Surface Structure Of Catalysts Research Articles

Frustrating Surface Segregation by Nanoconfinement: Boosting Electrochemical Ozone Production over a B13C2-Encapsulated PtNi Alloy Electrocatalyst

A major challenge that limits the applications of nanostructured electrocatalysts is precise surface structure regulation. The critical performance-impeding factors for the important electrochemical ozone production (EOP) lie in the leaching-induced poor stability as well as the competing oxygen evolution and ozone production reactions over the most promising platinum-based electrocatalysts. Although composition diversification by alloying appears to be a prevailing strategy to optimize platinum-based electrocatalysts, a practical restriction turns out to be the inevitable surface segregation and termination of platinum-enriched structures due to their lower surface energies. In this work, we introduce the nanoconfinement of intermetallic platinum–nickel nanostructures encapsulated by boron carbide, which effectively frustrates the surface segregation of alloy nanostructures and well maintains the pristine termination of the alloy. Precise atomic-level structural elucidation and model construction of the encapsulated alloy nanostructures are achieved by quantitative electron microscopy. The composite nanoalloy with a unique surface termination evokes synergetic catalytic effects that promote the charge transfer between the surface and adsorbed oxygen intermediates, which entails outstanding EOP performance with a high Faraday efficiency of 14.8% in neutral media and long-term stability of up to 120 h as a qualified electrocatalyst for the EOP electrolyzer devices. More importantly, the current work paves a new route to overwhelm the thermodynamically limited surface structures of bare nanoalloy catalysts through diverse nanoconfinement strategies.

CuC(O) Interfaces Deliver Remarkable Selectivity and Stability for CO2 Reduction to C2+ Products at Industrial Current Density of 500mA cm-2.

The electrocatalytic CO2 reduction reaction (CO2 RR) is an attractive technology for CO2 valorization and high-density electrical energy storage. Achieving a high selectivity to C2+ products, especially ethylene, during CO2 RR at high current densities (>500mA cm-2 ) is a prized goal of current research, though remains technically very challenging. Herein, it is demonstrated that the surface and interfacial structures of Cu catalysts, and the solid-gas-liquid interfaces on gas-diffusion electrode (GDE) in CO2 reduction flow cells can be modulated to allow efficient CO2 RR to C2+ products. This approach uses the in situ electrochemical reduction of a CuO nanosheet/graphene oxide dots (CuOC(O)) hybrid. Owing to abundant CuOC interfaces in the CuOC(O) hybrid, the CuO nanosheets are topologically and selectively transformed into metallic Cu nanosheets exposing Cu(100) facets, Cu(110) facets, Cu[n(100) × (110)] step sites, and Cu+ /Cu0 interfaces during the electroreduction step, the faradaic efficiencie (FE) to C2+ hydrocarbonswasreached as high as 77.4% (FEethylene ≈ 60%) at 500mA cm-2 . In situ infrared spectroscopy and DFT simulations demonstrate that abundant Cu+ species and Cu0 /Cu+ interfaces in the reduced CuOC(O) catalyst improve the adsorption and surface coverage of *CO on the Cu catalyst, thus facilitating CC coupling reactions.

Designing Superhydrophilic Hydrogels as Binder-Free Catalysts for Enhanced Oxygen Evolution Performance

Water electrolysis is an environmentally friendly and sustainable hydrogen production method. The proper design of the catalyst surface is essential for the oxygen evolution reaction (OER) in the water electrolysis process because the catalytic effect is highly dependent on contact surface properties such as the homogeneity of the coating and the stability of the catalyst, as well as the wettability of the electrolyte. Herein, hydrogel [consisting of poly(vinyl alcohol) (PVA) cross-linked with quaternized chitosan (HACC)] loaded on nickel foam (NF) was chosen to study the OER properties of iron (Fe) in organic molecules. Owing to the unique hydrophilicity, uniformity, and stability of hydrogel, the superhydrophilic Fe-HACC-PVA/NF exhibits a low overpotential of 225 mV versus reversible hydrogen electrode at 10 mA cm–2 and shows favorable stability (only 2.3% loss of current density after 24 h at 100 mA cm–2), which outperforms most Fe-based transition-metal OER catalysts. This work demonstrates that introducing a superhydrophilic catalyst surface structure to dissociate the adsorbed water is a productive strategy to enhance the performance of OER. Furthermore, the rational design of hydrophilic interface materials in this work provides a facile method to developing OER catalysts.

Structure-catalytic functionality of size-facet-performance in pentlandite nanoparticles

As one of the pentlandites, Fe5Ni4S8 (FNS) based materials have attracted increasing attention due to their excellent catalytic properties and promising applicability. The control over the catalyst surface structure often benefits its heterogeneous catalytic activity. However, this has not been investigated for FNS materials at the nanoscale regarding the catalytic activity related to high-index facets. Herein, FNS nanoparticles (FNSNPs) with enclosed continuous tunable high-index facets were prepared and studied to clarify the relationship between the structure and catalytic functionality. The results suggested strong dependence between exposed facets of FNSNPs and their sizes. The decline in the average size to 5.8 nm led to enclosing by high-index facets (422) and (511) to yield optimal electrocatalytic activities toward the hydrogen evolution reaction. The catalytic activity of FNSNPs was closely related to the surface energy of the main exposed facets. These findings clarified the relationship between high-index-facet and high-surface-energy FNSNPs, as promising approaches in crystal surface control engineering.

Ethane Dehydrogenation over the Core–Shell Pt-Based Alloy Catalysts: Driven by Engineering the Shell Composition and Thickness

Pt-based catalysts as the commercial catalysts in ethane dehydrogenation (EDH) face one of the main challenges of realizing the balance between coke formation and catalytic activity. In this work, a strategy to drive the catalytic performance of EDH on Pt-Sn alloy catalysts is proposed by rationally engineering the shell surface structure and thickness of core-shell Pt@Pt3Sn and Pt3Sn@Pt catalysts from a theoretical perspective. Eight types of Pt@Pt3Sn and Pt3Sn@Pt catalysts with different Pt and Pt3Sn shell thicknesses are considered and compared with the industrially used Pt and Pt3Sn catalysts. Density functional theory (DFT) calculations completely describe the reaction network of EDH, including the side reactions of deep dehydrogenation and C-C bond cracking. Kinetic Monte Carlo (kMC) simulations reveal the influences of the catalyst surface structure, experimentally related temperatures, and reactant partial pressures. The results show that CHCH* is the main precursor for coke formation, and Pt@Pt3Sn catalysts generally have higher C2H4(g) activity and lower selectivity compared to those of Pt3Sn@Pt catalysts, which is attributed to the unique surface geometrical and electronic properties. 1Pt3Sn@4Pt and 1Pt@4Pt3Sn are screened out as catalysts exhibiting excellent performance; especially, the 1Pt3Sn@4Pt catalyst has much higher C2H4(g) activity and 100% C2H4(g) selectivity compared to those of 1Pt@4Pt3Sn and the widely used Pt and Pt3Sn catalysts. The two descriptors C2H5* adsorption energy and reaction energy of its dehydrogenation to C2H4* are proposed to qualitatively evaluate the C2H4(g) selectivity and activity, respectively. This work facilitates a valuable exploration for optimizing the catalytic performance of core-shell Pt-based catalysts in EDH and reveals the great importance of the fine control of the catalyst shell surface structure and thickness.

Tuning CO2 Hydrogenation Selectivity through Reaction-Driven Restructuring on Cu-Ni Bimetal Catalysts.

Tuning the selectivity of CO2 hydrogenation is of significant scientific interest, especially using nickel-based catalysts. Fundamental insights into CO2 hydrogenation on Ni-based catalysts demonstrate that CO is a primary intermediate, and product selectivity is strongly dependent on the oxidation state of Ni. Therefore, modifying the electronic structure of the nickel surface is a compelling strategy for tuning product selectivity. Herein, we synthesized well dispersed Cu-Ni bimetallic nanoparticles (NPs) using a simple hydrothermal method for CO selective CO2 hydrogenation. A detailed study on the monometallic (Ni and Cu) and bimetallic (CuxNi1-x) catalysts supported on γ-Al2O3 was performed to increase CO selectivity while maintaining the high reaction rate. The Cu0.5Ni0.5/γ-Al2O3 catalyst shows a high CO2 conversion and more CO product selectivity than its monometallic counterparts. The surface electronic and geometric structure of Cu0.5Ni0.5 bimetallic NPs was studied using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier-transform spectroscopy under reaction conditions. The Cu core atoms migrate toward the surface, resulting in the restructuring of the Cu@Ni core-shell structure to a Cu-Ni alloy during the reaction and functioning as the active site by enhancing CO desorption. A systematic correlation is obtained between catalytic activity from a continuous fixed-bed flow reactor and the surface electronic structural details derived from AP-XPS results, establishing the structure-activity relationship. This investigation contributes to providing a strategy for controlling CO2 hydrogenation selectivity by modifying the surface structure of bimetallic NP catalysts.

A review of in situ/operando studies of heterogeneous catalytic hydrogenation of CO2 to methanol

Repurposing CO2 into chemicals, one of the Carbon Dioxide Removal (CDR) strategies, still faces significant challenges in conversion and energy efficiency due to the lack of effective catalysts and processes. Fundamental understanding through in situ/operando investigations of the reaction mechanisms and catalyst structures is pivotal for developing the efficient catalysts. This paper reviews the past and recent in situ/operando studies of methanol synthesis from heterogeneous CO2 hydrogenation over a few typical catalysts including Cu-based, oxide-based, and noble-metal-based catalysts. With the development of high-pressure reactors, in situ/operando IR, X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), neutron diffraction and imaging have been used to reveal the surface intermediates and structures of working catalysts under CO2 hydrogenation conditions. On the one hand, the combined operando techniques shed light on working mechanisms for some catalytic systems. On the other hand, due to the complexity of selective CO2 hydrogenation reaction and limited sensitivity of current accessible operando techniques to the surface structure of catalysts, it is still murky about the exact nature of the active sites at the surface/interface and how different sites promote different reaction paths. It is concluded that new methodologies for differentiating signals from different sites, and the development of surface-sensitive techniques for high pressure reactions are needed for providing structural descriptors of highly active and selective CO2 conversion catalysts.

Engineering Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe3O4–Fe3C heterostructures for efficient hydrogen evolution in alkaline and acidic media

Tailoring surface composition and structures of catalysts affects their catalytic performance in hydrogen evolution reaction owing to the geometric and electronic effects. Herein, Ru nanoparticles embedded in 2D N-doped carbon nanosheets decorated with 2D Fe3O4–Fe3C heterostructures (Ru/Fe3O4–Fe3C/NC) are fabricated via pyrolysis of the mixture containing 2D-Fe2O3 nanosheets, dopamine hydrochloride, RuCl3·xH2O, and melamine. Interestingly, the good hydrogen evolution behavior is achieved on Ru/Fe3O4–Fe3C/NC with the high reactivity and stability. Ru/Fe3O4–Fe3C/NC offers an overpotential of 141 mV to realize the current density of 10 mA/cm2 in 0.5 mol/L (M) H2SO4 electrolyte. As for 1 M KOH, Ru/Fe3O4–Fe3C/NC promotes hydrogen evolution reactivity with 148 mV to achieve 10 mA/cm2. The current density slightly degrades after continuous I-t tests, verifying the good stability for Ru/Fe3O4–Fe3C/NC. The high reactivity might stem from high dispersion of Ru nanoparticles, enhanced conductivity due to doping N into carbon nanosheets, and heterointerfaces between Fe–O and Fe–C.

Data‐Driven Machine Learning for Understanding Surface Structures of Heterogeneous Catalysts

AbstractThe design of heterogeneous catalysts is necessarily surface‐focused, generally achieved via optimization of adsorption energy and microkinetic modelling. A prerequisite is to ensure the adsorption energy is physically meaningful is the stable existence of the conceived active‐site structure on the surface. The development of improved understanding of the catalyst surface, however, is challenging practically because of the complex nature of dynamic surface formation and evolution under in‐situ reactions. We propose therefore data‐driven machine‐learning (ML) approaches as a solution. In this Minireview we summarize recent progress in using machine‐learning to search and predict (meta)stable structures, assist operando simulation under reaction conditions and micro‐environments, and critically analyze experimental characterization data. We conclude that ML will become the new norm to lower costs associated with discovery and design of optimal heterogeneous catalysts.

Data-Driven Machine Learning for Understanding Surface Structures of Heterogeneous Catalysts.

The design of heterogeneous catalysts is necessarily surface-focused, generally achieved via optimization of adsorption energy and microkinetic modelling. A prerequisite is to ensure the adsorption energy is physically meaningful is the stable existence of the conceived active-site structure on the surface. The development of improved understanding of the catalyst surface, however, is challenging practically because of the complex nature of dynamic surface formation and evolution under in-situ reactions. We propose therefore data-driven machine-learning (ML) approaches as a solution. In this Minireview we summarize recent progress in using machine-learning to search and predict (meta)stable structures, assist operando simulation under reaction conditions and micro-environments, and critically analyze experimental characterization data. We conclude that ML will become the new norm to lower costs associated with discovery and design of optimal heterogeneous catalysts.

The promotional roles of multivalent metal ions and oxygen vacancies on nitrogen-doped carbon-combined CuMn-based catalysts for cyclohexylbenzene oxidation

In this work, we fabricated nitrogen-doped carbon (NC)-combined CuMn-based catalysts derived from layered double hydroxide and melamine mixture precursor and further explored their activity in the aerobic oxidation of cyclohexylbenzene (CHB) to produce cyclohexylbenzene-1-hydroperoxide (CHBHP) using molecular oxygen as the oxidant. Series of structural characterizations demonstrated that multivalent Cu and Mn species and abundant surface defective oxygen vacancies could form in catalysts, due to comprehensive redox processes between Cu and Mn atoms upon high-temperature calcination of precursors under inert atmosphere, as well as the promotional effect of melamine added on the reduction of metal ions. As-fabricated NC-combined CuMn catalyst bearing a 1:1 Cu:Mn molar ratio showed a higher catalytic oxidation activity, in comparison to other NC-decorated CuMn-based catalysts, NC-free CuMn-based one, and pure single metal oxides (i.e., CuO, MnO2). It was revealed that the presence of favorable multivalent Cu and Mn ions and abundant oxygen vacancies was conducive to the effective adsorption and activation of CHB and oxygen molecules, thus accelerating the selective oxidation of CHB to form CHBHP. Moreover, surface NC overlayer on catalysts could protect surface structures of catalysts during the oxidation. The present study provides deep understanding of the roles of surface-active metal species and oxygen vacancies of CuMn-based catalysts for efficient oxidation of CHB to form CHBHP.

Improving time-resolution and sensitivity of in situ X-ray photoelectron spectroscopy of a powder catalyst by modulated excitation.

Ambient pressure X-ray photoelectron spectroscopy (APXPS) is a powerful tool to characterize the surface structure of heterogeneous catalysts in situ. In order to improve the time resolution and the signal-to-noise (S/N) ratio of photoemission spectra, we collected consecutive APXP spectra during the periodic perturbation of a powder Pd/Al2O3 catalyst away from its equilibrium state according to the modulated excitation approach (ME). Averaging of the spectra along the alternate pulses of O2 and CO improved the S/N ratio demonstrating that the time resolution of the measurement can be limited solely to the acquisition time of one spectrum. Through phase sensitive analysis of the averaged time-resolved spectra, the formation/consumption dynamics of three oxidic species, two metal species, adsorbed CO on Pd0 as well as Pdn+ (n > 2) was followed along the gas switches. Pdn+ and 2-fold surface PdO species were recognised as most reactive to the gas switches. Our approach demonstrates that phase sensitive detection of time-resolved XPS data allows following the dynamics of reactive species at the solid-gas interface under different reaction environments with unprecedented precision.

Polyaniline-coated glassy carbon microspheres decorated with nano-palladium as a new electrocatalyst for methanol oxidation

• A composite electrocatalyst platform was decorated with nanoPd. • The 3D electrocatalyst was easy to fabricate. • The fabricated catalyst showed high catalytic activity and stability toward methanol oxidation reaction. We propose a 3D catalyst of polyaniline-coated glassy carbon microspheres decorated with nano-palladium (3D nanoPd@PANi/GCM) for methanol oxidation in direct methanol fuel cells (DMFCs). The 3D nanoPd@PANi/GCM catalyst was synthesized by a green, low-cost method using two-step chemical deposition. The surface morphology and structure of the 3D catalyst were characterized by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectrometry (FTIR), and X-ray diffractometry (XRD). Electrochemical properties were evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). The 3D nanoPd@PANi/GCM catalyst exhibited a larger effective surface area, higher specific activity and catalytic stability, and more durability than a commercial Pd/C catalyst for methanol oxidation. The novel catalyst showed great potential as a new electrode material for DMFCs.

EFEITO DOS DEFEITOS DE SUPERFÍCIE E DO pH NA ADSORÇÃO E NA CATÁLISE DA ELETRO-OXIDAÇÃO DE CO EM SUPERFÍCIES MODELOS DE PLATINA

SURFACE DEFECTS AND pH EFFECTS ON ADSORPTION AND CATALYSIS OF CO ELECTRO-OXIDATION ON MODEL PLATINUM SURFACES. Platinum is one of the well-known catalytic materials for which the electro-oxidation of carbon monoxide better behaves as a sensitive reaction to the catalyst surface structure. For the electro-catalytic reactions that behave like this, the rate (faradaic current density) is the result of the sum of the activity of the different active sites working with very different efficiencies or abilities. In this scenario, different atomic arrangements on the catalyst surface are expected to play different roles in surface-catalyzed reactions. In this article, the functionalities that surface defects (steps) can play in the adsorption and electrocatalytic oxidation of CO on model platinum surfaces are reviewed. Surface defects are indirectly related to the up catalysis as well as to the inhibition of reaction pathways of CO electro-oxidation under very particular conditions; these surface entities are also indirectly related to restrictions for the mobility of adsorbed CO on the (111) terraced surfaces. We analyze the selective activation and deactivation of surface sites by the pH effect, and typical catalytic properties of extended surfaces and shaped-controlled nanoparticles have been discussed thoroughly. We present a model of most active sites involved in the pathways of CO2 formation from the electro-oxidation of adsorbed CO.

Surface and Interface Coordination Chemistry Learned from Model Heterogeneous Metal Nanocatalysts: From Atomically Dispersed Catalysts to Atomically Precise Clusters.

The surface and interface coordination structures of heterogeneous metal catalysts are crucial to their catalytic performance. However, the complicated surface and interface structures of heterogeneous catalysts make it challenging to identify the molecular-level structure of their active sites and thus precisely control their performance. To address this challenge, atomically dispersed metal catalysts (ADMCs) and ligand-protected atomically precise metal clusters (APMCs) have been emerging as two important classes of model heterogeneous catalysts in recent years, helping to build bridge between homogeneous and heterogeneous catalysis. This review illustrates how the surface and interface coordination chemistry of these two types of model catalysts determines the catalytic performance from multiple dimensions. The section of ADMCs starts with the local coordination structure of metal sites at the metal-support interface, and then focuses on the effects of coordinating atoms, including their basicity and hardness/softness. Studies are also summarized to discuss the cooperativity achieved by dual metal sites and remote effects. In the section of APMCs, the roles of surface ligands and supports in determining the catalytic activity, selectivity, and stability of APMCs are illustrated. Finally, some personal perspectives on the further development of surface coordination and interface chemistry for model heterogeneous metal catalysts are presented.

Selective Conversion of Glycerol to Value‐Added C3 Products: Effect of Catalyst Surface Structure

AbstractGlycerol, a major byproduct of biodiesel processing, could be leveraged as a platform to higher‐value products if the selectivity of its transformations could be improved. Herein, density functional theory (DFT) calculations are used to identify reactivity trends for the initial glycerol dehydrogenation steps involving C−H and O−H bond cleavage on a variety of transition metals including Ag, Au, Cu, Pd, Pt, and Rh considering both (111) and (100) surface facets. Additional activation energies calculated on Pt(111), Pt(100), Au(111), and Au(100) surfaces indicate that the most energetically favorable pathway is highly sensitive to the local surface structure and depends on the adsorption strength of reactive intermediates to the metal surface. Finally, adsorbate‐based and structure‐based energy scaling approaches for glycerol are identified, suggesting the ability to screen candidate materials using both structure‐ and composition‐based reactivity descriptors.

Anomalous Ru dissolution enabling efficient integrated CO2 electroreduction in strong acid

Recently, emerging acidic conditions CO2 electrolyzer overcomes the limitations of lower carbon utilization efficiency due to carbonate/bicarbonate formation in neutral/alkaline media, which offers a promising route to the realization of carbon cycle and environment optimization. Nevertheless, an integral CO2 conversion electrolyzer must consider the sluggish reaction kinetics of the oxygen evolution reaction (OER), especially in acid media. Herein, we demonstrate a significant improvement in anodic OER performance by tailoring the surface structure of RuO2 catalyst with potassium. The obtained K-RuO2 electrocatalyst can reach 10 mA/cm2 only with an overpotential of 170 mV and exhibits prolonged stability, showing overwhelming catalytic performance compared to RuO2. Advanced synchrotron radiation-based multi-techniques (SRMS) and theory calculations demonstrate the remarkable performance originating from the anomalous dissolution, which caused by consciously initiated K generating enhanced ratio of active RuCUS sites for K-RuO2. When K-RuO2 pairs with cathodic CO2RR catalyst of bismuth, it achieves the result of lower cell voltage and nearly 4-fold longer durability in strong acid compared to RuO2 catalyst. This work provides a deep insight into the true active structure of anode RuO2 catalyst, paves a new way to design high-performance noble metal-based catalysts for acidic OER, and finally contributes to the advancement of CO2 electrolysis.

Facet-Dependent Electron Transfer Regulates Photocatalytic Valorization of Biopolyols.

The electron transfer (ET) from the conduction band of the semiconductor to surface-bound species is a key step in the photocatalytic reaction and strongly affects the reactivity and selectivity, while the effect of catalyst surface structure on this process has rarely been explored due to the lack of an effective method. Herein, we have developed a strategy to detect and measure surface electrons' transfer energy to the adsorbates and disclosed a facet-dependent electron transfer energy over anatase TiO2. The photogenerated electrons are shallowly confined in the five-coordinated Ti atom (Ti5c) on the surface of the (101) facet with a transfer energy below 1.0 eV, while deeply confined in the six-coordinated Ti atom (Ti6c) on the subsurface of the (001) facet with a transfer energy higher than 1.9 eV. The different electron trap states strongly affect the ET process, thus regulating the photocatalytic activity. Taking formic acid (FA) dehydration as the probe reaction, a shallow trap of photoexcited electrons on the (101) facet of anatase TiO2 favors the dehydration of FA to CO, while a deep trap of photoexcited electrons on the (001) facet makes FA stable. Based on this knowledge, we successfully controlled the selectivity in the photocatalytic oxidation of biopolyols via selectively exposing the facet of TiO2. Through controlling the (001)/(101) facet, a wide range of biopolyols can be selectively converted into FA or CO with a selectivity of up to 80%. The present work disclosed a facet-dependent electron transfer process and provides a new horizon to the design of photocatalytic systems.

Supported Ru nanocatalyst over phosphotungstate intercalated Zn-Al layered double hydroxide derived mixed metal oxides for efficient hydrodeoxygenation of guaiacol

In this work, a strategy for rational design of high-performance heterogenous supported Ru nanocatalysts over mixed metal oxides for aqueous phase partial hydrodeoxygenation (HDO) of guaiacol in the batch reactor was developed taking advantage of supramolecular structure of Zn-Al layered double hydroxides (LDHs) with different interlayer anions. It was interestingly found that in the case of phosphotungstate intercalated ZnAl-LDH as the support precursor, strong interactions between Ru species and intercalated LDH-derived mixed metal oxide supports could be formed, in addition to the formation of surface reductive ZnWOx component and P-O species. Notably, as-fabricated supported Ru nanocatalyst showed much higher activity in the aqueous phase HDO of guaiacol to produce cyclohexanol at an extraordinarily low Ru/guaiacol molar ratio of 0.0009, along with a higher cyclohexanol yield of ∼86% under reaction conditions (250 °C, 2.0 MPa initial H2 pressure), compared to other two supported Ru ones over mixed metal oxides derived from tungstate- and nitrate-intercalated ZnAl-LDH precursors (cyclohexanol yield of 29.7 and 10.1%, respectively). Studies on structure-property correlations revealed that surface defective and acidic sites facilitated the activation of guaiacol and phenol intermediate, thereby enabling the catalyst with a strong ability to break Cring−OCH3 bond and promote the ring hydrogenation. This finding provides a promising way to tune surface structures of metal-based catalysts for the upgrading of biomass.

Shedding Synchrotron Light on Catalyst Strain Dynamics in Electrochemical Environment

In the case of heterogeneous catalysis (where the reactions occur onto the catalyst surface), the most promising approach in material design follows the Sabatier principle: the ability of the surface to bind adsorbates and the strength of the bonds define the reaction thermodynamics and kinetics. In this respect, the catalyst surface chemistry and structure (crystallographic orientation of the facets and/or strain) are used as levers to optimize its performance. However, it is largely accepted that the structure of PEMWE anode and PEMFC cathode catalysts does not remain unaltered over the long term operation due to harsh (electro)chemical conditions and it is of a high interest to understand the structural changes during the electrocatalysis. In this contribution we use X-ray diffraction techniques to qualitatively and quantitatively describe those changes and shed light on the strain evolution in nanostructured catalysts during operation in the electrochemical environment.Using the newly upgraded 4th generation EBS source at European Synchrotron Radiation Facility, we study Pt and Pd catalysts in liquid half cells at various potentials. In the Pd case we focus on the phase and structural dynamics during H insertion, allowing to unveil the electrochemically-driven Pd hydrides phase transition, which was until now mostly investigated in the gas phase. The fine XRD patterns measured operando provided the first detection of theoretically predicted supersaturated and undersaturated metastable states, involved in a core-shell mechanism of the phase transition (Figure 1) [1].In the case of Pt nanocatalyst, monitoring the structural features of the catalyst during cyclic voltammetry permits studying adsorption and oxidation processes. Deconvoluting both effects (adsorption and oxidation) is possible by following different parameters of the analyzed XRD patterns with high temporal resolution. Such experiments reveal important dynamic trends linked to the surface oxidation and degradation, directly impacting the output of accelerated stress tests (AST) [2]. Carefully determining the charge passed through the circuit during the CV also allows to establish a near-linear correlation between the expansion of the bulk lattice parameter of Pt nanoparticles and their oxide surface coverage. Since the latter is known to be a descriptor of catalysts activity toward numerous reactions (oxygen reduction and fuel oxidation), the measurement of the lattice parameter according to this simple diffraction approach allows experimental access to this descriptor during operando measurements in device-relevant sample environments [2]. This constitutes a main advantage compared to spectroscopic techniques and is foreseen to find a wide range of applications, as demonstrated by measuring the structural behavior of the state-of-the-art PtNiIr octahedra catalyst in operating PEMFC. In this case, the results allow correlating the degradation of the catalysts cycled to different lower potentials with the oxidation and strain dynamics. Based on this data, the operating conditions for this catalyst can be determined, further defining the application of this material.[1] Chattot, R. et al., J. Am. Chem. Soc. 143(41), 17068–17078 (2021).[2] Martens, I. et al., ACS Appl. Energy Mater. 2 (11), 7772-7780 (2019). Figure 1