Controlling the Phase Transformation of Alumina for Enhanced Stability and Catalytic Properties

Current transition alumina catalysts require the presence of significant amounts of toxic, environmentally deleterious dopants for their stabilization. Herein, we report a simple and novel strategy to engineer transition aluminas to withstand aging temperatures up to 1200 °C without inducing the transformation to low-surface-area α-Al2O3 and without requiring dopants. By judiciously optimizing the abundance of dominant facets and the interparticle distance, we can control the temperature of the phase transformation from θ-Al2O3 to α-Al2O3 and the specific surface sites on the latter. These specific surface sites provide favorable interactions with supported metal catalysts, leading to improved metal dispersion and greatly enhanced catalytic activity for hydrocarbon oxidation. The results presented herein not only provide molecular-level insights into the critical factors causing deactivation and phase transformation of aluminas but also pave the way for the development of catalysts with improved activity for catalytic hydrocarbon oxidation.

Understanding of Active Sites and Interconversion of Pd and PdO during CH4 Oxidation

Pd-based catalysts are widely used in the oxidation of CH₄ and have a significant impact on global warming. However, understanding their active sites remains controversial, because interconversion between Pd and PdO occurs consecutively during the reaction. Understanding the intrinsic active sites under reaction conditions is critical for developing highly active and selective catalysts. In this study, we demonstrated that partially oxidized palladium (PdO_x) on the surface plays an important role for CH₄ oxidation. Regardless of whether the initial state of Pd corresponds to oxides or metallic clusters, the topmost surface is PdO_x, which is formed during CH4 oxidation. A quantitative analysis using CO titration, diffuse reflectance infrared Fourier-transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy demonstrated that a surface PdO layer was formed on top of the metallic Pd clusters during the CH₄ oxidation reaction. Furthermore, the time-on-stream test of CH₄ oxidation revealed that the presence of the PdO layer on top of the metallic Pd clusters improves the catalytic activity. Our periodic density functional theory (DFT) calculations with a PdO_x slab and nanoparticle models aided the elucidation of the structure of the experimental PdO particles, as well as the experimental C-O bands. The DFT results also revealed the formation of a PdO layer on the metallic Pd clusters. This study helps achieve a fundamental understanding of the active sites of Pd and PdO for CH₄ oxidation and provides insights into the development of active and durable Pd-based catalysts through molecular-level design.

Engineering Catalysis within a Saturated In(III)-Based MOF Possessing Dynamic Ligand-Metal Bonding

Metal-organic frameworks have developed into a formidable heterogeneous catalysis platform in recent years. It is well established that thermolysis of coordinated solvents from MOF nodes can render highly reactive, coordinatively unsaturated metal complexes which are stabilized via site isolation and serve as active sites in catalysis. Such approaches are limited to frameworks featuring solvated transition-metal complexes and must be stable toward the formation of "permanent" open metal sites. Herein, we exploit the hemilability of metal-carboxylate bonds to generate transient open metal sites in an In(III) MOF, pertinent to In-centered catalysis. The transient open metal sites catalyze the Strecker reaction over multiple cycles without loss of activity or crystallinity. We employ computational and spectroscopic methods to confirm the formation of open metal sites via transient dissociation of In(III)-carboxylate bonds. Furthermore, the amount of transient open metal sites within the material and thus the catalytic performance can be temperature-modulated.

Design of a Metal/Oxide/Carbon Interface for Highly Active and Selective Electrocatalysis

Sustainable energy-conversion and chemical-production require catalysts with high activity, durability, and product-selectivity. Metal/oxide hybrid structure has been intensively investigated to achieve promising catalytic performance, especially in neutral or alkaline electrocatalysis where water dissociation is promoted near the oxide surface for (de)protonation of intermediates. Although catalytic promise of the hybrid structure is demonstrated, it is still challenging to precisely modulate metal/oxide interfacial interactions on the nanoscale. Herein, we report an effective strategy to construct rich metal/oxide nano-interfaces on conductive carbon supports in a surfactant-free and self-terminated way. When compared to the physically mixed Pd/CeO₂ system, a much higher degree of interface formation was identified with largely improved hydrogen oxidation reaction (HOR) kinetics. The benefits of the rich metal-CeO₂ interface were further generalized to Pd alloys for optimized adsorption energy, where the Pd₃Ni/CeO₂/C catalyst shows superior performance with HOR selectivity against CO poisoning and shows long-term stability. We believe this work highlights the importance of controlling the interfacial junctions of the electrocatalyst in simultaneously achieving enhanced activity, selectivity, and stability.

Surface Density Dependent Catalytic Activity of Single Palladium Atoms Supported on Ceria*

The analogy between single-atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria-supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO₂ reducibility. The long-range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide-supported single-atom catalysts can be tuned by varying the surface density of single metal atoms.

High-Field One-Dimensional and Two-Dimensional 27Al Magic-Angle Spinning Nuclear Magnetic Resonance Study of θ-, δ-, and γ-Al2O3 Dominated Aluminum Oxides: Toward Understanding the Al Sites in γ-Al2O3

Herein, a detailed analysis was carried out using high-field (19.9 T) ²⁷Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) on three specially prepared aluminum oxide samples where the γ-, δ-, and θ-Al₂O₃ phases are dominantly expressed through careful control of the synthesis conditions. Specifically, two-dimensional (2D) multiquantum (MQ) MAS ²⁷Al was used to obtain high spectral resolution, which provided a guide for analyzing quantitative 1D ²⁷Al NMR spectra. Six aluminum sites were resolved in the 2D MQ MAS NMR spectra, and seven aluminum sites were required to fit the 1D spectra. A set of octahedral and tetrahedral peaks with well-defined quadrupolar line shapes was observed in the θ-phase dominant sample and was unambiguously assigned to the θ-Al₂O₃ phase. The distinct line shapes related to the θ-Al₂O₃ phase provided an opportunity for effectively deconvoluting the more complex spectrum obtained from the δ-Al₂O₃ dominant sample, allowing the peaks/quadrupolar parameters related to the δ-Al₂O₃ phase to be extracted. The results show that the δ-Al₂O₃ phase contains three distinct Al_O sites and three distinct Al_T sites. This detailed Al site structural information offers a powerful way of analyzing the most complex γ-Al₂O₃ spectrum. It is found that the γ-Al₂O₃ phase consists of Al sites with local structures similar to those found in the δ-Al₂O₃ and θ-Al₂O₃ phases albeit with less ordering. Spin-lattice relaxation time measurement further confirms the disordering of the lattice. Collectively, this study uniquely assigns ²⁷Al features in transition aluminas, offering a simplified method to quantify complex mixtures of aluminum sites in transition alumina samples.

A General Strategy to Atomically Dispersed Precious Metal Catalysts for Unravelling Their Catalytic Trends for Oxygen Reduction Reaction

Atomically dispersed precious metal catalysts have emerged as a frontier in catalysis. However, a robust, generic synthetic strategy toward atomically dispersed catalysts is still lacking, which has limited systematic studies revealing their general catalytic trends distinct from those of conventional nanoparticle (NP)-based catalysts. Herein, we report a general synthetic strategy toward atomically dispersed precious metal catalysts, which consists of "trapping" precious metal precursors on a heteroatom-doped carbonaceous layer coated on a carbon support and "immobilizing" them with a SiO₂ layer during thermal activation. Through the "trapping-and-immobilizing" method, five atomically dispersed precious metal catalysts (Os, Ru, Rh, Ir, and Pt) could be obtained and served as model catalysts for unravelling catalytic trends for the oxygen reduction reaction (ORR). Owing to their isolated geometry, the atomically dispersed precious metal catalysts generally showed higher selectivity for H₂O₂ production than their NP counterparts for the ORR. Among the atomically dispersed catalysts, the H₂O₂ selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e^- ORR activity, the atomically dispersed Rh catalyst showed the best activity. Our general approach to atomically dispersed precious metal catalysts may help in understanding their unique catalytic behaviors for the ORR.

Molecular Engineered Safer Organic Battery through the Incorporation of Flame Retarding Organophosphonate Moiety

Here, we report the first electrochemical assessment of organophosphonate-based compound as a safe electrode material for lithium-ion batteries, which highlights the reversible redox activity and inherent flame retarding property. Dinickel 1,4-benzenediphosphonate delivers a high reversible capacity of 585 mA h g^-1 with stable cycle performance. It expands the scope of organic batteries, which have been mainly dominated by the organic carbonyl family to date. The redox chemistry is elucidated by X-ray absorption spectroscopy and solid-state ³¹P NMR investigations. Differential scanning calorimetry profiles of the lithiated electrode material exhibit suppressed heat release, delayed onset temperature, and endothermic behavior in the elevated temperature zone.

Acidic effect of porous alumina as supports for Pt nanoparticle catalysts in n-hexane reforming

Catalytic activity and selectivity of n-hexane reforming are changed significantly by the surface acidic properties of the alumina support following halogen treatment.

Cross-linking Zr-based metal-organic polyhedra via postsynthetic polymerization

Metal organic polyhedra (MOPs) have potential as supramolecular building blocks, but utilizing MOPs for postsynthetic polymerization has not been explored. Although MOPs with flexible organic moieties have been recently reported to target enhanced processability, permanent porosity has not been demonstrated. Here, a novel synthetic strategy involving the cross-linking of MOPs via a covalent bond is demonstrated by exploiting a condensation reaction between the MOP and flexible organic linkers. An amine-functionalized Zr-based MOP is cross-linked with acyl chloride linkers in the crystalline state to form cross-linked MOPs. The condensation reaction results in a cross-linked system without significant changes to the structure of the Zr-based MOP. Such cross-linked MOPs provide a microporous tetrahedral cage based on gas sorption analysis. This cross-linking strategy highlights the potential of MOPs as building blocks and provides access to a new class of porous material.

Association of Condylar Bone Quality with TMJ Osteoarthritis

The etiology and treatment of temporomandibular joint (TMJ) osteoarthritis (TMJOA) remain complex and unclear. Based on clinical observations, we hypothesized that low condylar bone quality is significantly correlated with TMJOA and explored this association in a cross-sectional study with human patients. A total of 254 postmenopausal female participants were included in this study. Radiographic findings from cone beam computed tomography (CBCT) and clinical symptoms were used to classify each TMJ data sample as healthy control ( n = 124) or TMJOA ( n = 130). Condylar bone mineral density (BMD) (computed tomography Hounsfield unit [CT HU]) and bone volume fraction (BV/TV) were measured and modeled as predictors of healthy control versus TMJOA status in multilevel logistic regression analyses. Both CT HU (adjusted odds ratio [AOR] = 0.9989, interquartile odds ratio [IOR] = 0.4206) and BV/TV (AOR= 0.8096, IOR = 0.1769) were negatively associated with TMJOA ( P = 0.049, 0.011, respectively). To assess the diagnostic performance of CT HU and BV/TV for identification of TMJOA, receiver operating characteristic (ROC) curves were plotted. The estimated areas under the curve (AUC) were 0.6622 for BV/TV alone, 0.6074 for CT HU alone, and 0.7136 for CT HU and BV/TV together. The model incorporating CT HU and BV/TV together had a significantly higher AUC than the models using BV/TV alone ( P = 0.038) or HU alone ( P = 0.021). In conclusion, we found that low condylar bone quality was significantly correlated with TMJOA development and that condylar CT HU and BV/TV can be used together as a potential diagnostic tool for TMJOA. Careful clinical evaluation of the condyle coupled with appropriate radiographic interpretation would thus be critical for the early detection of TMJOA.

Efficient CO Oxidation by 50-Facet Cu2O Nanocrystals Coated with CuO Nanoparticles

As carbon monoxide oxidation is widely used for various chemical processes (such as methanol synthesis and water-gas shift reactions H₂O + CO ⇄ CO₂ + H₂) as well as in industry, it is essential to develop highly energy efficient, inexpensive, and eco-friendly catalysts for CO oxidation. Here we report green synthesis of ∼10 nm sized CuO nanoparticles (NPs) aggregated on ∼400 nm sized 50-facet Cu₂O polyhedral nanocrystals. This CuO-NPs/50-facet Cu₂O shows remarkable CO oxidation reactivity with very high specific CO oxidation activity (4.5 μmol_CO m^-2 s^-1 at 130 °C) and near-complete 99.5% CO conversion efficiency at ∼175 °C. This outstanding catalytic performance by CuO NPs over the pristine multifaceted Cu₂O nanocrystals is attributed to the surface oxygen defects present in CuO NPs which facilitate binding of CO and O₂ on their surfaces. This new material opens up new possibilities of replacing the usage of expensive CO oxidation materials.

Evolution of form in metal-organic frameworks

Self-assembly has proven to be a widely successful synthetic strategy for functional materials, especially for metal-organic materials (MOMs), an emerging class of porous materials consisting of metal-organic frameworks (MOFs) and metal-organic polyhedra (MOPs). However, there are areas in MOM synthesis in which such self-assembly has not been fully utilized, such as controlling the interior of MOM crystals. Here we demonstrate sequential self-assembly strategy for synthesizing various forms of MOM crystals, including double-shell hollow MOMs, based on single-crystal to single-crystal transformation from MOP to MOF. Moreover, this synthetic strategy also yields other forms, such as solid, core-shell, double and triple matryoshka, and single-shell hollow MOMs, thereby exhibiting form evolution in MOMs. We anticipate that this synthetic approach might open up a new direction for the development of diverse forms in MOMs, with highly advanced areas such as sequential drug delivery/release and heterogeneous cascade catalysis targeted in the foreseeable future.

Characterization of Fe2+ ions in Fe,H/SSZ-13 zeolites: FTIR spectroscopy of CO and NO probe molecules

FTIR spectra of adsorbed NO and CO were used to characterize Fe²⁺ ions in different cationic positions in Fe,H/SSZ-13 zeolites.

Molecular Active Sites in Heterogeneous Ir-La/C-Catalyzed Carbonylation of Methanol to Acetates

We report that when Ir and La halides are deposited on carbon, exposure to CO spontaneously generates a discrete molecular heterobimetallic structure, containing an Ir-La covalent bond that acts as a highly active, selective, and stable heterogeneous catalyst for the carbonylation of methanol to produce acetic acid. This catalyst exhibits a very high productivity of ∼1.5 mol acetyl/mol Ir·s with >99% selectivity to acetyl (acetic acid and methyl acetate) without detectable loss in activity or selectivity for more than 1 month of continuous operation. The enhanced activity can be mechanistically rationalized by the presence of La within the ligand sphere of the discrete molecular Ir-La heterobimetallic structure, which acts as a Lewis acid to accelerate the normally rate-limiting CO insertion in Ir-catalyzed carbonylation. Similar approaches may provide opportunities for attaining molecular (single site) behavior similar to homogeneous catalysis on heterogeneous surfaces for other industrial applications.

Dissecting the steps of CO2 reduction: 2. The interaction of CO and CO2 with Pd/γ-Al2O3: an in situ FTIR study

Surface species formed on Pd/γ-Al₂O₃ upon CO_x exposure will aid mechanistic studies of CO₂ reduction.

Dissecting the steps of CO2 reduction: 1. The interaction of CO and CO2 with γ-Al2O3: an in situ FTIR study

The adsorption of CO₂ on γ-Al₂O₃ produces calcination temperature-dependent surface species.

The outcome and efficacy of recanalization in patients with acute internal carotid artery occlusion

BACKGROUND AND PURPOSE

Acute occlusion of the ICA is often associated with poor outcomes and severe neurologic deficits. This study was conducted to evaluate outcome of the occluded ICA and efficacy of recanalization under protective flow arrest.

MATERIALS AND METHODS

Fifty consecutive patients who underwent endovascular treatment for acute ICA occlusion were identified from the prospectively collected data base. We assessed NIHSSo, occlusion type (cardioembolism vs atherosclerosis), occlusion level (supraclinoid-terminal, petrocavernous, or bulb-cervical), recanalization degree (TICI), and efficacy of recanalization (protective flow arrest vs nonprotection) leading to better outcome.

RESULTS

Successful recanalization (TICI ≥ 2) was obtained in 90% of patients and good recovery (mRS ≤ 2) in 60% of patients. Good outcome was related to National Institutes of Health Stroke Scale score on admission (P < .001), TICI (P < .007), occlusion type (P = .022), and occlusion level (P = .038). Poor initial patient status, less recanalization, cardioembolism, and supraclinoid-terminal occlusion were associated with poor prognosis. Application of protective flow arrest led to better outcome in the distal ICA segment than in the bulb-cervical segment.

CONCLUSIONS

In addition to the initial patient status and successful recanalization, the occlusion level or type of the occluded ICA could affect clinical outcome. In this study, treatment benefits of protective flow arrest were accentuated in patients with ICA occlusion above the bulb-cervical segment.

Anti-influenza virus activity of green tea by-products in vitro and efficacy against influenza virus infection in chickens

Polyphenolic compounds present in green tea, particularly catechins, are known to have strong anti-influenza activity. The goal of this study was to determine whether green tea by-products could function as an alternative to common antivirals in animals compared to original green tea. Inhibition of viral cytopathic effects ascertained by neutral red dye uptake was examined with 50% effective (virus-inhibitory) concentrations (EC₅₀)determined. Against the H1N1 virus A/NWS/33, we found the anti-influenza activity of green tea by-products (EC₅₀ = 6.36 µg/mL) to be equivalent to that of original green tea (EC₅₀= 6.72 µg/mL). The anti-influenza activity of green tea by-products was further examined in mouse and chicken influenza infection models. In mice, oral administration of green tea by-products reduced viral titers in the lungs in the early phase of infection, but they could not protect these animals from disease and death. In contrast, therapeutic administration of green tea by-products via feed or water supplement resulted in a dose-dependent significant antiviral effect in chickens, with a dose of 10 g/kg of feed being the most effective (P < 0.001). We also demonstrated that unidentified hexane-soluble fractions of green tea by-products possessed strong anti-influenza activity, in addition to ethyl acetate-soluble fractions, including catechins. This study revealed green tea by-product extracts to be a promising novel antiviral resource for animals.

Magnetic mesoporous materials for removal of environmental wastes

We have synthesized two different magnetic mesoporous materials that can be easily separated from aqueous solutions by applying a magnetic field. Synthesized magnetic mesoporous materials, Mag-SBA-15 (magnetic ordered mesoporous silica) and Mag-OMC (magnetic ordered mesoporous carbon), have a high loading capacity of contaminants due to high surface area of the supports and high magnetic activity due to the embedded iron oxide particles. Application of surface-modified Mag-SBA-15 was investigated for the collection of mercury from water. The mercury adsorption using Mag-SBA-15 was rapid during the initial contact time and reached a steady-state condition, with an uptake of approximately 97% after 7h. Application of Mag-OMC for collection of organics from water, using fluorescein as an easily trackable model analyte, was explored. The fluorescein was absorbed into Mag-OMC within minutes and the fluorescent intensity of solution was completely disappeared after an hour. In another application, Mag-SBA-15 was used as a host of tyrosinase, and employed as recyclable catalytic scaffolds for tyrosinase-catalyzed biodegradation of catechol. Crosslinked tyrosinase in Mag-SBA-15, prepared in a two step process of tyrosinase adsorption and crosslinking, was stable enough for catechol degradation with no serious loss of enzyme activity. Considering these results of cleaning up water from toxic inorganic and organic contaminants, magnetic mesoporous materials have a great potential to be employed for the removal of environmental contaminants and potentially for the application in large-scale wastewater treatment plants.