Catalysis Science & Technology最新文献

Sulfates formed on the catalyst surface have been the main cause of its rapid deactivation during the NH₃-SCR reaction. Here, after loading ABS onto nanotube structured Ce–Mn-TNTs and nanoparticle CeMnTiO_x catalysts, the low-temperature activities of the catalysts deactivated rapidly. After in situ decomposition of ABS on the catalyst surface under the reaction atmosphere, it was found that the de-NO_x efficiency of the regenerated Ce–Mn-TNTs-R catalyst was significantly restored. This was mainly attributed to the lower vapor pressure inside the nanotube structure compared to nanoparticles, which promoted the rapid decomposition of ABS. In addition, the decomposition process of ABS was accompanied by the formation of metal sulfates, which disrupted the redox cycle between the active metals, causing a certain inhibitory effect on the recovery of catalytic activity. However, the presence of SO₄²⁻ improved the content of chemisorbed oxygen on the nanotube structured catalyst surface and increased the numbers of Brønsted acid sites on the catalyst surface, which enhanced the adsorption capacity of the Ce–Mn-TNTs catalyst for NH₃ and was favorable for the recovery of catalytic activity. Thus, the presence of sulfates on the surface of nanotube structured catalysts had contradictory effects in the NH₃-SCR reaction process. The surface interface of nanotube structured catalysts is extremely advantageous for the decomposition of ABS. The above findings provided reliable theoretical bases for the design of catalysts with good SO₂ tolerance.

The reduction of CO₂ (1 atm) with 9-BBN in DMSO selectively produces either formoxy- or methoxyborane in excellent yields, depending on the amount of DMSO in the reaction at room temperature. CO₂ reacts with 9-BBN in DMSO as a solvent to selectively produce HCOOBBN in 98% NMR yield. On the contrary, the reduction of CO₂ with 9-BBN in the presence of 4.5 or 7 mol% of DMSO in toluene or THF produces CH₃OBBN as the sole product. In both cases, DMSO first reacts with 9-BBN to form a reactive adduct in situ, through which these reduced products are formed. The adduct formation is supported by the structural characterization of the DMSO adduct of formoxyborane, representing the first X-ray structure of its type, which is analysed using DFT calculations. A mechanistic study suggested that CH₃OBBN is formed from HCOOBBN via its acetal precursor. Similar reduction reactions of CO₂ with 9-BBN in the presence of various sulfoxides, sulfone, sulfide and pyridine showed that not all adducts are able to reduce CO₂, and only sulfoxide adducts reduce CO₂ to CH₃OBBN up to an NMR yield of 60%. Furthermore, the adduct formation is controlled by the steric factor of sulfoxides. As a proof of concept, the methylene group of the acetal product was transferred to N-methyl- and N-unsubstituted indoles to produce bis(indolyl)methane derivatives in good isolated yields with detailed mechanistic studies.

Acid-catalyzed reactions play an important role in the field of organic synthesis in synthesizing a large number of organic compounds. However, conventional acid catalysts have many shortcomings, such as low stability, difficulty in product separation and poor reusability. In this study, we achieved efficient and recyclable acid catalysis via a pH-responsive O/W emulsion system stabilized by dodecyl phosphonic acid (DPA) alone. The O/W emulsion exhibited excellent characteristics of high-temperature resistance and adjustable oil-droplet size at different temperatures. Moreover, the emulsion state can undergo rapid and reversible transitions between emulsification and demulsification by adjusting the pH levels. Impressively, the emulsified acid-catalysis system significantly enhanced the reaction efficiency of the Knoevenagel condensation reaction. Subsequently, a straightforward pH adjustment effortlessly realized product separation and ensured the recyclability of the catalytic system. This environmentally friendly and economically viable system offers a new approach to achieve efficient and green catalysis in organic synthesis processes.

DFT calculations were performed to evaluate the mechanisms of the Au-catalyzed reaction of N-(o-alkynylphenyl)imines and vinyldiazo ketones. It was found that the C–N cleavage/C–C bonding mechanism proposed in the previous literature cannot rationalize the experimental findings due to high energy demand involved. Alternatively, after the Au–π-coordination, intramolecular N-nucleophilic cyclization, C-attack of vinyldiazo ketone and OTf⁻ assisted H-shift, the de-diazotization promoted O-nucleophilic cyclization route was proposed. For further conversion, we established a unique Au⋯N σ-induced C–N cleavage/C–C bonding mechanism, over the usually known Au–π-coordination promoted one, in which (i) the presence of the Au⋯N σ-coordination contributes to the adjacent C¹–N¹ rupture, and (ii) the resultant sp²-C site is flexible to the energy-efficient configuration retention during the critical nucleophilic attack, effectively circumventing the high-energy inversion of configuration in the conventional anti-attack with the sp³-C site.

A highly efficient and selective aqueous phase hydrogenolysis of furfural (FFald) to 1,5-pentanediol (1,5-PeD) was achieved in the presence of gamma-alumina-supported bimetallic ruthenium–tin (Ru–(x)Sn/γ-Al₂O₃; x = Sn co-loaded (wt%)) catalysts. The Ru–(x)Sn/γ-Al₂O₃ catalysts were synthesised using a coprecipitation-hydrothermal method at 150 °C for 24 h, followed by reduction with H₂ at 400 °C for 2 h. The XRD and XPS analyses confirmed the presence of Ru₃Sn₇ alloy phases, Ru⁰, Sn⁰, and oxidative tin (SnO_x) species on the sole surface of γ-Al₂O₃, which can synergistically catalyse the partial hydrogenation of CC of FFald and hydrogenolysis of C–O furan ring, thereby producing a high yield of 1,5-PeD (up to 94%) at 180 °C, under H₂ = 30 bar and after reacting for 7 h. ATR-IR spectra of the reaction mixture under controlled reaction conditions exhibited a sharp absorption peak at 1637 cm⁻¹, which was the band for trisubstituted CC in the 4,5-dihydrofuranmethanol (4,5-DHFM) intermediate. Ru–(1.30)Sn/γ-Al₂O₃ was found to be reusable with a compromising reduction in the yield of 1,5-PeD and the recoverability of the catalyst after repeated reaction run.

Porous single crystals (PSCs) are a novel class of solid-phase materials with tailored porosity. The long-range ordered lattice and interconnected pore structure in three dimensions enable them to minimize energy losses and maintain heightened catalytic activity and stability in electrochemical systems. In the process of electrocatalytic water splitting, transition metal oxides Fe₂O₃ and Co₃O₄ are regarded as highly promising catalytic materials for the oxygen evolution reaction (OER). Here, we employed a lattice reconstruction strategy to grow porous single crystals of Fe₂O₃ and Co₃O₄ through solid–solid phase transformation, utilizing FeS₂ and CoS₂ nano-octahedron single crystals as the parent crystals. PSC Fe₂O₃ and Co₃O₄ have large specific surface areas to provide enough electrocatalytic active sites while retaining the intrinsic properties of porous single crystals. Meanwhile, we quantitatively engineered Pt clusters/metal oxide interfaces on the surfaces of PSC Fe₂O₃ and Co₃O₄ to enhance the electrocatalytic performance. The PSC Pt/Co₃O₄ catalyst with lower overpotential (269 mV at 10 mA cm⁻²) exhibits optimal electrochemical performance in the OER, with no degradation observed within 25 hours. The structural consistency of these porous single crystal oxide catalysts, coupled with the construction of active interfaces, offers advantages in enhancing electrocatalytic activity and durability.

The utilization of carbon dioxide as a C1 feedstock to construct molecules has been extensively studied and successfully employed in diverse catalytic processes. In this context, asymmetric organic transformations leveraging the abundant, inexpensive, and renewable CO₂ to synthesize chiral molecules appear to be a highly attractive and powerful strategy. Recently, this approach has been successfully extended to photo and electrochemical aspects and leads to new synthetic opportunities with extensive applications. Here, we summarize the advances of the last two decades in asymmetric CO₂ fixation including chemical, photochemical and electrochemical pathways, highlighting the reaction strategies, activation modes, mechanistic insights, and reactivity of various substrates.

Transition metal doping for Fe-based catalysts has been demonstrated in promoting the activity and regulating the selectivity in both the reverse water gas shift reaction and Fischer–Tropsch synthesis. However, there are few studies that concern their catalytic performance tailored by transition metal promoters under photothermal conditions. In this study, a series of typical MFeO_x (M = Mn, Co, Cu, Zn) catalysts were synthesized with a facile co-precipitation method and their photothermal CO₂ hydrogenation properties were evaluated. The results showed that the doping of Co, Cu, and Zn enhanced the activity and regulated the selectivity of Fe-based catalysts, e.g., CoFe achieving a C₂₊ yield of 1.73 mmol h⁻¹ g⁻¹ while ZnFe almost doubling the CO₂ conversion under irradiation. Mechanistic studies suggest that Co and Cu facilitated the reduction of Fe species, resulting in favorable CO₂ and H₂ activation. Lastly, a light-induced direct CO₂ dissociation pathway was proposed with in situ EPR and DRIFTS characterization and analysis of the undoped Fe and ZnFe catalysts. This study provides a novel perspective on transition metal promoters for photothermal CO₂ hydrogenation over Fe-based catalysts.

Regulating the microenvironment of Ti active centers in titanosilicates is of great significance in both theoretical research and practical application of titanosilicate/H₂O₂ systems. Herein, a novel six-coordinated Ti species containing an organic amine ligand, Ti(OSi)₂(OH)₂(H₂O)TPA, was constructed in the TS-1 zeotype in the process of dissolution and recrystallization by hydrothermal post-treatment with tetrapropylammonium hydroxide and ammonium chloride. The newly formed hexa-coordinated Ti species promoted the activation of H₂O₂ significantly, responsible for the superior catalytic activity in 1-hexene epoxidation with a conversion of 35.5% compared with the untreated TS-1 (18.0%). After removal of organics by calcination, Ti(OSi)₂(OH)₂(H₂O)TPA was transformed into Ti(OSi)₂(OH)₂(H₂O)₂ sites, which also exhibited higher epoxidation activity compared to the original framework Ti(OSi)₄ sites. In addition, the acid sites of Si–OH in TS-1 zeotype were quenched by the basic amine molecules, which effectively inhibited the occurrence of side reactions such as epoxide ring opening, leading to a high epoxide selectivity of 98.6%. With the construction of highly active Ti(OSi)₂(OH)₂(H₂O)TPA sites and without further calcination process, the obtained catalyst (denoted as TS-PN-am) exhibited not only excellent catalytic capacity but also application potential in continuous liquid-phase epoxidation.

Even though α-arylation of ketones is attractive for direct C–H functionalization of organic substrates, the method largely relies on phosphine-ligated palladium complexes. Only recently, efforts have focused on developing nitrogen-based ligands as a more sustainable alternative to phosphines, with pyridine-functionalized pyridinium amidate (pyr-PYA) N,N′-bidentate ligands displaying good selectivity and activity. Here, we report on a second generation set of catalyst precursors that feature a 5-membered N-heterocycle instead of a pyridine as chelating unit of the PYA ligand to provide less steric congestion for the rate-limiting transmetalation of the enolate. To this end, new heterocycle-functionalized PYA palladium(II) complexes containing an oxazole (5b), N-phenyl-triazole (5c), N-methyl pyrazole (5d), N-phenyl-pyrazole, (5e), N-xylyl-pyrazole (5f), and N-isopropyl-pyrazole (5g) were synthesized compared to the parent pyr-PYA complex 5a. Less packing of the palladium coordination sphere was evidenced from solid state X-ray diffraction analysis. While the catalytic activity of the oxazole system was lower, all other complexes showed higher activity. In particular, complex 5g comprised of an electron-donating and sterically demanding iPr-pyrazole chelating PYA ligand is remarkably stable towards air and moisture and shows outstanding catalytic activity with complete selectivity (>99% yield) and turnover frequencies up to 1200 h⁻¹, surpassing that of parent 5a by one order of magnitude and rivalling the most active phosphine-based palladium systems. Kinetic studies demonstrate a first order rate-dependence on palladium and the substrate. Some deviation of linearity together with poisoning experiments suggest a mixed homogeneous/heterogeneous pathway, though the reproducible kinetics of in situ catalyst recycling experiments strongly point to a molecularly defined active species, demonstrating the high potential of PYA-based ligands.