Managing STEMIs without a Catheterization Lab: A Simulated Scenario to Improve Emergency Clinician Recognition and Execution of Thrombolysis in the Setting of Rural STEMI Management.

Audience: The targeted audience for this simulation is Emergency Medicine (EM) residents. Medical students, advanced practice providers, and staff physicians could all also find educational merit in this scenario. Background: Cardiovascular disease is the leading cause of death in the United States according to the CDC.1 Coronary artery disease caused 375,000 deaths 2021 alone, and about 5% of all adult patients have a prior history of coronary artery disease.2 Furthermore, chest pain itself is a common chief complaint encountered in the ED, with nearly 8 million visits annually occurring throughout the United States, with 10-20% of those patients ultimately being diagnosed with an acute coronary syndrome3, including ST-elevation myocardial infarction (STEMI). Given this, it is essential that EM residents are well prepared to care for all patients presenting with chest pain, regardless of the acute care or emergency setting.Throughout their training, most EM residents typically learn and evaluate patients at a large tertiary or quaternary medical center with 24-hour catheterization laboratory availability. For patients presenting with electrocardiogram (EKG) findings consistent with STEMI, the standard of care is for the patient to undergo cardiac catheterization and stent placement within 90 minutes of arrival. Unfortunately, only half of patients living in rural areas have a cardiac catheterization-capable facility available to them within a 60-minute driving radius, making it difficult for those patients to undergo cardiac catheterization within the desired time frame.4 These patients remain candidates for thrombolytic therapy, but given infrequent opportunities to learn about and deploy thrombolytic agents during residency training, graduating EM residents may be unfamiliar with indications, dosing, and contraindications before they begin practice. Furthermore, the recent EM workforce data suggests that although there may be an oversupply of 8,000 emergency physicians by 2030, robust practice opportunities for emergency physicians remain in rural settings.5 Although historically EM graduates have not selected rural areas for practice, with only approximately 8% of emergency physicians practicing in rural areas,6 it is likely that given the opportunities present and perceived saturation in many non-rural settings, more EM graduates will pursue practice in a rural setting. With these changing practice dynamics in mind, this simulation provides the opportunity for residents and medical students to experience the management of a STEMI in the rural setting, with a focus upon the indications, contraindications, dosing, and disposition of a patient receiving thrombolytics. Educational Objectives: By the end of this simulation, learners will be able to:Diagnose ST elevation myocardial infarction accurately and initiate thrombolysis in the rural setting without timely access to cardiac catheterization.Engage the simulated patient in a shared decision-making conversation, clearly outlying the benefits and risks of thrombolysis.Identify the indications and contraindications for thrombolysis in ST elevation myocardial infarction.Arrange for transfer to a tertiary care center following completion of thrombolysis. Educational Methods: This scenario is a simulated encounter in a rural emergency department setting requiring the diagnosis of a STEMI, a discussion with the patient regarding the risks and benefits of thrombolysis prior to administration, administration of thrombolysis, and transfer of patient to a higher level of care. Research Methods: The educational content of this simulation as a teaching instrument was evaluated by the learner utilizing an internally developed survey after case completion. This survey was reviewed for precision of language and assessment of learning objectives by our simulation faculty and other members of our West Virginia University Emergency Medicine Department of Medical Education. The learner was asked to specify any prior experience with rural STEMI management as well as quantify via a five-point Likert Scale, where 1 = very uncomfortable and 5 = very comfortable, their level of comfort with thrombolysis before and after the scenario as well as their comfort with having a shared decision-making conversation with patients with regards to thrombolysis. Learners were also asked to rank the helpfulness of this simulation in preparing them for administering thrombolytics for STEMI in a rural setting on a five-point Likert scale, where 1 = not helpful and 5 =very helpful. An open response section was also provided to allow learners the opportunity to comment directly on any aspect of the simulation. Results: Data was collected anonymously from 16 PGY1-3 resident learners via surveys with a 100% response rate. Overall, the feedback received regarding the simulation was positive. There was a low average comfort level with administering thrombolytics and having a shared decision-making conversation regarding administering thrombolytics. There was a high average rating of the helpfulness of this simulation in preparing residents for this conversation as well as managing STEMIs in a rural setting. Subjective comments regarding the simulation were universally positive. Discussion: The management of STEMI in the rural emergency department differs significantly from the environment in which many EM residents train. As a leading cause of death in the United States, STEMI management is a vital component of EM resident education. Although the concept of thrombolysis in the rural setting is discussed, the opportunity for real-world experience in its execution is often limited despite many graduates ultimately working in rural emergency departments. This simulation sought to provide a realistic patient encounter to promote familiarity and comfort in the identification, patient discussion and execution of thrombolysis in the treatment of a STEMI. The educational content was shown to be effective via learner survey completion.

Does the Subtalar or Tibiotalar Joint Need Fused in Primary Retrograde Tibiotalocalcaneal Nailing for Fragility Ankle Fractures?

BACKGROUND: As an alternative to traditional open reduction internal fixation of ankle fragility fractures, primary retrograde tibiotalocalcaneal (TTC) nailing has been investigated as a treatment option. These results suggest that this treatment is an acceptable alternative treatment option for these injuries. There are still questions about the need for formal joint preparation at the subtalar or tibiotalar joint when performing primary TTC nailing for fragility fractures. METHODS: In this study, we retrospectively evaluated 32 patients treated with primary retrograde TTC nail without subtalar or tibiotalar joint preparation for a mean of 2.4 years postoperatively. We specifically reviewed the charts for nail breakages at either joint, patients developing subtalar or tibiotalar joint pathology requiring additional treatment, including return to the operating room for formal joint preparation. RESULTS: Fracture union occurred in 100% of patients. There were 3 cases (10.0%) of hardware failure, and 2 of these cases were asymptomatic and did not require any treatment. One patient (3.3%) developed hardware failure with nail breakage at the subtalar joint. This patient developed progressive pain and symptoms requiring revision surgery with formal arthrodesis of the subtalar and tibiotalar joint. CONCLUSIONS: This study shows that retrograde hindfoot nailing without formal subtalar or tibiotalar joint preparation is an acceptable potential treatment option in ankle fragility fractures. Mid-term follow-up demonstrates favorable outcomes without the need for formal joint preparation in this high-risk population. Comparative studies with higher patient numbers and long-term follow-up are needed to confirm the results of this study.Levels of Evidence: Level IV.

Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations.

Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.

The relations between growth mindset, motivational beliefs, and career interest in math intensive fields in informal STEM youth programs.

Past research has shown that growth mindset and motivational beliefs have an important role in math and science career interest in adolescence. Drawing on situated expectancy-value theory (SEVT), this study extends these findings by investigating the role of parental motivational beliefs (e.g., expectancy beliefs, utility values) and parent growth mindset in math on adolescent career interest in math-intensive fields (e.g., mathematics, computer science, statistics, and engineering; MCSE) through adolescent motivational beliefs in math. Structural equation modeling was used to test the hypothesized model using data from 290 adolescents (201 girls, 69.3%; Mage = 15.20), who participate in informal STEM (science, technology, engineering, mathematics) youth programs, and their parents (162 parents, 87.7% female) in the United Kingdom and the United States. As hypothesized, adolescent expectancy beliefs, utility values, and growth mindset in math had a significant direct effect on MCSE career interest. Further, there was a significant indirect effect of parental expectancy beliefs in math on MCSE career interest through adolescents' expectancy beliefs. Similarly, there was a significant indirect effect from parental utility values in math to MCSE career interest through adolescents' utility values. The findings suggest that parents' math motivational beliefs play a critical role in adolescent math motivational beliefs and their career interest in math-intensive fields.

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation.

The reduction of CO2 is known to promote increased alkene yields from alkane dehydrogenations when the reactions are cocatalyzed. The mechanism of this promotion is not understood in the context of catalyst active-site environments because CO2 is amphoteric, and even general aspects of the chemistry, including the significance of competing side reactions, differ significantly across catalysts. Atomically dispersed chromium cations stabilized in highly siliceous MFI zeolite are shown here to enable the study of the role of parallel CO2 reduction during ethylene-selective ethane dehydrogenation. Based on infrared spectroscopy and X-ray absorption spectroscopy data interpreted through calculations using density functional theory (DFT), the synthesized catalyst contains atomically dispersed Cr cations stabilized by silanol nests in micropores. Reactor studies show that cofeeding CO2 increases stable ethylene-selective ethane dehydrogenation rates over a wide range of partial pressures. Operando X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra indicate that during reaction at 650 °C the Cr cations maintain a nominal 2+ charge and a total Cr-O coordination number of approximately 2. However, CO2 reduction induces a change, correlated with the CO2 partial pressure, in the population of two distinct Cr-O scattering paths. This indicates that the promotional effect of parallel CO2 reduction can be attributed to a subtle change in Cr-O bond lengths in the local coordination environment of the active site. These insights are made possible by simultaneously fitting multiple EXAFS spectra recorded in different reaction conditions; this novel procedure is expected to be generally applicable for interpreting operando catalysis EXAFS data.

Children's and adolescents' evaluations of wealth-related STEM inequality.

The fields of science, technology, engineering, and mathematics (STEM) are rife with inequalities and under-representation that have their roots in childhood. While researchers have focused on gender and race/ethnicity as two key dimensions of inequality, less attention has been paid to wealth. To this end, and drawing from the Social Reasoning Development approach, we examined children's and adolescents' perceptions of STEM ability and access to opportunities as a function of wealth, as well as their desire to rectify such inequalities. Participants (n = 234: early childhood, n = 70, mean age = 6.33, SD = .79; middle childhood, n = 92, mean age = 8.90, SD = .83 and early adolescence, n = 62, mean age = 12.00; SD = 1.16) in the U.K. (64% White British) and U.S. (40% White/European American) read about two characters, one high-wealth and one low-wealth. In early childhood, participants reported that the high-wealth character would have greater STEM ability and were just as likely to invite either character to take part in a STEM opportunity. By middle childhood, participants were more likely to report equal STEM abilities for both characters and to seek to rectify inequalities by inviting the low-wealth character to take part in a STEM opportunity. However, older participants reported that peers would still prefer to invite the high-wealth character. These findings also varied by ethnic group status, with minority status participants rectifying inequalities at a younger age than majority status participants. Together these findings document that children are aware of STEM inequalities based on wealth and, with age, will increasingly seek to rectify these inequalities.

Developmental Trajectories of Adolescents' Math Motivation: The Role of Mindset and Perceptions of Informal STEM Learning Site Inclusivity.

Motivation is a key factor in engagement, achievement, and career choices in science, technology, engineering, and mathematics (STEM). While existing research has focused on student motivation toward math in formal school programs, new work is needed that focuses on motivation for those involved in informal STEM programs. Specifically, the role of math mindset and perceived inclusivity of informal STEM sites (to those of varying gender and ethnic backgrounds) on longitudinal trajectories of adolescents' math motivation has not been explored. This study investigates longitudinal changes in math expectancy, interest, and utility values and the effects of math fixed mindset, math growth mindset, and perceptions of the inclusivity of informal STEM learning sites on these changes for adolescents participating in STEM programs at these informal sites in the United Kingdom and the United States (n = 249, MT1age = 15.2, SD = 1.59). Three latent growth curve models were tested. The data suggest that math expectancy, interest, and utility values declined over three years. Growth mindset positively predicted changes in utility, while fixed mindset negatively predicted changes in utility. Inclusivity positively influenced the initial levels of utility. Girls reported lower initial expectancy than boys. Age influenced both the initial levels and rate of change for expectancy. Older adolescents had lower levels of expectancy compared to their younger counterparts; however, they had a less steep decline in expectancy over three years. These findings suggest that designing inclusive learning environments and promoting growth mindset may encourage math motivation.

Dynamic Behavior of Platinum Atoms and Clusters in the Native Oxide Layer of Aluminum Nanocrystals.

Strong metal-support interactions (SMSIs) are well-known in the field of heterogeneous catalysis to induce the encapsulation of platinum (Pt) group metals by oxide supports through high temperature H2 reduction. However, demonstrations of SMSI overlayers have largely been limited to reducible oxides, such as TiO2 and Nb2O5. Here, we show that the amorphous native surface oxide of plasmonic aluminum nanocrystals (AlNCs) exhibits SMSI-induced encapsulation of Pt following reduction in H2 in a Pt structure dependent manner. Reductive treatment in H2 at 300 °C induces the formation of an AlOx SMSI overlayer on Pt clusters, leaving Pt single-atom sites (Ptiso) exposed available for catalysis. The remaining exposed Ptiso species possess a more uniform local coordination environment than has been observed on other forms of Al2O3, suggesting that the AlOx native oxide of AlNCs presents well-defined anchoring sites for individual Pt atoms. This observation extends our understanding of SMSIs by providing evidence that H2-induced encapsulation can occur for a wider variety of materials and should stimulate expanded studies of this effect to include nonreducible oxides with oxygen defects and the presence of disorder. It also suggests that the single-atom sites created in this manner, when combined with the plasmonic properties of the Al nanocrystal core, may allow for site-specific single-atom plasmonic photocatalysis, providing dynamic control over the light-driven reactivity in these systems.

Impact of Local Structure in Supported CaO Catalysts for Soft-Oxidant-Assisted Methane Coupling Assessed through Ca K-Edge X-ray Absorption Spectroscopy.

Soft-oxidant-assisted methane coupling has emerged as a promising pathway to upgrade methane from natural gas sources to high-value commodity chemicals, such as ethylene, at selectivities higher than those associated with oxidative (O2) methane coupling (OCM). To date, few studies have reported investigations into the electronic structure and the microscopic physical structure of catalytic active sites present in the binary metal oxide catalyst systems that are known to be effective for this reaction. Correlating the catalyst activity to specific active site structures and electronic properties is an essential aspect of catalyst design. Here, we used X-ray absorption spectroscopy at the Ca K-edge to ascertain the most probable local environment of Ca in the ZnO-supported Ca oxide catalysts. These catalysts are shown here to be active for N2O-assisted methane coupling (N2O-OCM) and have previously been reported to be active for CO2-assisted methane coupling (CO2-OCM). X-ray absorption near edge structure features at multiple Ca loadings are interpreted through simulated spectra derived from ab initio full multiple scattering calculations. These simulations included consideration of CaO structures organized in multiple spatial arrangements-linear, planar, and cubic-with separate analyses of Ca atoms in the surfaces and bulk of the three-dimensional structures. The morphology of the oxide clusters was found to influence the various regions of the X-ray absorption spectrum differently. Experiment and theory show that for low-Ca-loading catalysts (≤1 mol %), which contain sites particularly active for methane coupling, Ca primarily exists in an oxidized state that is consistent with the coordination environment of Ca ions in one- and two-dimensional clusters. In addition to their unique nanoscale structures, the spectra also indicate that these clusters have varying degrees of undercoordinated surface Ca atoms that could further influence their catalytic activities. The local Ca structure was correlated to methane coupling activity from N2O-OCM and previously reported CO2-OCM reactor studies. This study provides a unique perspective on the relationship between the catalyst physical and electronic structure and active sites for soft-oxidant-assisted methane coupling, which can be used to inform future catalyst development.

Daily Fluctuations in Adolescents' Perceived Friend Dominance and Friendship Clout: Associations with Mood and the Moderating Role of Anxiety.

Emerging evidence suggests that whereas occupying high peer status promotes adolescents' well-being, feeling dominated by friends confers psychological costs. However, little is known about day-to-day power dynamics of adolescents' friendships or their acute affective consequences. This 14-day intensive longitudinal study introduced novel daily assessments of friend dominance and friendship clout, examined their associations with mood, and tested anxiety as a moderator. Participants were 195 11th-graders (Mage = 16.48, SDage = 0.35; 66% female). Multilevel models revealed that adolescents experienced worse mood on days they felt dominated by friends and better mood on days they felt powerful and influential among friends. Associations with negative mood were strongest for adolescents higher in anxiety. The findings underscore the dynamic nature of power in adolescents' friendships.

Reciprocal Associations Between Science Efficacy, STEM Identity and Scientist Career Interest Among Adolescent Girls within the Context of Informal Science Learning.

Limited research has explored the longitudinal pathway to youth career interests via identity and efficacy together. This study examined the longitudinal associations between science efficacy, STEM (science, technology, engineering and math) identity, and scientist career interest among girls who are historically considered as an underrepresented group among scientists. The sample included 308 girls (M age = 15.22, SD age = 1.66; 42.8% White) from six STEM youth programs, each at a different informal science learning site within the U.K. and the U.S. Longitudinal structural equation modelling demonstrated that science efficacy consistently predicted STEM identity and scientist career interest, and similarly, STEM identity consistently predicted science efficacy over a two-year period. Scientist career interest at 12 months predicted science efficacy at 24 months. The coefficients of efficacy predicting STEM identity and scientist career interest were significantly larger compared to STEM identity and scientist career interest in predicting science efficacy from 12 months to 24 months. Further mediation analysis supported a significant pathway from STEM identity at 3 months to scientist career interest at 24 months via 12-month science efficacy. The findings highlight that science efficacy and STEM identity for girls relate to their scientist career interest and these longitudinal associations are reciprocal. This study suggests that science efficacy and STEM identity mutually influence each other, and enhancing science efficacy and STEM identity is key to promoting adolescents' interest in being a scientist.

Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials.

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

Aqueous Structure of Lanthanide-EDTA Coordination Complexes Determined by a Combined DFT/EXAFS Approach.

Sustainable production of rare earth elements (REEs) is critical for technologies needed for climate change mitigation, including wind turbines and electric vehicles. However, separation technologies currently used in REE production have large environmental footprints, necessitating more sustainable strategies. Aqueous, affinity-based separations are examples of such strategies. To make these technologies feasible, it is imperative to connect aqueous ligand structure to ligand selectivity for individual REEs. As a step toward this goal, we analyzed the extended X-ray absorption fine structure (EXAFS) of four lanthanides (La, Ce, Pr, and Nd) complexed by a common REE chelator, ethylenediaminetetraacetic acid (EDTA) to determine the aqueous-phase structure. Reference structures from density functional theory (DFT) were used to help fit the EXAFS spectra. We found that all four Ln-EDTA coordination complexes formed 9-coordinate structures with 6 coordinating atoms from EDTA (4 carboxyl oxygen atoms and 2 nitrogen atoms) and 3 oxygen atoms from water molecules. All EXAFS fits were of high quality (R-factor < 0.02) and showed decreasing average first-shell coordination distance across the series (2.62-2.57 Å from La-Nd), in agreement with DFT (2.65-2.56 Å from La-Nd). The insights determined herein will be useful in the development of ligands for sustainable rare earth elements (REE) separation technologies.

CatMass: software for calculating optimal sample masses for X-ray absorption spectroscopy experiments involving complex sample compositions.

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.

Preparing the Next Generation for STEM: Adolescent Profiles Encompassing Math and Science Motivation and Interpersonal Skills and Their Associations With Identity and Belonging.

Science, technology, engineering, and math (STEM) workers need both motivation and interpersonal skills in STEM disciplines. The aims of the study were to identify clusters of adolescents who vary in math and science motivation and interpersonal skills and to explore what factors are related to membership in a high math and science motivation and interpersonal skills cluster. Participants included 467 adolescents (312 female; Mage = 15.12 to SD = 1.71 year) recruited from out-of-school STEM programs in the US and UK. Findings from latent class analyses revealed four clusters, including a "High Math and Science Motivation and Interpersonal Skills" group, as well as groups that exhibited lower levels of either motivation or interpersonal skills. STEM program belonging, and STEM identity are related to membership in the high motivation and skills cluster. Findings provide insight into factors that may encourage motivation and interpersonal skills in adolescents, preparing them for STEM workforce entry.

Size-Dependent Dispersion of Rhodium Clusters into Isolated Single Atoms at Low Temperature and the Consequences for CO Oxidation Activity.

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 Al2 O3 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.

Observations of Ethylene-for-CO Ligand Exchanges on a Zeolite-Supported Single-Site Rh Catalyst by X-ray Absorption Spectroscopy.

Quick-scanning X-ray absorption fine structure (QXAFS) measurements were used to characterize the exchanges of ethylene and CO ligands in a zeolite HY-supported single-site Rh complex at a sampling rate of 1.0 Hz. The two ligands were reversibly exchanged on the rhodium, with quantitative results determined for the C2H4-for-CO exchange that are consistent with a first-order process. The apparent rate constant for the exchange decreased with increasing temperature. Fourier-transform infrared spectra characterizing the C2H4 sorbed in the zeolite showed that the amount decreased with increasing temperature, consistent with the decrease in the exchange rate with increasing temperature. The results, illustrating the dynamics of ligand exchanges on a single-site supported metal catalyst, demonstrate the broad emerging applicability of the QXAFS technique for characterizing the dynamics of reactive intermediates on catalysts.

Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation.

Single atoms of platinum group metals on CeO2 represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt1) on CeO2, i.e., adsorbed Pt1 in Pt/CeO2 and square planar Pt1 in PtATCeO2, fabricated at 500 °C and by atom-trapping method at 800 °C, respectively. Adsorbed Pt1 in Pt/CeO2 is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order in CO. In contrast, square planar Pt1 in PtATCeO2 is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO2 and PtATCeO2 in CO transforms Pt1 to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt1 state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.

Dynamic Evolution of Palladium Single Atoms on Anatase Titania Support Determines the Reverse Water-Gas Shift Activity.

Research interest in single-atom catalysts (SACs) has been continuously increasing. However, the lack of understanding of the dynamic behaviors of SACs during applications hinders catalyst development and mechanistic understanding. Herein, we report on the evolution of active sites over Pd/TiO2-anatase SAC (Pd1/TiO2) in the reverse water-gas shift (rWGS) reaction. Combining kinetics, in situ characterization, and theory, we show that at T ≥ 350 °C, the reduction of TiO2 by H2 alters the coordination environment of Pd, creating Pd sites with partially cleaved Pd-O interfacial bonds and a unique electronic structure that exhibit high intrinsic rWGS activity through the carboxyl pathway. The activation by H2 is accompanied by the partial sintering of single Pd atoms (Pd1) into disordered, flat, ∼1 nm diameter clusters (Pdn). The highly active Pd sites in the new coordination environment under H2 are eliminated by oxidation, which, when performed at a high temperature, also redisperses Pdn and facilitates the reduction of TiO2. In contrast, Pd1 sinters into crystalline, ∼5 nm particles (PdNP) during CO treatment, deactivating Pd1/TiO2. During the rWGS reaction, the two Pd evolution pathways coexist. The activation by H2 dominates, leading to the increasing rate with time-on-stream, and steady-state Pd active sites similar to the ones formed under H2. This work demonstrates how the coordination environment and nuclearity of metal sites on a SAC evolve during catalysis and pretreatments and how their activity is modulated by these behaviors. These insights on SAC dynamics and the structure-function relationship are valuable to mechanistic understanding and catalyst design.