Catalytic Conditions Research Articles

Solar light promoted CO2 hydrogenation to CH4 over photo-thermal responsive dispersed Co on defective CeO2 composite derived from MOFs

The conversion of the greenhouse gas CO2 represents a pragmatic and environmentally friendly approach. However, the substantial energy demands of the reaction hamper its widespread application. Here, we designed an efficient catalyst prepared by Ce-MOF and ZIF-67 precursor, namely Co/CeO2, for photothermal CO2 methanation under light and auxiliary heating. CeO2 synthesized by Ce-MOF has a good structure and abundant oxygen vacancies, meanwhile, Co has abundant active sites and strong adsorption capacity and is well-dispersed on CeO2. As a result, the catalyst exhibits high CH4 yield of 885.27 mmol⋅g−1⋅h−1 and CO yield of 24.5 mmol⋅g−1⋅h−1. Moreover, it has good selectivity and catalytic durability. Through the analysis of the reaction pathway under the conditions of photothermal catalysis, the hydrogenation reaction of formate can efficiently generate CH4 and H2O due to the promotion of hot carriers. This work demonstrated the advantages of photothermal co-catalysis and provides a potential strategy for efficient CO2 reduction.

Palladates of the [NHC⋅H][Pd(NH2)(CC)Cl2] Type as Effective Pre‐catalysts for the Formation of C−C and C−N Bonds

AbstractThe environmentally friendly, simple synthesis of a family complexes of the general formula [NHC⋅H][Pd(NH2)(CC)Cl2] (CC=biphenyl) is presented. The catalytic activity of these air‐ and moisture‐stable complexes was evaluated as a function of the imidazolium counterion. These pre‐catalysts can be converted, under catalytic conditions, to Pd‐NHC species enabling the Suzuki–Miyaura, Sonogashira, and Buchwald–Hartwig amination reactions under very mild operating conditions.

Chiral-Boron-Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of β-Trifluoromethyl α,β-Unsaturated Ketones with N,N'-Cyclic Azomethine Imines.

The (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-boron-complex-catalyzed asymmetric 1,3-dipolar cycloaddition of β-trifluoromethyl α,β-unsaturated ketone with N,N'-cyclic azomethine imines was developed to afford N,N'-bicyclic pyrazolidine derivatives bearing a stereogenic carbon center containing CF3 motifs in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr, and >99% ee). This catalytic system features mild reaction conditions, high efficiency, and a broad substrate scope.

Engineering the activity and stability of ZIF-8(Zn/Co)@g-C3N4 nanocomposites and their synergistic action in converting atmospheric CO2 into cyclic carbonates

The development of novel catalytic materials that integrate multifunctional sites has significant implications for expanding the utilization of CO2 resources. However, simultaneously achieving high activity and stability remains a formidable challenge. In this study, a series of ZIF-8(Zn/Co)@g-C3N4 nanocomposites were prepared by employing a thermo-physical compounding strategy that involved the combination of nitrogen-rich graphitic carbon nitride (g-C3N4) nanosheets with ZIF-8(ZnCo). The influences of different compositions of g-C3N4 and ZIF-8(Zn/Co) on the catalyst structure were systematically investigated. Subsequently, the catalytic activities of these nanocomposites towards the cycloaddition reaction between CO2 and epoxide were examined under different conditions. The presence of abundant Lewis base sites in g-C3N4 facilitates CO2 activation, while multiple Lewis acid sites in ZIF-8(Zn/Co) enable efficient epoxide activation. By working synergistically with a co-catalyst, tetrabutylammonium bromide (TBAB), CO2 and epoxides can be efficiently reacted to synthesize the corresponding cyclic carbonates under mild or even atmospheric pressure conditions. The catalytic reaction conditions were optimized, and both the catalyst's recycling performance and the scope of epoxides with various substituents were investigated. The integration of g-C3N4 and ZIF-8(Zn/Co) endows the catalytic material with exceptional structural stability and remarkable catalytic activity, thereby providing a new platform for highly efficient CO2 conversion.

Total synthesis of cassane‐type diterpenoid pikrosalvin

AbstractThis paper presents the first successful total synthesis of pikrosalvin, a compound naturally derived from Salvia officinalis, grounded on the structural framework delineated by Brieskorn and Fuchs. Our synthetic approach was underpinned by a biomimetic strategy inspired by the Stork–Eschenmoser hypothesis for the biosynthesis of terpenes via polyene cyclization. Starting with commercially available vanillic acid and geraniol, we strategically assembled pikrosalvin's structural core, consisting of a decalin A/B ring, an aromatic C ring, and a butyrolactone D ring. Challenges related to protective groups and specific catalytic conditions were effectively addressed, resulting in high product yields. We further demonstrated the efficacy and broad applicability of a combined‐acid‐catalyzed polyene cyclization methodology in the context of complex natural product synthesis. This study sets the stage for future biological and pharmacological investigations of pikrosalvin.

Ligand-based electron transfer enables molecular polypyridyl Zn(II) complexes for efficient photocatalytic CO2 reduction

Electron transfer process plays a critical role in photocatalytic CO2 reduction. Owing to low redox activity of Zn(II) cation under catalytic conditions, it remains a challenge to use Zn(II) complexes as efficient molecular catalysts for CO2 photoreduction. Herein, we overcome the obstacle and demonstrate two polypyridyl Zn(II) complexes can be utilized for selective photoreduction of CO2 to CO. Thanks to more efficient ligand-based electron transfer, the polypyridyl Zn(II) complex modified with electron-donating carbazole groups displays a higher TON of CO up to 116 than the other unsubstituted polypyridyl Zn(II) complex, which is among the most efficient Zn(II) complexes molecular catalysts in CO2 photoreduction. Photocatalytic mechanism has been studied by UV–vis absorption spectroscopy and computational calculations. These results show a promising way to develop Zn(II) complexes for efficient CO2 photoreduction through ligand modification and ligand-based electron transfer.

Alcohol‐Treated Nickel‐Aluminium Catalyst for One‐Step Highly‐Selective Butane‐1,4‐Diol Synthesis from 2‐Butyne‐1,4‐Diol

AbstractThe development of low‐cost nickel‐based catalysts for direct and selective hydrogenation of 2‐butyne‐1,4‐diol (BYD) to butane‐1,4‐diol (BAD) under mild conditions is an important and attractive target both in fundamental research and industrialization but remains a formidable challenge. The primary industrial production method for BAD synthesis is a two‐step reaction route, which suffers from complicated catalysis conditions and high equipment costs. Herein, we develop a high‐performance catalyst via a facile alcohol‐treated strategy for highly selective BAD synthesis at moderate operation conditions. The as‐synthesized NA‐80E catalyst exhibits outstanding BAD selectivity of 98.82 % and BYD conversion of 100 % at 60 °C and 4 MPa, outperforming most reported results for BAD formation in a one‐step process and even being comparable to those obtained by the two‐step hydrogenation reaction route under much high temperatures and pressures. Crucially, we found that after facile alcohol (ethanol) treatment, an intriguing phenomenon of suppression of adjacent acid‐assisted hydrogenolysis via extra acidic Al species at the NiO‐Al2O3 interface is observed, contributing to the precise enhancement of BAD selectivity by inhibiting the production of butanol (BOL). This facile alcohol‐treated method along with the revealed mechanism of blocked hydrogenolysis opens vast possibilities for designing high‐performance and highly‐selective hydrogenation catalysts.

Single-component systems of iron(II) half-sandwich complexes catalyze epichlorohydrin/CO2 condensation

Half-sandwich Fe(II) complexes bearing 2-(diphenylphosphino)ethylamine chelating ligand [(η5-C5H5)Fe(CO)(NH2(CH2)2PPh2)]X, where X = I (1), Br (2), Cl (3), OTf (4) were successfully prepared under mild reaction conditions. Their catalytic activity was evaluated systematically on the (chloromethyl)ethylene carbonate synthesis starting from CO2 and epichlorohydrin. The influence of the counterion has been established, where the single-component catalyst 1 showed low catalytic activity under mild conditions for CO2 and epoxide condensation. The exchange of iodide by bromide showed a higher catalytic activity and a higher conversion with compound 2 as a catalyst, while a decrease and no conversion were observed for 3 (X = Cl) and 4 (X = OTf), respectively. Optimization of the catalytic conditions was carried out using epichlorohydrin in dry chloroform, along with modification of the reaction conditions. Of the synthesized compounds (1–4), only 2 showed conversions to (chloromethyl)ethylene carbonate >99 % at 100 °C, 0.34 MPa of CO2, 14 h and 2 % mol of catalyst, or by modifying the temperature to 80 °C and the pressure to 0.69 MPa of CO2. Catalyst 2 proved to be very selective, although it has modest activity, reaching low values of TON (124) and TOF (8.17 h−1).

Synthesis of Inexpensive Ternary Metal Oxides by a Co-Precipitation Method for Catalytic Oxidation of Carbon Monoxide.

By using a simple co-precipitation method, new Fe2 O3 -based nanocatalysts (samples) were synthesized. The samples were composites of two or three transition metal oxides, MOx (M=Fe, Mn, Co, Ni, and Cu). The average size of CuO crystallites in the composites composed of two oxide components (CuO-Fe2 O3 ) was about 14.3 nm, while in those composed of three (CuO-MnOx -Fe2 O3 ), the composite's phase compositions were almost in the amorphous form when annealing the sample at 300 °C. The latter sample had a specific surface area higher than that of the former, 207.9 and 142.1 g/m2 , respectively, explaining its higher catalytic CO oxidation. The CO conversion over the CuO-MnOx -Fe2 O3 -300 catalyst (1 g of catalyst, 2600 ppm of CO concentration in air, and 1.0 L/min of gas flow rate) begins at about 40 °C; the temperature for 50 % CO conversion (t50 ) is near 82 °C; and CO removal is almost complete at t99 ≈110 °C. The activity of the optimal sample was tested in different catalytic conditions, thereby observing a high durability of 99-100 % CO conversion at 130 °C. The obtained results were derived from XRD, FTIR, BET, SEM, elemental analysis and mapping, as well as catalytic experiments.

Catalytic C-H Trifluoromethylation of Arenes and Heteroarenes via Visible Light Photoexcitation of a Co(III)-CF3 Complex.

A cobalt photocatalyst for direct trifluoromethylation of (hetero)arene C(sp2)-H bonds is described and shown to operate via visible light activation of a Co-CF3 intermediate, which functions as a combined chromophore and organometallic reaction center. Chemical oxidations of previously reported (OCO)Co complexes containing a redox-active [OCO] pincer ligand afford a Co-CF3 complex two oxidation states above Co(II). Computational and spectroscopic studies are consistent with formulation of the product as [(OCO•)CoIII(CF3)(THF)(OTf)] (II) containing an open-shell [OCO•]1- radical ligand bound to a S = 0 Co(III) center. II is thermodynamically stable, but exposure to blue (440 nm) light induces Co-CF3 bond homolysis and release of •CF3, which is trapped by radical acceptors including TEMPO•, (hetero)arenes, or the radical [OCO•] ligand in II. The latter comprises a competitive degradation pathway, which is overcome under catalytic conditions by using excess substrate. Accordingly, generation of II from the reaction of [(OCO)CoIIL] (III) (L = THF, MeCN) with Umemoto's dibenzothiophenium trifluoromethylating reagent (1) followed by photolytic Co-CF3 bond activation completes a photoredox catalytic cycle for C-H (hetero)arene trifluoromethylation utilizing visible light. Electronic structure and photophysical studies, including time-dependent density functional theory (TDDFT) calculations, suggest that Co-CF3 bond homolysis at II occurs via an ligand-to-metal charge-transfer (LMCT) (OCO0)CoII(CF3) state, revealing ligand redox activity as a critical design feature and establishing design principles for the use of base metal chromophores for selectivity in photoredox bond activations occurring via free radical intermediates.

Immobilization of horseradish peroxidase on metal-organic framework to improve enzyme activity for enhanced chemodynamic therapy

Bio-enzymes have the advantages of strong substrate specificity, high catalytic efficiency, and minimal toxic side effects, making them promising drugs in cancer therapy. However, the poor stability and cellular penetrability of uncoated protein in the physiological environment severely restricts the direct application of Bio-enzyme. To address it, we report a metal-organic framework (MOF), Hf-DBA (H2DBA, biphenyl carboxylic acid ligands). The morphology of the Hf-DBA was revealed by TEM and the diameter was in the range of 200 to 350 nm. Hf-DBA acted a carrier for intracellular delivery and protection of horseradish peroxidase (HRP). The prepared HRP@Hf-DBA can catalyze the excess H2O2 in the tumor cells to generation of •OH for chemodynamic therapy (CDT). Compared with free HRP, the catalytic activity of HRP@Hf-DBA is significantly improved, and the optimal catalytic conditions are explored. The catalytic stability of HRP@Hf-DBA remained above 70% after 12 cycles of catalysis. After treatment with HRP@Hf-DBA, the apoptosis rates of A549 and Hela cells was 71.64%, and 76.86%. The results in vitro show that HRP@Hf-DBA can effectively inhibit the growth of tumor cells through enhanced CDT.

Group I Alkoxides and Amylates as Highly Efficient Silicon-Nitrogen Heterodehydrocoupling Precatalysts for the Synthesis of Aminosilanes.

Group I alkoxides are highly active precatalysts in the heterodehydrocoupling of silanes and amines to afford aminosilane products. The broadly soluble and commercially available KOt Amyl was utilized as the benchmark precatalyst for this transformation. Challenging substrates such as anilines were found to readily couple primary, secondary, and tertiary silanes in high conversions (>90 %) after only 2 h at 40 °C. Traditionally challenging silanes such as Ph3 SiH were also easily coupled to simple primary and secondary amines under mild conditions, with reactivity that rivals many rare earth and transition-metal catalysts for this transformation. Preliminary evidence suggests the formation of hypercoordinated intermediates, but radicals were detected under catalytic conditions, indicating a mechanism that is rare for Si-N bond formation.

Assessing the changes in thermal and catalytic pyrolysis of lignocellulose when shifting from batch to continuous biomass feeding modes

Lignocellulosic biomass pyrolysis has been earlier studied in a large variety of reaction systems. However, there is a lack of information on the effects of passing from batch to continuous feeding mode (BM vs CM) despite being a necessary step in the scaling up of the process. In this sense, the main aim of this work is to conduct a comparative study of lignocellulosic biomass pyrolysis using the same reactor but varying the biomass feeding methods under thermal and catalytic conditions and different thermal zone temperatures (350 and 500 °C). Under thermal conditions, significant differences have been observed between both feeding systems. When operating in CM, the production of char decreases, particularly at 500 °C, from 27.3 to 18.9 wt % while the generation of gases increases. This can be attributed to the differences in the feeding mode since the CM allows a higher biomass heating rate, resulting in a more efficient lignocellulose decomposition. On the other hand, the balance between the higher residence time and the lower concentration of the vapours reduces the occurrence of secondary cracking reactions. Consequently, the share of water in the liquid fraction diminishes in CM, although only a notable increase of bio-oil* (bio-oil in water-free basis) is observed at 500 °C (39.9 vs 45.0 wt %). The bio-oil* molecular composition is also modified by this shifting, leading to higher sugars and oxygenated-aromatics in the CM reactor at 500 °C. The different operation modes also affect the interaction between the vapours and the catalyst when the n-ZSM-5 is introduced into the reactor. The vapours are more diluted in CM in comparison with the batch one, allowing a more progressive and efficient catalytic conversion. As a result, less coke is deposited over the zeolite catalyst leading to an enhanced production of aromatic hydrocarbons, achieving yields of ca. 7.6 wt %.

Organocatalytic C−H Functionalization of Simple Alkanes

AbstractThe direct functionalization of inert C(sp3)‐H bonds to form carbon‐carbon and carbon‐heteroatom bonds offers vast potential for chemical synthesis and therefore receives increasing attention. At present, most successes come from strategies using metal catalysts/reagents or photo/electrochemical processes. The use of organocatalysis for this purpose remains scarce, especially when dealing with challenging C−H bonds such as those from simple alkanes. Here we disclose the first organocatalytic direct functionalization/acylation of inert C(sp3)‐H bonds of completely unfunctionalized alkanes. Our approach involves N‐heterocyclic carbene catalyst‐mediated carbonyl radical intermediate generation and coupling with simple alkanes (through the corresponding alkyl radical intermediates generated via a hydrogen atom transfer process). Unreactive C−H bonds are widely present in fossil fuel feedstocks, commercially important organic polymers, and complex molecules such as natural products. Our present study shall inspire a new avenue for quick functionalization of these molecules under the light‐ and metal‐free catalytic conditions.

Organocatalytic C-H Functionalization of Simple Alkanes.

The direct functionalization of inert C(sp3 )-H bonds to form carbon-carbon and carbon-heteroatom bonds offers vast potential for chemical synthesis and therefore receives increasing attention. At present, most successes come from strategies using metal catalysts/reagents or photo/electrochemical processes. The use of organocatalysis for this purpose remains scarce, especially when dealing with challenging C-H bonds such as those from simple alkanes. Here we disclose the first organocatalytic direct functionalization/acylation of inert C(sp3 )-H bonds of completely unfunctionalized alkanes. Our approach involves N-heterocyclic carbene catalyst-mediated carbonyl radical intermediate generation and coupling with simple alkanes (through the corresponding alkyl radical intermediates generated via a hydrogen atom transfer process). Unreactive C-H bonds are widely present in fossil fuel feedstocks, commercially important organic polymers, and complex molecules such as natural products. Our present study shall inspire a new avenue for quick functionalization of these molecules under the light- and metal-free catalytic conditions.

Application of Iodine as a Catalyst in Aerobic Oxidations: A Sustainable Approach for Thiol Oxidations.

Iodine is a well-known oxidant that is widely used in organic syntheses. Thiol oxidation by stoichiometric iodine is one of the most commonly employed strategies for the synthesis of valuable disulfides. While recent advancements in catalytic aerobic oxidation conditions have eliminated the need for stoichiometric oxidants, concerns persist regarding the use of toxic or expensive catalysts. In this study, we discovered that iodine can be used as a cheap, low-toxicity catalyst in the aerobic oxidation of thiols. In the catalytic cycle, iodine can be regenerated via HI oxidation by O2 at 70 °C in EtOAc. This protocol harnesses sustainable oxygen as the terminal oxidant, enabling the conversion of primary and secondary thiols with remarkable efficiency. Notably, all 26 tested thiols, encompassing various sensitive functional groups, were successfully converted into their corresponding disulfides with yields ranging from >66% to 98% at a catalyst loading of 5 mol%.

Plausible PEPPSI catalysts for direct C-H functionalization of furans and pyrroles

The worth of bi(hetero)arenes in ongoing medicinal and industrial research fields promotes their efficient synthesis by Pd-PEPPSI-bearing NHC spectator ligands encapsulated as site-selective direct C-H functionalization agents. Eight new asymmetric N-heterocyclic carbenes ligands and their plausible pyridine-assisted Pd (II) complexes are reported in this work. The synthesized compounds were thoroughly characterized by respective spectroscopic techniques, such as 1H, 13C, FTIR and elemental analysis. The structures of synthesized pro-ligand salts and complexes were determined by Single Crystal XRD. The on/off mechanism of pyridine assisted Pd-NHC complexes made them the best C-H functionalized catalysts for regioselective C5 arylated products. Five membered heterocyclic compounds such as 2-acetyl furan, furfuryl acetate and 1-methyl-2-pyrrole-carboxylaldehyde were treated with numerous aryl bromides under optimal catalytic reaction conditions. Furfuryl acetate was used for the first time as a substrate in the present research work. Interestingly, all the prepared catalysts possessed essential structural features that facilitated the formation of desired coupled products in quantitative yield with excellent selectivity.

Prediction of volatile composition of coal pyrolysis under various swelling and catalytic conditions based on recurrent neural network

Solvent swelling and catalyst have significant effects on the volatile release behavior during coal pyrolysis process, not only affecting the total amount, but also affecting the release trend when the temperature rises. An accurate quantification of this relationship can promote the efficient utilization of pyrolysis volatiles. This work adopts machine learning (ML) methods to construct prediction models for four primary volatiles (CO, CH4, aromatic and aliphatic hydrocarbons) during the pyrolysis of coal samples treated by different metal loading and solvent swelling, to predict the instantaneous volatile content at any time in the pyrolysis process. The deep learning models constructed by Recurrent neural networks (RNN) were compared with traditional machine learning methods of artificial neuron network (ANN), random forest (RF) and support vector machine (SVM), and realized an obvious preponderance on prediction performance for hole release curve. The best long short-term memory (LSTM) models achieve the average R2 of 0.978, 0.900, 0.950 and 0.936 for the release curve prediction of CO, CH4, aromatic and aliphatic volatile. Further adjustments shown that the reduction of sampling points on curves has little effect on the model’s performance, which makes it feasible to condense the models and decrease the dimensions of input. An easy signal processing of integral transformation had an obvious improvement on the predictive power of models, with a highest increase of R2 with 0.14 for aromatics predicting. All of these results provide a good method for real-time tracking of the conversion process.

Unraveling the role of nanocrystalline in amorphous nanoporous FeCoB catalysts for turning oxygen evolution activity and stability

The sluggish kinetics and high-power consumption of the oxygen evolution reaction (OER) are recognized as major barriers in electrocatalysis. Therefore, exploring cheap and highly-efficient OER electrocatalysts is highly desired for improving energy storage and conversion. Related Fe-based materials have been widely applied in OER electrocatalyst field due to their excellent OER activity. Herein, we adopt the vacuum annealing and electrochemical dealloying methods to produce a self-supporting np-Fe40Co40B20-800-5min catalyst enriched with nanocrystalline. The self-supporting np-Fe40Co40B20-800-5min catalyst exhibits superior OER performance with an overpotential of 315 mV at a current density of 10 mA cm−2 and a small Tafel slope of 26 mV dec−1. The overpotential of the np-Fe40Co40B20-800-5min catalyst is boosted by more than 20 percent over that obtained np-Fe40Co40B20 catalyst. The active intermediates were explored by in situ Raman under catalytic conditions. The in-depth mechanism research suggests that the nanocrystalline may serve as an advantageous electrocatalytic species in amorphous np-Fe40Co40B20-x-ymin catalyst. This study offers a novel approach to promoting catalytic properties in an amorphous np-Fe40Co40B20-800-5min catalyst based on enriched nanocrystalline.

Reactivation of Ni-TiO2 catalysts in hydrogen flow and in supercritical 2-propanol-Comparative study by electron spin resonance in situ.

Highly dispersed Ni-TiO2 catalyst has been studied in the process of preparation and under catalytic transfer hydrogenation reaction conditions in supercritical 2-propanol (250°C, 70 bar) using electron spin resonance in situ. Electron spin resonance in situ has been used to study the process of the catalyst passivation and subsequent reduction of the oxide layer in the gas flow. Reduction of the NiO layer on the surface of passivated Ni nanoparticles has been detected in supercritical 2-propanol, which is in agreement with kinetic modeling data. It has been found that the reduction of the nickel oxide layer in supercritical 2-propanol occurs at a lower temperature compared with the reduction in hydrogen flow, according to in situ electron spin resonance study.