Hydrothermal carbonization (HTC) is widely regarded as a sustainable route for converting biomass into carbon materials; however, the formation mechanisms of structurally diverse biomass feedstocks remain insufficiently understood. This work systematically investigates HTC reaction pathways of both solid and liquid products using wheat straw (second-generation biomass), wet corn gluten feed (first-generation by-product), and sugars as model systems under varying pH, temperature, and residence time, while directly linking structural evolution of the solids to their electrochemical applicability. A key novelty is the comprehensive, quantitative analysis of liquid filtrates by 1D- and 2D-NMR spectroscopy, enabling access to possible green platform chemicals (levulinic acid, 3-hydroxypyridine, furfurals) as well as considerations regarding toxicology for downstream processing. 3-Hydroxypyridine derivatives form the main N-containing molecular motif in the filtrate, likely formed via Strecker degradation of amino acids with C5-sugar-derived diketones-confirmed through model reactions of C5 and C6 sugars with glycine. Overall, HTC as a pretreatment before pyrolysis increases the carbon content, sp(2)/sp(3) ratio, and bulk conductivity due to increased interparticle connectivity of sugar-derived hydrochar, while reducing alkali contaminants (<0.1 wt%) compared to direct pyrolysis of the biomass. As a proof of concept, selected pyrolyzed carbons are decorated with Pt nanoparticles and exhibit oxygen reduction reaction activity, electrochemical surface area, and kinetic currents approaching those of commercial Pt/C catalysts on a rotating disk electrode, indicating their potential as catalyst supports while highlighting the surface area-conductivity trade-off that limits their applicability.

Direct conversion of methane into value-added chemicals is vital for sustainable development. Achieving this goal requires a fundamental understanding of the role of active catalytic sites and reaction mechanisms to design optimized materials with enhanced performance. In this work, a multi-technique approach was employed to investigate Pd(Ag)-Fe3-δO4 nanocomposite catalysts for the low-temperature partial oxidation of methane. Through a combination of in situ X-ray Absorption Spectroscopy (XAS) and Grazing Incidence X-ray Diffraction (GI-XRD), on-site X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM), Energy-Dispersive X-ray Spectroscopy (EDX), Electron Energy-Loss Spectroscopy (EELS), and X-Ray Emission Spectroscopy (XES), new insights into the electronic and structural evolution of catalyst atoms under reaction conditions are provided. High catalytic activities were achieved at 250 and 300°C (ca. 1.5 and 6 molCH4 kgcat−1 h−1 respectively), along with excellent formaldehyde selectivity (>95%). Lattice contraction induced by iron oxidation and the withdrawal of Pd (and Ag) from interstitial sites, together with Pd complete reduction and agglomeration, were found to accompany catalyst deactivation and loss of catalytic performance under reaction conditions. While silver incorporation has a negligible effect at 300°C, a lower degree of Pd agglomeration is observed for the PdAg-containing catalyst at 250°C, correlating with its higher catalytic activity previously reported under these conditions.

Developing acid-stable, earth-abundant oxygen evolution catalysts remains a central challenge for proton exchange membrane water electrolyzers (PEM-WE), due to catalyst degradation via overoxidation under strongly anodic conditions. Here, we introduce a cation-anion co-doping strategy that induces lattice-level electronic stabilization in manganese dioxide (MnO2) through incorporation of niobium (Nb5+) and fluoride (F-) into a γ/β-MnO2 framework. Structural and spectroscopic analyses, including operando X-ray absorption spectroscopy, show that co-doping stabilizes an electron-enriched Mn environment and suppresses oxidation to unstable high-valence states under OER conditions. This originates from charge redistribution across the Mn-O-Nb framework, enabling controlled Mn3+/Mn4+ dynamics and mitigating overoxidation-driven dissolution. As a result, MnO2-Nb-F catalyst demonstrates an overpotential of 410 mV at 10 mA cm-2 in 0.5 M H2SO4, a Tafel slope of 90 mV dec-1, and reduced charge transfer resistance compared to pristine MnO2. When integrated into a PEM electrolyzer (5 cm2, 60 °C), the catalyst achieves a cell voltage of 1.91 V at 1 A cm-2 and exhibits operational stability for 380 h at 0.4 A cm-2. These results demonstrate that synergistic cation-anion engineering decouples the activity-stability trade-off in MnO2, establishing a viable design strategy for noble-metal-free PEM-WE anodes.

This work introduces a nanostructured copper catalyst supported on biochar derived from spent coffee grounds, designed for the electrochemical depolymerization of lignin in aqueous solutions. Copper nanoparticles were synthesized in situ and subsequently converted via pyrolysis, resulting in copper nanoparticles with a predominantly metallic Cu core and a Cu(I)-enriched surface. Combined XRD, XPS, and STEM analyses revealed copper nanoparticles with a Cu-rich metallic interior and partial surface oxidation to Cu(I). Operando X-ray absorption spectroscopy was employed to probe the Cu(I) surface and assess its stability under the applied potential. Reusability tests demonstrate sustained product selectivity over four catalytic cycles, with only minor structural alterations detected in the fourth run. DFT calculations revealed mixed dispersion and covalent lignin-surface interactions, with arene groups preferentially oriented parallel to the interface at low coverage and perpendicular to the interface at high coverage. This study presents the first nanoscopic copper-based catalyst for lignin depolymerization, providing fundamental insights into the dynamic Cu/Cu2O interface and highlighting its gradual reduction and sustained activity in electrochemical lignin valorization. In contrast to previous studies on bulk Cu electrodes for electrochemical reductive lignin depolymerization, we observe significant surface restructuring of nanoparticles, leading to larger nanostructured copper agglomerates as active electrocatalytic species.

The selective hydrogenation of alkynes to either alkanes or alkenes is an important step in synthetic processes across the entire chemical value chain with a broad range of applications especially for fine chemical and pharmaceutical production. While traditional developments aim at individual catalysts optimized for either one or the other product, catalytic systems capable of adaptively targeting both classes of products with high activity and selectivity could enable flexible production schemes. Here, we show that CO can be used as a molecular trigger to dynamically adjust the selectivity of supported palladium nanoparticles (NPs) in alkyne hydrogenation. In particular, Pd NPs immobilized on an imidazolium-based supported ionic liquid phase (Pd@SILP) hydrogenate a wide range of structurally diverse alkynes, delivering synthetically relevant alkane or Z-alkene products under H2 or H2/CO as feed gas, respectively. Reference experiments, kinetic studies including isotope labeling, and near-ambient-pressure XPS studies reveal that the rapid and robust selectivity switch originates from the reversible adsorption of CO competing with alkene at the Pd surface. In contrast to its notorious reputation as a catalyst poison in hydrogenation, these findings establish CO as an effective molecular trigger for adaptive catalysis, paving the way toward even broader applications for reversible selectivity control.

A rationally designed catalyst based on ruthenium nanoparticles on acidic aluminum phosphate support (Ru@AlPO x ) enables highly selective and tunable hydrogenation of biomass-derived levulinic acid into 4-hydroxypentanoic acid (97%), gamma-valerolactone (97%), 1,4-pentanediol (68%), or 2-butanol (91%) by a simple adjustment of reaction conditions. Characterization techniques including solid-state nuclear magnetic resonance, temperature-programmed experiments, and X-ray spectroscopies show that the precise and reversible control over product selectivity arises from the fine-tuning of the surface acidity of the AlPO x support and the electronic properties of the ruthenium nanoparticles in the catalyst. The developed approach allows flexible production of different valuable products using a single catalyst and reactor, thus opening exciting opportunities for the valorization of levulinic acid as a bio-based platform chemical.

Selective electrochemical reduction of nitrous oxide to dinitrogen is catalyzed using a nickel(II) bipyridine complex. The system evolves from a homogeneous catalysis regime toward a heterogeneous process. Ni(OH)2 nanoparticulate deposits, generated from the catalyst decomposition, are identified in post-electrolysis characterizations, suggesting the role of this phase in catalytic activity.

Abstract The pursuit of green hydrogen production highlights a persistent gap in electrocatalyst research: while academic efforts prioritize cost-efficiency via activity enhancement, industrial viability demands greater emphasis on electrochemical stability. Carbon-based electrocatalysts, particularly those incorporating transition metals, have shown promise in alkaline oxygen evolution (OER) due to their high activity, cost-efficiency, and resource-efficiency. However, these catalysts suffer from insufficient stability under oxidizing conditions compared to pure transition metal catalysts due to erosion of the carbon support resulting from carbon corrosion, among other degradation mechanisms. In this systematic study, the influence of ultra-low amounts (<1 wt %) of iron, cobalt, nickel, and their most common combinations on the stability of a hydrothermally derived, N-doped carbon support and the overall catalyst performance during alkaline OER is systematically explored. By identifying critical stability descriptors and correlating them with synthesis conditions and catalyst properties, primary and secondary corrosion pathways are unraveled. Subsequently, through careful adjustment of carbonization temperature and composition of incorporated transition metals, overall catalyst corrosion can be suppressed immensely. Especially, the inclusion of Ni and Fe is paramount for the formation of stable catalyst materials under laboratory conditions (10 mA/cm2 in 0.1 M KOH), which is surprisingly unconstrained by the degree of graphitization of the carbon support. Mixing this electrochemically stable material with a graphitic carbon powder results in an excellent stability of over 400 h at 100 mA/cm2 in 1 M KOH, implying great potential for the future improvement of carbon-based electrodes under oxidizing conditions toward industrial application.

Equilibrium‐limited endothermic reactions play a crucial role in the transition toward a more sustainable chemical industry, but are typically plagued by the need for high operation temperatures (>500°C). Here, we show that the temperature gradients generated by the selective and localized heating of catalyst materials in a colder reactor environment shift the equilibrium of thermodynamically‐limited endothermic reactions and improve their performance. In particular, the reverse water gas shift reaction and magnetic induction are selected as the model reaction and selective catalyst heating method, respectively. Magnetically induced catalysis using standard Cu–Al spinel‐derived catalyst functionalized with carbon‐coated iron nanoparticles enables high CO yield (up to 62%) at mild catalyst and reactor temperatures (estimated at 300°C and determined as 25–123°C, respectively). We demonstrate that the catalyst temperature and not the reactor temperature governs the equilibrium product composition of the rWGS, and that the temperature gradient promotes the in situ removal of water to shift the gas phase thermodynamic equilibrium. These two points synergistically result in a CO yield that would require a reactor temperature of 650°C in a conventionally heated gas phase reaction.

A new heterogeneous platinum catalyst on the styrene-divinylbenzene resin (Pt/XAD-4) was developed for the hydrosilylation of various functional alkenes (2b-f) and alkynes (2a-j) using high-molecular-weight silsesquioxanes (1a-d) and applied in supercritical CO2 (scCO(2)) as a reaction medium. The obtained Pt/XAD-4 catalyst is competitive to previous Pt heterogeneous systems in these transformations and provides possibilities for effective catalyst reuse. Comparing the processes in scCO(2) to commonly used toluene showed that the catalyst was significantly more active and stable upon application of this green solvent. Extraction of the products with scCO(2) allowed for simple catalyst recycling over up to 40 cycles without visible loss of its activity, providing much higher accumulative total turnover numbers (TTONs) of 2375 vs 739 in toluene. The present work represents the first example of effective reaction and separation of high-molecular-weight silsesquioxyl derivatives in scCO(2), demonstrating the feasibility of synthesizing and isolating high-molecular-weight polyhedral oligomeric silsesquioxane (POSS) derivatives without the necessity of organic solvents.

Transmission electron microscopy (TEM) is a fundamental tool for many research fields like catalysis or material research. Many experiments require measurements under environmental TEM (ETEM) conditions, in which an atmosphere of a selected gas is in the vicinity of the sample, resulting in a higher pressure in the octagon of the microscope. However, the comparably high pressure in the octagon also influences how long volatile organic components (VOCs), which are often part of the sample itself, remain in the sample environment and can result in carbon contamination and undesired reactions during (E)TEM experiments. We have analyzed contamination in an ETEM octagon by investigating the impact of different organic solvents used in the sample synthesis and preparation, but also how tedious the removal of VOCs is once these contaminants are present inside a microscope. With proton-transfer-reaction mass spectrometry, we have quantified the outgassing contamination of samples consisting of THF, toluene or mesitylene depending on their drying time. We found that high amounts of contaminants adsorb on the inner surfaces of the octagon and we measured how well these VOCs desorb when, after removing the sample, pumping the octagon to typical TEM pressures. For persistent solvents or samples that were not sufficiently dried before insertion, contaminant removal is an extensive process that can be accelerated by plasma cleaning. Our investigation of residual solvents suggests that changes in the sample preparation (i.e. solvent choice and drying time ) can improve the contamination effects in both TEM and ETEM experiments.

Transmission electron microscopy (TEM) is a versatile tool for the characterization of (catalytic) materials on the nanoscale. This is very important for understanding the structure-function relationships of the investigated samples. However, TEM experiments can induce significant changes in materials due to the electron-beam irradiation which in turn can lead to misinterpretation of results. Here, we systematically investigate the effect of beam-induced damage on layered double hydroxides (LDHs) and derived materials, focusing on NiCuAl LDHs with different Ni:Cu ratios. Using electron diffractograms, we confirm that all LDH samples exhibit high sensitivity to electron irradiation, resulting in structural modifications, which are not always accompanied by observable morphological changes. Ni-containing LDHs transform into metal oxides, while the CuAl LDH shows more pronounced indications for the formation of metallic species. For the NiCu(4:1)Al LDH after thermal treatment, the results indicate the formation of structural voids in the calcined sample, while the reduced sample shows the partial formation of a spinel structure. Our systematic study reveals that the degree of damage decreases in the order: LDH > LDH-calcined > LDH-reduced sample. Our findings underscore the general importance of considering beam damage and performing systematic experiments to avoid misinterpreting electron microscopy data.

Catalytically active hydroxyapatite (ca-HAp) decorated with zirconia nanoparticles (ZrO2 NPs) is presented as a nanocomposite catalyst (ca-HAp/ZrO2) capable of performing highly efficient nitrogen to ammonia (N2-to-NH3) fixation reactions under mild conditions. Accordingly, reactions were carried out in a batch reactor operating at 120 °C, 6 bar of N2, and 20 mL of water, under UV irradiation (14 W) for 72 h. The yield of NH3 obtained was 1.592 ± 0.146 mmol·gc -1, which represents a N2 fixation efficiency of 6.4%. Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) studies under in situ conditions (i.e., at elevated pressure and temperature and during UV irradiation) and density functional theory simulations (DFT) allowed us to elucidate the catalytic mechanism of the system. The ca-HAp/ZrO2 nanocomposites exhibit a strong synergy arising from the initial photoactivation of N2 by means of the π-backdonation mechanism in ZrO2 (N2 is anchored by four Zr4+ atoms) followed by the dinitrogen spillover toward the Ca-(I)2+ binding sites. Such sites, preferentially exposed in the (001) crystallographic planes of ca-HAp, show high activity due to the enhanced electron transfer properties of ca-HAp. These catalytic nanocomposites represent a viable alternative to the conventional catalysts used for N2-to-NH3 fixation reactions.

The integrated one-pot synthesis of valuable E-chalcones from aryl iodides, phenylacetylenes, CO and H2 is achieved using a single catalyst material. The multifunctional catalytic system is composed of a silica support on which ruthenium nanoparticles and covalently functionalized palladium N-heterocyclic carbene (NHC) complexes are jointly assembled. The resulting Ru@SiO2-[Pd-NHC] catalyst was characterized by a variety of techniques including N2 physisorption, solid-state nuclear magnetic resonance, electron microscopy, and X-ray photoelectron spectroscopy to collect information on its textural, structural, morphological, and electronic properties. Ru@SiO2-[Pd-NHC] was found to be active and selective for the one-pot synthesis of a wide variety of E-chalcones, valuable products with widespread applications in the fine chemical, agrochemical, and pharmaceutical industries. The heterogenized Pd-NHC complex catalyzed the carbonylative Sonogashira coupling step, while CO-covered Ru NPs were found to be responsible for the highly selective hydrogenation of the ynones intermediates to E-chalcones. This study outlines the potential of hybrid multifunctional catalytic systems combining molecular and nanoparticle sites to open up new and more sustainable complex reaction sequences toward valuable compounds.

Metastable, i.e., kinetically favored but thermodynamically not stable, interstitial solid solutions of carbon in iron are well-understood. Carbon can occupy the interstitial atoms of the host metal, altering its properties. Alloying of the host metal results in the stabilization of the FeCx phases, widening its application. Pure nickel finds niche applications, mainly focusing on catalysis, while nickel alloys are widely applied, e.g., in gas turbines, reactors, and seawater piping. Nickel carbide (Ni3C) is the well-known stable Ni-C system displaying a rhombohedral (R3̅c) crystal structure. Some reports describe an elusive cubic Ni-C system, observed during certain catalytic reactions occurring on nickel and formed by the occupation of the interstitials of the metal with carbon: to date, the stabilization and characterization of this phase have not been accomplished. Hereby, we report on the synthesis of a cubic metastable NiCx phase using chemical vapor deposition of methane on supported nickel nanoparticles. The structure was predicted by DFT/ReaxFF, synthesized and monitored with in situ time-resolved synchrotron XRD, and experimentally confirmed by Rietveld refinement and (S)TEM-EELS under ambient conditions. The results show an Fm3̅m phase with a lattice parameter of a = 3.749 ± 0.037 Å at room temperature, with the highest ever reported atomic percentage of carbon occupying the octahedral interstices of 23.1%, resulting in a NiC0.3 phase. The degree of occupation of the interstitial voids by carbon can be controlled, enabling the tuning of the host metal's d-spacing and composition, highlighting the applicability of this synthesis route for catalytic nanoparticle preparation.

As the demand for hydrogen production increases, the economic viability and stability of Ir-based catalysts are crucial in proton exchange membrane water electrolysis (PEMWE). In this study, stable low-loading Ir electrodes (0.2 mg(Ir) cm(-2)) with nanometer-thick electrodeposited layers are prepared on Pt-deposited Ti felts. State-of-the-art techniques, such as operando quick extended X-ray absorption fine structure spectroscopy (QEXAFS) and identical-location transmission electron microscopy (IL-TEM) employing an ultramicroelectrode (UME), were used to demonstrate the structural transformation of surface Ir during oxygen evolution reaction (OER) and the pivotal role of catalyst film thickness control on the self-terminated growth of crystalline IrO2, which enhances catalyst stability. A lack of a stabilizing IrO2 sublayer in thin electrodeposited Ir layers (<10 nm) leads to a fully amorphous catalyst structure, directly impacting its durability. The obtained Ir/IrO2/IrOx electrodes achieve catalytic activities of 1.8-12 A mg(-1) at 1.6 V-Cell while maintaining a degradation rate of 8.7 mu V h(-1) @ 2 A cm(-2) during accelerated stress tests (>1000 h) and 1.6 times greater stability (corresponding to a lifespan of 55,000 h) and 3.6 times higher mass activity compared to commercial Ir oxide electrodes.

The selective hydrodeoxygenation of benzylic esters with molecular hydrogen (H2) provides a synthetic approach to methyl-substituted aromatic compounds used widely as intermediates and products in the chemical and pharmaceutical industries in accordance with green chemistry principles. In particular, it can open novel pathways for the use of biomass-derived substrates or waste plastics as chemical feedstocks. We present here an efficient catalytic approach focusing on the use of earth abundant iron in the form of iron carbide nanoparticles (ICNPs) activated by magnetic induction, allowing the reaction to proceed at pressures of only 3 bar of H2. The activity of the ICNPs responds in real time to on/off switches of the alternating current magnetic field (ACMF, 350 kHz, 70 mT), mimicking the use of intermittent renewable electricity, and the magnetic properties of the ICNPs allow for their easy separation and reuse. The reaction proceeds with higher yield and selectivities at global temperatures more than 130 °C below thermal activation, leading to at least four times higher energy efficiency. The method was successfully applied to a range of synthetic targets and to the selective depolymerization of real polyester (PET) products.

Metal nanoparticles (NPs) immobilized on molecularly modified supports form versatile hybrid materials, offering extensive combinatorial flexibility and synergistic interactions between the organic and inorganic components, making them ideal for applications such as catalysis, and sensing. In catalysis, e.g., NPs‐ionic liquid combinations are shown to enhance activity, selectivity, and recyclability compared to NPs alone systems, though typically used powder‐based supports often hinder a detailed nanoscale structural analysis for an in‐depth understanding due to undefined surfaces. Here, an approach is developed to transfer such a system onto well‐defined surfaces for extended analysis, demonstrated on a model system composed of an imidazolium/NTf₂ ionic liquid and Ru NPs on Si. A comprehensive characterization suite is applied to probe the material properties at the nano‐ and macroscale including spatial arrangement, molecular orientation, surface homogeneity, hydrophilicity, and work function. The efficacy of the utilized approaches in obtaining a homogeneous ionic liquid monolayer decorated with Ru NPs of controlled distribution is demonstrated. It is identified that the particle deposition disturbs the conformational order of the molecular layer. The presented versatile methodological approach can be broadly expanded to multifunctional hybrid materials composed of metal NPs on molecularly modified supports, unlocking numerous possibilities for knowledge‐driven and rational material design.