The development of highly selective catalysts has been remarkably relying on the understanding of catalytic active sites. Pd-catalyzed semihydrogenation of propyne has been a focus of research with industrial applications toward the production of polymer-grade propylene. In this work, combining density functional theory (DFT) calculations and experimental observations, we propose that, different from the existing debates where the formation of palladium carbide (Pd–C) species or specific facets of Pd nanoparticles are critical, the apexes of Pd (111) octahedrons are the active sites for highly selective propyne semihydrogenation. The propylene selectivity on Pd octahedrons can be ascribed to site-selective propyne adsorption on the apexes prior to reactions and subsequent difficult to access intermediate states toward overhydrogenation. To reveal the active sites of Pd, propyne semihydrogenation was performed on shaped-Pd nanoparticles with designed exposed facets: e.g., (111) and (100) facets. Of practical importance, the propyne conversion and propylene selectivity exceed ∼94% and ∼96% on Pd octahedrons, respectively, at low temperature (35 °C) and atmospheric pressure. In addition, more control experiments have been performed to verify the effects of apexes of Pd octahedrons on propylene selectivity. It is shown that the propylene selectivity decreases to ∼50% when the apexes of Pd octahedrons are gradually removed. The experimental observations have further confirmed that the apexes of Pd octahedrons can be used as the active sites for propyne semihydrogenation, which is in good agreement with the results from theoretical calculations. This work may not only reveal the active sites of Pd nanoparticles for selective semihydrogenation of propyne but also open an avenue for designing highly active and selective catalysts in the chemical industry.
The role of elevated temperatures in electrolysis has generally been regarded as accelerations of electron transport, mass transport, and adsorption/desorption processes. In the present work, with first-principles calculations, we demonstrate that thermally activated on-surface reactions can significantly increase the efficiency of energy conversions in electrolysis via a thermally and electrically cascaded mechanism. In the oxygen evolution reaction (OER), to be specific, the formation of high-energy *OOH on Fe can be assisted by thermally activated combination of *O and *OH on the surface of ironbenzenehexathiol coordination polymer (Fe-BHT). Such theoretical predictions are then confirmed by our experimental measurements. The OER efficiency on Fe-BHT increases with increasing temperature and outperforms the state-of-the-art IrO 2 catalyst at around 80 °C. This research may shed light on an avenue for designing and preparing electrocatalysts with enhanced catalytic performance.
BACKGROUND In this study, we evaluated the combined effect of cinnamon essential oil (CEO) microemulsions, and a temperature buffering package using phase‐change material (PCM) microcapsules on the physicochemical property, lipid oxidation, and bacterial load of traditional Chinese pork balls (shi zi tou) during temperature fluctuation storage for 9 days. RESULTS Transmission electron microscope characterization revealed that n‐tetradecane microcapsules possessed a core‐shell spherical shape with a size ranging from 300 to 600 nm. The use of n‐tetradecane microcapsule packaging was found to maintain cold storage temperature efficiently. After 9 days of storage, the combination of CEO microemulsions with n‐tetradecane microcapsules did not lead to changes in the color parameters of pork balls. At day 9, n‐tetradecane microcapsules, used alone or in combination with CEO microemulsions, showed lower thiobarbituric acid reactive substances (TBARS) values than the control group, while their combination exhibited the lowest pH and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) values. Furthermore, the combination treatment retarded the growth of total plate count, lactic acid bacteria, Enterobacteriaceae, and Staphylococcus spp. after 4 and 9 days. CONCLUSIONS The combinations of CEO microemulsions and PCM microcapsules could extend the shelf‐life of cooked pork products, suggesting a feasible strategy for meat preservation. © 2020 Society of Chemical Industry
Aqueous rechargeable batteries are promising candidates for safe and large-scale energy storage systems, but their electrochemical performances are limited by anode degradation. Herein, poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) is introduced as a typical benzoquinone-based anode material in an aqueous rechargeable battery. A superior higher specific capacity and longer cycling life (255 mA h g–1 and 83% capacity retention for 700 cycles at 1 C) were obtained in a mixed 1 M Li2SO4//2 M ZnSO4 electrolyte, which is better than that in a 1 M Li2SO4 (150 mA h g–1 and 76% for 700 cycles) or in a 2 M ZnSO4 electrolyte (206 mA h g–1 and 76% for 700 cycles). A defined synergistic mechanism of Li+ and Zn2+ during redox reactions is presented, in which Zn2+ ions previously occupied the out-of-plane sites with respect to the benzene rings so that the Li+ ions occupied the in-plane sites in subsequent reducing reactions. Such synergistic bonding of Li+ and Zn2+ with the polymer anode was first confirmed by density functional theory calculations and was defined as an “ion dense stacking effect”. Then, a full battery was constructed using the PDBM anode and LiMn2O4 cathode, where an average voltage of 1.15 V, an ultrahigh capacity of 228 mA h g–1 (vs anode), and a long lifespan of over 700 cycles (i.e., capacity retention, 81% at 1 C) were obtained. This is a pioneering study toward designing large-scale energy storage with a low-cost, high energy density, and ultralong life.
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