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In situ and operando X‐ray absorption spectroscopy (XAS) provides fundamental insight into the working principles of electrocatalysts and is an important tool for future catalyst development. However, the design of an operando XAS electrocatalytic cell is not facile, and researchers designing cells, whether new cells or modifications to previous cells, often spend many hours on cell design before obtaining high‐quality XAS data. Here, we describe the design, with engineering drawings, and operation of a versatile XAS cell with options for gas flow, electrolyte flow, pH monitoring, temperature monitoring, and the ability to handle many catalyst forms (any catalyst that can be deposited onto a conductive X‐ray transparent substrate). We benchmarked XAS spectra collected using the new experimental cell to a previous cell design showing its ability to produce quality XAS data. We demonstrate the viability of this cell by providing insight into electrocatalysts by studying cation effects and show the tetrabutylammonium cation prevents bulk oxidation of copper. We hope the availability of this cell allows researchers to convert time typically spent on cell design to time spent on breakthroughs in electrocatalysis. [ABSTRACT FROM AUTHOR]

The design of supported heterogeneous catalysts requires a detailed understanding of the structure and chemistry of the active surface. Although the chemical components of the active phase, support material, and process feed are typically considered to be the most important factors governing catalyst structure and performance, many common commercial supports contain trace impurities, which can have profound effects on catalyst properties. In this work, we study silica‐supported cobalt‐based catalysts, which are widely used in syngas conversion to value‐added products. Supported metallic Co is a commercial Fischer‐Tropsch catalyst, whereas Co2C has shown promise for the direct conversion of syngas to higher oxygenates. This study examines the effects of Na, a commonly detected support impurity and a frequently used promoter, on the structure and reactivity of Co and Co2C. We show that trace Na impurities significantly decrease catalyst activity of supported metallic Co, and that high Na concentrations result in Co2C formation and a loss in Fischer‐Tropsch activity. However, in Co2C catalysts, Na plays an important role in stabilizing the Co2C phase, but excess Na decreases catalyst activity. We use in situ X‐ray absorption spectroscopy to study Co2C formation and decomposition in the Na‐free catalyst under carburization and reaction conditions. The work reveals the importance of carefully controlling alkali metal content, particularly at trace levels, in catalyst design. [ABSTRACT FROM AUTHOR]

• Improved syngas conversion to oxygenates over mixed Mo/Co carbide catalysts. • Catalysts form well mixed, amorphous carbidic and bimetallic nanoparticles. • Mo and Co reaction sites are in close contact at the catalyst surface. Recently metal carbide catalysts have attracted attention as alternatives to pure metals for the conversion of syngas to higher oxygenates, a process which could enable the sustainable production of fuels, polymers, and chemicals. Although Mo and Co carbides have both shown promise for higher oxygenate production, they have not achieved the requisite activity and selectivity for practical implementation. In this work we synthesize and characterize a binary Mo and Co carbide catalyst that exhibits improved activity and oxygenate selectivity relative to either pure metal carbide. We apply a combination of advanced electron microscopy and X-ray diffraction to show that the binary Mo/Co carbide catalyst forms uniformly mixed amorphous nanoparticles. Through in situ X-ray absorption spectroscopy studies, we determine that the structure of the mixed metal carbide catalyst under reaction conditions consists of both carbidic and bimetallic components. By testing the catalytic properties of a series of Mo/Co carbide catalysts prepared by different synthesis methods, we find that the Mo and Co sites must be in close contact to achieve improved syngas conversion to higher alcohols. Through in situ DRIFTS measurements, both Mo and Co atoms at the surface of the catalyst are identified as adsorption sites for reactive species. [ABSTRACT FROM AUTHOR]

• Supports and ionic liquids (ILs) act as ligands on supported metals enveloped by ILs. • Supported iridium species of varying metal nuclearity were synthesized and coated with ILs. • Data resolve the strength of individual ligand effects on butadiene hydrogenation. • The IL coatings exerted dominant effects on iridium clusters as catalysts. • In contrast, the supports exerted dominant effects on the isolated iridium atoms. Supported iridium complexes were synthesized by the reaction of Ir(CO) 2 (acac) (acac = acetylacetonato) with SiO 2 , γ-Al 2 O 3 , and MgO. Extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectra demonstrate that the iridium was present as atomically dispersed species anchored to each support. The samples were treated in flowing H 2 at 673 K to form supported iridium clusters. EXAFS spectra and high-angle annular dark-field scanning transmission electron microscopy images demonstrate that the average diameter of the iridium clusters on each support was approximately 1.2 nm. The catalysts before and after cluster formation were coated with each of a family of 1,3-dialkylimidazolium ionic liquids (ILs) having varying electron-donor tendencies probed by their υ(C2H) frequencies determined by IR spectroscopy. The coated and uncoated samples were tested as catalysts for partial hydrogenation of 1,3-butadiene in a flow reactor at 333 K, with turnover frequencies determined from differential conversions. The individual influences of the IL coatings and supports on the catalyst performance were found to depend strongly on whether the iridium was site-isolated complexes or present in clusters. The IL coatings as ligands exerted dominant effects on the clusters as catalysts, whereas the supports exerted dominant effects on the isolated iridium atoms. The results indicate how to tune the effects of metal nuclearity, IL coatings, and supports on the electronic environments and catalytic properties of the metals. [ABSTRACT FROM AUTHOR]

Controlling selectivity is a key goal in the design of a heterogeneous catalyst. Herein, we present detailed characterization and activity of silica‐supported cobalt catalysts modified by atomic layer deposition of ZnO. After reduction, the resulting catalysts exhibit substantial selectivity towards alcohol production during CO hydrogenation compared to catalysts containing only cobalt. The prepared catalysts have up to 46 % selectivity toward alcohols with 39 % of the alcohols corresponding to ethanol and other higher alcohols, albeit with reduced activity. In situ characterization of the catalyst by X‐ray diffraction and X‐ray absorption spectroscopy reveals details on the structural evolution in syngas, CO+H2, and shows that ZnO promotion of Co results in the formation of Co2C under catalytic conditions. A mechanism is proposed, supported by density functional theory calculations, which explains Co2C formation by the blocking of Co step sites by Zn species. The ZnO acts a dual promoter both by facilitating Co2C formation and by modifying the resulting Co2C. The Co2C formed from the ZnO‐promoted Co catalysts displays improved thermal stability and selectivity compared with similar Co2C catalysts without Zn. Staying active for alcohol! In situ X‐ray absorption spectroscopy, X‐ray diffraction and DFT calculations have been used to elucidate the active phase of an ALD‐ZnO‐modified Co catalyst for the synthesis of higher alcohols from syngas, which is identified as a Zn‐modified Co2C. [ABSTRACT FROM AUTHOR]

In situ characterization of catalysts gives direct insight into the working state of the material. Here, the design and performance characteristics of a universal in situ synchrotron‐compatible X‐ray diffraction cell capable of operation at high temperature and high pressure, 1373 K, and 35 bar, respectively, are reported. Its performance is demonstrated by characterizing a cobalt‐based catalyst used in a prototypical high‐pressure catalytic reaction, the Fischer–Tropsch synthesis, using X‐ray diffraction. Cobalt nanoparticles supported on silica were studied in situ during Fischer–Tropsch catalysis using syngas, H2 and CO, at 723 K and 20 bar. Post reaction, the Co nanoparticles were carburized at elevated pressure, demonstrating an increased rate of carburization compared with atmospheric studies. An in situ catalysis powder X‐ray diffraction cell compatible with scattering beamlines at the Stanford Synchrotron Radiation Lightsource has been designed, fabricated and tested. The experimental cell's performance was tested by the characterization of a silica‐supported Co catalyst for Fischer–Tropsch synthesis and demonstrated that metallic Co can be carburized at a faster rate at 20 bar compared with at ambient pressure. [ABSTRACT FROM AUTHOR]

The CATOFIN© process produces propylene from propane using a CrO x /Al 2 O 3 catalyst. Despite its use, there are still uncertainties surrounding the nature of Cr species formed during synthesis, regeneration, and aging. It has been observed that ppm levels of Cr 2 O 3 can be oxidized to Cr(VI) in air; however, when Cr 2 O 3 is in direct contact with Al 2 O 3 , Cr(VI) formation increased more than 100-fold. To confirm physical contact between Cr 2 O 3 and Al 2 O 3 results in increased Cr(VI) formation, Cr 2 O 3 and Cr 2 O 3 /Al 2 O 3 samples were synthesized, calcined, and characterized. Catalytic activity measurements confirm propylene selectivity inversely tracks with Cr(VI). Wet chemical titration and X-ray absorption spectroscopy (XAS) quantified and determined the structure of the Cr(VI) species. FEFF X-ray absorption near edge structure simulations determined the potential sensitivity of the XAS to the presence of Al3+/Cr3+ neighboring atoms. XAS correlated to FEFF simulations suggested that Al3+ x Cr3+ 2−x Cr6+ 3 O 12 comprises a significant fraction of the Cr(VI) species formed. [Display omitted] • Al 2 O 3 facilitates the oxidation of Cr(III)O x species to Cr(VI) species under oxidative pretreatments for CrO x /Al 2 O 3 catalysts. • FEFF XANES calculations show that the Cr K-edge is sensitive to Cr(VI) species being a next-neighbor to Cr(III) or Al(III). • XAX identifies spectral features of Cr(VI) existing as a Al3+ x Cr3+ 2−x Cr6+ 3 O 12 species at the Al 2 O 3 surface. [ABSTRACT FROM AUTHOR]

We report high-energy-resolution X-ray absorption spectroscopy detection of ethylene and CO ligands adsorbed on catalytically active iridium centers isolated on zeolite HY and on MgO supports. The data are supported by density functional theory and FEFF X-ray absorption near-edge modelling, together with infrared (IR) spectra. The results demonstrate that high-energy-resolution X-ray absorption spectra near the iridium LIII (2p3/2) edge provide clearly ascribable, distinctive signatures of the ethylene and CO ligands and illustrate effects of supports and other ligands. This X-ray absorption technique is markedly more sensitive than conventional IR spectroscopy for characterizing surface intermediates, and it is applicable to samples having low metal loadings and in reactive atmospheres and is expected to have an increasing role in catalysis research by facilitating the determination of mechanisms of solid-catalyzed reactions through identification of reaction intermediates in working catalysts. [ABSTRACT FROM AUTHOR]

An atomically dispersed reduced graphene aerogel (rGA)‐supported iridium catalyst having reactive ethylene ligands was synthesized at an iridium loading of 9.9 wt % and coated with an ionic liquid, 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). Continuous‐scan X‐ray absorption spectra demonstrated that the iridium remained site‐isolated in flowing equimolar C2H4 and H2 during a temperature ramp to 100 °C. The data further showed the lack of detectable iridium aggregation when the feed was H2‐rich or even pure H2 at 100 °C. An Arrhenius plot determined for ethylene hydrogenation catalysis with the sample in flowing equimolar ethylene and hydrogen showed no variation in the apparent activation energy at temperatures up to 100 °C, confirming that the active sites remained intact at the higher temperatures. The results point to opportunities for overcoming the stability limitations of atomically dispersed supported noble metal catalysts by choice of electron‐donor supports and ionic liquid sheaths. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2 O 3 atomic layer deposition occurs selectively on and near Rh nanoparticles. • Fe 2 O 3 surface promoter atoms enhance alcohol-forming active sites on Rh. • Catalyst promoter improves the activity, selectivity, and stability. Converting syngas to higher oxygenates is a promising strategy for sustainably producing fuels and chemicals used every day. Rh-based catalysts promoted with metal oxides have long been of interest for oxygenate synthesis, but the role of promoters and the structure of the catalyst during reaction are often not well understood. In this work, we characterize a Rh/SiO 2 catalyst modified by Fe 2 O 3 deposited by atomic layer deposition (ALD). We show that Fe 2 O 3 deposits selectively on the Rh nanoparticles and enhances both the turnover frequency and the oxygenate selectivity of the catalysts. A maximum 29% selectivity towards higher oxygenates is achieved with just 1 cycle of Fe 2 O 3 ALD, and we relate the trends in selectivity to the changing availability of surface sites that drive higher alcohol (e.g., ethanol and propanol) formation. Further, we show that the ALD promoter mitigates catalyst sintering, improving the stability of these materials. In-situ X-ray absorption spectroscopy experiments reveal that the Fe 2 O 3 undergoes reduction during the catalyst pretreatment and forms Fe clusters on the surface of the Rh that migrate but remain stable under syngas reaction conditions. We find that modification of the Rh with these surface Fe species is key to the enhanced alcohol production observed in these materials. [ABSTRACT FROM AUTHOR]

Keywords: Cobalt; Cobalt Carbide; EXAFS Spectroscopy; Impurity Effects; Syngas Conversion EN Cobalt Cobalt Carbide EXAFS Spectroscopy Impurity Effects Syngas Conversion 1036 1036 1 02/20/21 20210218 NES 210218 B The Cover Feature b illustrates the significant effects of trace impurities on the structure and syngas conversion reactivity of SiO SB 2 sb -supported Co SB 2 sb C catalysts. Cobalt, Cobalt Carbide, EXAFS Spectroscopy, Impurity Effects, Syngas Conversion. [Extracted from the article]

[Display omitted] • Iridium pair sites supported on MOF UiO-66 synthesized from dimeric precursor. • Iridium pair sites located on interior MOF nodes. • Iridium pair sites more selective than isolated iridium atoms for ethylene hydrogenation. • HERFD-XANES helps to identify the ligand environment of iridium pair sites. • MOFs offer opportunities for precise synthesis of supported catalytic sites. Isolated metal pair sites on metal oxide and zeolite supports are drawing attention as catalysts, because—in contrast to single atomically dispersed metals—they provide neighboring metal centers that can act cooperatively. We now report pairs of iridium atoms anchored to the Zr 6 O 8 nodes of the metal–organic framework (MOF) UiO-66, synthesized by chemisorption of Ir 2 (μ-OCH 3) 2 (COD) 2 (COD is cyclooctadienyl) followed by removal of the COD ligands. The supported species were characterized with infrared spectra of adsorbed CO combined with iridium L III -edge extended X-ray absorption fine structure and high-energy-resolution fluorescence detection X-ray absorption near edge (HERFD XANES) spectra. The HERFD XANES spectra were recorded with the sample in a variety of atmospheres in which the iridium pair sites were stable, including CO, H 2 , and C 2 H 4 + H 2 at temperatures in the range of 35–80 °C. The data provide sensitive measures of the electronic structure of the iridium in the pair sites. The samples were evaluated as catalysts for ethylene hydrogenation, with the pair-sites being more selective for hydrogenation than analogous isolated atomically dispersed iridium, which catalyzes both hydrogenation and isomerization. Metal pair sites on MOFs offer uncharted opportunities for catalysts having reactivities associated with neighboring metal centers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomically dispersed supported metal catalysts are an emerging class of catalysts. • Maintaining atomic dispersion is a main challenge. • Ligands play a crucial role in this regard, but at the expense of loss in activity. • Carbonyl ligands were replaced with acetylene on supported rhodium complexes. • Acetylene ligands maintain atomic dispersion and do not inhibit hydrogenation. Facile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. Here, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in-situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti-sintering ability while retaining the hydrogenation activity. [ABSTRACT FROM AUTHOR]

We report the effects of alloying Cu into silica supported Pd nanoparticles on the catalytic activity, surface composition, and particle structure during CO oxidation Pd is highly active for CO oxidation but is inhibited by relevant competitive reagents (e.g. NO) at low temperatures (< 150 °C). By alloying Cu into Pd nanoparticles, NO inhibition is suppressed without any CO oxidation activity loss. Infrared spectroscopy illustrates the formation of surface nitrosyl (NO-Pd) is eliminated in the PdCu alloy catalyst, preventing CO oxidation inhibition by NO. X-ray absorption spectroscopy studies show that Pd in the monometallic catalyst forms a surface oxide after light-off. Conversely, in the PdCu catalyst, Pd remains metallic during reaction, independent of temperature, whereas the Cu oxidizes when the catalyst becomes active, after light-off. Furthermore, DRIFTS studies show that the Cu segregates to the surface as the catalyst becomes active for diesel oxidation, presumably becoming the O 2 adsorption site. [Display omitted] • PdCu alloys are more resistant than monometallic Pd to NO poisoning during CO oxidation. • FT-IR results show that the presence of Cu prevents surface nitrosyl formation on PdCu alloys. • Cu migrates to the surface of the catalyst nanoparticles during CO oxidation. • XAS measurements show Cu prevents the formation of Pd surface oxide during CO oxidation independent of reaction conditions. [ABSTRACT FROM AUTHOR]

High‐energy‐resolution fluorescence detection (HERFD) X‐ray absorption spectroscopy at SSRL is combined with density functional theory and FEFF simulations ascribing spectral features to ethylene and CO ligands adsorbed on catalytically active iridium centers isolated on zeolite HY and on MgO, pushing detection limits below those of conventional infrared spectroscopy, and allowing XAS to identify reactionary intermediates. More information can be found in the Full Paper by D. A. Dixon, S. R. Bare, B. C. Gates et al. on page 14760. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue are the groups of David A. Dixon at the University of Alabama, Simon R. Bare at Stanford Synchrotron Radiation Lightsource and Bruce C. Gates at the University of California, Davis. The image depicts a visual representation of the key conclusion of the work. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al2O3 using in situ/operando spectroscopy and ex situ aberration‐corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation. Rh clusters partially disperse into single atoms at room temperature and the extent of dispersion increases as the Rh size decreases and as the reaction temperature increases. A strong correlation is found between the extent of dispersion and the CO oxidation kinetics. More importantly, dispersing Rh clusters into single atoms increases the activity at room temperature by more than two orders of magnitude due to the much lower activation energy on single atoms (40 vs. 130 kJ/mol). This work demonstrates that the structure and reactivity of small Rh clusters are very sensitive to the reaction environment. [ABSTRACT FROM AUTHOR]

Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al2O3 using in situ/operando spectroscopy and ex situ aberration‐corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation. Rh clusters partially disperse into single atoms at room temperature and the extent of dispersion increases as the Rh size decreases and as the reaction temperature increases. A strong correlation is found between the extent of dispersion and the CO oxidation kinetics. More importantly, dispersing Rh clusters into single atoms increases the activity at room temperature by more than two orders of magnitude due to the much lower activation energy on single atoms (40 vs. 130 kJ/mol). This work demonstrates that the structure and reactivity of small Rh clusters are very sensitive to the reaction environment. [ABSTRACT FROM AUTHOR]

This paper presents software for calculating the optimal mass of samples with complex compositions (e.g. supported metal catalysts) for X-ray absorption spectroscopy (XAS) and scattering measurements. The ability to calculate the sample mass and other relevant parameters needed for an XAS measurement allows experimentalists to be better prepared in terms of detector selection, energy range of scan and overall time needed to complete the measurement, thus increasing efficiency. CatMass builds on existing sample mass calculators allowing users to determine the optimum sample preparation, collection geometry, usable energy range for a scan and approximate edge step of the absorption event. Visualization tools present the absorption calculation results in a format familiar to XAS experimentalists, with the added ability to save calculations and plots for future reference or recalculation. CatMass is a program broadly applicable in catalysis and is helpful for users with complex samples due to composition/stoichiometry or multiple competing elements. [ABSTRACT FROM AUTHOR]

Pd- and Pt-based catalysts are highly studied materials due to their widespread use in emissions control catalysis. However, claims continue to vary regarding the active phase and oxidation state of the metals. Different conclusions have likely been reached due to the heterogeneous nature of such materials containing various metal nanoparticle sizes and compositions, which may each possess unique redox features. In this work, using uniform nanocrystal catalysts, we study the effect of particle size and alloying on redox properties of Pd-based catalysts and show their contribution to methane combustion activity using operando quick extended x-ray absorption fine structure measurements. Results demonstrate that for all studied Pd sizes (3 nm–16 nm), Pd oxidation directly precedes CH4 combustion to CO2, suggesting Pd oxidation as a prerequisite step to methane combustion, and an oxidation pretreatment shows equal or better catalysis than a reduction pretreatment. Results are then extended to uniform alloyed PtxPd1−x nanoparticles, where oxidative pretreatments are shown to enhance low-temperature combustion. In these uniform alloys, we observe a composition-dependent effect with Pt-rich alloys showing the maximum difference between oxidative and reductive pretreatments. In Pt-rich alloys, we initially observe that the presence of Pt maintains Pd in a lower-activity reduced state. However, with time on stream, PdO eventually segregates under oxidizing combustion conditions, leading to a slowly increasing activity. Overall, across particle sizes and alloy compositions, we relate increased catalytic activity to Pd oxidation, thus shedding light on previous contrasting results related to the methane combustion activity of these catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ir(C 2 H 4) 2 complexes were synthesized on reduced graphene aerogel at 9.9 wt% Ir. • XAS data showed transformation of complexes into Ir 4 clusters in C 2 H 4 :H 2 = 1:1 flow. • Ir 4 clusters were further transformed into Ir 6 clusters when the feed was H 2 -rich. • Data further showed that Ir 6 clusters were even stable in pure H 2 at 100 °C. • Having neighboring metal centers in the clusters boosted hydrogenation performance. Transformation of atomically dispersed reduced graphene aerogel (rGA)-supported complexes, IrI(C 2 H 4) 2 +, with an iridium loading of 9.9 wt%, to form low-nuclearity clusters was investigated during ethylene hydrogenation catalysis. Continuous-scan X-ray absorption spectra demonstrate the formation of clusters well approximated as Ir 4 during reaction at 100 °C in flowing equimolar ethylene and H 2. The Ir 4 clusters transformed into clusters well approximated as Ir 6 when the feed molar ratio was switched to H 2 :C 2 H 4 = 2 and remained stable in pure H 2 at 100 °C. Catalyst performance data show that hydrogenation activity increased with metal nuclearity in the order of atomically dispersed iridium/rGA≪ Ir 4 /rGA < Ir 6 /rGA. Continuous scan X-ray absorption data, complemented with aberration-corrected scanning transmission electron microscopy images, demonstrate that the supported clusters approximated as Ir 6 are stable even in H 2 at atmospheric pressure and 100 °C. These supported iridium clusters are among the ones having the highest metal loadings reported for a supported metal cluster catalyst. [ABSTRACT FROM AUTHOR]

The conversion of CO2 into fuels and chemicals is an attractive option for mitigating CO2 emissions. Controlling the selectivity of this process is beneficial to produce desirable liquid fuels, but C-C coupling is a limiting step in the reaction that requires high pressures. Here, we propose a strategy to favor C-C coupling on a supported Ru/TiO2 catalyst by encapsulating it within the polymer layers of an imine-based porous organic polymer that controls its selectivity. Such polymer confinement modifies the CO2 hydrogenation behavior of the Ru surface, significantly enhancing the C2+ production turnover frequency by 10-fold. We demonstrate that the polymer layers affect the adsorption of reactants and intermediates while being stable under the demanding reaction conditions. Our findings highlight the promising opportunity of using polymer/metal interfaces for the rational engineering of active sites and as a general tool for controlling selective transformations in supported catalyst systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Specific parameters and suggestions are given for improving X-ray Absorption spectroscopy experimental reporting. • Standardization in reporting of XAS data analysis will improve reproducibility in fitting across the community. • Researchers are encouraged to plan experiments with beamline scientists to maximize their potential impact. [ABSTRACT FROM AUTHOR]

A single‐atom Pt1/CeO2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt2+ in a highly symmetric square‐planar Pt1O4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt2+ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt1/CeO2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO2 to generate Pt single atoms in an asymmetric Pt1O4 configuration. Owing to this unique coordination, Pt1δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt1/CeO2_TS catalyst was retained under oxidizing conditions. [ABSTRACT FROM AUTHOR]

A single‐atom Pt1/CeO2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt2+ in a highly symmetric square‐planar Pt1O4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt2+ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt1/CeO2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO2 to generate Pt single atoms in an asymmetric Pt1O4 configuration. Owing to this unique coordination, Pt1δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt1/CeO2_TS catalyst was retained under oxidizing conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • ALD Fe 2 O 3 -promoted Cu nanoparticles form interfaces for higher oxygenate synthesis. • Cu/Fe interfaces form via selective Fe 2 O 3 ALD on SiO 2 and reduction to Fe near Cu. • ALD Fe 2 O 3 inhibits sintering of silica-supported Cu nanoparticles. The conversion of syngas to higher oxygenates is an important step in the pathway towards the long-term sustainable production of fuels and chemicals. Mixed Cu/Fe catalysts combine metals with different CO activation characteristics, a property that makes them promising candidates for higher oxygenate production. However, Cu/Fe catalysts suffer from instability due to sintering and phase separation, and the active sites for higher oxygenate formation on these materials are not well understood. In this work, we use atomic layer deposition (ALD) to modify silica-supported Cu nanoparticles with monolayer precise amounts of Fe 2 O 3 and study the effects on catalyst structure, reactivity, and stability. We demonstrate that the Fe 2 O 3 ALD process is inherently selective towards deposition on the SiO 2 surface versus the Cu nanoparticles. As a result, a sufficiently thick Fe 2 O 3 layer surrounding the Cu nanoparticles acts as a barrier against Cu migration, preventing catalyst deactivation through sintering without covering the Cu. In syngas conversion reactions, we find that higher oxygenate selectivity increases with Fe 2 O 3 loading at low and intermediate ALD cycle numbers. Furthermore, using in situ X-ray absorption spectroscopy, we demonstrate that the Fe near the Cu nanoparticles is reduced to a metallic state under reaction conditions. From these measurements, we identify these metallic Cu/Fe interfaces as the active sites for higher oxygenate formation, which are most abundant at intermediate Fe 2 O 3 ALD cycle numbers. As the Fe 2 O 3 loading increases, higher oxygenate selectivity falls, resulting from encapsulation of the Cu nanoparticles by thick Fe 2 O 3 layers. The results demonstrate how thickness-controlled ALD Fe 2 O 3 can be used as both a promoter and stabilizer of Cu-based higher oxygenate synthesis catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rhodium has heretofore been known to be unselective for acetylene semi-hydrogenation. • Electronic properties of rhodium are tuned by choice of support and metal nuclearity. • Selectivity is maximized when Rh is atomically dispersed on a weak electron donor. • Zeolite-supported Rh complex with C 2 H 2 ligands offers a stable C 2 H 4 selectivity > 90 %. • Results demonstrate unprecedented catalytic properties of Rh for semi-hydrogenation. Supported rhodium catalysts are known to be unselective for semi-hydrogenation reactions. Here, by tuning the electronic structure of supported mononuclear rhodium sites determined by the metal nuclearity and the electron-donor properties of the support, we report that atomically dispersed HY zeolite-supported rhodium with reactive acetylene ligands affords a stable ethylene selectivity > 90 % for acetylene semi-hydrogenation at 373 K and atmospheric pressure, even when ethylene is present in a large excess over acetylene. Infrared and X-ray absorption spectra and measurements of rates of the catalytic reaction complemented with calculations at the level of density functional theory show how the catalyst performance depends on the electronic structure of the rhodium, influenced by the support as a ligand that is a weak electron donor. [ABSTRACT FROM AUTHOR]

Co2C, an emerging catalyst for the conversion of syngas to oxygenates, shows support‐sensitive behavior that has not yet been fully explained. Here, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO2, carbon, CeO2, and Al2O3 supports. We find that under syngas conditions, ZnO‐promoted Co transforms into Co2C on SiO2, carbon, and CeO2, but not on Al2O3. Moreover, the support affects the extent of carburization: while the SiO2‐supported catalyst carburizes completely, carbon‐ and CeO2‐supported catalysts show incomplete conversion of Co to Co2C. These three catalysts also exhibit different oxygenate selectivities. In contrast, the modified Al2O3‐supported catalyst retains the Fischer‐Tropsch catalytic properties of metallic Co. By depositing increasing amounts of Al2O3 by ALD on the SiO2 support, decreasing Co2C formation and oxygenate selectivity occurs. In‐situ XANES reveals that Al2O3 prevents Co2C formation by enabling the ZnO to restructure into ZnAl2O4 during reduction. Thus, in addition to modifying the active catalyst phase, the promoter can also strongly interact with the support, significantly impacting catalyst performance. [ABSTRACT FROM AUTHOR]

The effect of the Si/Al ratio of the ZSM-5 support on the structure and activity of Mo/HZSM-5 catalysts in methane dehydroaromatization (MDA) was studied. ZSM-5 (with Si/Al = 15, 25, and 40) supported Mo oxide catalysts (MoO x /ZSM-5) with 3 and 10 wt% Mo loading were prepared by incipient wetness impregnation followed by calcination in air at 500 °C. The as-prepared catalysts were activated by temperature programmed reduction in hydrogen in order to maximize Mo dispersion. To understand the structure-activity relationship, the fresh and spent samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N 2 adsorption isotherms, Scanning Transmission Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (STEM-EDS), X-ray absorption spectroscopy (EXAFS and XANES), thermogravimetric analysis (TGA), and Raman spectroscopy. The results show that the Si/Al ratio does not influence the the local structure around the Mo centers. It does however affect the number of available Brønsted acid sites in the support and the amount of Mo species entering the zeolite channels. A lower Si/Al ratio and higher Mo loading resulted in a higher Mo occupation within the zeolite channels. The higher channel occupation directly correlated with higher benzene selectivity and yield, as well as a lower catalyst deactivation rate. [ABSTRACT FROM AUTHOR]

Catalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water‐gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes. [ABSTRACT FROM AUTHOR]

Catalytic CO2 reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. One approach utilizes the reverse water‐gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes. [ABSTRACT FROM AUTHOR]

• Quantification of surface sites using reaction kinetics is demonstrated. • Ir single atoms and nanoparticles site fractions were measured using CO oxidation. • The results are in agreement with AC-STEM, DRIFTS and EXAFS. • Reaction conditions can be tailored to maximize sensitivity to a specific site. Supported metal single-atom catalysts have shown unique activity and selectivity for several reactions. Investigating the reaction mechanism on single-atom catalysts and unambiguous assignment of the activity and selectivity requires catalysts with exclusively single atoms. However, it is challenging to prepare pure single-atom catalysts with conventional impregnation methods, which typically result in a mixture of single atoms and nanoparticles. Here, we show that owing to different reaction mechanisms on single atoms and nanoparticles, reaction kinetics can serve as a surface sensitive characterization technique for quantifying their surface site fractions. As a case study, we use CO oxidation kinetics on Ir/MgAl 2 O 4 to quantify the surface site fractions of single atoms and nanoparticles and the results are consistent with aberration-corrected scanning transmission electron microscopy, X-ray absorption fine structure and infrared spectroscopies. Additionally, by carefully choosing the reaction conditions, the activity of single atoms (or nanoparticles) can be made dominant, enabling detection of a small fraction, or allowing a study of their reaction mechanism on a catalyst containing a mixture of single atoms and nanoparticles. These results are general and could be applied to other systems where two types of sites have different reaction mechanisms. [ABSTRACT FROM AUTHOR]

Keywords: CO oxidation; metal-support interactions; platinum; single-atom catalysis; thermal-shock synthesis EN CO oxidation metal-support interactions platinum single-atom catalysis thermal-shock synthesis 1 1 1 12/01/21 20211206 NES 211206 B Single-Atom Catalysis b Tailoring the local environment of platinum in single-atom Pt SB 1 sb /CeO SB 2 sb catalysts for robust low-temperature CO oxidation is reported by Abhaya K. Datye, Liangbing Hu, Yong Wang et al. in their Research Article on page 26054. Frontispiece: Tailoring the Local Environment of Platinum in Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation CO oxidation, metal-support interactions, platinum, single-atom catalysis, thermal-shock synthesis. [Extracted from the article]

Keywords: CO oxidation; metal-support interactions; platinum; single-atom catalysis; thermal-shock synthesis EN CO oxidation metal-support interactions platinum single-atom catalysis thermal-shock synthesis 1 1 1 12/01/21 20211206 NES 211206 B Einzelatomkatalyse b Die gezielte Abstimmung der lokalen Umgebung von Platin in Pt SB 1 sb /CeO SB 2 sb -Einzelatomkatalysatoren für die CO-Oxidation wird von Abhaya K. Datye, Liangbing Hu, Yong Wang et al. im Forschungsartikel auf S. 26258 beschrieben. Frontispiz: Tailoring the Local Environment of Platinum in Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation CO oxidation, metal-support interactions, platinum, single-atom catalysis, thermal-shock synthesis. [Extracted from the article]

We acquired Pd K-edge and Au L 3 -edge EXAFS spectra of two libraries of titania-supported Pd-doped Au nanoparticle catalysts representing the as-prepared and post-catalysis state. The nanoparticles have narrow particle size distributions, in the range 2.8–6.6 nm, and were synthesized to preferentially locate the palladium atoms on the surface of a gold core, with Pd mole fractions of 1.4–38%. EXAFS spectra of both the as-prepared samples and post-catalysis Pd-Au particles were collected and modeled. EXAFS refinement of all samples showed contributions from both Pd-Au and Pd-Pd scattering paths, revealing that Pd and Au components alloyed together. Pd was in a partially oxidized state as evidenced by a Pd-O scattering contribution, unlike Au. Overlaying measured coordination numbers from the libraries with predicted values, using models of surface and bulk alloying, showed that Pd restructures among Au as a result of exposure to the reaction conditions. • Data collected by two groups from two different synchrotrons. • Structural model developed for predicting coordination numbers for surface and bulk alloying. • Detailed modeling of EXAFS data from a library of Pd-doped Au nanoparticles. • Insight gained on the alloying as function particle size and composition. [ABSTRACT FROM AUTHOR]