Néstor Guijarro

Text Finding strategies to maximize the density of catalytically active sites is pivotal to enhancing the electrooxidative depolymerization of lignin. Here, we present a Ni ₃ S ₂ precatalyst grown on nickel foam that, upon electrochemical activation, self-reconstructs into a NiOOH electrocatalyst with a high density of Ni ³⁺ active sites. This proliferation of active sites drastically increases the anodic currents for the oxygen evolution reaction as well as for benzyl alcohol oxidation. Operando Raman spectroscopy confirms the formation of the active NiOOH phase at low operating potential, while depth-profiling analysis reveals that this active phase extends tens of nanometers deep before transitioning to the underlying sulfide core. Electrooxidation of veratrylglycerol-beta-guaiacyl ether, a model dimer bearing a β-O-4 interunit linkage, selectively yields veratric acid and veratraldehyde, confirming the C _α -C _β bond cleavage. Applied to organosolv lignin extracted from pine wood, the electrocatalyst achieves substantial depolymerization, reducing the average molecular weight three-fold and releasing vanillic acid and vanillin as major monomeric products, reaching 22.4 % of the theoretical maximum monomer yield. Overall, this self-reconstructed architecture offers a compelling route for boosting the activity of oxyhydroxide-based electrodes while retaining their intrinsic selectivity.

Lignin valorization remains a roadblock in the development of green biorefineries. Currently, depolymerization strategies predominantly depend on energy- and resource-intensive thermochemical methods, while potential applications of the resulting bio-based products are often overlooked. Here, we show a scalable photocatalytic flow reactor for lignin deconstruction that operates at ambient conditions, along with a downstream process that yields commercially viable products at gram scale. An anthraquinone-based photocatalytic platform, when packed in a flow bed reactor, is demonstrated to selectively and nearly quantitatively cleave lignin’s β-O-4 moieties, achieving a benchmark yield of 7.1 wt% for vanillin. The utilization of residual oligomers as plasticizers for biobased polylactic acid resulted in improved mechanical properties and shape memory effects, while maintaining its suitability for conventional 3D printing. This aldehyde-oriented platform represents a key advancement that complements existing ketone-oriented photocatalytic approaches targeting valuable chemicals from lignin conversion, and it ultimately contributes to the holistic utilization of lignin.

DFT theoretical and experimental insights into transition metal tungstates reveal electronic structure–property relationships controlling photoanode activity, which enable selecting CuWO ₄ and FeWO ₄ as promising electrode materials.

Organic electrosynthesis is gaining momentum, driven by the inherent advantages of using electricity in place of stoichiometric chemical oxidants, such as the improved atom efficacy, the minimization of waste, and the lower cost. However, electrosynthesis methods rely on volatile organic solvents such as acetonitrile to solubilize the reagents, combined with expensive and nonrecyclable electrolytes, which compromise the environmental and economic viability of the approach. Taking the electrosynthesis of 2‐arylsulfonylquinolines as representative case, the aforementioned issues by incorporating a deep eutectic solvent that functions simultaneously as the reaction medium and supporting electrolyte are addressed. The method delivers excellent yields, and products are isolated at gram scale via simple water washing and filtration. Interestingly, the eutectic solvent is recovered and reused for up to five cycles without significant loss in reaction yields. In a more general vein, this strategy not only eliminates volatile organic solvents throughout both the reaction and purification stages, but also integrates a recyclable solvent–electrolyte system, there for enabling a fully sustainable electrosynthetic process.

Organic electrosynthesis is gaining momentum, driven by the inherent advantages of using electricity in place of stoichiometric chemical oxidants, such as the improved atom efficacy, the minimization of waste and the lower cost. However, electrosynthesis methods rely on volatile organic solvents such as acetonitrile to solubilize the reagents, combined with expensive and non-recyclable electrolytes which compromise the environmental and economic viability of the approach. Taking the electrosynthesis of 2-arylsulfinylquinolines as representative case, we addressed the aforementioned issues by incorporating a deep eutectic solvent that functions simultaneously as the reaction medium and supporting electrolyte. The method delivered excellent yields, and products were isolated at gram scale via simple water washing and filtration. Interestingly, the eutectic solvent was recovered and reused for up to five cycles without significant loss in reaction yields. In a more general vein, this strategy affords not only to eliminate volatile organic solvents throughout both the reaction and purification stages, but also to integrate a recyclable solvent-electrolyte system, therefore enabling a fully sustainable electrosynthetic process.

Lignin valorization remains a significant roadblock in the development of green biorefineries. Currently, depolymerization strategies predominantly depend on energy- and resource-intensive thermochemical methods, while potential applications of the resulting bio-based products are often overlooked. Here, we demonstrate a scalable photocatalytic flow reactor for lignin deconstruction that operates at ambient conditions, along with a downstream process that yields commercially viable products at gram scale. An anthraquinone-based photocatalytic platform, when packed in a flow bed reactor, is demonstrated to selectively and nearly quantitatively cleave lignin’s -O-4 moieties, achieving a benchmark yield of 7.1 wt% for vanillin isolation. The utilization of residual oligomers as plasticizers for biobased polylactic acid resulted in improved mechanical properties and shape memory effects, while maintaining its suitability for conventional 3D printing. This aldehyde-oriented platform represents a key advancement that complements existing ketone-oriented photocatalytic approaches targeting valuable chemicals and products from lignin conversion, and it ultimately contributes to the holistic utilization of lignin.

Covalent organic frameworks (COFs) have been developed as photosensitizers for photocatalytic energy conversion over the past decade; however, COF photocatalysts have yet to demonstrate the ability to harvest near-infrared light (above 760 nm, approximately 53% of the solar spectrum) for fuel or chemical conversion. In this work we introduce a post-synthetic functionalization strategy for COFs by incorporating a palladacycle directly into the COF backbone, extending the light absorption of an azobenzene-based COF into the near-infrared region. This approach enables homogeneous, atomically distributed palladium functionalization with a high loading of 12 wt% and without noticeable formation of palladium nanoparticles. The cyclopalladated COF, TpAzo-CPd, was used as a catalyst for photocatalytic hydrogen peroxide production under 810 nm illumination. This study demonstrates the use of COFs for near-infrared photocatalysis and opens the door to palladium-single-site COF catalysts for a wide range of chemical transformations.

The efficient transformation of biomass into high-value chemicals remains a significant challenge, with surface ligand manipulation offering a promising approach to enhance catalytic performance. In this study, we investigate the role of organic ligands in the photocatalytic conversion of lignin into functionalized aromatics using cadmium sulfide (CdS) quantum dots (QDs). By tuning the hydrophilicity/hydrophobicity of ligands, we successfully form stable QD colloidal solutions, ensuring effective contact between the QDs and lignin. We determined that thiyl ligands triggered the photocatalytic conversion of lignin models. These ligand modifications, including the anchor group and alkyl chain length, are shown to play a critical role in facilitating electron transfer during photocatalysis. Furthermore, it was discovered that the mechanism of C-C and C-O bond cleavage at the β-O-4 linkages can be influenced by the substituents on the aromatic rings of lignin, a finding that has not been previously reported. Our findings not only advance the understanding of ligand-controlled catalysis but also present a new pathway for efficient lignin biomass valorization and organic transformation processes using QD-based photocatalysts.

The use of lignin as a renewable feedstock for valuable chemicals has gained significant momentum due to the ongoing depletion of fossil fuel reserves and the environmental harm caused by their overuse. However, extracting useful products from this recalcitrant biopolymer requires a highly selective fragmentation process. This article demonstrates that such a process can be effectively achieved through an electrochemical approach. While Ni- and Co-based catalysts have been previously employed for lignin electrooxidation, the optimal composition of mixed metal oxyhydroxides—crucial for achieving higher yields and faradaic efficiencies—has not been thoroughly investigated until now. This optimization was made possible by a comprehensive study beginning with lignin model compounds, which elucidated the reaction mechanism and facilitated the subsequent scaling of the reaction using organosolv pine lignin. Remarkably, this approach yielded up to 6.0 wt% vanillic acid. These unprecedented results were achieved through the meticulous design of an electrochemical flow cell, ensuring that the electrochemical production of lignin monomers is not only cost-effective and selective but also easily scalable.