Selective C-H Bond Activation in Propane with Molecular Oxygen over Cu(I)-ZSM-5 at Ambient Conditions.

Selective activation of C-H bonds in light alkanes under mild conditions is challenging but holds the promise of efficient upgrading of abundant hydrocarbons. In this work, we report the conversion of propane to propylene with ∼95% selectivity on Cu(I)-ZSM-5 with O2 at room temperature and pressure. The intraporous Cu(I) species was oxidized to Cu(II) during the reaction but could be regenerated with H2 at 220 °C. Diffuse reflectance ultraviolet spectroscopy indicated the presence of both Cu+-O2 and Cu2(µ-O2)2+ species in the zeolite pores during the reaction, and electron paramagnetic resonance results showed that propane activation occurred via a radical-mediated pathway distinct from that with H2O2 as the oxidant. Correlation between spectroscopic and reactivity results on Cu(I)-ZSM-5 with different Cu loadings suggests that the isolated intraporous Cu(I) species is the main active species in propane activation.

Incidence and risk factors of active tuberculosis among older individuals with latent tuberculosis infection: a cohort study in two high-epidemic sites in eastern China.

Background: The influencing factors of the process from latent tuberculosis infection (LTBI) to the onset of active tuberculosis (TB) remain unknown among different population groups, especially among older individuals in high-incidence areas. This study aimed to investigate the development of active TB among older adults with LTBI and identify groups in greatest need of improved prevention and control strategies for TB. Methods: In 2021, we implemented an investigation among older individuals (≥ 65 years old) in two towns in Zhejiang Province with the highest incidence of TB. All participants underwent assessment using standardized questionnaires, physical examinations, interferon-gamma release assays, and chest radiography. All the participants with suspected TB based on the clinical symptoms or abnormal chest radiography results, as well as those with LTBI, were referred for diagnostic investigation in accordance with the national guidelines. Those with an initial diagnosis of TB were then excluded, whereas those with LTBI were included in a follow-up at baseline. Incident patients with active TB were identified from the Chinese Tuberculosis Management Information System, and a multivariate Cox regression model was used to estimate the incidence and risk of TB among those with LTBI. Results: In total, 667 participants with LTBI were followed up for 1,315.3 person-years, revealing a disease density of 1,292.5 individuals/100,000 person-years (17/1,315.3). For those with LTBI, chest radiograph abnormalities had adjusted hazard ratios for active TB of 4.9 (1.6-15.3). Conclusions: The presence of abnormal chest radiography findings increased the risk of active TB among older individuals with LTBI in high-epidemic sites in eastern China.

Constructing Metal(II)-Sulfate Site Catalysts toward Low Overpotential Carbon Dioxide Electroreduction to Fuel Chemicals.

Precise regulation of the active site structure is an important means to enhance the activity and selectivity of catalysts in CO2 electroreduction. Here, we creatively introduce anionic groups, which can not only stabilize metal sites with strong coordination ability but also have rich interactions with protons at active sites to modify the electronic structure and proton transfer process of catalysts. This strategy helps to convert CO2 into fuel chemicals at low overpotentials. As a typical example, a composite catalyst, CuO/Cu-NSO4/CN, with highly dispersed Cu(II)-SO4 sites has been reported, in which CO2 electroreduction to formate occurs at a low overpotential with a high Faradaic efficiency (-0.5 V vs. RHE, FEformate=87.4 %). Pure HCOOH is produced with an energy conversion efficiency of 44.3 % at a cell voltage of 2.8 V. Theoretical modeling demonstrates that sulfate promotes CO2 transformation into a carboxyl intermediate followed by HCOOH generation, whose mechanism is significantly different from that of the traditional process via a formate intermediate for HCOOH production.

Influence of electric double layer rigidity on CO adsorption and electroreduction rate.

Understanding the structure of the electric double layer (EDL) is critical for designing efficient electrocatalytic processes. However, the interplay between reactant adsorbates and the concentrated ionic species within the EDL remains an aspect that has yet to be fully explored. In the present study, we employ electrochemical CO reduction on Cu as a model reaction to reveal the significant impact of EDL structure on CO adsorption. By altering the sequence of applying negative potential and elevating CO pressure, we discern two distinct EDL structures with varying cation density and CO coverage. Our findings demonstrate that the EDL comprising densely packed cations substantially hinders CO adsorption on the Cu as opposed to the EDL containing less compact cations. These two different EDL structures remained stable over the course of our experiments, despite their identical initial and final conditions, suggesting an insurmountable kinetic barrier present in between. Moreover, we show that the size and identity of cations play decisive roles in determining the properties of the EDL in CO electroreduction on Cu. This study presents a refined adaptation of the classical Gouy-Chapman-Stern model and highlights its catalytic importance, which bridges the mechanistic gap between the EDL structure and cathodic reactions.

Dual-site segmentally synergistic catalysis mechanism: boosting CoFeSx nanocluster for sustainable water oxidation.

Efficient oxygen evolution reaction electrocatalysts are essential for sustainable clean energy conversion. However, catalytic materials followed the conventional adsorbate evolution mechanism (AEM) with the inherent scaling relationship between key oxygen intermediates *OOH and *OH, or the lattice-oxygen-mediated mechanism (LOM) with the possible lattice oxygen migration and structural reconstruction, which are not favorable to the balance between high activity and stability. Herein, we propose an unconventional Co-Fe dual-site segmentally synergistic mechanism (DSSM) for single-domain ferromagnetic catalyst CoFeSx nanoclusters on carbon nanotubes (CNT) (CFS-ACs/CNT), which can effectively break the scaling relationship without sacrificing stability. Co3+ (L.S, t2g6eg0) supplies the strongest OH* adsorption energy, while Fe3+ (M.S, t2g4eg1) exposes strong O* adsorption. These dual-sites synergistically produce of Co-O-O-Fe intermediates, thereby accelerating the release of triplet-state oxygen ( ↑ O = O ↑ ). As predicted, the prepared CFS-ACs/CNT catalyst exhibits less overpotential than that of commercial IrO2, as well as approximately 633 h of stability without significant potential loss.

Efficient conversion of propane in a microchannel reactor at ambient conditions.

The oxidative dehydrogenation of propane, primarily sourced from shale gas, holds promise in meeting the surging global demand for propylene. However, this process necessitates high operating temperatures, which amplifies safety concerns in its application due to the use of mixed propane and oxygen. Moreover, these elevated temperatures may heighten the risk of overoxidation, leading to carbon dioxide formation. Here we introduce a microchannel reaction system designed for the oxidative dehydrogenation of propane within an aqueous environment, enabling highly selective and active propylene production at room temperature and ambient pressure with mitigated safety risks. A propylene selectivity of over 92% and production rate of 19.57 mmol mCu-2 h-1 are simultaneously achieved. This exceptional performance stems from the in situ creation of a highly active, oxygen-containing Cu catalytic surface for propane activation, and the enhanced propane transfer via an enlarged gas-liquid interfacial area and a reduced diffusion path by establishing a gas-liquid Taylor flow using a custom-made T-junction microdevice. This microchannel reaction system offers an appealing approach to accelerate gas-liquid-solid reactions limited by the solubility of gaseous reactant.

Mechanistic insights into C-C coupling in electrochemical CO reduction using gold superlattices.

Developing in situ/operando spectroscopic techniques with high sensitivity and reproducibility is of great importance for mechanistic investigations of surface-mediated electrochemical reactions. Herein, we report the fabrication of highly ordered rhombic gold nanocube superlattices (GNSs) as substrates for surface-enhanced infrared absorption spectroscopy (SEIRAS) with significantly enhanced SEIRA effect, which can be controlled by manipulating the randomness of GNSs. Finite difference time domain simulations reveal that the electromagnetic effect accounts for the significantly improved spectroscopic vibrations on the GNSs. In situ SEIRAS results show that the vibrations of CO on the Cu2O surfaces have been enhanced by 2.4 ± 0.5 and 18.0 ± 1.3 times using GNSs as substrates compared to those on traditional chemically deposited gold films in acidic and neutral electrolytes, respectively. Combined with isotopic labeling experiments, the reaction mechanisms for C-C coupling of CO electroreduction on Cu-based catalysts are revealed using the GNSs substrates.

Mechanistic Implications of Low CO Coverage on Cu in the Electrochemical CO and CO2 Reduction Reactions.

Electrochemical CO or CO2 reduction reactions (CO(2)RR), powered by renewable energy, represent one of the promising strategies for upgrading CO2 to valuable products. To design efficient and selective catalysts for the CO(2)RR, a comprehensive mechanistic understanding is necessary, including a comprehensive understanding of the reaction network and the identity of kinetically relevant steps. Surface-adsorbed CO (COad) is the most commonly reported reaction intermediate in the CO(2)RR, and its surface coverage (θCO) and binding energy are proposed to be key to the catalytic performance. Recent experimental evidence sugguests that θCO on Cu electrode at electrochemical conditions is quite low (∼0.05 monolayer), while relatively high θCO is often assumed in literature mechanistic discussion. This Perspective briefly summarizes existing efforts in determining θCO on Cu surfaces, analyzes mechanistic impacts of low θCO on the reaction pathway and catalytic performance, and discusses potential fruitful future directions in advancing our understanding of the Cu-catalyzed CO(2)RR.

Action at a distance: organic cation induced long range organization of interfacial water enhances hydrogen evolution and oxidation kinetics.

Engineering efficient electrode-electrolyte interfaces for the hydrogen evolution and oxidation reactions (HOR/HER) is central to the growing hydrogen economy. Existing descriptors for HOR/HER catalysts focused on species that could directly impact the immediate micro-environment of surface-mediated reactions, such as the binding energies of adsorbates. In this work, we demonstrate that bulky organic cations, such as tetrapropyl ammonium, are able to induce a long-range structure of interfacial water molecules and enhance the HOR/HER kinetics even though they are located outside the outer Helmholtz plane. Through a combination of electrokinetic analysis, molecular dynamics and in situ spectroscopic investigations, we propose that the structure-making ability of bulky hydrophobic cations promotes the formation of hydrogen-bonded water chains connecting the electrode surface to the bulk electrolyte. In alkaline electrolytes, the HOR/HER involve the activation of interfacial water by donating or abstracting protons. The structural diffusion mechanism of protons in aqueous electrolytes enables water molecules and cations located at a distance from the electrode to influence surface-mediated reactions. The findings reported in this work highlight the prospect of leveraging the nonlocal mechanism to enhance electrocatalytic performance.

CO Binding Energy is an Incomplete Descriptor of Cu-Based Catalysts for the Electrochemical CO2 Reduction Reaction.

CO binding energy has been employed as a descriptor in the catalyst design for the electrochemical CO2 reduction reactions (CO2 RR). The reliability of the descriptor has yet been experimentally verified due to the lack of suitable methods to determine CO binding energies. In this work, we determined the standard CO adsorption enthalpies ( Δ H C O ∘ ${\Delta {H}_{CO}^{^\circ{}}}$ ) of undoped and doped oxide-derived Cu (OD-Cu) samples, and for the first time established the correlation of Δ H C O ∘ ${\Delta {H}_{CO}^{^\circ{}}}$ with the Faradaic efficiencies (FE) for C2+ products. A clear volcano shaped dependence of the FE for C2+ products on Δ H C O ∘ ${\Delta {H}_{CO}^{^\circ{}}}$ is observed on OD-Cu catalysts prepared with the same hydrothermal durations, however, the trend becomes less clear when all catalysts investigated are taken into account. The relative abundance of Cu sites active for the CO2 -to-CO conversion and the further reduction of CO is identified as another key descriptor.

Rationalizing kinetic behaviors of isolated boron sites catalyzed oxidative dehydrogenation of propane.

Boron-based catalysts exhibit high alkene selectivity in oxidative dehydrogenation of propane (ODHP) but the mechanistic understanding remains incomplete. In this work, we show that the hydroxylation of framework boron species via steaming not only enhances the ODHP rate on both B-MFI and B-BEA, but also impacts the kinetics of the reaction. The altered activity, propane reaction order and the activation energy could be attributed to the hydrolysis of framework [B(OSi≡)3] unit to [B(OSi≡)3-x(OH···O(H)Si≡)x] (x = 1, 2, "···" represents hydrogen bonding). DFT calculations confirm that hydroxylated framework boron sites could stabilize radical species, e.g., hydroperoxyl radical, further facilitating the gas-phase radical mechanism. Variations in the contributions from gas-phase radical mechanisms in ODHP lead to the linear correlation between activation enthalpy and entropy on borosilicate zeolites. Insights gained in this work offer a general mechanistic framework to rationalize the kinetic behavior of the ODHP on boron-based catalysts.

Bifunctional Near-Neutral Electrolyte Enhances Oxygen Evolution Reaction.

Performance of electrocatalytic reactions depends on not only the composition and structure of the active sites, but also their local environment, including the surrounding electrolyte. In this work, we demonstrate that BF2 (OH)2 - anion is the key fluoroborate species formed in the mixed KBi/KF (KBi=potassium borate) electrolyte to enhance the rate of the oxygen evolution reaction (OER) at near-neutral pH. Through a combination of electrokinetic and in situ spectroscopic studies, we show that the mixed KBi/KF electrolyte promotes the OER via two pathways: 1) stabilizing the interfacial pH during the proton-producing reaction with its high buffering capacity; and 2) activating the interfacial water via strong hydrogen bonds with F-containing species. With the KBi/KF electrolyte, electrodeposited Co(OH)2 is able to achieve 100 mA/cm2 at 1.74 V, which is among the highest reported activities with earth-abundant electrocatalysts at near neutral conditions. These findings highlight the potential of leveraging electrolyte-engineering for improving the electrochemical performance of the OER.

Benchmarking of commercial Cu catalysts in CO2 electro-reduction using a gas-diffusion type microfluidic flow electrolyzer.

In this work, three commercial Cu catalysts were benchmarked in the CO2RR using a gas-diffusion type microfluidic flow electrolyzer. We showed that commercial Cu could deliver a high FE of near 80% for C2+ product formations at 300 mA cm-2. By tuning the catalyst loading, a high reaction rate of near 1 A cm-2 with a C2+ product FE over 70% was achieved. Our results demonstrated that commercial Cu could achieve similar or better performances compared to many current catalysts by design in the CO2RR using similar electrolyzers. In addition, we showed that high CO reduction reaction (CORR) performance could also be achieved on commercial Cu, and disparities between CO and CO2 electrolysis were discussed.

Interface synergism and engineering of Pd/Co@N-C for direct ethanol fuel cells.

Direct ethanol fuel cells have been widely investigated as nontoxic and low-corrosive energy conversion devices with high energy and power densities. It is still challenging to develop high-activity and durable catalysts for a complete ethanol oxidation reaction on the anode and accelerated oxygen reduction reaction on the cathode. The materials' physics and chemistry at the catalytic interface play a vital role in determining the overall performance of the catalysts. Herein, we propose a Pd/Co@N-C catalyst that can be used as a model system to study the synergism and engineering at the solid-solid interface. Particularly, the transformation of amorphous carbon to highly graphitic carbon promoted by cobalt nanoparticles helps achieve the spatial confinement effect, which prevents structural degradation of the catalysts. The strong catalyst-support and electronic effects at the interface between palladium and Co@N-C endow the electron-deficient state of palladium, which enhances the electron transfer and improved activity/durability. The Pd/Co@N-C delivers a maximum power density of 438 mW cm-2 in direct ethanol fuel cells and can be operated stably for more than 1000 hours. This work presents a strategy for the ingenious catalyst structural design that will promote the development of fuel cells and other sustainable energy-related technologies.

Site Diversity and Mechanism of Metal-Exchanged Zeolite Catalyzed Non-Oxidative Propane Dehydrogenation.

Metal-exchanged zeolites are well-known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal-exchanged zeolite catalysts is described in detail. The case of Ga/H-ZSM-5 is employed to showcase that advances in the understanding of structure-activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H-ZSM-5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal-exchanged zeolite catalysts and reaction mechanisms are discussed in the final section.

Weak CO binding sites induced by Cu-Ag interfaces promote CO electroreduction to multi-carbon liquid products.

Electrochemical reduction of carbon monoxide to high-value multi-carbon (C2+) products offers an appealing route to store sustainable energy and make use of the chief greenhouse gas leading to climate change, i.e., CO2. Among potential products, C2+ liquid products such as ethanol are of particular interest owing to their high energy density and industrial relevance. In this work, we demonstrate that Ag-modified oxide-derive Cu catalysts prepared via high-energy ball milling exhibit near 80% Faradaic efficiencies for C2+ liquid products at commercially relevant current densities (>100 mA cm-2) in the CO electroreduction in a microfluidic flow cell. Such performance is retained in an over 100-hour electrolysis in a 100 cm2 membrane electrode assembly (MEA) electrolyzer. A method based on surface-enhanced infrared absorption spectroscopy is developed to characterize the CO binding strength on the catalyst surface. The lower C and O affinities of the Cu-Ag interfacial sites in the prepared catalysts are proposed to be responsible for the enhanced selectivity for C2+ oxygenates, which is the experimental verification of recent computational predictions.

Correlating the Experimentally Determined CO Adsorption Enthalpy with the Electrochemical CO Reduction Performance on Cu Surfaces.

CO binding energy has been widely employed as a descriptor for effective catalysts in the electrochemical CO2 and CO reduction reactions (CO(2) RR), however, it has yet to be determined experimentally at electrochemical interfaces due to the lack of suitable techniques. In this work, we developed a method to determine the standard adsorption enthalpy of CO on Cu surfaces with quantitative surface enhanced infrared absorption spectroscopy. On dendritic Cu at -0.75 V vs. SHE, the standard adsorption enthalpy, entropy and Gibbs free energy were determined to 1.5±0.5 kJ mol-1 , ≈37.9±13.4 J/(mol K), and ≈-9.8±4.0 kJ mol-1 , respectively. Comparison of the standard adsorption enthalpy of oxide-derived Cu and dendritic Cu, as well as their CORR activities, suggests the presence of stronger binding sites on OD Cu, which could favor multicarbon products. The method developed in this work will help establish the correlation between the CO binding energy and the CO(2) RR activity.

Recent Progress in Electrochemical Nitrogen Reduction on Transition Metal Nitrides.

Distributed electrochemical nitrogen reduction reaction (ENRR) powered by renewable energy for the on-site production of ammonia is an attractive alternative to the industrial Haber-Bosch process, which is responsible for roughly 2 % of global energy consumption. In this Review, we summarize recent progress in the ENRR catalyzed by transition metal nitrides (TMNs). The unique electronic structures of TMNs make them promising ENRR catalysts for active and selective ammonia production, which have been predicted theoretically and demonstrated experimentally. Reaction pathways and deactivation mechanisms of the ENRR on different TMNs are surveyed, and current understanding of structure-activity relations is discussed. To develop highly active, selective, and stable TMN catalysts for industrial-scale ENRR, membrane electrode assembly configuration is recommended in catalyst evaluation. Furthermore, we highlight the importance of developing mechanistic understanding on ENRR with different operando spectroscopic techniques.

Correlating CO Coverage and CO Electroreduction on Cu via High-Pressure in Situ Spectroscopic and Reactivity Investigations.

The absolute coverage of CO has been a missing piece in the mechanistic puzzle of the CO reduction reaction (CORR) on Cu. For the first time, we revealed the upper bound of the CO coverage under electrocatalytic conditions to be 0.05 monolayer at atmospheric pressure and the saturation CO coverage to be ∼0.25 monolayer by conducting surface enhanced infrared spectroscopy at CO pressures up to 60 barg in a custom-designed spectroelectrochemical cell. CORR activities on Cu were also determined in the same pressure range. Calculated reaction orders of C2+ products with respect to adsorbed CO are substantially less than unity, clearly indicating that the coupling of adsorbed CO is not the rate-determining step leading to multicarbon products. The increase in CO coverage can reduce the C affinity on the Cu surface and favor the selectivity towards oxygenates, especially acetate, over ethylene. Uncommon products, including ethane, glycolaldehyde, and ethylene glycol, were detected in appreciable amounts, likely due to a new C-C coupling mechanism taking place at elevated CO pressures.

Intercepting Elusive Intermediates in Cu-Mediated CO Electrochemical Reduction with Alkyl Species.

Understanding of the reaction network of Cu-catalyzed CO2/CO electroreduction reaction [CO(2)RR] remains incomplete despite intense research efforts. This is in part because the rate-determining step occurs early in the reaction network, leading to short lifetimes of subsequent surface-bound intermediates, the knowledge of which is key to selectivity control. In this work, we demonstrate that alkyl groups can effectively couple with surface intermediates in the Cu-catalyzed CORR and, for the first time, intercept elusive C1 and C2 intermediates. Combined reactivity data and in situ spectroscopic results demonstrated that surface-bound alkyl groups derived from the corresponding alkyl iodides are able to couple with adsorbed CO to form carboxylates and ketones via one and two successive nucleophilic attacks, respectively. Leveraging this new chemistry, CHx (x ≤ 3) and C2Hx (x ≤ 4) are intercepted and identified as precursors for methane and n-propanol in the CORR, respectively. Importantly, reaction pathways leading to methane and C2+ products are not intrinsically orthogonal, but their connection is mainly impeded by low coverages of energetic intermediates. This study shows that perturbing the reaction of interest by introducing a slightly interacting probe reaction network could be an effective and general strategy in mechanistic studies of catalytic reactions.