Jonas Wuyts

Publication date: October 2024

Source: Chemical Engineering Research and Design, Volume 210

Author(s): Alexis Tirado, Guillermo Félix, Ameen A. Al-Muntaser, Mikhail A. Varfolomeev, Jorge Ancheyta

Heterogeneously catalyzed reductive depolymerization is a promising approach for lignin valorization, leveraging heterogeneous catalysts and various hydrogen sources to selectively cleave lignin bonds and produce value-added chemicals.

Abstract

Lignin is an abundant renewable source of aromatics, but its complex heterogeneous structure poses challenges for its depolymerization and valorization. Heterogeneously catalyzed reductive depolymerization (HCRD) has emerged as a promising approach, utilizing heterogeneous catalysts to facilitate selective bond cleavage in lignin and hydrogen transfer to stabilize the products under mild conditions. This review provides a comprehensive understanding of the hydrogen transfer mechanisms in HCRD, involving different hydrogen sources, including molecular hydrogen, alcohols, formic acid, etc., and the native hydrogen donor groups in lignin. The interaction between hydrogen sources and catalyst design is explored, emphasizing how catalyst characteristics must align with specific hydrogen transfer pathways to optimize efficiency and selectivity. Precious metal-based and non-precious metal-based catalysts are examined, highlighting advances that enhance hydrogen activation and transfer. Comparative analyses of hydrogen sources reveal distinct advantages and limitations. The significance of HCRD in lignin valorization and the development of integrated biorefineries is underscored, emphasizing its potential to contribute to a sustainable bioeconomy through improved process integration and economic viability.

Pd-catalyzed carboxylation of ethylene into sodium acrylate is an industrially relevant reaction aiming at transforming CO₂ into value-added chemicals. Herein, we combine experimental and DFT studies to understand the reactivity and catalytic performance of the Pd/dicyclohexylphoshpinoethane (dcpe) system. Combination of DMF as solvent, PdBr₂ as precursor and P(C₆FH₄)₃ as additive, permitted us to rationally improve the catalytic performance.

Abstract

Pd-catalyzed carboxylation of ethylene into sodium acrylate is an industrially relevant reaction that has gained increasing attention in the last years. By this process, CO₂ can be transformed into a value-added molecule in a single, high atom economy step. However, there is still some room for improvement since the productivity of the reference catalyst is rather low. A key aspect to achieve this goal concerns the good understanding of reaction mechanism. Herein, we combine experimental and DFT studies to gain some knowledge on the reactivity and catalytic performance of the Pd/dicyclohexylphosphinoethane (dcpe) system. First, we were able to understand the influence of the solvent on the reaction, and we demonstrated that DMF was the best candidate due to the more efficient formation of the Pd-metallalactone. Moreover, we have demonstrated that highly available and less costly PdBr₂ can be a suitable precursor, as Pd^II is reduced in situ in DMF in the presence of an excess of NaOtBu. Finally, the role of different monophosphine additives has been elucidated, which permitted us to rationally improve the catalytic performance.

Nature Synthesis, Published online: 28 August 2024; doi:10.1038/s44160-024-00621-6

Nature Catalysis, Published online: 19 August 2024; doi:10.1038/s41929-024-01205-5

A novel green solvent, γ-valerolactone (GVL), efficiently facilitates the photocatalytic activation of C−H bonds in benzylic compounds. Mechanistic studies reveal that GVL′s high dielectric constant (ϵ) increases the driving force (−ΔG), and its large refractive index (n) reduces reorganization energy (λ), collectively reducing the reaction barrier (ΔG ^≠). This research advances the overlooked solvent effects in semiconductor photocatalysis.

Abstract

Solvents can significantly influence chemical reactions in condensed phases. Their critical properties are increasingly recognized in various research domains such as organic synthesis and biomass valorization. However, in semiconductor photocatalysis, solvents are primarily viewed as mediums for dissolving and diffusing substances, with their potential beneficial effects on photocatalytic conversions often overlooked. Additionally, common photocatalysis solvents like acetonitrile (ACN) pose serious safety and environmental concerns. In this study, we demonstrate that novel and safe green solvents, such as γ-valerolactone (GVL), can significantly enhance the performance of semiconductor photocatalysis for C−H bond activation. Non-specific solvent-solute interactions are the primary contributors to increased photocatalytic activity in the self-coupling of benzylic compounds. Specifically, GVL′s large dielectric constant and high refractive index lower the energy barrier for the rate-determining C−H bond activation step, facilitating a faster coupling reaction. The versatility of GVL is further demonstrated in reactions with multiple reagents and in various oxidation and reduction photocatalytic systems beyond classic C−H bond activation. This work not only pioneers the use of green solvents but also provides comprehensive insights for proper solvent selection in semiconductor photocatalysis.

The transition from fossil fuels to sustainable resources of the near future demands a shift in catalysis research – from investigating reactions in isolation to developing coupled catalytic reactions. This Perspective discusses the status and emerging prospects of coupled catalytic reactions across various scales, from active sites to processes.

Abstract

Transitioning from both the direct and indirect use of fossil fuels to the renewable and sustainable resources of the near future demands a focal shift in catalysis research – from investigating catalytic reactions in isolation to developing coupled reactions for modern chemical value chains. In this Perspective, we discuss the status and emerging prospects of coupled catalytic reactions across various scales and provide key examples. Besides being a sustainable and essential alternative to current fossil-based processes, the coupling of catalytic reactions offers novel and scalable pathways to value-added chemicals. By emphasizing the specific requirements and challenges arising from coupled reactions, we aim to identify and underscore research needs that are critical to expedite their development and to fully unlock their potential for chemical and fuel production.

The product distribution of the direct transfer hydrogenation of furfural can be steered between 2-methyl(tetrahydro)furan and 2-(tetrahydro)furfurylalcohol by adjusting the ratio of formic acid and sodium formate. The disclosed protocols use commercially available palladium on alumina catalyst and can furnish several valuable products in good selectivity.

Abstract

Furfural is an attractive bio-based platform chemical that has many derivatives of commercial interest. Herein, we show that the selectivity of the direct furfural reduction can be steered from 2-methylfuran and 2-methyltetrahydrofuran to furfuryl alcohol and tetrahydrofurfuryl alcohol by varying the ratio of formic acid and sodium formate. These reagents take the role of terminal reductants in the disclosed heterogeneous Pd-catalysed process. We report the development and optimisation of the reaction conditions for three different products directly from furfural: 2-methyltetrahydrofuran, tetrahydrofurfuryl alcohol and 2-methylfuran which were obtained in 59 %, 46 %, and 63 % selectivity, respectively. Furthermore, the protocol uses commercially available Pd/Al₂O₃ as catalyst and the formic acid and sodium formate can be obtained from biogenous sources.

Publication date: 12 September 2024

Source: Chem, Volume 10, Issue 9

Author(s): Stephen Don Sarkar, Huong Dau, Eva Harth

α,β-Unsaturated compounds are one of the most important functional compounds. They usually occur as the key intermediates for the synthesis of pharmaceuticals and biological materials The early approaches to α,β-unsaturated compounds are mainly about transition-metal-free methods, such as halogenation-dehydrohalogenation methods and strong oxidants methods. This review mainly focuses on transition-metal-catalyzed α,β-dehydrogenation, which is categorized by functional groups.

Abstract

α,β-Unsaturated compounds are one of the most important functional compounds. Due to their unique property and versatile utility, they usually occur as the key intermediates for the synthesis of pharmaceuticals and biological materials. Thus, their synthesis has attracted more attentions than before. The early approaches to α,β-unsaturated compounds are mainly about transition-metal-free methods, such as halogenation-dehydrohalogenation methods and strong oxidants methods (organosulfur, organoselenium, benzoquinone). Subsequently, palladium and the other transition-metals catalyzed dehydrogenation of carbonyl compounds appeared respectively. In this review, transition-metal-catalyzed α,β-dehydrogenation is discussed, which is categorized by functional groups.

Publication date: April 2024

Source: Chemical Engineering Research and Design, Volume 204

Author(s): Vinicius Lima Ferreira, Marco Aurélio Suller Garcia, Donato Alexandre Gomes Aranda, Pedro Nothaft Romano

Nature Catalysis, Published online: 13 February 2024; doi:10.1038/s41929-024-01110-x

Nature Catalysis, Published online: 13 February 2024; doi:10.1038/s41929-024-01107-6

The butterfly metamorphosis Within the cocoon's shell (aryl methyl ethers) is encased a secret beauty (phenols), how to liberate it? In their Review (e202317257), Bert U. W. Maes, and Bert F. Sels et al. comprehensively summarize the advancements and perspectives of lignin O-demethylation (metamorphosis). The presence of methoxy groups (cocoon) limits the chemical reactivity and the applicability of lignin-derived compounds. Through O-demethylation (metamorphosis), the reborn product (butterfly) rich in phenolic functionality can start a versatile new life with broader applications.

Nature, Published online: 12 February 2024; doi:10.1038/d41586-024-00369-1

Catalytic upgrading of levulinic acid is highly relevant in biorefinery and heterogeneous catalysis. A 3 wt. % Ru catalyst supported on zirconia-alumina efficiently and selectively converted levulinic acid to γ-valerolactone under mild reaction conditions and using water as solvent. The catalyst was tested in five consecutive cycles, keeping its activity and selectivity. Characterization provided valuable insight into physicochemical properties and catalytic performance.

Abstract

γ-Valerolactone (GVL) can be obtained by efficient hydrogenation of levulinic acid using ruthenium-based catalysts in an aqueous medium. This paper reports an in-depth study on the activity and selectivity of Ru catalysts supported on zirconia-alumina, focusing on the effect of Ru concentration (0.5, 1.5 and 3 wt. % of Ru) and the selection of operational reaction variables. The results showed that the activity strongly depends on the number and oxidation state of the supported ruthenium particles. The most active catalyst, Ru3/ZA, presented the highest number of nanometric particles of zerovalent Ru and the highest number of acid sites. This catalyst gave ca. 100 % selectivity towards GVL, at high conversion of levulinic acid (over 99 %) under the best operating conditions evaluated (120 °C, 3 MPa H₂ pressure, 1 h of reaction, and 0.1 g of catalyst). In addition, this catalyst kept high levels of conversion and selectivity after successive reuse cycles.

Nature Communications, Published online: 07 February 2024; doi:10.1038/s41467-024-45331-x

Nature, Published online: 31 January 2024; doi:10.1038/s41586-023-06939-z

This Concept spotlights the recent advancements in the selective reductive aminations of carboxylic acids.

Abstract

The broad applications of primary alkyl amines in various fields have spurred extensive interests in synthetic organic chemistry. Recently, the reductive amination of carboxylic acids has become an attractive and practical strategy for synthesizing primary alkyl amines, due to their wide availability and bench stability. However, the inherent stability and higher oxidation state of carboxylic acids render this new strategy with new challenges. This Concept provides a summary of the recent advancements in the reductive aminations of carboxylic acids, specifically focusing on the catalytic tactics, underlying mechanisms, and applications in the synthesis of valuable products.

Heterolytic H₂ activation can enhance the yield of target products in heterogeneous catalytic hydrogenation and hydroprocessing thanks to accelerated reaction kinetics and reduced catalyst poisoning. This concept involves intrinsic catalyst properties (e. g., single metal atom, basicity, supports’ oxygen vacancy, and so on) necessary for heterolytic H₂ activation in heterogeneous catalysis to design and synthesize efficient catalysts with this activation behavior.

Abstract

In heterogeneous catalysis, heterolytic H₂ activation for (selective) hydrogenation and hydroprocessing reactions involves the dissociation of adsorbed H₂ molecules into proton (H^δ+) and hydride (H^δ−) on the catalyst surface. This approach offers several advantages, including high selectivity for polar bond (s), a low energy barrier for H₂ dissociation, a high capacity for reaction-favorable H₂ adsorption, and reduced catalyst poisoning. This requires the construction of frustrated Lewis pairs on the catalyst surface, satisfying specific criteria, such as having an abundant quantity of Lewis pairs with steric hindrance and maintaining a certain distance of 3–5 Å between the pairs. This review highlights intrinsic catalyst properties for heterolytic H₂ activation based on state-of-the-art reports. The main components necessary for this activation include supports with strong basic sites and/or oxygen vacancies, and/or metals of single atom. For this purpose, designed catalytic materials aim to strengthen the Lewis acidity and basicity, improve the polarization of Lewis pairs, enrich oxygen vacancies, maximize the interfacial area between metal species and Lewis base, and enhance metal–support interaction. Therefore, heterogeneous catalysts retaining such heterolytic H₂ activation characteristics will be significantly effective in various hydrogenation and hydroprocessing reactions.

Constructing a bridge between single-atom catalysts and organocatalysts, organic molecules anchored on single-atom supports exhibit high efficiency, durability, and bifunctional properties on both electrodes used in the chlor-alkali industry. This work not only provides an alternative choice for the chlor-alkali industry but also provides a new platform to study the catalyst consisting of inorganic and organic species together, which performs well in both reduction and oxidation process.

Abstract

Consuming one of the largest amount of electricity, the chlor-alkali industry supplies basic chemicals for society, which mainly consists of two reactions, hydrogen evolution (HER) and chlorine evolution reaction (CER). Till now, the state-of-the-art catalyst applied in this field is still the dimensional stable anode (DSA), which consumes a large amount of noble metal of Ru and Ir. It is thus necessary to develop new types of catalysts. In this study, an organocatalyst anchored on the single-atom support (SAS) is put forward. It exhibits high catalytic efficiency towards both HER and CER with an overpotential of 21 mV and 20 mV at 10 mA cm⁻². With this catalyst on both electrodes, the energy consumption is cut down by 1.2 % compared with the commercial system under industrial conditions. Based on this novel catalyst and the high activity, the mechanism of modifying non-covalent interaction is demonstrated to be reliable for the catalyst's design. This work not only provides efficient catalysts for the chlor-alkali industry but also points out that the SACs can also act as support, providing new twists for the development of SACs and organic molecules in the next step.

A new family of metal nanoparticles loaded COFs catalysts have been prepared via one-pot construction strategy without lab-cost procedures, demonstrating excellent hydrogenation performance under mild conditions. The new strategy can be further evolved as into a versatile platform to create new COFs materials and explore the resultant applications.

Abstract

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.