Catalysis Today最新文献

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.

In recent years, numerous methods have been reported for the preparation of bio-jet fuel. However, the cost remained the most vital determinant for the practical application of these methods. In 2019, our research team reported a synthetic process for bio-JP-10 fuel. It was suggested the production cost of bio-JP-10 fuel can be greatly reduced to $2547/ton that is significantly lower than the market price (∼7091 US$/ton) of fossil energy-based JP-10 fuel. However, energy consumption constituted as much as 42 % of the bio-JP-10 fuel production cost. In the present work, the initial 1,3-cyclopentanediol concentration in the dehydration step of the original route was amplified by six-fold by the optimization of solvent. Upon further optimization of reaction conditions, higher than 80 % cyclopentadiene carbon yields were achieved. Furthermore, a tandem reaction process involving the dehydration, Diels-Alder reaction and hydrogenation steps was developed, eliminating the need to separate the products. Both innovations considerably enhanced the production efficiency of bio-JP-10 fuel. Following the process simulation and energy balance of Aspen Plus 11, the energy consumption cost of bio-JP-10 fuel can be reduced by 67 %.

The highly exothermic nature and wide range of products of the Fischer-Tropsch (FT) synthesis motivated the study of the influence of different fixed bed configurations on the conversion stability and selectivity of the system. A cobalt catalyst (Co-Ru/Al₂O₃) was synthesized as a fixed-bed powder reference and compared with monoliths (230 and 770 cpsi) loaded by the washcoating method. The monolith with the lowest cell density showed the greatest stability among the systems evaluated, with no drop in CO conversion during the 50-hour test. The same powder bed was compared with dual-bed configurations and physical mixing with HZSM-5 zeolite. These experiments showed that by adding HZSM-5 zeolite bed after the FT catalyst one can effectively increase the gasoline range selectivity, without favoring the formation of methane and C₂-C₄ gases. However, when the same mass of zeolite was physically mixed in a single bed, the formation of the C₁-C₄ fraction increased from 23 % to 33 %. The strategies employed improved product distribution and reduced the deactivation rate compared to the conventional single bed.

Glucose and fructose are valuable compounds, which have the potential to displace fossil fuels as a feedstock for highly valued products. One of the promising reactions is the oxi-dehydration of fructose to produce Hydroxymethylfurfural, 2,5-diformylfuran, and furfural. Current processes to produce platform chemicals like Hydroxymethylfurfural, furfural, and 2,5-diformylfuran operate in liquid phase with homogeneous heterogeneous catalyst, but commercialization is limited by scale and environmental impact of the large volume solvent required. Here we developed a gas-phase process to convert fructose in a fluidized bed reactor over Mo − V − WO₃/TiO₂. However, in the catalytic oxi-dehydration of fructose, coke forms on active sites and decreases conversion but increases selectivity. Coke and reactor performance depends on fructose concentration and O₂/fructose ratio. In the first 2 h, acidic amorphous coke accumulates (based on TPO, FTIR, and UV–vis). Feeding excess O₂ maintains coke in an amorphous structure and liberates oxide sites. Whereas coke promotes, water block active site reducing yield. In this work, we optimized the operating parameters of fructose concentration (%) and O₂/fructose ratio, while simultaneously mitigating the issues associated with coke formation and its detrimental effects.

Gamma-valerolactone (GVL) has been converted into a mixture of methyl pentenoate isomers (MPs) in presence of methanol using Zr/SiO₂ catalysts. These isomers are valuable precursors in fine chemistry and for polymer production. The terminal alkene methyl 4-pentenoate (M4P) is bio-based intermediate to produce caprolactam in excellent yield via hydroformylation to methyl 5-formylvalerate (M5FV) with subsequent reductive amination and ring-closure. For an economic process, a high selectivity of M4P is desired. In this paper, the dependency of the product selectivities on various key reaction parameters (e.g. Zr loading, temperature, GVL/MeOH ratio etc.) is presented. In addition, a set of control experiments were performed using the products (MPs) as educts under similar reaction conditions with the aim to investigate CC double bond isomerisation. The initial ring opening of GVL leads to a mixture of M4P and methyl 3-pentenoate (M3P) with small amounts of M2P. Surprisingly, M4P can be converted back to GVL and also to M3P. However, M3P can be converted mainly to M2P and vice-versa. GVL formation is not observed from the conversion of M3P and M2P. The underlying isomerizations limit the selectivity of M4P to ≤80 %, whereas the space time yield could be remarkably improved to 35.3 kg_MP/kg_Cath⁻¹ under optimum conditions. Interestingly, the best catalyst (25Zr/SiO₂) developed through the present study exhibited an excellent long-term stability for a period of >340 h-on-stream.

The catalytic selective etherification of 5-hydroxymethyl furfural (5-HMF) is considered as a feasible route to prepare the biofuels from biomass feedstocks. In this work, a novel solid acid catalyst derived from the flower-like MoS₂ is synthesized by combination of the facile hydrothermal method and reduction process. Therein, the number of Lewis and Bronsted acidic sites derived from the exposed Mo edges of MoS₂ can be efficiently regulated by changing the hydrogen annealing conditions. The prepared MoS₂-450-R catalyst exhibited a prominent activity for the conversion of 5-HMF to 5-(methoxymethyl)furanal dimethyl acetal (5-MFDMA) through the tandem acetalization and etherification under N₂ atmosphere, in which a 99.0 % conversion with 83.7 % selectivity of 5-MFDMA is obtained. Further investigations revealed that the abundant acidic sites of MoS₂-450-R plays a crucial role on the reaction of 5-HMF with methanol. Finally, based on the characterization of catalyst and reaction phenomena, a possible reaction network for the acetalization and etherification of 5-HMF with the methanol has been proposed.

Herein we show that the Ti₃SiC₂ MAX phase can be used as a support for deposition of different amounts of metal oxides (MO_x, M = Cu or V) (5, 10 and 20 wt%) for the direct oxidation of methane to formaldehyde using molecular oxygen, at relatively low temperatures and atmospheric pressure. The oxides were deposited using a hydrothermal method at 180 °C without affecting the bulk MAX phase structure. However, during the hydrothermal treatment (HT) a thin oxide layer - found to play an important role in the reaction's selectivity– was evidenced by X-ray photoelectron spectroscopy. We thus conclude that the MO_x species are responsible for the CH₄ activation, while the Ti₃SiC₂ surface is responsible for the high selectivity to formaldehyde indicating that, Ti₃SiC₂ has great potential for designing innovative catalysts for direct oxidation of methane using molecular oxygen and at atmospheric pressure.