Operando spatially and time-resolved X-ray absorption spectroscopy and infrared thermography during oscillatory CO oxidation

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano-Islands

CeO2-supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2-Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Pt nanoparticles under oxidizing conditions - implications of particle size, adsorption sites and oxygen coverage on stability

Platinum nanoparticles are efficient catalysts for different reactions, such as oxidation of carbon and nitrogen monoxides. Adsorption and interaction of oxygen with the nanoparticle surface, taking place under reaction conditions, determine not only the catalytic efficiency but also the stability of the nanoparticles against oxidation. In this study, platinum nanoparticles in oxygen environment are investigated by systematic screening of initial nanoparticle-oxygen configurations and employing density functional theory and a thermodynamics-based approach. The structures formed at low oxygen coverages are described by adsorption of atomic oxygen on the nanoparticles whereas at high coverages oxide-like species are formed. The relative stability of adsorption configurations at different oxygen coverages, including the phase of fully oxidized nanoparticles, is investigated by constructing p-T phase diagrams for the studied systems.

Modeling surface spin polarization on ceria-supported Pt nanoparticles

In this work, we employ density functional theory simulations to investigate possible spin polarization of CeO₂-(111) surface and its impact on the interactions between a ceria support and Pt nanoparticles. With a Gaussian type orbital basis, our simulations suggest that the CeO₂-(111) surface exhibits a robust surface spin polarization due to the internal charge transfer between atomic Ce and O layers. In turn, it can lower the surface oxygen vacancy formation energy and enhance the oxide reducibility. We show that the inclusion of spin polarization can significantly reduce the major activation barrier in the proposed reaction pathway of CO oxidation on ceria-supported Pt nanoparticles. For metal-support interactions, surface spin polarization enhances the bonding between Pt nanoparticles and ceria surface oxygen, while CO adsorption on Pt nanoparticles weakens the interfacial interaction regardless of spin polarization. However, the stable surface spin polarization can only be found in the simulations based on the Gaussian type orbital basis. Given the potential importance in the design of future high-performance catalysts, our present study suggests a pressing need to examine the surface ferromagnetism of transition metal oxides in both experiment and theory.

Stationary stripe patterns and chemical waves on the bimetallic Rh(110)/Ni surface during the H2 + O2 reaction

Chemical wave patterns that develop in the O₂ + H₂ reaction on a bimetallic Rh(110)/Ni surface have been studied with photoelectron emission microscopy (PEEM) in the 10^-6 to 10^-4 mbar range. The bifurcation diagram for Ni coverages up to 3 monolayers (ML) was mapped out for T = 770 K. Stationary concentration patterns of macroscopic stripes as well as target patterns and irregular chemical waves were observed.

Grain-growth mediated hydrogen sorption kinetics and compensation effect in single Pd nanoparticles

Grains constitute the building blocks of polycrystalline materials and their boundaries determine bulk physical properties like electrical conductivity, diffusivity and ductility. However, the structure and evolution of grains in nanostructured materials and the role of grain boundaries in reaction or phase transformation kinetics are poorly understood, despite likely importance in catalysis, batteries and hydrogen energy technology applications. Here we report an investigation of the kinetics of (de)hydriding phase transformations in individual Pd nanoparticles. We find dramatic evolution of single particle grain morphology upon cyclic exposure to hydrogen, which we identify as the reason for the observed rapidly slowing sorption kinetics, and as the origin of the observed kinetic compensation effect. These results shed light on the impact of grain growth on kinetic processes occurring inside nanoparticles, and provide mechanistic insight in the observed kinetic compensation effect.

Grains are the building blocks of crystalline solids. Here the authors show how hydrogen-sorption induced grain-growth in Pd nanoparticles slows down the hydrogen sorption kinetics and constitutes the physical origin of corresponding kinetic compensation.

Catalytic CO Oxidation and H2O2 Direct Synthesis over Pd and Pt-Impregnated Titania Nanotubes

Titania nanotubes (TNTs) impregnated with Pd and Pt nanoparticles are evaluated as heterogeneous catalysts in different conditions in two reactions: catalytic CO oxidation (gas phase, up to 500 °C) and H2O2 direct synthesis (liquid phase, 30 °C). The TNTs are obtained via oxidation of titanium metal and the intermediate layer-type sodium titanate Na2Ti3O7. Thereafter, the titanate layers are exfoliated and show self-rolling to TNTs, which, finally, are impregnated with Pd or Pt nanoparticles at room temperature by using Pd(ac)2 and Pt(ac)2. The resulting crystalline Pd/TNTs and Pt/TNTs are realized with different lengths (long TNTs: 2.0–2.5 µm, short TNTs: 0.23–0.27 µm) and a specific surface area up to 390 m2/g. The deposited Pd and Pt particles are 2–5 nm in diameter. The TNT-derived catalysts show good thermal (up to 500 °C) and chemical stability (in liquid-phase and gas-phase reactions). The catalytic evaluation results in a low CO oxidation light-out temperature of 150 °C for Pt/TNTs (1 wt-%) and promising H2O2 generation with a productivity of 3240 molH2O2 kgPd−1 h−1 (Pd/TNTs, 5 wt-%, 30 °C). Despite their smaller surface area, long TNTs outperform short TNTs with regard to both CO oxidation and H2O2 formation.

Insights into the Structural Dynamics of Pt/CeO2 Single-Site Catalysts during CO Oxidation

Despite their high atomic dispersion, single site catalysts with Pt supported on CeO2 were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO2 single site catalyst under more complex gas mixtures, including CO, C3H6 and CO/C3H6 oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt4+ to Pt2+ due to the increase of temperature, CO adsorbs and reduces Pt2+ to Ptδ+ and assists its migration with final formation of PtxΔ+ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria.

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment.

Shedding Light on CO Oxidation Surface Chemistry on Single Pt Catalyst Nanoparticles Inside a Nanofluidic Model Pore

Investigating a catalyst under relevant application conditions is experimentally challenging and parameters like reaction conditions in terms of temperature, pressure, and reactant mixing ratios, as well as catalyst design, may significantly impact the obtained experimental results. For Pt catalysts widely used for the oxidation of carbon monoxide, there is keen debate on the oxidation state of the surface at high temperatures and at/above atmospheric pressure, as well as on the most active surface state under these conditions. Here, we employ a nanoreactor in combination with single-particle plasmonic nanospectroscopy to investigate individual Pt catalyst nanoparticles localized inside a nanofluidic model pore during carbon monoxide oxidation at 2 bar in the 450-550 K temperature range. As a main finding, we demonstrate that our single-particle measurements effectively resolve a kinetic phase transition during the reaction and that each individual particle has a unique response. Based on spatially resolved measurements, we furthermore observe how reactant concentration gradients formed due to conversion inside the model pore give rise to position-dependent kinetic phase transitions of the individual particles. Finally, employing extensive electrodynamics simulations, we unravel the surface chemistry of the individual Pt nanoparticles as a function of reactant composition and find strongly temperature-dependent Pt-oxide formation and oxygen spillover to the SiO2 support as the main processes. These results therefore support the existence of a Pt surface oxide in the regime of high catalyst activity and demonstrate the possibility to use plasmonic nanospectroscopy in combination with nanofluidics as a tool for in situ studies of individual catalyst particles.

Versatile and high temperature spectroscopic cell for operando fluorescence and transmission x-ray absorption spectroscopic studies of heterogeneous catalysts

A modular high-temperature cell consisting of a plug-flow microreactor with a fixed catalyst bed and long heating zone has been established for operando x-ray absorption/fluorescence spectroscopic and diffraction studies. The functionality of the cell is demonstrated for two important areas: emission control using 2 wt. % Pd/Al₂O₃ acting as a three-way catalyst and direct conversion of methane to olefins and aromatics on a 0.5% Fe/SiO₂ catalyst. The performance has been determined by online infrared spectroscopy and mass spectrometry, respectively. In addition, the cell can be combined with optical spectroscopy, such as Raman spectroscopy. The catalyst, present as powdered/sieved samples, can be measured under reaction conditions at temperatures of up to 1050 °C. Another key aspect is a long isothermal heating zone with a small temperature gradient (<3 °C/mm at 1000 °C without reaction) including an inert zone for pre-heating of the reactant gas. Due to the small size of the microreactor and the heating system including a water cooling system, heating/cooling rates of up to 100 °C/min can be achieved. Moreover, due to the compact design and the autonomous control system, the high temperature operando setup fits to the space at the majority of synchrotron beamlines. In many cases, the concentration of the element of interest in the catalysts is low requiring x-ray absorption spectroscopy measurements in the fluorescence measurement mode. Hence, the microreactor was designed to fit such needs as well. More specifically, the case of Fe-containing catalysts was particularly considered by using iron-free materials for the reactor housing.

Self-Regeneration Process of Ni-Cu Alloy Catalysts during a Three-Way Catalytic Reaction-An Operando Study

It is important to understand the reduction processes of mixed metal oxides or metal oxide interfaces in three-way catalytic reactions toward replacing the currently used high-cost Pt group metal catalysts. The redox behavior of simple Ni-Cu alloy catalysts, which exhibit high catalytic activity and durability during a three-way catalytic reaction, was studied by operando X-ray absorption spectroscopy (XAS). The operando XAS analyses revealed that Ni-Cu species changed from the NiO-Cu₂O to Ni-Cu alloy and vice versa under reductive and oxidative conditions, respectively. The real-time monitoring of the oxidation states of Ni and Cu species indicated that the Cu species assisted the reduction of Ni species, in agreement with the density functional theory-based study of NiO reduction by carbon monoxide in the presence of metallic Cu nanoparticles.

Copper catalysis at operando conditions-bridging the gap between single nanoparticle probing and catalyst-bed-averaging

In catalysis, nanoparticles enable chemical transformations and their structural and chemical fingerprints control activity. To develop understanding of such fingerprints, methods studying catalysts at realistic conditions have proven instrumental. Normally, these methods either probe the catalyst bed with low spatial resolution, thereby averaging out single particle characteristics, or probe an extremely small fraction only, thereby effectively ignoring most of the catalyst. Here, we bridge the gap between these two extremes by introducing highly multiplexed single particle plasmonic nanoimaging of model catalyst beds comprising 1000 nanoparticles, which are integrated in a nanoreactor platform that enables online mass spectroscopy activity measurements. Using the example of CO oxidation over Cu, we reveal how highly local spatial variations in catalyst state dynamics are responsible for contradicting information about catalyst active phase found in the literature, and identify that both surface and bulk oxidation state of a Cu nanoparticle catalyst dynamically mediate its activity.

Operando detection of single nanoparticle activity dynamics inside a model pore catalyst material

Nanoconfinement in porous catalysts may induce reactant concentration gradients inside the pores due to local conversion. This leads to inefficient active material use since parts of the catalyst may be trapped in an inactive state. Experimentally, these effects remain unstudied due to material complexity and required high spatial resolution. Here, we have nanofabricated quasi-two-dimensional mimics of porous catalysts, which combine the traits of nanofluidics with single particle plasmonics and online mass spectrometry readout. Enabled by single particle resolution at operando conditions during CO oxidation over a Cu model catalyst, we directly visualize reactant concentration gradient formation due to conversion on single Cu nanoparticles inside the "model pore" and how it dynamically controls oxidation state-and, thus, activity-of particles downstream. Our results provide a general framework for single particle catalysis in the gas phase and highlight the importance of single particle approaches for the understanding of complex catalyst materials.

Infrared Thermography as a Powerful, Versatile, and Elegant Research Tool in Chemistry: Principles and Application to Catalysis and Adsorption

In this Review, diverse chemical problems that have been approached by means of infrared thermography (IRT) are covered in depth. Moreover, some novel steps forward in this field are made, described and discussed. Namely, the latest-generation IRT performance capabilities are harnessed in full; the initial phase of catalytic CO oxidation (called "fast ignition") is presented at the 0.01 s temporal resolution; at the same resolution, the thermal manifestation of the adsorption-desorption wave propagation after the gaseous reactant pulsed (0.6 s) wetting is exhibited. Furthermore, a radical difference in the thermal behavior of differently calcined γ-Al₂ O₃ supported Au catalysts, which underwent successive H₂ O and CO attacks, is demonstrated, and the generally accepted fact that the catalyst temperature reflects the catalytic activity is validated experimentally. It is shown that latest-generation IRT may serve as unique and highly informative research tool in chemistry.

Versatile Homebuilt Gas Feed and Analysis System for Operando TEM of Catalysts at Work

Understanding how catalysts work during chemical reactions is crucial when developing efficient catalytic materials. The dynamic processes involved are extremely sensitive to changes in pressure, gas environment and temperature. Hence, there is a need for spatially resolved operando techniques to investigate catalysts under working conditions and over time. The use of dedicated operando techniques with added detection of catalytic conversion presents a unique opportunity to study the mechanisms underlying the catalytic reactions systematically. Herein, we report on the detailed setup and technical capabilities of a modular, homebuilt gas feed system directly coupled to a quadrupole mass spectrometer, which allows for operando transmission electron microscopy (TEM) studies of heterogeneous catalysts. The setup is compatible with conventional, commercially available gas cell TEM holders, making it widely accessible and reproducible by the community. In addition, the operando functionality of the setup was tested using CO oxidation over Pt nanoparticles.

Exploiting the dynamic properties of Pt on ceria for low-temperature CO oxidation

Low-temperature redispersion leads to an intermediate Pt monolayer arrangement, very active for CO oxidation.

Mechanistic insights into the selective oxidation of 5-(hydroxymethyl)furfural over silver-based catalysts

Silver-catalyzed oxidation of 5-(hydroxymethyl)furfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HFCA) was investigated using in situ X-ray absorption spectroscopy under reaction conditions over Ag/ZrO₂ and Ag/TiO₂ catalysts.

Unravelling the Different Reaction Pathways for Low Temperature CO Oxidation on Pt/CeO2 and Pt/Al2O3 by Spatially Resolved Structure-Activity Correlations

Spatially resolved operando HERFD-XANES (high energy resolution fluorescence detected X-ray absorption near edge structure) complemented by CO concentration gradient profiles along the catalyst bed (SpaciPro) was used to identify the dominant reaction paths for the low and high temperature CO oxidation on Pt/CeO₂ and Pt/Al₂O₃. At low temperatures, features associated with CO adsorption on Pt were found for both catalysts. During the oxidation reaction light-off, the evolution of the spectral and catalytic profile diverged along the catalyst bed. The CO oxidation rate was high on Pt/CeO₂ from the beginning of the catalyst bed with CO being adsorbed on Pt, whereas low CO conversion due to strong CO poisoning was found on Pt/Al₂O₃. This correlation of the CO concentration gradient with unique insight by HERFD-XANES gave direct proof of the crucial contribution of the Pt-CeO₂ perimeter sites overcoming the CO self-inhibition effect at low temperatures.

Active Complexes on Engineered Crystal Facets of MnOx-CeO2 and Scale-Up Demonstration on an Air Cleaner for Indoor Formaldehyde Removal

Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnO_x-CeO₂ was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnO_x-CeO₂ with exposed {111} facet showed higher activity for formaldehyde oxidation and CO₂ selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid-base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnO_x-CeO₂-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong.

On isothermality in some commonly used plug flow reactors for X-ray based investigations of catalysts

We compare two reactor setups commonly used to make operando measurements of catalyst behavior using X-rays in terms of the degree to which they may be considered to yield radial and axial isothermality.

Critical Review of Low-Temperature CO Oxidation and Hysteresis Phenomenon on Heterogeneous Catalysts

There is a growing demand for new heterogeneous catalysts for cost-effective catalysis. Currently, the hysteresis phenomenon during low-temperature CO oxidation is an important topic in heterogeneous catalysis. Hysteresis provides important information about fluctuating reaction conditions that affect the regeneration of active sites and indicate the restoration of catalyst activity. Understanding its dynamic behavior, such as hysteresis and self-sustained kinetic oscillations, during CO oxidation, is crucial for the development of cost-effective, stable and long-lasting catalysts. Hysteresis during CO oxidation has a direct influence on many industrial processes and its understanding can be beneficial to a broad range of applications, including long-life CO2 lasers, gas masks, catalytic converters, sensors, indoor air quality, etc. This review considers the most recent reported advancements in the field of hysteresis behavior during CO oxidation which shed light on the origin of this phenomenon and the parameters that influence the type, shape, and width of the conversion of the hysteresis curves.

Chemical waves in the O2 + H2 reaction on a Rh(111) surface alloyed with nickel. II. Photoelectron spectroscopy and microscopy

Chemical waves in the H₂ + O₂ reaction on a Rh(111) surface alloyed with Ni [Θ_Ni < 1.5 monolayers (ML)] have been investigated in the 10^-7 and 10^-6 mbar range at T = 773 K using scanning photoelectron microscopy and x-ray photoelectron spectroscopy as in situ methods. The local intensity variations of the O 1s and the Ni 2p signal display an anticorrelated behavior. The coincidence of a high oxygen signal with a low Ni 2p intensity, which seemingly contradicts the chemical attraction between O and Ni, has been explained with a phase separation of the oxygen covered Rh(111)/Ni surface into a 3D-Ni oxide and into a Ni poor metallic phase. Macroscopic NiO islands (≈1 μm size) formed under reaction conditions have been identified as 2D-Ni oxide. Titration experiments of the oxygen covered Rh(111)/Ni surface with H₂ demonstrated that the reactivity of oxygen is decreased by an order of magnitude through the addition of 0.6 ML Ni. An excitation mechanism is proposed in which the periodic formation and reduction of NiO modulate the catalytic activity.

Tuning the Structure of Platinum Particles on Ceria In Situ for Enhancing the Catalytic Performance of Exhaust Gas Catalysts

A dynamic structural behavior of Pt nanoparticles on the ceria surface under reducing/oxidizing conditions was found at moderate temperatures (<500 °C) and exploited to enhance the catalytic activity of Pt/CeO₂ -based exhaust gas catalysts. Redispersion of platinum in an oxidizing atmosphere already occurred at 400 °C. A protocol with reducing pulses at 250-400 °C was applied in a subsequent step for controlled Pt-particle formation. Operando X-ray absorption spectroscopy unraveled the different extent of reduction and sintering of Pt particles: The choice of the reductant allowed the tuning of the reduction degree/particle size and thus the catalytic activity (CO>H₂ >C₃ H₆ ). This dynamic nature of Pt on ceria at such low temperatures (250-500 °C) was additionally confirmed by in situ environmental transmission electron microscopy. A general concept is proposed to adjust the noble metal dispersion (size, structure), for example, during operation of an exhaust gas catalyst.

Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR

Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

In the future, (electro-)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power-to-chemical processes require a shift from steady-state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well-known that the structure of catalysts is very dynamic. However, in-depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time-resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions.

Operando chemistry of catalyst surfaces during catalysis

The chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of the mechanisms of a catalytic reaction performed on the catalyst in the gas or liquid phase.

Transient structural and catalytic behaviour of Pt-particles probed by operando spectroscopy during a realistic driving cycle

Pt catalysts investigated with operando XAS under rapid transient temperature automotive driving cycle conditions.

Detecting and utilizing minority phases in heterogeneous catalysis

Highly active phases in carbon monoxide oxidation are known, however they are transient in nature. Here, we determined for the first time the structure of such a highly active phase on platinum nanoparticles in an actual reactor. Unlike generally assumed, the surface of this phase is virtually free of adsorbates and co-exists with carbon-monoxide covered and surface oxidized platinum. Understanding the relation between gas composition and catalyst structure at all times and locations within a reactor enabled the rational design of a reactor concept, which maximizes the amount of the highly active phase and minimizes the amount of platinum needed.