Lanthanide Catalysts Research Articles

Titanium Silicate‐1 Coupled with Sn and Er as Effective Catalysts for the Production of Lactic Acid from Saccharides

AbstractBiomass‐based saccharide valorization to produce lactic acid (LaA) via chemocatalysis has emerged as a promising approach to meet the substantial demand of the global LaA market, whereas the manufacture of prominent heterogeneous catalyst is still challenging. Herein, we fabricate a series of heterogeneous rare earth catalysts and indicate that Er supported onto titanium silicate‐1 (TS‐1) exhibits better activity than other rare earth catalysts for glucose transformation towards LaA. Remarkably, coupling Sn with Er onto TS‐1 enabled the sharp increment of LaA yield, and 3Sn15Er/TS‐1 catalyst outperformed other heterogeneous rare earth catalysts as reported to date, giving as high as 82.2% and 76.2% yields of LaA from sorbose and glucose, respectively. The catalyst characterization demonstrated the coexistence of Er2O3 and Sn2Er2O7 on 3Sn15Er/TS‐1 catalyst, both of which contributed to LaA production. Sn doping favored the formation of active particles in smaller size and increased the Lewis acidic sites when compared to single 15Er/TS‐1, thereby promoting the isomerization and retro‐aldol reaction of glucose to C3 intermediates. 3Sn15Er/TS‐1 catalyst also showed universal activity for diverse biomass‐based saccharides. This work might give useful insights to explore heterogeneous rare earth catalysts with superior activity in biomass valorization.

Mg-modified layered erbium hydroxides promoting glucose transformation to lactic acid

Layered rare earth hydroxides (LREHs) with unique layer structure and tunable properties have shown attractive potentials as heterogeneous catalyst, but is still challenging in biomass valorization towards valuable chemical production due to the poor catalytic activity. Herein, Mg-modified erbium hydroxides (Mg-LErHs) with well-constructed layered structure have been first fabricated, where the properties and structure of Mg-LErHs significantly depend on the proportion of Mg. The results of catalyst characterizations reveal that Mg introduction increases the interlayer spacing and the content of Er(III)-O. Mg modification also hinders the desorption of crystallized H2O and dehydroxylation, thereby increasing the degree of crystallinity and promoting the stability of the catalyst. The activity test indicate that Mg modification greatly promotes the production of lactic acid from monosaccharides, where Mg(5.8)-LErHs affords the highest lactic acid yield of 60.9 %. Mg-LErHs also outperform other Mg-LREHs catalysts for the production of lactic acid. The highest catalytic activity of Mg(5.8)-LErHs are possibly attributed to its highest degree of crystallinity, and the increased layer spacing after Mg modification might have an advantage in facilitating the entry of substrate. The increased Er(III)-O content with high Lewis acidity might facilitate the combination with electronic-rich carbonyl oxygen in substrate. This research may provide a novel strategy to design the layered rare earth catalysts with tunable catalytic activity for biomass valorization.

A Recyclable Inorganic Lanthanide Cluster Catalyst for Chemoselective Aerobic Oxidation of Thiols.

Optimizing lanthanide catalyst performance with organic ligands often encounters significant challenges, including susceptibility to water or oxygen and complex synthesis pathways. To address these issues, our research focuses on developing inorganic lanthanide clusters with enhanced stability and functionality. In this study, we introduce the [Sm6O(OH)8(H2O)24]I8(H2O)8 cluster (Sm-OC) as a sustainable and efficient catalyst for the aerobic oxidation of thiols under heating conditions. The Sm-OC catalyst demonstrated remarkable stability, outstanding recyclability, and excellent chemoselectivity across a diverse range of functional groups in 38 different tests. Notably, it enables efficient unsymmetrical disulfide synthesis and prevents the formation of over-oxidized by-products, highlighting its superior performance. This Sm-OC catalyst provides a practical and robust tool for the precise construction of versatile disulfides, thus establishing a template for the broader use of lanthanide clusters in organic synthesis.

Atomically dispersed Au single sites and nanoengineered structural defects enable a high electrocatalytic activity and durability for hydrogen evolution reaction and overall urea electrolysis

The development of exceptionally active and stable trifunctional electrocatalysts is essential to facilitate industrial applications of proton exchange membrane electrolyzers. Rare earth catalysts have a wide range of applications in alkaline solution oxidation, but limitations in their stability and activity prevent their further application. In this paper, Au doped CeO2 coated porous Aux/CeO2 (x = 1,2,3) was designed as a three-function electrocatalyst with excellent performance and stability. At 1 M KOH conditions, both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) reactions exhibit excess potentials of 159.6 and 320.8 mV at a current density of 10 mA cm-2. In addition, when incorporated into an Au2/CeO2 (0.05 mmol, HAuCl4·4H2O) microparticles, the catalyst exhibits the potential of 1.42 V(10 mA cm-2) containing 0.33 M urea in 1 M KOH. Remarkably, for hydrogen production driven by urea electrolysis, Au2/CeO2 demonstrated exceptional performance by requiring only a voltage input of 1.63 V. The reducing agent that forms the Au/CeO2 heterojunction modulates the electronic structure of the Au active site and optimizes the adsorption of the intermediate. In addition, the interaction of the Au monolayer with the CeO2 nanosphere effectively prevents excessive oxidation and dissolution of Au, and the porous hollow structure provides additional exposed active sites and facilitates mass transfer.

Origins of Ligand-Controlled Stereoselective Polymerization of ortho-Methoxystyrene by Rare-Earth Catalysts: A Theoretical Perspective.

The stereoselective polymerization of polar vinyl monomers has recently received much attention due to their excellent physicochemical properties. Over the past decade, breakthroughs have been achieved in this field by rare-earth catalysts. However, the mechanistic origins of those stereoselective polymerizations still remain unclear. Herein, stereoselective polymerization of ortho-methoxystyrene (oMOS) by several representative rare-earth catalysts bearing different ligands (i.e., η5-C5Me5, pyridinyl-methylene-fluorenyl, quinolyl-anilido, β-diketiminato) were systematically investigated by density functional theory (DFT) calculations. After achieving agreement between the calculations and experiments, we focused on discussing the role of ligands in controlling stereoselectivity. Our results reveal that the stereoregularity of oMOS polymerization is mainly controlled by the steric effect of the catalyst-monomer structures. Specifically, the type of ligand influences the orientation and configuration of the inserting monomer, thereby affecting the tacticity of the polymers. In the cases of η5-C5Me5-, pyridinyl-methylene-fluorenyl, and quinolyl-anilido-ligated yttrium catalysts, we observe consistent insertion directions and alternating insertion sides of oMOS monomers, leading to syndiotactic selectivity. The opposite insertion directions and the alternating insertion sides of oMOS monomers were observed in the case of the β-diketiminato yttrium catalyst, leading to isotactic selectivity. These findings reported here offer valuable insights into the role of ligands in controlling stereoselectivity in rare-earth catalyzed coordination polymerization of polar vinyl monomers, thus providing guidance for the rational design of new ligands for stereospecific polymerization of polar monomers in the future.

Regio- and Diastereoselective Annulation of α,β-Unsaturated Aldimines with Alkenes via Allylic C(sp3)-H Activation by Rare-Earth Catalysts.

The [3 + 2] or [4 + 2] annulation of α,β-unsaturated aldimines with alkenes via β'- or γ-allylic C(sp3)-H activation is, in principle, an atom-efficient route for the synthesis of five- or six-membered-ring cycloalkylamines, which are important structural motifs in numerous natural products, bioactive molecules, and pharmaceuticals. However, such a transformation has remained undeveloped to date probably due to the lack of suitable catalysts. We report herein for the first time the regio- and diastereoselective [3 + 2] and [4 + 2] annulations of α,β-unsaturated imines with alkenes via allylic C(sp3)-H activation by half-sandwich rare-earth catalysts having different metal ion sizes. The reaction of α-methyl-substituted α,β-unsaturated aldimines with alkenes by a C5Me4SiMe3-ligated scandium catalyst took place in a trans-diastereoselective [3 + 2] annulation fashion via C(sp3)-H activation at the α-methyl group (β'-position), exclusively affording alkylidene-functionalized cyclopentylamines with excellent trans-diastereoselectivity. In contrast, the reaction of β-methyl-substituted α,β-unsaturated aldimines with alkenes by a C5Me5-ligated cerium catalyst proceeded in a cis-diastereoselective [4 + 2] annulation fashion via γ-allylic C(sp3)-H activation, selectively yielding multisubstituted 2-cyclohexenylamines with excellent cis-diastereoselectivity. The mechanistic details of these transformations have been elucidated by deuterium-labeling experiments, kinetic isotope effect studies, and the isolation and transformations of key reaction intermediates. This work offers an efficient and selective protocol for the synthesis of a new family of cycloalkylamine derivatives, featuring 100% atom efficiency, high regio- and diastereoselectivity, broad substrate scope, and an unprecedented reaction mechanism.

Mononuclear binding and catalytic activity of europium(III) and gadolinium(III) at the active site of the model metalloenzyme phosphotriesterase.

Lanthanide ions have ideal chemical properties for catalysis, such as hard Lewis acidity, fast ligand-exchange kinetics, high coordination-number preferences and low geometric requirements for coordination. As a result, many small-molecule lanthanide catalysts have been described in the literature. Yet, despite the ability of enzymes to catalyse highly stereoselective reactions under gentle conditions, very few lanthanoenzymes have been investigated. In this work, the mononuclear binding of europium(III) and gadolinium(III) to the active site of a mutant of the model enzyme phosphotriesterase are described using X-ray crystallography at 1.78 and 1.61 Å resolution, respectively. It is also shown that despite coordinating a single non-natural metal cation, the PTE-R18 mutant is still able to maintain esterase activity.

Divergent Synthesis of Multi-Substituted Aminotetralins via [4+2] Annulation of Aldimines with Alkenes by Rare-Earth-Catalyzed Benzylic C(sp3 )-H Activation.

The search for efficient and selective methods for the divergent synthesis of multi-substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2-methyl aromatic aldimines with alkenes via benzylic C(sp3 )-H activation by half-sandwich rare-earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi-substituted 1-aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C5 Me4 SiMe3 or C5 Me5 exclusively afforded the trans-selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis-selective annulation products. This protocol features 100 % atom-efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates.

Unveiling the Detailed Mechanism and Origins of Chemo-, Regio-, and Stereoselectivity of Rare-Earth Catalyzed Alternating Copolymerization of Polar and Nonpolar Olefins.

The direct copolymerization of polar and nonpolar olefins is of great interest and significance, as it is the most atom-economical and straightforward strategy for the synthesis of functional polyolefin materials. Despite considerable efforts, the precise control of monomer-sequence and their regio- and stereochemistry is full of challenges, and the related mechanistic origins are still in their infancy to date. Herein, the mechanistic studies on the model reaction of Sc-catalyzed co-syndiospecific alternating copolymerization of anisylpropylene (AP) and styrene were performed by DFT calculations. The results suggest that the subtle balance between electronic and steric factors plays an important role during monomer insertions, and a new amino-dissociated mechanism was proposed for AP insertion at chain initiation. AP insertion follows the 2,1-si-insertion pattern, which is mainly controlled by steric factors caused by the restricted MeO···Sc interaction. As for styrene insertion, it prefers the 2,1-re-insertion manner and its regio- and stereoselectivities are influenced by steric repulsions between the inserting styrene and the polymer chain or the ligand. More interestingly, it is found that the alternating monomer-sequence is mainly determined by the "steric matching" principle, which is quantitatively expressed by the buried volume of the metal center of the preinserted species. The concept of steric pocket has been successfully applied to explain the different performances of several catalysts and other alternating copolymerization reactions. The insightful mechanistic findings and the quantitative steric pocket model present here are expected to promote rational design of new rare-earth catalysts for developing regio-, stereo-, and sequence-controlled copolymerization of specific polar and nonpolar olefins.

Research Advances in Rare Earth Oxide‐Based Catalysts for Soot Combustion

AbstractEnvironmental issues exert a significant influence on the human life. Soot particles have attracted attention as a major source of pollution. Significant progress has been made in the research of efficient soot combustion catalysts. The distinctive bonding properties on the 4 f orbitals of rare earth elements exhibit excellent catalytic performance for soot combustion. This comprehensive review explores recent advancements in the design of catalysts based on rare earth oxides, with a specific focus on various catalytic materials (La‐based, Ce‐based, Pr‐based and other rare earth elements), synthesis methods, catalyst morphology, catalytic performance and the intricate mechanisms governing their performance in catalytic soot combustion. The activity and selectivity of different rare earth catalysts in various reaction atmospheres are also summarized in the article. Finally, the challenges associated with rare earth oxide‐based catalysts and their potential for future development in the soot combustion are highlighted. This review establishes a fundamental basis for the further design of catalytic materials that exhibit enhanced efficiency and stability.

Synthesis of Self-Healing Syndiotactic Polyolefins by Rare-Earth Catalysts

Synthesis of Self-Healing Syndiotactic Polyolefins by Rare-Earth Catalysts

Research and synthesis of polyolefins materials

Polyolefins are widely used in our lives, such as food packaging materials, agricultural films, and lubricants, but the lack of polar groups that can make polyolefins compatible with other types of materials has limited the use of polyolefins. This has been a challenging and highly concerned issue in academia and industry. Therefore, it is great significance that we introduce polar groups into polyolefins to improve the use of performance to synthesize functional polyolefins. In this paper, we introduce the direct catalytic polymerization of polar α olefin monomers using rare earth catalysts, and the experimental data shows that we have obtained a higher molecular weight and better selectivity polar α olefin monomer of homopolymer. Subsequently, we determined the optimal reaction conditions for the synthetic polymer through screening of different reaction conditions.

Samarium and Ytterbium in Organic Electrosynthesis

AbstractLow-valent lanthanide catalysts and reagents are well-established as versatile and tunable mediators for a variety of synthetic transformations. Despite the contemporary interest in electricity as a sustainable alternative to stoichiometric redox reagents, electrochemical (re)generation of such low-valent metal complexes in a synthetic setting is surprisingly limited. With focus on samarium and ytterbium, this review presents a comprehensive overview of electroreductive-mediated transformations with the hope of inspiring further work in this very useful field of research.1 Introduction2 Compounds Containing Carbon–Oxygen Bonds2.1 Ethers2.2 Aldehydes and Ketones2.3 Esters and Phthalimides3 Compounds Containing Nitrogen–Oxygen Bonds4 Compounds Containing Carbon–Halide Bonds5 Conclusions

Synthesis of new macrocyclic triperoxides

An efficient method has been developed for the synthesis of dialkyl hexaoxadispiroalkanedicarboxylates by the recyclization reaction of heptaoxadispiroalkanes with alkyl malonates (malonic acid dimethyl ester, malonic acid diethyl ester, malonic acid diisopropyl ester) under the action of lanthanide catalysts.

Lanthanide-catalyzed deamidative cyclization of secondary amides and ynones through tandem C-H and C-N activation.

The tandem inert α-C-H and C-N bond activation of amides represents a highly valuable but challenging transformation in organic synthesis. Herein, a simple rare earth metal amido complex has been shown to catalyse unprecedented cyclization of amides with ynones to form trisubstituted 2-pyrones. This protocol significantly enables the selective merger of inert α-C-H and C-N bond activations of amides and indicates a particular role of rare earth catalysts in enhancing the selectivity for the α-C-H bond of amides in the presence of N-H bonds.

La-Catalyzed Decarbonylation of Formamides and Its Applications.

Herein we report the first catalytic decarbonylation and decarbonylative hydroamination of formamides without using additives enabled by a redox-neutral rare earth catalyst. The protocol displays complete N-aryl/alkenyl formamide-selectivity, thus providing a wide variety of creative uses of the N-formylation and N-deformylation method and opening up new prospects for minimizing waste and controlling the required selectivity in amine transformation events.

Experimental investigation on biodiesel production through simultaneous esterification and transesterification using mixed rare earth catalysts

In this study, biodiesel production through simultaneous esterification and transesterification of palm oil with 10 wt% of oleic acid using the mixed rare earth catalyst was investigated. The mixed rare earth catalysts were prepared via the co-precipitation method. The effects of the precipitating parameters such as temperature, stirring speed and pH on the physicochemical and morphology of the catalysts were studied. All catalysts were thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), fourier transform-infrared spectroscopy (FTIR), N2 adsorption/desorption, CO2 temperature programmed desorption (CO2-TPD) and NH3 temperature programmed desorption. (NH3-TPD). The results indicated that the mixed rare earth catalyst prepared under the precipitation conditions: at pH 9, a stirring of 400 rpm and temperature of 30 °C showed the highest catalytic of 90% FAME content. High surface area of the catalyst, a significant larger amount of Ce and La contents in the catalyst and an appropriate amount of acid and basic sites on the catalyst led to the high catalytic activity. The catalyst could also accelerate the initial reaction rate to achieve the high FAME content of 50% within 30 min.

Exo-Selective Intramolecular C–H Alkylation with 1,1-Disubstituted Alkenes by Rare-Earth Catalysts: Construction of Indanes and Tetralins with an All-Carbon Quaternary Center

Exo-Selective Intramolecular C–H Alkylation with 1,1-Disubstituted Alkenes by Rare-Earth Catalysts: Construction of Indanes and Tetralins with an All-Carbon Quaternary Center

Regio- and Diastereoselective Formal [2+2] Cycloaddition of Allenes with Amino-Functionalized Alkenes by Rare-Earth-Catalyzed C(sp2 )-H Activation.

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four-membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio- and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino-functionalized alkenes by half-sandwich rare-earth catalysts. The reaction proceeded through an allene C(sp2 )-H activation mechanism initiated by the site-selective deprotonation of the allene unit by a rare-earth metal alkyl species followed by alkene insertion into the resulting metal-allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously.

Highly selective catalytic conversion of raw sugar and sugarcane bagasse to lactic acid over YbCl3, ErCl3, and CeCl3 Lewis acid catalysts without alkaline in a hot-compressed water reaction system

To improve the process efficiency for lactic acid production, catalytic conversion of raw cane sugar and sugarcane bagasse (SCB) to lactic acid under subcritical water condition over Lanthanide catalysts was investigated. The effect of different types of Lanthanide (III) ion catalyst namely YbCl3, ErCl3, and CeCl3 on enhancement of lactic acid (LA) yield, selectivity, turnover number [TON] and turnover frequency [TOF] was studied in the aqueous solution. The results were compared with conventional catalytic reaction for lactic acid production in strongly alkaline solution. For raw sugar-to-lactic acid conversion, ErCl3 catalyst exhibited greatest performance at 240 °C for 15 min and achieve the highest TOF and TON with 91.8% LA yield (91.79%theoretical yield) and 90.5% selectivity. In case of SCB conversion, aqueous ammonia solution (LHWAA) was the best pretreatment to eliminate lignin and hemicellulose and attain cellulose-rich fraction. The LHWAA pretreated SCB conversion to lactic acid over YbCl3 at 240 °C for 15 min achieved supreme performance for highest TOF and TON and accomplished 98.7% LA yield (88.81% theoretical yield) and 94.2% selectivity with trace amount of formic acid, acetic acid and levulinic acid as side products. The findings provided crucial information for a combined cellulose hydrolysis step with catalytic conversion of mono- and polysaccharides to lactic acid in a very shorter time relative to conventional catalytic process and biotechnological fermentation process. Lanthanide catalysts, especially ErCl3 and YbCl3, were found as promising alternative environmentally friendly catalysts providing a potential cost-efficient process of lactic acid from bioresources in a larger scale production.