Catalysis Today最新文献

Defatted wheat bran, an industrial waste of the food chain, represents a strategic renewable material for modern biorefinery schemes. Through a combination of chemical and biological catalysis, a cascade process was developed to produce high-value fine chemicals, such as carotenoids and lipids, from polysaccharide fraction. Due to the low lignin content and suitable particle size of defatted wheat bran, pretreatment steps are unnecessary, allowing the direct enzymatic or chemical hydrolysis of polysaccharide components (glucan, xylan, and arabinan) to give fermentable sugars. Regarding the biocatalytic approach, the optimisation of the main reaction parameters, such as enzyme dosage (15, 30, 45, 60 FPU Cellic® CTec 3 HS/g glucan) and biomass loading (5, 10, 15, 20 wt%), was performed to improve the monosaccharide yield. Regarding the chemical route, a microwave-assisted FeCl₃-catalysed approach was optimised in terms of catalyst amount (1.0, 1.3, 1.6 wt%) and reaction time (2.5, 5, 10 min) to maximise the sugar yield, minimizing the formation of furanic derivatives which are strong inhibitors for the subsequent fermentation step. The biological conversion of sugars obtained by both enzymatic and chemical routes into carotenoids and lipids was then performed by adopting the commercial yeast Rhodosporidium toruloides DSM 4444. The simultaneous production of carotenoids and lipids was optimised by investigating the effect of the C/N ratio in the fermentation medium. Under the optimised process conditions (C/N 60), by fermenting hydrolysate obtained by chemical and enzymatic routes, carotenoid productions of 120 and 180 mg/L and lipids productions of 5.2 and 3.5 g/L were achieved, respectively. The highest carotenoids cell content achieved in this study (14.8 mg/g) is about 5 times higher than the maximum value reported in the literature to date for this yeast. Moreover, Rhodosporidium toruloides achieved the complete conversion of sugars into desired bioproducts for both the biomass hydrolysates demonstrating the effectiveness of the two different catalytic approaches adopted for biomass hydrolysis.

Ceria is an important technological material that finds wide application as an oxygen storage component in heterogeneous oxidation catalysis. In these applications the removal of lattice oxygen results in two reduced Ce³⁺ centres whose location relative to the vacancy site has a profound influence on the vacancy formation energy. Here we present DFT calculations on the bulk and surface oxygen defect formation highlighting the distribution of structures that are thermally accessible in such a situation. We also demonstrate that the Ce³⁺ locations influence the barrier to oxygen anion migration.

Catalytic hydrogenation at ambient conditions represents an essential and practical methodology, which allows for the more convenient access of fine and bulk chemicals. Here, we report Pd-based nanoparticles (Pd-NPs@SiO₂) as an efficient catalyst for the hydrogenation of nitroarenes to anilines at atmospheric pressure of hydrogen and at room temperature. This specific Pd-catalyst allows for the hydrogenation of various functionalized and structurally challenging nitroarenes to valuable anilines, which serve as key building blocks and versatile intermediates in chemical, pharmaceutical and agrochemical industries as well as material technologies. These Pd-nanoparticles exhibited excellent stability and can be recycled and reused at least 6 times without any significant drop in the activity. Notably, this ambient hydrogenation process can be scaled up to several grams.

Hydrolases are well-known for hydrolyzing esters, amides, carbamates, peptides, or acid anhydrides in the presence of water. However, some of them are also capable of catalyzing the reverse reaction (condensation) under certain conditions in aqueous systems. Hence, these enzymes are called promiscuous hydrolases/acyltransferases. This review deals with their discovery, background information on their mechanism of action, and significant improvements by enzyme engineering to both enhance product formation and decrease the undesired hydrolysis of the targeted acyl products. Their applications in biocatalysis are exemplified by the synthesis of a wide range of esters or amides in aqueous systems, including preparative-scale processes and the combination of hydrolases/acyltransferases with other enzymes in cascade reactions to utilize alternative feedstocks from renewable resources, for example. Complementary, the use of ATP-dependent amide synthesizing enzymes is covered. Together, promiscuous hydrolases/acyltransferases represent practically useful alternatives to well-established chemical reactions, operating in aqueous solutions that also appeal to different industries.

Chiral surfactants can provide asymmetric environments in water that can enhance the stereoselectivity of chiral metal catalysts. Due to the high dynamic nature of micelles, this specific field of research has been seldom investigated. The design of the surfactant and its interaction with the catalyst is crucial to improve stereoselectivity. We report a series of chiral surfactants bearing rigid aromatic hydrophobic units based on the BINOL scaffold decorated with hydrophilic side chains. In particular, the use of anionic side chains provide better interaction with chiral Pt(II) catalysts due to ion pairing leading to improvements in the enantioselectivity of the sulfoxidation reaction of thioethers with hydrogen peroxide. This proof of concept contribution opens the way to the design of new classes of chiral designer surfactants that could be applied to move to water many classes of stereoselective reactions traditionally carried out in organic media.

Methyl lactate (MLA) is a versatile high value platform chemical prepared from biomass carbohydrates, with widely application in the pharmaceutical, food, pesticide, and cosmetics. The current study presented a one-pot catalytic conversion of sugars to MLA over poly (ionic liquid)s functionalized Sn/Beta zeolites under mild conditions. The Sn/Beta zeolites were prepared by an impregnation method, followed by modification with poly (vinyl imidazole) ([PVIM]) via an in-situ free radical polymerization method. Dosages of polymer and Sn, calcination temperature, reaction temperature, catalyst amount, substrate concentration, and reaction times were optimized. Results showed that an MLA yield of 61.4 % was obtained over 3[PVIM]-Sn/Beta with complete conversion of fructose at 140 °C for 8 h. The physicochemical properties were characterized by XRD, BET, FTIR, CO-DRIFTS, NH₃-TPD and pyridine-FTIR analysis, indicating the coexistence of Lewis and Brønsted acid sites. Finally, a possible reaction mechanism was proposed that the weak Lewis acidity of imidazole rings of [PVIM] effectively regulated the local microenvironment of active sites, thus promoting the interaction of the active sites with electronegative oxygens of sugars. This study can provide as a reference for the development of solid acid catalysts for the catalytic conversion of biomass to platform chemicals.

The large-scale production of 5-hydroxymethylfurfural (HMF), a “sleeping giant” in sustainable chemistry, is frequently hampered by the severe formation of humins during the acid-catalyzed dehydration of high-concentration fructose. In this work, we demonstrate that the HMF yield could be remarkably enhanced by boosting the catalytic performance of a commercially used Amberlyst-15 solid acid organocatalyst, wherein the formation of humins could be effectively inhibited. We show that the modification of Amberlyst-15 with a typical cationic surfactant (i.e., cetyltrimethylammonium bromide (CTAB)) via charge interaction between sulfonic acid groups and quaternary ammonium cations led to an improved surface hydrophobicity and a reduced Brønsted acid density on the modified catalyst, thereby contributing to a complete suppression of HMF rehydration and remarkable suppression of humin formation via paths of both etherification-dehydration-condensation and degradative-condensation of fructose and/or HMF. As a result, the catalytic conversion of fructose over the CTAB-modified Amberlyst-15 catalyst in a low-boiling mixed solvent composed of 1,4-dioxane and H₂O at 140 °C within 2 h led to high HMF yields in range of 53.3 ∼ 63.1 mol% in converting high-concentration fructose (10.0 ∼ 50.0 wt%), wherein an average enhancement of 20 mol% in product yield was achieved when compared with that over un-modified Amberlyst-15. Moreover, the adsorption of humins on solid catalyst was significantly reduced due to the enhanced surface hydrophobicity and alleviated formation of humins, which accounted for a stable catalytic performance of the modified Amberlyst-15 catalyst for at least five runs. This work highlights the rational adjustment of the surface wettability of a commercial solid acid catalyst to suppress the undesired humin formation for future HMF biorefinery.

For the catalytic hydrogenation of furfural (FFR) over supported metal catalysts, acetals and ethers were often observed as by-products when alcohols were used as solvents. The presence of specific acid sites on the catalyst led to the conversion of FFR to acetals and ethers. To understand the effect of the interaction between metal species and oxide supports on the acid properties of catalysts and the conversion of FFR to acetals and ethers, anatase TiO₂ (TiO₂-A), rutile TiO₂ (TiO₂-R) and these TiO₂ supported Ni catalysts were studied as models. The relationship between the acid properties of these samples and FFR conversion pathways in isopropanol was revealed. The interaction between Ni species and TiO₂ supports was found to selectively remove Brønsted acid sites on the TiO₂ supports in the absence of H₂, thereby inhibiting the conversion of FFR to acetals and ethers in N₂. However, the presence of high-pressure H₂ during the reaction induced the formation of new Brønsted acid sites on Ni/TiO₂ catalysts via hydrogen spillover, promoting the acetalization of FFR to acetals and the hydrogenolysis of acetals to ethers. The Ni/TiO₂-A catalyst exhibited higher activity in catalyzing the conversion of FFR to acetals and ethers compared to the Ni/TiO₂-R catalyst. This work provides reference information for the selective regulation of acid-catalyzed reaction pathways of FFR in alcohols.

The present contribution is a review paper that summarizes the structure, properties and catalytic applications of hydrotalcite based materials when they are modified by the incorporation of oxide metals from groups 4, 5 and 6. The unique properties of hydrotalcites, with a double layer structure able to host ions in the interlayer space and its basicity, together with the properties of transitions metal oxides from groups 4, 5 and 6, leads to materials highly promising as catalysts. The incorporation can form dispersed species of those oxides on the hydrotalcite-like structure, which acts as support, or by the incorporation of those elements into the hydrotalcite structure. The structure and properties of these materials have been reviewed and analyzed, in order to give a detailed description of the main factors that affect the catalytic properties of these interesting materials.

The hydrogenation of ethyl levulinate (EL) to γ-valerolactone (GVL) is an important process in biomass conversion to value-added chemicals. However, it remains challenging to develop efficient non-noble metal catalysts with high activity and selectivity for this reaction. Herein, we investigated the effect of second metal modification on Ni₃P catalysts, where a series of Ni-P-M/Al₂O₃ and Ni-M/Al₂O₃ catalysts (M = Fe, Co, Cu, and Zn) were prepared for EL hydrogenation. The results show that Ni-P-Cu/Al₂O₃ exhibited the highest activity, being 2.3 and 1.7 times more active than Ni-Cu/Al₂O₃ and Ni-P/Al₂O₃, respectively. Reaction evaluations at different temperatures revealed that Ni-P/Al₂O₃ and Ni-P-Cu/Al₂O₃ have a similar activation energy of ∼65 kJ/mol, lower than that of Ni-Cu/Al₂O₃ (86 kJ/mol). The combined characterization and reaction results suggested that the introduction of Cu enriched surface P in the Ni-P-Cu/Al₂O₃ catalyst, providing more active sites to enhance CO hydrogenation. These findings provide insights for optimizing non-noble metal catalysts for EL hydrogenation.