Sustainable Chemical Synthesis Research Articles

Transition metal enhanced chromium nitride as composite nitrogen carrier for sustainable chemical looping ammonia synthesis

Chemical looping ammonia synthesis (CLAS) is promising to achieve decentralized ammonia synthesis under ambient pressure. Here, we develop a highly selective composite nitrogen carrier for efficient CLAS based on transition metals (TMs=Co, Ni, Fe) decorated chromium nitride (CrN). Systematic studies indicate that the pristine CrN is extremely inert: only 4.5% lattice nitrogen can be consumed in reacting with H2 (700 °C, 1 bar). Upon loading cobalt, the composite nitrogen carrier achieves lattice nitrogen conversion of 50.7% and ammonia selectivity up to 98.1%. Furthermore, Co-CrN exhibits excellent CLAS performance, attaining an average ammonia production rate of 466.1 μmol g−1 h−1 in 12 chemical loopings, which is ∼10 times that of the pristine CrN. Theoretical calculations reveal that the nitrogen vacancies generated in hydrogenation play a crucial role as activation centers for N2 fixation through a Mars–van Krevelen mechanism. This work provides a novel strategy to optimize nitrogen carriers for enhanced CLAS.

Bioelectrocatalytic Synthesis: Concepts and Applications

AbstractBioelectrocatalytic synthesis is the conversion of electrical energy into value‐added products using biocatalysts. These methods merge the specificity and selectivity of biocatalysis and energy‐related electrocatalysis to address challenges in the sustainable synthesis of pharmaceuticals, commodity chemicals, fuels, feedstocks and fertilizers. However, the specialized experimental setups and domain knowledge for bioelectrocatalysis pose a significant barrier to adoption. This review introduces key concepts of bioelectrosynthetic systems. We provide a tutorial on the methods of biocatalyst utilization, the setup of bioelectrosynthetic cells, and the analytical methods for assessing bioelectrocatalysts. Key applications of bioelectrosynthesis in ammonia production and small‐molecule synthesis are outlined for both enzymatic and microbial systems. This review serves as a necessary introduction and resource for the non‐specialist interested in bioelectrosynthetic research.

Bioelectrocatalytic Synthesis: Concepts and Applications.

Bioelectrocatalytic synthesis is the conversion of electrical energy into value-added products using biocatalysts. These methods merge the specificity and selectivity of biocatalysis and energy-related electrocatalysis to address challenges in the sustainable synthesis of pharmaceuticals, commodity chemicals, fuels, feedstocks and fertilizers. However, the specialized experimental setups and domain knowledge for bioelectrocatalysis pose a significant barrier to adoption. This review introduces key concepts of bioelectrosynthetic systems. We provide a tutorial on the methods of biocatalyst utilization, the setup of bioelectrosynthetic cells, and the analytical methods for assessing bioelectrocatalysts. Key applications of bioelectrosynthesis in ammonia production and small-molecule synthesis are outlined for both enzymatic and microbial systems. This review serves as a necessary introduction and resource for the non-specialist interested in bioelectrosynthetic research.

Pressure dependence in aqueous-based electrochemical CO2 reduction

Electrochemical CO2 reduction (CO2R) is an approach to closing the carbon cycle for chemical synthesis. To date, the field has focused on the electrolysis of ambient pressure CO2. However, industrial CO2 is pressurized—in capture, transport and storage—and is often in dissolved form. Here, we find that pressurization to 50 bar steers CO2R pathways toward formate, something seen across widely-employed CO2R catalysts. By developing operando methods compatible with high pressures, including quantitative operando Raman spectroscopy, we link the high formate selectivity to increased CO2 coverage on the cathode surface. The interplay of theory and experiments validates the mechanism, and guides us to functionalize the surface of a Cu cathode with a proton-resistant layer to further the pressure-mediated selectivity effect. This work illustrates the value of industrial CO2 sources as the starting feedstock for sustainable chemical synthesis.

Sustainable Chemical Synthesis of 2,3-Dihydrobenzofurans/1,2,3-Trisubstituted Indanes in Water by Using a Permethylated β-Cyclodextrin-Tagged N-Heterocyclic Carbene–Gold Catalyst

AbstractAn environmentally friendly stereoselective synthesis of 2,3-dihydrobenzofurans and 1,2,3-trisubstituted indanes in water has been achieved by using a permethylated β-cyclodextrin-tagged N-heterocyclic carbene–gold complex. The gold catalyst can be recycled at least five times.

Unraveling the electrophilic oxygen-mediated mechanism for alcohol electrooxidation on NiO.

Aqueous organic electrosynthesis such as nucleophile oxidation reaction (NOR) is an economical and green approach. However, its development has been hindered by the inadequate understanding of the synergy between the electrochemical and non-electrochemical steps. In this study, we unravel the NOR mechanism for the primary alcohol/vicinal diol electrooxidation on NiO. Thereinto, the electrochemical step is the generation of Ni3+-(OH)ads, and the spontaneous reaction between Ni3+-(OH)ads and nucleophiles is an electrocatalyst-induced non-electrochemical step. We identify that two electrophilic oxygen-mediated mechanisms (EOMs), EOM involving hydrogen atom transfer (HAT) and EOM involving C-C bond cleavage, play pivotal roles in the electrooxidation of primary alcohol to carboxylic acid and the electrooxidation of vicinal diol to carboxylic acid and formic acid, respectively. Based on these findings, we establish a unified NOR mechanism for alcohol electrooxidation and deepen the understanding of the synergy between the electrochemical and non-electrochemical steps during NOR, which can guide the sustainable electrochemical synthesis of organic chemicals.

Sustainable Synthesis of Drop-In Chemicals from Biomass via Chemical Catalysis: Scopes, Challenges, and the Way Forward

A handful of small organics, namely, ethylene, propylene, butadiene, benzene, toluene, xylenes, and methanol, produced from petroleum and other fossilized carbon-based resources, can produce practically all petrochemicals and synthetic organic polymers used in the industrialized societies. The molecules mentioned above, often referred to as primary petrochemicals, must be sourced from renewable carbon feedstock to achieve the long-aspired all-around sustainability in chemical manufacturing. Significant efforts have been devoted to developing efficient chemical–catalytic pathways for selectively converting biomolecules and biopolymers into these petroleum-derived chemical platforms. The processes take advantage of prevalent petrorefinery infrastructure, well-documented synthetic value addition pathways of the chemical platforms, and established markets of the derived products. Relative merits and demerits of various catalytic routes in producing the aforementioned primary petrochemicals from renewable biomass have been deliberated. This review elaborates on the synthetic methodologies available for synthesizing the drop-in replacement of primary petrochemical from renewable biomass, focusing on process selectivity, feedstock selection, and catalyst performance. The critical analyses presented in this review will assist in appraising the research accomplishments to date, identifying the bottlenecks, and realigning the future perspectives.

Catalysis and inhibition of ester hydrolysis by encapsulation in micelles derived from designer surfactant TPGS-750-M

The designer surfactant TPGS-750-M is an important technology for green and sustainable chemical synthesis that facilitates a wide variety of organic transformations in water. Despite its growing importance in organic synthesis, many basic aspects of binding and reactivity within TPGS-750-M micelles remain poorly understood. In this work, the impact of TPGS-750-M on the rate of p-nitrophenyl ester hydrolysis kinetics was investigated to probe binding strength within TPGS-750-M micelles and the chemical environment of the micelle interior. We found that the hydrolysis rates of p-nitrophenyl acetate and p-nitrophenyl hexanoate were slowed by the presence of TPGS-750-M by up to 92%, consistent with a hydrophobic encapsulation environment within the micelle interior. The hydrolysis rates of p-nitrophenyl decanoate and p-nitrophenyl hydroxycinnamate were accelerated up to 74-fold by the presence of TPGS-750-M, but only at low surfactant concentrations. We propose that these rate enhancements are due to mixed micelle formation between ester and TPGS-750-M, which positions the reactive ester group within the hydrophilic region of the micelle. This study suggests that there are two distinct chemical environments present in the interior of micelles derived from TPGS-750-M, and that it is possible for very hydrophobic substrates to interact with the polar, hydrophilic region of the micelle. This work also demonstrates that increased hydrophobicity leads to stronger substrate binding within TPGS-750-M micelles.

Protonic Ceramic Electrochemical Cells for Synthesizing Sustainable Chemicals and Fuels.

Protonic ceramic electrochemical cells (PCECs) have been intensively studied as the technology that can be employed for power generation, energy storage, and sustainable chemical synthesis. Recently, there have been substantial advances in electrolyte and electrode materials for improving the performance of protonic ceramic fuel cells and protonic ceramic electrolyzers. However, the electrocatalytic materials development for synthesizing chemicals in PCECs has gained less attention, and there is a lack of systematic and fundamental understanding of the PCEC reactor design, reaction mechanisms, and electrode materials. This review comprehensively summarizes and critically evaluates the most up-to-date progress in employing PCECs to synthesize a wide range of chemicals, including ammonia, carbon monoxide, methane, light olefins, and aromatics. Factors that impact the conversion, selectivity, product yield, and energy efficiencies are discussed to provide new insights into designing electrochemical cells, developing electrode materials, and achieving economically viable chemical synthesis. The primary challenges associated with producing chemicals in PCECs are highlighted. Approaches to tackle these challenges are then offered, with a particular focus on deliberately designing electrode materials, aiming to achieve practically valuable product yield and energy efficiency. Finally, perspectives on the future development of PCECs for synthesizing sustainable chemicals are provided.

Transition metal-catalysis in interrupted borrowing hydrogen strategy.

In recent times, the transition metal-catalyzed borrowing hydrogen (BH) and interrupted borrowing hydrogen (IBH) strategies have attracted much attention and represent atom- and step-economic processes to access diverse building blocks via various C-C and C-heteroatom bond-forming reactions. The advantages of these approaches include (i) use of feedstock chemicals, (ii) high atom economy, (iii) no pre-activation of the substrates, and (iv) producing water as the only by-product. In this context, several synthetic strategies have been developed in this regime for the past few decades. To the best of our knowledge, no review article describes the important concepts of interrupted borrowing hydrogen (IBH) reaction. This review article highlights the recent advances in the IBH strategy and its application in sustainable chemical synthesis, particularly C-C bond formation using methanol as a C1 source, synthesis of 3,3'-bisindolylmethanes (3,3'-BIMs), α-branched ketones/diketones, and regioselective alkylation of N-heterocycles.

Microreactor-based micro/nanomaterials: fabrication, advances, and outlook.

Micro/nanomaterials are widely used in optoelectronics, environmental materials, bioimaging, agricultural industries, and drug delivery owing to their marvelous features, such as quantum tunneling, size, surface and boundary, and Coulomb blockade effects. Recently, microreactor technology has opened up broad prospects for green and sustainable chemical synthesis as a powerful tool for process intensification and microscale manipulation. This review focuses on recent progress in the microreactor synthesis of micro/nanomaterials. First, the fabrication and design principles of existing microreactors for producing micro/nanomaterials are summarized and classified. Afterwards, typical examples are shown to demonstrate the fabrication of micro/nanomaterials, including metal nanoparticles, inorganic nonmetallic nanoparticles, organic nanoparticles, Janus particles, and MOFs. Finally, the future research prospects and key issues of microreactor-based micro/nanomaterials are discussed. In short, microreactors provide new ideas and methods for the synthesis of micro/nanomaterials, which have huge potential and inestimable possibilities in large-scale production and scientific research.

Expanding the chemical space of enol silyl ethers: catalytic dicarbofunctionalization enabled by iron catalysis.

Enol silyl ethers are versatile, robust, and readily accessible substrates widely used in chemical synthesis. However, the conventional reactivity of these motifs has been limited to classical two electron (2-e) enolate-type chemistry with electrophilic partners or as radical acceptors in one electron (1-e) reactivity leading, in both cases, to exclusive α-monofunctionalization of carbonyls. Herein we describe a mild, fast, and operationally simple one-step protocol that combines readily available fluoroalkyl halides, silyl enol ethers, and, for the first time, hetero(aryl) Grignard reagents to promote selective dicarbofunctionalization of enol silyl ethers. From a broader perspective, this work expands the synthetic utility of enol silyl ethers and establishes bisphosphine-iron catalysis as enabling technology capable of orchestrating selective C-C bond formations with short-lived α-silyloxy radicals with practical implications towards sustainable chemical synthesis.

Sustainable synthesis of fine chemicals using biocatalysis

Sustainable synthesis of fine chemicals using biocatalysis

Developing electrochemical hydrogenation towards industrial application.

Electrochemical hydrogenation reactions gained significant attention as a sustainable and efficient alternative to conventional thermocatalytic hydrogenations. This tutorial review provides a comprehensive overview of the basic principles, the practical application, and recent advances of electrochemical hydrogenation reactions, with a particular emphasis on the translation of these reactions from lab-scale to industrial applications. Giving an overview on the vast amount of conceivable organic substrates and tested catalysts, we highlight the challenges associated with upscaling electrochemical hydrogenations, such as mass transfer limitations and reactor design. Strategies and techniques for addressing these challenges are discussed, including the development of novel catalysts and the implementation of scalable and innovative cell concepts. We furthermore present an outlook on current challenges, future prospects, and research directions for achieving widespread industrial implementation of electrochemical hydrogenation reactions. This work aims to provide beginners as well as experienced electrochemists with a starting point into the potential future transformation of electrochemical hydrogenations from a laboratory curiosity to a viable technology for sustainable chemical synthesis on an industrial scale.

Photosensitized biohybrid for terminal oxygenation of n-alkane to α, ω-dicarboxylic acids

To date, oxyfunctionalization of saturated hydrocarbons in a selective fashion is a prime challenge in industry. Currently, Inorganic-biohybrid catalysts have shown tremendous potential for sustainable conversion of fine chemicals by integrating light harvesting potential of inorganic materials with metabolic activity of microbes. Herein, we have developed a biohybrid system combining a highly efficient light-harvesting inorganic material MoS2-CNT-Eosin-Y and yeast Candida tropicalis (C.tropicalis) for efficient preparation of α, ω- dicarboxylic acid (α, ω-DCA) using saturated n-alkanes. The yeast C.tropicalis harvests photo generated electrons from the illuminated MoS2-CNT-Eosin-Y and uses them for the activation of the P450 catalytic cycle. This process enables the efficient regeneration of nicotinamide cofactors (NADH/NAD+) facilitating production of α, ω-DCA. Under irradiation condition the biohybrid catalyst shows 4.01 times higher dodecanedioic acid production compared to that of native yeast strain. Analysis of NADH/NAD+ ratio and alcohol dehydrogenases (ADH) activity clearly indicates that light illumination on MoS2-CNT-Eosin-Y/C.tropicalis promotes regeneration of cofactor during cellular metabolism of C. tropicalis thereby improving the activity of ADH enzyme resulting higher production of α, ω-DCA. The present work opens up a new avenue for the sustainable synthesis of fine chemicals through tailoring of complex biohybrid pathways.

Solar Panel Technologies for Light-to-Chemical Conversion.

ConspectusThe sustainable synthesis of fuels and chemicals is key to attaining a carbon-neutral economy. This can be achieved by mimicking the light-harvesting and catalytic processes occurring in plants. Solar fuel production is commonly performed via established approaches, including photovoltaic-electrochemical (PV-EC), photoelectrochemical (PEC), and photocatalytic (PC) systems. A recent shift saw these systems evolve into integrated, compact panels, which suit practical applications through their simplicity, scalability, and ease of operation. This advance has resulted in a suite of apparently similar technologies, including the so-called artificial leaves and PC sheets. In this Account, we compare these different thin film technologies based on their micro- and nanostructure (i.e., layered vs particulate), operation principle (products occurring on the same or different sides of the panel), and product/reaction scope (overall water splitting and CO2 reduction, or organics, biomass, and waste conversion).For this purpose, we give an overview of developments established over the past few years in our laboratory. Two light absorbers are generally required to overcome the thermodynamic challenges of coupling water oxidation to proton or CO2 reduction with good efficiency. Hence, tandem artificial leaves combine a lead halide perovskite photocathode with a BiVO4 photoanode to generate syngas (a mixture of H2 and CO), whereas PC sheets involve metal-ion-doped SrTiO3 and BiVO4 particles for selective formate synthesis from CO2 and water. On the other hand, only a single light absorber is needed for coupling H2 evolution to organics oxidation in the thermodynamically less demanding photoreforming process. This can be performed by immobilized carbon nitride (CNx) in the case of PC sheets or by a single perovskite light absorber in the case of PEC reforming leaves. Such systems can be integrated with a range of inorganic, molecular, and biological catalysts, including metal alloys, molecular cobalt complexes, enzymes, and bacteria, with low overpotentials and high catalytic activities toward selective product formation.This wide reaction scope introduces new challenges toward quantifying and comparing the performance of different systems. To this end, we propose new metrics to evaluate the performance of solar fuel panels based on the areal product rates and commercial product value. We further explore the key opportunities and challenges facing the commercialization of thin film technologies for solar fuels research, including performance losses over larger areas and catalyst/device recyclability. Finally, we identify emerging applications beyond fuels, where such light-driven panels can make a difference, including the waste management, chemical synthesis, and pharmaceutical industries. In the long term, these aspects may facilitate a transition toward a light-driven circular economy.

Direct activation of PMS by highly dispersed amorphous CoOx clusters in anatase TiO2 nanosheets for efficient oxidation of biomass-derived alcohols

Developing a green and cost-effective catalytic system for the selective oxidation of biomass-derived alcohols is vital for the sustainable synthesis of fine chemicals. Herein, highly dispersed subnanometric amorphous CoOx clusters in anatase TiO2 nanosheets (Co-TiO2) fabricated by green solvent CO2-assisted approach could directly activate peroxymonosulfate (PMS) for the highly selective oxidation of various biomass-derived alcohols. Advanced characterizations (e.g., EXAFS, EPR, AC HAADF-STEM) reveal that a strong interaction of CoOx clusters and the anatase TiO2 support exist in Co-TiO2 and Co atom in Co-TiO2 is mainly consisted of Co2+ and Co3+. The Co-TiO2 catalyst offers superior catalytic performance in the conversion of six types of alcohols (e.g., benzyl alcohol (BAL), 5-hydroxymethylfurfural (HMF)) with high selectivity to produce corresponding aldehydes. Highly dispersed CoOx clusters and the interaction between CoOx clusters and TiO2 support contribute to the superior performance. Mechanism studies show that SO4•− radicals play the dominant role in the selective oxidation of model reactant BAL and 1O2 participates in the non-radical pathway. DFT calculations are well matched with experiment and decipher that the strong interaction between CoOx clusters and TiO2 support promotes the formation of SO4•– and SO5•–.

Lost Green Chemistries: History of Forgotten Environmental Trajectories

Green chemistry is a successful new paradigm reshaping the way we think about sustainable chemical synthesis. And yet, its official story, placing the birth of green chemistry in the 1990s within the walls of the Environmental Protection Agency (EPA), is riddled with contradictions and simplifications. Beneath the mainstream narrative, there is another, somewhat forgotten history of numerous attempts to respond to environmental challenges in chemistry with different frameworks and conceptualisations. The frontiers of the concept were far from clear and multiple green chemistries struggled for recognition, both within and beyond the US, with a tremendous amount of theoretical reflection on how to combine sustainability with chemistry conducted in Europe. In Italy, France, and Germany, many scholars anticipated what would become green chemistry in parallel to their American colleagues. And yet, even though the American success story dominated the imaginary of chemists all over the world, these forgotten green-chemistry frameworks developed in the 1990s, be they American or European, present a number of distinct, original features that set them apart. They were not merely imperfect forerunners to a more mature EPA-based concept, but in fact constituted full-fledged alternatives, many of which have a lot to offer to modern practitioners of green chemistry who are unsatisfied with the way the field has evolved. This article tries to recover this forgotten past and to highlight those features that can contribute to contemporary debates on the place of sustainability in chemistry.

Design of fusion enzymes for biocatalytic applications in aqueous and non-aqueous media.

Biocatalytic cascades play a fundamental role in sustainable chemical synthesis. Fusion enzymes are one of the powerful toolboxes to enable the tailored combination of multiple enzymes for efficient cooperative cascades. Especially, this approach offers a substantial potential for the practical application of cofactor-dependent oxidoreductases by forming cofactor self-sufficient cascades. Adequate cofactor recycling while keeping the oxidized/reduced cofactor in a confined microenvironment benefits from the fusion fashion and makes the use of oxidoreductases in harsh non-aqueous media practical. In this mini-review, we have summarized the application of various fusion enzymes in aqueous and non-aqueous media with a focus on the discussion of linker design within oxidoreductases. The design and properties of the reported linkers have been reviewed in detail. Besides, the substrate loadings in these studies have been listed to showcase one of the key limitations (low solubility of hydrophobic substrates) of aqueous biocatalysis when it comes to efficiency and economic feasibility. Therefore, a straightforward strategy of applying non-aqueous media has been briefly discussed while the potential of using the fusion oxidoreductase of interest in organic media was highlighted.

Facile synthesis of Ni/Fe3O4 derived from layered double hydroxides with high performance in the selective hydrogenation of benzaldehyde and furfural

Efficient upgrading of biomass-derived platform chemicals plays a crucial role in the sustainable synthesis of fine chemicals. Herein, the noble-metal free and robust Ni/Fe3O4 catalysts originated from NiFe-layered double hydroxides (LDHs) was efficient for the selective upgrading of benzaldehyde (BzH) and furfural (Fur), accordingly, the highest yield of fine chemical benzyl alcohol (99.0%, BAL) and biofuel 2-methylfuran (78.4%, 2-MF) were obtained under mild conditions over the Ni/Fe ratio of 1, respectively. These performance is far superior to most of preciously reported candidates and their counterpartners. Systematic characterizations further revealed that Ni2+/Fe3+ ratio was closely related to the dispersion and the surface acidity of catalysts, which played crucial roles in achieving excellent catalytic performance. Besides, the solvent effect, reaction parameters and reusability of catalysts in the hydrogenation process of benzaldehyde were then studied as example. Finally, the reaction pathways of benzaldehyde and furfural hydrogenation were rationally proposed. This work provides a promising way to upgrade biomass-derived chemicals.