to two reactions (under 5 bar ethylene in a glass reactor), although presenting a considerable loss in activity due to the formation of metallic Ni.

Ammonia, a significant atmospheric pollutant, requires effective emission control due to its inherent toxicity and the generation of secondary pollutants like particulate matter. This control can be achieved through various methods, including catalytic processes. Therefore, our study focuses on evaluating the potential of catalysts based on iron oxide and nickel oxide supported on γ–Al₂O₃ for the selective catalytic oxidation of NH₃ to N₂ (NH₃-SCO). The γ–Al₂O₃ was obtained by thermal decomposition of aluminum hydroxide, and 5 or 10 wt% of Fe or Ni was added through wetness incipient impregnation. XRD diffractograms confirmed the formation of the γ–Al₂O₃ phase. XRD, H₂-TPR, and UV–vis DRS data showed the presence of Fe₂O₃, NiO, and NiAl₂O₄ in the catalysts. Introducing metal oxides onto the support led to a drop in the specific area, pore size, pore volume, and NH₃ desorption, which was higher for the catalysts containing Fe. The catalysts were active in NH₃-SCO, and the insertion of Fe or Ni was essential because it promoted a significant increase in the NH₃ conversion (∼75 % Fe and ∼55 % Ni), compared to pure support (∼8 %), mainly from 400 °C. However, doubling the metal content has not resulted in a considerable increase in NH₃ conversion. The N₂ selectivity was higher for the catalysts containing Ni (∼85 %) from 400 °C compared to catalysts containing Fe (∼76 %). Such behavior was due to the larger surface area of the Ni-containing catalysts. Despite that, the 5Fe/γ–Al₂O₃ catalyst emerged as the most effective option for NH₃-SCO applications, combining higher NH₃ conversion and good N₂ selectivity.

The energetic demands of modern society urge a transition that relies on alternative and sustainable sources. Among the available possibilities focused on mitigating the use of fossil fuels, the biodiesel industry stands out. However, the excess of glycerol generated as a coproduct still raises debate regarding how it could be better used. A well-established approach is the use of the platform molecule, i.e., glycerol, in the presence of heterogeneous catalysts to obtain added value products. Zeolites are well-known for their versatility in numerous applications, such as in the oil industry. Besides, different types of aluminosilicates are being studied in the catalytic conversion of glycerol to acrolein, acetol, acrylic acid, allyl alcohol, solketal, etc. This review addresses the general properties, fundaments, synergetic aspects, theoretical modeling, resistance, and coke formation, as well as the zeolites limitations that pose obstacles for those reactions. This highlights the importance of developing zeolite materials with specific acid sites, synchronizing their amount and strength with the pore interconnectivity so that reagents diffusion within the zeolitic channels can be maximized, leading to a decrease in the obstruction of active sites and pores caused by coke deposition. A number of modifications, including hierarchization, isomorphic substitution, acidity tuning, and additional phases (SMSI effect), have been reported as alternatives for improving the performance of glycerol conversion and the resistance to deactivation. Several developments involving reactional mechanisms, coke deposition, and catalysts applied to glycerol conversion have been the subject of studies centered on process optimization, which is translated into the development of solids more resistant to deactivation. Among the zeolites with the best catalytic performance, the following stand out: BEA, MCM-22, MFI, ITQ-2, SAPO-34, and ZSM-5. Some complex technical aspects still need to be better understood so that the scalability of the catalytic conversion of glycerol becomes economically feasible, thereby arousing the interest of both the public and private sectors.

In the present paper a comparison between different parameter estimation procedures commonly used for the kinetic modeling of chemical reaction is performed, based on experimental measurements of the cyclohexane dehydrogenation to benzene. The obtained results show that, when the Arrhenius equation parameters are estimated from estimates of the rate constant taken at different temperatures, larger parameter uncertainties and correlations are obtained, particularly when the variances of the experimental measurements are not considered during the estimation process. It is also observed that an apparent kinetic compensation effect occurs when the experimental data are separated according to the inlet partial pressure and catalyst mass in the reactor, mainly due to the existing and unavoidable experimental uncertainties and parameter correlations. Additionally, it is shown that larger uncertainties and correlations are obtained when the parameter estimates are computed through the differential method, which can also lead to poorer model predictions of the experimental data. Finally, it is shown that the simultaneous one-step estimation of all model parameters through the integral method and considering the available experimental uncertainties can provide the most accurate parameter estimates, making use of mathematical expressions that describe how variances of the experimental measurements depend on the experimental conditions.

Carbon quantum dots (CQDs) have recently attracted attention across various fields due to their small size, high conductivity, fluorescence emission, low toxicity, and other desirable characteristics. In this study, highly fluorescent CQDs with an average diameter of 3.7 nm were prepared via microwave irradiation using a standard commercial microwave oven and glycerol as solvent. Several cation promoters were examined for CQD synthesis, with copper ions ultimately chosen for comprehensive characterization and application. The CQDs were impregnated onto both commercially available and microwave-synthesized TiO₂ nanoparticles. The photocatalytic activity was evaluated with respect to the hydrogen and oxygen generation. Under the employed conditions, the oxygen evolution reaction (OER) exhibited over 12 times higher efficiency than the hydrogen evolution reaction (HER). The enhanced OER activity is attributed to the high electronic conductivity of the small Cu doped CQDs@TiO₂ (Cu-CQDs@TiO₂) facilitating an efficient electron transfer for the OER . Visible light activity (λ ≥ 400 nm) was demonstrated by photodegradation of the indigo carmine (IC) solution used as a model pollutant. Irradiation in the presence of the Cu-CQDs@TiO₂ photocatalyst resulted in complete degradation of the dye in less than 3 hours. The results presented here provide a promising methodology for designing high-performance photocatalysts based on environmentally friendly CQD syntheses. Crucial applications, from renewable energy production to environmental remediation, will benefit from strategies using the carbon abundance on Earth.

The high methane availability and its significant role as a greenhouse gas have led the scientific community to pursue methods for its use. This paper proposes the usage of the oxidative coupling of methane (OCM) as a promising path to transform methane directly into value-added hydrocarbons, mostly ethylene, which serves as a crucial compound in the petrochemical sector. An efficient OCM catalyst should contain substantial basicity and oxygen vacancies for providing surface electrophilic oxygen species, such as superoxides and peroxides, instrumental for boosting selectivity towards C₂ products. Mixed lanthanum-cerium oxide (La-Ce) catalysts have emerged as strong candidates in OCM due to their high thermal stability, oxygen mobility, and high alkalinity. In this study, they were prepared through a surfactant-assisted hydrothermal method with different La/Ce ratios for fine-tuning their basic properties and promoting oxygen mobility on the surface of the catalysts. Samples followed a volcano-shaped relationship between C₂ yield and La content, with optimal performance at a La/Ce molar ratio of 2.1, attributed to the interplay between the high amount of basic sites and oxygen vacancies, increasing the presence of superoxide species over lattice oxygen. Moreover, the Sr-promoted catalyst showed high density of strong basic sites while preserving the reactive oxygen species, achieving 20 % CH₄ conversion, with 57 % C₂ compounds selectivity at 750 °C and GHSV of 18.000 mL.g_cat⁻¹.h⁻¹.

In this work, photoelectrochemical route for biodiesel production using an electrochemical cell configured with platinum and α-Fe₂O₃ modified with Pt nanoparticles as electrodes was investigated. XRD patterns registered for film prepared by modified hydrothermal method revealed a trigonal structure of the hematite (α-Fe₂O₃) phase. The α-Fe₂O₃ film surface was decorated by metallic Pt nanoparticles (Pt^NP) in order to reduce the charge recombination and improve the photocatalytic efficiency. The band gap energy (E_BG) of the α-Fe₂O₃ and Pt^NP/α-Fe₂O₃ films was estimated by UV-Vis spectroscopy at approximately 2.1 eV. Electrochemical measurements showed that the oxide is an n-type semiconductor adequate to be used as a photoanode in biodiesel synthesis. Under polarization conditions, the electrochemical cell changed the pH from 7 to 14 when the system was polarized at 5.0 V. In the synthesis of biodiesel by esterification reaction, oleic acid, 300 µL of 0.1 mol L⁻¹ aqueous KCl solution and methanol were used as precursor reagents. The reaction was carried out free of strong base, such as KOH or NaOH, as a supporting electrolyte. In this route, the reduction of the water molecule occurred on the cathode, with the formation of hydroxyl (OH^-) species, methoxy, and consequently fatty acid methyl esters (FAMEs). Thermogravimetric analysis (TGA) and Gas chromatography coupled to mass spectrometry (CG-MS) were performed to evaluate the catalysis products. GC-MS analyzes show that the reaction has a yield of about 7 % with the formation of FAMEs, such as methyl 9-octadecenoate, methyl hexadecanoate and methyl hexadecanoate.

The preparation of the binary metal NiCe-based catalysts involved a 2-step protocol, the ceria was first coated on SiO₂ which was then utilized to disperse Ni nanoparticles. Various techniques including N₂ adsorption/desorption, ICP-OES, XRD, HRTEM, XPS, H₂-chemisorption, H₂-TPR, NH₃-TPD, and TG etc. were performed to study the microstructure, redox, acid property and deactivation. The results revealed that CeO₂ and metallic Ni were well dispersed on the support surface, the synergistic effect between the two metal species was conserved well. The content of CeO₂ had considerable effects on redox and metallic properties rather than the acidic property. The dispersion of metallic Ni played a dominant role in promoting the catalytic activity. The levulinic acid conversion attained 84.0 % with a γ-valerolactone selectivity of 98.8 % on Ni/SiO₂@2CeO₂ sample with the highest dispersion of 9.8 %. The amorphous CeO₂ suppressed the sintering of metallic Ni nanoparticles and improved the coke resistance, leading to better catalytic activity within 20 h time on stream.

Contamination of wastewater with organic dyes has caused a serious threat to humans and aquatic life due to the hazardous effect of these contaminants. In this context, the present work aims to carry out a Machine Learning (ML) study to evaluate the photocatalytic activity of a nanozeolite (nANA) in the degradation of Rhodamine B (RhB) dye. Three machine learning algorithms (Random Forest, Artificial Neural Network and Xtreme Gradient Boosting) were used in the regression model development. The dataset used in the machine learning and data correlation was generated by Central Composite Rotational Design (CCRD 2²). Regarding the machine learning study, the ANN with structure 3:6:1 showed the best performance as a predictive model (R² = 0.98 and 0.9 for training and testing, RMSE < 5.0), resulting in the 50.37 ± 1.01 % RhB removal at pH 5.7, [RhB] = 200 mg L⁻¹ and [nANA] = 2.75 g L⁻¹ after 180 min under visible light. Feature importance revealed that all parameters (pH, [RhB], [nANA]) were relevant to the response. Therefore, this work confirms the potentiality of machine learning algorithms to develop predictive models as well as a good starting point for the scale-up of advanced oxidation processes.

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a key approach to sustainable upgrading of furfural based biomass resources. In this work, small Pt nanoparticles (about 2.1 nm) loaded on MnP_nO_x composite were shown to effectively drive the base-free aerobic oxidation of HMF to FDCA in water. Regulating the P content in carrier enabled to tune HMF conversion and product distribution. The optimal Pt/MnP_0.5O_x catalyst can reach 98% yield of FDCA at 110 °C under 10 bar of O₂ after 24 h. It also showed the highest initial conversion rate of HMF (13 mmol mol_Pt⁻¹ s⁻¹) and productivity of FDCA (4.1 mmol mol_Pt⁻¹ h⁻¹) among all the Pt/MnP_nO_x catalysts. The carrier effect of P addition on promoting Pt oxidation catalysis was elucidated by using rigorous kinetic investigations and comprehensive characterizations. The initial conversion rate, rate constant and apparent activation energy were independently measured on oxidation of HMF and its derived intermediates. ICP-MS, XRD, TEM, H₂-TPR, O₂-TPD and XPS were used to acquire catalytic properties. It was demonstrated that P addition led to changes in carrier structure and metal-support interaction, which eventually promoted the formation of highly active electron-rich Pt⁰ sites and mobile reactive defect oxygen species. These features allowed improving the selective oxidation catalysis of supported-Pt nanoparticles for the base-free conversion of HMF to FDCA.