ZUSAMMENFASSUNG Auf Misch‐Metalloxiden basierende Hybrid‐Materialien liefern durch einen redox‐induzierten Grenzflächeneffekt eine effektive Strategie, um die katalytische Performance zu steigern. In dieser Arbeit wird ein effizienter Katalysator zur N 2 O‐Zersetzung vorgestellt, der auf Co 3 O 4 ‐Spinell geträgerte RhO x ‐ und CeO x ‐Spezies besteht. Die Aktivitätssteigerung zu reinem Co 3 O 4 basiert nicht ausschließlich auf RhO x /Co 3 O 4 ‐ und CeO x /Co 3 O 4 ‐Grenzflächen, sondern auch vor allem auf einer einzigartigen Modulation des Co‐ und Rh‐Oxidationszustandes an einer synergierenden Rh‐O‐Co‐O‐Ce‐Grenzfläche. Dieses Zusammenspiel liefert eine gesteigerte Redox‐Flexibilität und vereinfacht die Aktivierung der Gittersauerstoffe, welches in einer eindeutigen Steigerung der N 2 O‐Zersetzungsaktivität resultiert. Kinetische Analysen und operando ‐anregungsmodulierte Röntgenabsorptionsspektroskopie (ME‐XAS) liefern direkte reaktionsmechanistische Beweise für den Ablauf der N 2 O‐Zersetzung über einen multi‐positionellen, kooperativen Mars‐van‐Krevelen‐Mechanismus. Darin agiert Co 3 O 4 ‐CeO 2 als Sauerstoffreservoir, welches den Redox‐Zyklus der RhO x ‐Species ermöglicht. Diese Studie beleuchtet die Fähigkeit der Misch‐Metalloxid‐Katalysatoren Grenzflächeneffekte auszunutzen, um eine Aktivitätssteigerung in Redox‐Reaktionen zu erwirken. Ebenfalls liefert sie eine Motivation zur Optimierung von Metalloxid‐Metalloxid‐Katalysatoren durch operando ‐Spektroskopie.

Time-resolved, high-energy X-ray total scattering measurements, allied to time-resolved Pt L3-edge X-ray absorption spectroscopy, show that the ambient temperature oxidation of CO to CO2 over a commercial Pt/Al2O3 catalyst when conducted in a redox cycling manner is highly correlated to the presence of reactive (toward CO) and extended platinum surface oxides after the oxidizing part of the cycle. This part of the cycle is barely affected by preliminary in situ reduction in H2 to 573 K. The reducing part of the cycle, wherein the sample is initially covered in molecular CO, is characterized by very different kinetics, which is significantly modified by preliminary in situ reduction, yet the same intermediate visible by infrared spectroscopy appears in both sides of the redox cycle. The steady-state production of CO2, investigated using diffuse reflectance infrared spectroscopy and mass spectrometry for 4 <= O2/CO <= 333 and 298 <= T <= 323 K, while comprising only ca. 1% of the post light-off activity of this Pt catalyst (O2/CO = 4), is maintained at O2/CO = 4 even though the infrared spectroscopy shows that the Pt particles are covered with molecular CO as of O2/CO = 20. From the combination of methods used in both transient and steady-state cases, it appears that the Pt nanoparticles behave in a different way to single-crystal surfaces with respect to their response to CO adsorption in comparable pressure regimes, and compression structures are not formed. Instead, increasing fractions of CO are suggested to induce the rearrangement of the nanoparticles to yield vicinal surfaces from exposed (100) facets that are less reactive toward CO oxidation, while Pt (111) facets, which are indicated to support the adsorption of CO, remain intact and capable of turning over CO to CO2 at ambient temperature. From the sum of these investigations, we suggest possible explanations for this chemistry.

Hybrid materials based upon mixed metal oxides provide an effective strategy to boost catalytic performance through redox-induced interfacial engineering. Herein, we present an efficient catalyst toward N2O decomposition containing short-range ordered RhOx and CeOx species anchored to the Co3O4 spinel. The activity enhancement relative to Co3O4 is non-additive with respect to the RhOx/Co3O4 and CeOx/Co3O4 interfaces and is uniquely linked to the modulation of the Co and Rh oxidation states at a synergistic Rh-O-Co-O-Ce interface. This ensemble provides increased redox flexibility and facilitated lattice oxygen activation, resulting in markedly enhanced N2O decomposition. Kinetic analysis and operando modulated excitation x-ray absorption spectroscopy (ME-XAS) provide direct mechanistic evidence that N2O decomposition proceeds via a multi-site, cooperative Mars-van Krevelen pathway, in which Co3O4-CeO2 acts as an oxygen reservoir enabling the redox cycling of RhOx species. This study highlights the ability of mixed metal oxide catalysts to exploit interfacial effects to achieve improved activity in redox-mediated reactions and offers a rationale for the engineering of metal oxide-metal oxide catalysts guided by operando spectroscopy.

Iron-exchanged zeolites are promising materials for mitigating N2O emissions and selectively transforming CH4 into CH3OH. The complex iron speciation in these materials, ranging from isolated centers to nanoparticles, still prevents thorough assessments of the active site structures. Here, we present a site-specific kinetic analysis of N2O activation over Fe-SSZ-13 in inert conditions and in the presence of reducing agents, including CH4, NH3, and H-2. Operando electron paramagnetic resonance measurements with phase-sensitive detection proved essential for distinguishing active sites from spectator species. To capture fast kinetics, a novel step-scan methodology is introduced that improves the temporal resolution of EPR by an order of magnitude. We found that isolated Fe2+ species in axial coordination contribute solely to N2O decomposition in an Ar atmosphere, while FexOy clusters and Fe2+ centers in distorted geometries exhibit redox activity in the presence of reducing agents. Quantitative kinetic analysis reveals that, in Ar or in the presence of CH4 or H-2, the reduction half-cycle is rate-limiting, whereas with NH3, the oxidation half-cycle becomes rate-limiting.

Ce-Ti-based catalysts exhibit high efficiency toward low- and medium-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) owing to the redox flexibility of the Ce3+/Ce4+ pair. However, the intrinsic redox mechanism governing catalytic activity remains insufficiently understood. In this study, dynamic conditions were created to induce NH3 inhibition and N-2 conversion inflection (N-2 eruption) phenomena, providing deeper insights into the reaction mechanism of NH3-SCR over Ce/TiO2. Operando diffuse reflectance visible (DR-vis) spectroscopy revealed dynamic and reversible changes in the Ce oxidation state under alternating NO + O-2 and NH3 atmospheres, directly reflecting the participation of the Ce3+/Ce4+ pair in the reaction. Transient experiments further demonstrate that the re-oxidation of Ce3+ to Ce4+ is closely correlated with the formation of the reactive surface, whereas the reduction of Ce4+ is closely correlated with the release of N-2 and H2O. These findings highlight the key role of Ce3+ re-oxidation as the rate-determining step in efficient NOx reduction, offering mechanistic insight and guidance for the rational design of next-generation Ce-based catalysts for deNO(x) processes.

The reducibility of Ru-based catalysts plays a central role in defining their activity in hydrogenation, yet their behavior during reduction remains elusive, especially for oxidic precursors. Here, we unveil how oxide-derived ruthenium phases can rival, and even surpass, metallic Ru in hydrogenation catalysis. Using a combination of H-2-temperature-programmed reduction (H-2-TPR), synchrotron X-ray total scattering, and Ru K-edge X-ray absorption spectroscopy, we track the reduction dynamics of unsupported and Al2O3-supported RuO2 catalysts synthesized via deposition-precipitation. Chemometric analysis (PCA/MCR) reveals a two-step reduction pathway via a Ru2O3 intermediate, modulated by the structural disorder and hydration of the initial RuOx(OH)(y) phase. Unexpectedly, the amorphous and hydrated oxidic phase in the unsupported system exhibits good hydrogenation performance at a mild temperature (50 degrees C), outperforming its crystalline and reduced counterparts. These findings challenge the conventional view that metallic Ru is the sole active species and suggest that structural disorder, hydration, and redox flexibility can offer alternative routes to efficient supported catalysis. Our integrated approach redefines the design rules for Ru-based hydrogenation catalysts, emphasizing the hidden potential of unconventional oxidic precursors.

Valorizing blast furnace slag (BFS) into high-performance environmental catalysts offers a sustainable "waste-to-treat-waste" pathway, yet understanding the active site dynamics on these complex low-silica Cu-based zeolites remains challenging. Here, we successfully upcycled BFS into Cu-exchanged zeolite X, where optimizing the Cu/Al ratio to 0.28 avoided framework collapse and achieved superior low-temperature selective catalytic reduction using ammonia (NH3-SCR) activity (>93% NO conversion at 150 degrees C), with the N-2 selectivity exceeding 90%. By exploring phase-resolved modulation excitation (ME) DRIFTS coupled with operando MS, we decoupled the reaction network, revealing a mechanism distinct from NH3 activation that preferentially occurs on Cu2+-OH sites below 200 degrees C, but shifts to isolated Cu2+ sites above this threshold. Crucially, transient spectroscopy confirmed NH3NOx and NH2NO as the governing intermediates driving the reduction and oxidation half-cycles. These findings provide the evolution laws of reduction half-cycle (RHC) and oxidation half-cycle (OHC) reactions at high and low temperatures for slag-derived zeolites, establishing a robust mechanistic basis for scaling up cost-effective, waste-derived catalysts for NOx abatement.

The reaction mechanism of the selective catalytic reduction of nitric oxide (NO) using NH3 (NH3-SCR) over Cr-exchanged beta zeolite (Cr-beta) was investigated. In situ Raman spectroscopy showed a consumption of [Cr(O)(2)](+) species in the reduction-half cycle at 300 degrees C (RHC, 0.1 vol % NH3 + 0.1 vol % NO). In the subsequent oxidation-half cycle (OHC, 10 vol % O-2, 300 degrees C), [Cr(O)(OH)(2)](+) species was generated whose fraction halved under SCR conditions (0.1 vol % NO + 0.1 vol % NH3 + 10 vol % O-2, 300 degrees C). Modulated-excitation X-ray absorption spectroscopy (ME-XAS) measurements provided the X-ray absorption near edge structure (XANES) spectra of kinetically distinct species and their relative concentrations, revealing that the OHC is faster than the RHC. Transition state and vibrational analyses based on density functional theory (DFT) calculations support the experimental findings that the isolated Cr species serve as the main catalytic centers for NH3-SCR by Cr-beta.

Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is becoming a widely-used technique in electrocatalysis thanks to its ability to track surface species during electrochemical reactions, providing valuable insights into the dynamic behavior of reaction intermediates. Here, a new design of a spectroelectrochemical ATR-SEIRAS flow cell is presented, offering a thin (approximate to 300 mu m) electrolyte layer at the working electrode side to enhance mass transport (e.g., bubble detachment), coupled with a gas chromatograph, mass spectrometer, and a custom-made liquid distribution system for real-time analysis of gaseous and liquid reaction products. To test this setup, we studied the electrochemical CO2 reduction reaction (CO2RR) on carbon-supported palladium nanoparticles by performing linear sweep voltammograms in CO2-saturated 0.1 M KHCO3. Thereby, we were able to monitor the formation and oxidative stripping of surface-adsorbed CO. Additionally, when performing potential holds in a range favorable for formate production (from -100 to -400 mV vs. the reversible hydrogen electrode), the progressive formation of this CO adsorption layer was found to correlate with the concomitant decrease in formate activity over time. Results emphasize the importance of combining time-resolved monitoring of the formation and depletion of surface intermediates with quantification of reaction products to gain a better understanding of catalytic mechanisms.

The removal of nitrous oxide (N2O) from industrial flue gases remains a significant environmental challenge due to the intrinsic kinetic stability of the N2O molecule. Among available abatement technologies, the direct catalytic decomposition of N2O into harmless N2 and O2 (deN2O) represents a promising, reagent-free solution. In this study, we systematically screened a series of catalysts obtained from Co3O4 by addition of transition elements, magnesium and aluminum (10wt%), and analog series with addition of rhodium (Rh; 1wt%), from which Co-Al-Rh emerged as the most active catalyst formulation. Characterization by H2-TPR and XPS indicated improvement in the redox performance and increasing weakening of the Co-O bond upon addition of a second element and of Rh. The addition of Rh resulted also in a significant enhancement in catalytic activity. Complementary kinetic studies revealed a shift in the rate-determining step (RDS) between N-O bond cleavage and O2 desorption, depending on catalyst composition. These results highlight the critical role of Co-O bond weakening in facilitating oxygen mobility and promoting activity.

ABSTRACT Hybrid materials based upon mixed metal oxides provide an effective strategy to boost catalytic performance through redox‐induced interfacial engineering. Herein, we present an efficient catalyst toward N 2 O decomposition containing short‐range ordered RhO x and CeO x species anchored to the Co 3 O 4 spinel. The activity enhancement relative to Co 3 O 4 is non‐additive with respect to the RhO x /Co 3 O 4 and CeO x /Co 3 O 4 interfaces and is uniquely linked to the modulation of the Co and Rh oxidation states at a synergistic Rh–O–Co–O–Ce interface. This ensemble provides increased redox flexibility and facilitated lattice oxygen activation, resulting in markedly enhanced N 2 O decomposition. Kinetic analysis and operando modulated excitation x‐ray absorption spectroscopy (ME‐XAS) provide direct mechanistic evidence that N 2 O decomposition proceeds via a multi‐site, cooperative Mars‐van Krevelen pathway, in which Co 3 O 4 –CeO 2 acts as an oxygen reservoir enabling the redox cycling of RhO x species. This study highlights the ability of mixed metal oxide catalysts to exploit interfacial effects to achieve improved activity in redox‐mediated reactions and offers a rationale for the engineering of metal oxide–metal oxide catalysts guided by operando spectroscopy.

The structure and nature of active sites are key aspects in determining the product selectivity of heterogeneously catalyzed reactions. In this work, we reveal that among a variety of hydrocarbon species formed within the pores of ZSM-5 by an olefin pretreatment, only a small fraction is accessible and catalytically active in the methanol-to-olefin (MTO) reaction. Pretreatment of ZSM-5 with C6-C7 olefins in a temperature program generated adsorbed aliphatic oligomers as well as acyclic and cyclic allylic carbenium ions, except for benzenium ions. Despite a different hydrocarbon pool composition, the pristine and olefin-pretreated ZSM-5 exhibited an almost identical product selectivity, which we ascribe to two causes: (i) Oligomers that could actively shifting the product selectivity toward higher hydrocarbons are instead converted to allylic carbenium ions by reaction with methanol. This is the origin of polymethylbenzenium ions and other allylic ions. (ii) Most of the deposited hydrocarbon species are a priori not catalytically active. Deuterium exchange experiments demonstrated that only ca. 10% of the adsorbed oligomers and ca. 35% of the cyclopentenyl cations are accessible to methanol and catalytically active. The catalytic function of adsorbed hydrocarbons is therefore closely related to their accessibility and the local reaction environment within the zeolite.

Catalyst reduction is a key step in heterogeneously catalysed liquid-phase reactions for fine chemicals production and biomass upgrade. However, the liquid-phase reduction of supported PdO remains poorly understood at the molecular level, despite its widespread use in synthetic protocols. Here, we investigate the reduction of PdO/Al2O3, containing PdO nanoparticles with a diameter of ca. 2 nm, using two widely employed aqueous reducing agents: sodium formate (HCOONa) and sodium borohydride (NaBH4). The formation of hydrides from the initial PdO phase was monitored in situ by X-ray total scattering and X-ray absorption spectroscopy. Phase fractions and dynamic structural features were evaluated using principal component analysis and multivariate curve resolution, Rietveld refinement, pair distribution function analysis and multiphase extended X-ray absorption fine structure analysis. The two reducing agents promote distinct reduction pathways: HCOONa induces the rapid and concurrent formation of Pd and PdHx, whereas NaBH4 promotes the development of metallic Pd prior to hydride formation. The final hydride phase exhibits a different degree of lattice expansion with respect to metallic Pd. The lattice expansion observed for the hydride formed with HCOONa is larger, pointing to more effective hydrogen intercalation. These insights provide a molecular-level understanding of how reductants shape structural reorganization in supported Pd catalysts, with implications for optimizing hydrogenation performance.

In Nature Catalysis, Barth et al. elucidate how the Cu-site structure in Cu-SSZ-13 governs hydrogen cyanide (HCN) emissions during the selective catalytic reduction of nitric oxides with ammonia. They demonstrate that although Z2Cu sites cause high HCN release, ZCuOH species efficiently catalyze HCN decomposition, providing a design strategy for minimizing emissions.

Fe-MOF-74 with Fe in oxidation state +2 was prepared at ambient conditions by following synthesis with IR and XRD.

The redox properties of oxides are critical in catalysis and can be modified at the interface between oxides and metals; as a consequence, working catalysts can be reconstructed. Herein, the influence of metal-support interactions on the interface between Pt and Co3O4 was disclosed during the batch ammonia borane decomposition. Co3O4 with and without decorating Pt were compared, and tested against Pt on a non-reducible oxide (PtAl2O3). The kinetic profiles were analysed using kinetic models, and both fresh and used samples were characterised using XRD, XPS, XAS, HR-TEM, CO adsorption by IR, and in situ ATR-IR. The combined study revealed an enhanced reaction rate for PtCo3O4 and its reconstruction under reaction conditions due to metalsupport interaction, and disclosed the nature of the stable active sites formed under reaction conditions. Indeed, during the reaction, metallic Pt re-distributed, and the H-spillover to the support reduced the surface of Co3O4, leading to Pt clusters on Co(II)-enriched Co3O4. Atomic-scale insights on the surface redox properties of the catalysts were then obtained through DFT, and the modification of PtCo3O4 was attributed to the facile reduction of octahedral Co(III) ions at the metal/oxide interface, and rationalised as a consequence of charge transfer from Pt to Co3O4.