Catalysis Today最新文献

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.

Hydrogenation reactions of biomass terpene derivatives constitute great chemical transformations, leading to key platform molecules for the production of high added value fine chemicals, such as citronellal of Florsantol®, for fragrances industries. One of the main challenges remains the high selectivity control to avoid the formation of co-products that could alter the quality of the follow-up products. For that purpose, metal nanoparticles are considered as unavoidable catalytic tools owing to their surface reactivity properties and their potential recycling under adapted conditions. Herein, we report the use of aqueous suspensions of ruthenium and palladium nanoparticles as relevant catalysts for the industrial transformation of terpenic agro-resources into value-added renewable perfume ingredients. First, α-pinene could selectively be hydrogenated into cis-pinane using ruthenium nanoparticles, while palladium is relevant to produce citronellal through the selective reduction of the conjugated double bond of citral as well as Florsantol® by the controlled ring opening of the corresponding epoxide. Interestingly, all these processes have been scaled-up, thus demonstrating the potential of reusable metallic nanocatalysts in water for industrial applications.

In the last four decades, one of the most important advances in organometallic catalysis has been the use of molecular catalysts in two-phase liquid-liquid systems, commonly known as biphasic catalysis, in which one of the phases is polar (where the catalyst is usually found) and the other non-polar (where the substrate and eventually the product are found). For the particular case when water is used as the polar phase it is called aqueous-biphasic catalysis. The role of transition metal complexes as catalysts for aqueous-biphasic hydrogenation and hydroformylation has been extensively investigated throughout this period of time. The present article provides an overview of the disclosed work by a number of research laboratories including ours, which shows the most recent industrial applications or possible applications of water-soluble complexes as pre-catalysts in hydrogenation and hydroformylation reactions, using mainly alkenes presents in refinery naphtha cuts and biomass components as substrates. This review also includes a study of the interfacial phenomena, which has allowed the development of several approaches for the study of the solubility of long chain substrates in hydrogenation and hydroformylation reactions in biphasic-aqueous media.

The catalytic hydrogenation of the levulinic acid key platform molecule into γ-valerolactone using formic acid as bio-derived internal hydrogen source is considered as one of the pivotal reactions to convert sustainably lignocellulosic-based biomass into renewable added value chemicals. In this work we present the influence of both the composition and the synthesis methodology on the catalytic activity and properties of Ru-Pd bimetallic catalysts supported on activated charcoal, and particulary the conditions for nano-alloy formation. The Ru-Pd alloy shows high activity in formic acid decomposition and subsequent hydrogenation of levulinic acid in water solvent. The Ru-rich bimetallic catalyst prepared by co-impregnation with final high temperature reduction at 500°C gave the highest γ-valerolactone yield, thanks to rearrangement and migration of Pd allowing for the formation of the Ru-Pd alloy with isolated (diluted) Pd atoms, and to stabilization of small particle sizes (1.3 nm) which showed high activity in the reaction.

CO₂ is a greenhouse gas, whose emissions into the atmosphere has intensified in recent decades. Mitigating approaches have been studied in several countries around the world, such as the catalytic hydrogenation of CO₂ via heterogeneous catalysis at gas-phase to produce chemical compounds with high added value. Typically, in this process, H₂ gas is used as a hydrogen source, and copper-based catalysts, temperatures of 200–300 ºC and pressures of 2–7 MPa are employed to obtain, mainly, products containing one-carbon atom chain. Thus, the investigation of more favorable conditions for the hydrogenation of CO₂ at gas-phase, utilizing copper-based materials, for the efficient and selective production of high energy density compounds, such as ethanol, is necessary. In this context, the present work provides information about the influence of the water steam and copper oxidation state on the CO₂ hydrogenation to ethanol. Our data show that the presence of water steam during the reaction generated a mixture of oxidized and metallic Cu species on the copper catalyst, which resulted in an 80-fold increase in the ethanol productivity at 200 °C and atmospheric pressure. When water steam is not used, the oxidized Cu species are reduced during the reaction and the ethanol productivity decreases drastically, indicating that water plays an important role in the conversion of CO₂ to ethanol.