Single-Atom Alloy Formation via Reaction-Driven Catalyst Restructuring.

We demonstrate that single-atom alloy catalysts can be made by exposing physical mixtures of monometallic supported Cu and Pd catalysts to vinyl acetate (VA) synthesis reaction conditions. This reaction induces the formation of mobile clusters of metal diacetate species that drive extensive metal nanoparticle restructuring, leading to atomic dispersion of the precious metal, smaller nanoparticle sizes than the parent catalysts, and high activity and selectivity for both VA synthesis and ethanol dehydrogenation reactions. This approach is scalable and appears to be generalizable to other alloy catalysts.

CoTe2 : A Quantum Critical Dirac Metal with Strong Spin Fluctuations.

Quantum critical points separating weak ferromagnetic and paramagnetic phases trigger many novel phenomena. Dynamical spin fluctuations not only suppress the long-range order, but can also lead to unusual transport and even superconductivity. Combining quantum criticality with topological electronic properties presents a rare and unique opportunity. Here, by means of ab initio calculations and magnetic, thermal, and transport measurements, it is shown that the orthorhombic CoTe2 is close to ferromagnetism, which appears suppressed by spin fluctuations. Calculations and transport measurements reveal nodal Dirac lines, making it a rare combination of proximity to quantum criticality and Dirac topology.

Structure-property correlations and scaling in the magnetic and magnetocaloric properties of GdCrO3particles.

The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrO3with six particle sizes: ⟨d⟩ = 87, 103, 145, 224, 318, and 352 nm are reported. The particle size was tailored by annealing under different temperatures and estimated by scanning electron microscopy. With increase in ⟨d⟩, Goldschmidt tolerance factort, orthorhombic strains, and out-of-plane Cr-O1-Cr bond angle first decrease, reaching minimum values for ⟨d⟩ = 224 nm, and then increase for sample with ⟨d⟩ = 318 nm and 352 nm, thus showing a V-shaped variation. Temperature dependence of the magnetization (M) reveals an antiferromagnetic transition atTNCr∼168K for ⟨d⟩ ⩾ 224 nm andTNCr∼167K for ⟨d⟩ < 224 nm and an essentiallyd-independent spin-reorientation atTSR= 9 K.Mmeasured at 5 K and 7 T first increases with increase in ⟨d⟩, reaching maximum value for sample with ⟨d⟩ = 224 nm, and then decreases for samples with ⟨d⟩ = 318 nm and 352 nm, showing an inverted-V variation with ⟨d⟩. Similar ⟨d⟩-dependence is observed for the magnetic entropy change (MEC) and relative cooling power (RCP) showing a close relationship between the structural and magnetic properties of GdCrO3nanoparticles investigated here. The 224 nm sample with the minimum values oft,s, and Cr-O1-Cr bond angle exhibits the maximum value of MEC (-ΔS) = 37.8 J kg-1 K-1at 5 K under a field variation (ΔH) of 7 T and its large estimated RCP of 623.6 J Kg-1is comparable with those of typical MC materials. Both (-ΔS) and RCP are shown to scale with the saturation magnetizationMS, suggesting thatMSis the crucial factor controlling their magnitudes. Assuming (-ΔS) ∼ (ΔH)n, the temperature dependence ofnfor the six samples are determined,nvarying between 1.3 at 5 K ton= 2.2 at 130 K in line with its expected magnitudes based on mean-field theory. These results on structure-property correlations and scaling in GdCrO3suggest that its MC properties are tunable for potential low-temperature magnetic refrigeration applications.

Effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria: Soot-ceria contact and interfacial oxygen evolution.

Ceria is widely used as a catalyst for soot combustion, but effects of Zr substitution on the reaction mechanism is ambiguous. The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria. The nanostructured CeO2, Ce0.92Zr0.08O2, and Ce0.84Zr0.16O2 composed of 5-6 nm crystallites display Tm-CO2 (the temperature at maximum CO2 yield) at 383, 355, and 375°C under 10 vol.% O2/N2, respectively. The size of agglomerate decreases from 165.5 to 51.9-57.3 nm, which is beneficial for the soot-ceria contact. Moreover, Zr increases the amount of surface oxygen vacancies, generating more active oxygen (O2- and O-) for soot oxidation. Thus, the activities of Ce0.92Zr0.08O2 and Ce0.84Zr0.16O2 in soot combustion are better than that of CeO2. Although oxygen vacancies promote the migration of lattice O2-, the enriched surface Zr also inhibits the mobility of lattice O2-. Therefore, the Tm-CO2 of Ce0.84Zr0.16O2 is higher than that of Ce0.92Zr0.08O2. Based on reaction kinetic study, soot in direct contact with ceria preferentially decomposes with low activation energy, while the oxidation of isolated soot occurs through diffusion with high activation energy. The obtained findings provide new understanding on the soot combustion over nanoceria.

Supported Pt Nanoparticles on Mesoporous Titania for Selective Hydrogenation of Phenylacetylene.

Semi-hydrogenation of alkynes to alkenes is one of the most important industrial reactions. However, it remains technically challenging to obtain high alkene selectivity especially at a high alkyne conversion because of kinetically favorable over hydrogenation. In this contribution, we show that supported ultrasmall Pt nanoparticles (2.5 nm) on mesoporous TiO2 (Pt@mTiO2) remarkably improve catalytic performance toward semi-hydrogenation of phenylacetylene. Pt@mTiO2 is prepared by co-assembly of Pt and Ti precursors with silica colloidal templates via an evaporation-induced self-assembly process, followed by further calcination for thermal decomposition of Pt precursors and crystallization of mTiO2 simultaneously. As-resultant Pt@mTiO2 discloses a high hydrogenation activity of phenylacetylene, which is 2.5 times higher than that of commercial Pt/C. More interestingly, styrene selectivity over Pt@mTiO2 remains 100% in a wide phenylacetylene conversion window (20-75%). The styrene selectivity is >80% even at 100% phenylacetylene conversion while that of the commercial Pt/C is 0%. The remarkable styrene selectivity of the Pt@mTiO2 is derived from the weakened styrene adsorption strength on the atop Pt sites as observed by diffuse reflectance infrared Fourier transform spectroscopy with CO as a probe molecule (CO-DRIFTS). Our strategy provides a new avenue for promoting alkyne to alkene transformation in the kinetically unfavorable region through novel catalyst preparation.

Toward Long-Term Accurate and Continuous Monitoring of Nitrate in Wastewater Using Poly(tetrafluoroethylene) (PTFE)-Solid-State Ion-Selective Electrodes (S-ISEs).

Long-term accurate and continuous monitoring of nitrate (NO3-) concentration in wastewater and groundwater is critical for determining treatment efficiency and tracking contaminant transport. Current nitrate monitoring technologies, including colorimetric, chromatographic, biometric, and electrochemical sensors, are not feasible for continuous monitoring. This study addressed this challenge by modifying NO3- solid-state ion-selective electrodes (S-ISEs) with poly(tetrafluoroethylene) (PTFE, (C2F4)n). The PTFE-loaded S-ISE membrane polymer matrix reduces water layer formation between the membrane and electrode/solid contact, while paradoxically, the even more hydrophobic PTFE-loaded S-ISE membrane prevents bacterial attachment despite the opposite approach of hydrophilic modifications in other antifouling sensor designs. Specifically, an optimal ratio of 5% PTFE in the S-ISE polymer matrix was determined by a series of characterization tests in real wastewater. Five percent of PTFE alleviated biofouling to the sensor surface by enhancing the negative charge (-4.5 to -45.8 mV) and lowering surface roughness (Ra: 0.56 ± 0.02 nm). It simultaneously mitigated water layer formation between the membrane and electrode by increasing hydrophobicity (contact angle: 104°) and membrane adhesion and thus minimized the reading (mV) drift in the baseline sensitivity ("data drifting"). Long-term accuracy and durability of 5% PTFE-loaded NO3- S-ISEs were well demonstrated in real wastewater over 20 days, an improvement over commercial sensor longevity.

Constructing Bifunctional 3D Holey and Ultrathin CoP Nanosheets for Efficient Overall Water Splitting.

Pursuing cost-effective water-splitting catalysts is still a significant scientific challenge to produce renewable fuels and chemicals from various renewable feedstocks. The construction of controllable binder-free nanostructures with self-standing holey and ultrathin nanosheets is one of the promising approaches. Herein, by employing a combination of the potentiodynamic mode of electrodeposition and low-temperature phosphidation, three-dimensional (3D) holey CoP ultrathin nanosheets are fabricated on a carbon cloth (PD-CoP UNSs/CC) as bifunctional catalysts. Electrochemical tests show that the PD-CoP UNSs/CC exhibits outstanding hydrogen evolution reaction performance at all pH values with overpotentials of 47, 90, and 51 mV to approach 10 mA cm-2 in acidic, neutral, and alkaline media, respectively. Meanwhile, only a low overpotential of 268 mV is required to drive 20 mA cm-2 for the oxygen evolution reaction in alkaline media. Cyclic voltammetry and impedance studies suggest the enhanced performance is mainly attributed to the unique 3D holey ultrathin nanosheets, which could increase the electrochemically active area, facilitate the release of gas bubbles from electrode surfaces, and improve effective electrolyte diffusion. This work suggests an efficient path to design and fabricate non-noble bifunctional electrocatalysts for water splitting at a large scale.