查看更多>>摘要：Efficient and selective dehydrogenation of aqueous formic acid (FA) for hydrogen production with non-noble-metal-based heterogeneous catalysts remains a great challenge. Herein, complete dehydrogenation of aqueous FA with a concentration as high as 40 vol% achieved a gas production rate of 293.9 mL/g_(cat)./h by using a biomass-derived multifunctional γ-Mo2N catalyst synthesized with a facile pyrolysis process. No significant deactivation of catalysts was found during the 108 h-stability-test. Mechanism investigations indicate that the solvent H2O could occupy the Brsnsted acid sites to prevent FA dehydration. The dehydrogenation activity was significantly improved by the cooperation of K-containing sites, N-doped sites, and the γ-Mo2N active sites, which could be responsible for the HCOO~- intermediate generation and adsorption, H~+ adsorption, and H-C bond cleavage of the adsorbed HCOO~-, respectively. This study provided a novel strategy to improve the dehydrogenation performance of aqueous FA with non-noble-metal-based heterogeneous catalysts.
查看更多>>摘要：Unlike the conversion of monosaccharides to the corresponding polyols, the production of maltitol by hydrogenation of maltose has been seldom investigated in the literature, despite its industrial importance. Monometallic Ni catalysts are known for their lack of stability, and the objective of the present paper is to determine through a kinetic study, to what extent a Ni-Fe/SiO2 bimetallic catalyst would outperform a Ni/SiO2 catalyst in the aqueous phase hydrogenation of maltose, as they have been reported to do for monosaccharides. The effect of reaction parameters (T = 80-150 °C, P_(H2)2 = 20-40 bar, maltose mass fraction in water = 4.4-17.5 wt%) on activity, selectivity, and stability was examined. In all cases, maltitol was the major product, with a carbon balance higher than 98%, but maltose hydrolysis to glucose occurred in the upper range of temperature. In order to preserve both the catalyst selectivity and stability, a temperature of 80 °C was selected for the kinetic study. A first order model including an inhibiting term based on maltose concentration could fit the evolution of the conversion of maltose as a function of time. The adsorption constant of maltose and the apparent hydrogenation rate constant for the Ni-Fe catalyst were both larger by a factor 2-3 compared with the Ni catalyst, indicating a stronger interaction of maltose with the Ni-Fe surface. Another major difference was a reaction order of 0.5 with respect to the hydrogen pressure on Ni-Fe/SiO2 compared with a near zero-order on Ni/SiO2, stressing significant differences in coverage of the bimetallic surface. The activity of the Ni-Fe catalyst remained constant for three runs of reaction without major structural changes, while the Ni catalyst deactivated by transforming to a phyllosilicate phase. As far as activity, selectivity and stability are concerned; Ni-Fe/SiO2 appeared as a better suited catalyst than Ni/SiO2 for the aqueous phase hydrogenation of maltose at 80 °C, with a more pronounced benefit than formerly reported for xylose on the same catalysts.
查看更多>>摘要：In the present work, the WS2 nanosheets were prepared through a liquid-phase exfoliation method (LPE). Various techniques were then used to characterize thickness, length, and concentration of these nanosheets. WS2 nanosheets were also loaded on α-Fe2O3 photoanodes to prepare core-shell structured α-Fe2O3/WS2/WOx photoanodes. These core-shell structured α-Fe2O3/WS2/WOx nanorods have advantages of effective separation, decreased recombination of photo-generated electron-hole pairs, and increased electron transport properties, resulting in improved PEC performance. The best photoanode (α-Fe2O3/#4-WS2/WOx) had photocurrent densities of 0.98 and 2.1 mA cm~(-2) (with the lowest onset potential 0.54 V_(RHE) and 0.47 V_(RHE)) under front and back-side illumination, respectively, at 1.23 V_(RHE) under 100 mW cm~(-2), which were about 13 and 30-fold higher than those of pure α-Fe2O3 photoelectrode. Furthermore, H2 and O2 production of α-Fe2O3/#4-WS2/WOx photoanode were 32 μmol.cm~(-2) and 15.3 μmol.cm~(-2), respectively at 1.23 V_(RHE) under 100 mW cm~(-2) after 2 h.
查看更多>>摘要：Air-to-fuel ratios fluctuating around the stoichiometric value enable the best CH4, NOx and CO abatement performance of the three-way catalytic converters implemented in NGVs after-treatment systems; however, this leads to undesired NH3 production and potential slip under rich combustion conditions. An additional Passive SCR catalytic device placed downstream of the TWC, based on a dual-layer SCR+PGM configuration, could represent the solution. Through both transient experimental tests and modelling analysis, we demonstrate that effective NH3 abatement is achieved at low temperatures by its adsorption onto the SCR catalyst during the rich phases, and its further consumption by NO+O2 under lean conditions. Differently, at high temperatures NH3 is efficiently and selectively converted to nitrogen by direct oxidation through a redox reaction mechanism. The developed model can predict the performances of both fresh and aged catalysts under the transient rich-lean cycling experimental conditions investigated.
查看更多>>摘要：The design of selective and stable non-precious metal catalysts for hydrogenation of alkyne is highly desirable. In this study, L-lysine modification strategy is applied to support Ni nanoparticles, which greatly improves the stability and photocatalytic performance in the hydrogenation of phenylacetylene to styrene. The robust stability is attributed to that both amino and carboxyl groups of L-lysine can function simultaneously as the anchor, much stronger than a single group, to strongly interact with metallic Ni via N and O coordination. The high selectivity to styrene is due to that L-lysine modification results in a larger adsorption energy difference between styrene and phenylacetylene on the surface of Ni, therefore phenylacetylene is preferentially adsorbed on Ni surface. This protocol shows that the modulation of interaction between ligands and Ni is favorable to design stable, active and selective catalysts for hydrogenation of alkynes.
查看更多>>摘要：Although the exciton-triggered photocatalysis has recently been confirmed, so far it is limited to the low-dimensional semiconductors, and the characterization approaches are impossible to image and characterize the photo-catalytic reaction on single semiconductor photocatalysts. Herein by combining dark-field microscopy with 3, 3', 5, 5'-tetramethylbenzidine as the chromogenic probe, we visually map the exciton-initiated photo-catalytic reaction on defective Cu2O microcrystals in real time at the single-particle level. Single-particle imaging results reveal the heterogeneity in reactivity among different individuals and at different regions within the same microcrystal. Moreover, the reaction rate constant of this photocatalytic reaction is determined as well. The theoretical simulations suggest that the introduction of Mn~(2+) can modulate the electronic structure and enhance the oxygen affinity of Cu2O, facilitating the production of ~1O2. This high spatio-temporal-resolution imaging approach is general, which is also appropriate for investigating the exciton effects on Fe~(2+)-doped Cu2O microcrystals.
查看更多>>摘要：A novel sillenite, Bi_(12)CoO_(20), is reported to effectively utilize a large portion of the solar spectrum up to the Near-IR region (1000 nm), and exhibits excellent photothermal degradation. The degradation is evaluated by using phenol as the model pollutant and correlated with a temperature-induced structure change through in-situ photoelectrochemical and spectroscopic characterizations. The degradation rate on Bi_(12)CoO_(20) is ca. 3.0 times higher than that on P25-TiO2 under simulated sunlight irradiation and the best by comparing with other reported photothermal catalysts. The thermal effect is demonstrated to cause the conversion of Co~(3+) to Co~(2+) at the octahedral sites of the Bi_(12)CoO_(20) increase the internal electric field, and facilitate charge separation. The conversion also positively shifts the band potential, increasing the oxidative reactive species. The photothermal activity is newly found to be enhanced by increasing the IEF and band edge potential, which may provide strategies for designing more effective photothermal catalysts.
查看更多>>摘要：An anodic oxidation-cathodic ORR coupling system originated from TiO2 nanotube array (TNAs)-based electrodes was established. We first thoroughly investigated the effects of cell voltage, electrolyte type and pH on anodic reactive radicals co-generation and cathodic ORR pathway in the divided cells. Based on the results of anodic and cathodic half-reactions, the strengthening effect of the pH-dependant ORR process on the synergistic sulfate activation and reactive radicals co-generation mechanism were systematically elucidated in the undivided cells, by means of berberine degradation/mineralization degree and kinetics, electron spin resonance, radical quenching and energy consumption estimation. The real service lifetime of blue TNAs anode was evaluated, and the possible degradation pathways of berberine was also proposed. This pH-dependent ORR-strengthened synergistic sulfate activation system provide a multi-radical joint-attack mechanism for the pre-treatment or point-source-treatment of sulfate-containing refractory organics wastewater.
查看更多>>摘要：Atomically dispersed iron-nitrogen-carbon catalysts offer great potential in oxygen reduction reaction (ORR), yet the poor exposure and low density of Fe-Nx sites causes relatively low ORR activity. Herein, a zinc-assisted MgO template strategy is reported to construct porous carbon-supported Fe-N4 sites (Fe-N-C). Iron atoms surrounded by zinc species are converted to abundant Fe-N4 sites rather than Fe containing nanoparticles. Meanwhile, both the zinc species and the MgO template can effectively produce porous structure so as to increase the utilization of Fe-N4 sites. Fe-N-C achieves superior ORR performance and stability in alkaline medium. Theoretical calculations manifest that Fe-N4 sites can narrow the energy barrier for ORR. Moreover, finite element simulation exhibits the porous framework in Fe-N-C could significantly accelerate the diffusion of O2. Therefore, Fe-N-C provides a high peak power density and superior discharge ability toward Zn-air batteries.
查看更多>>摘要：In electrochemical advanced oxidation processes (EAOPs), a series of transition metal encapsulated nitrogen-doped carbon nanotubes (M@N-C, M=Fe, Co, Ni, Cu) as bifunctional cathodes were synthesized to compare and uncover their activity trends, fulfilling the self-sufficient electrocatalytic degradation. The sulfamethazine (SMT) degradation activity trends were follows: Co@N-OFe@N-ONi@N-OCu@N-C cathode at pH≤ 7, while the Fe@N-C cathode exhibited the highest activity at pH 9 due to the more ~1O2 and atomic H*. In-situ Fourier transformed infrared (FTIR) spectroscopy and density functional theory (DFT) calculation suggested that the atomic H* was easier to generate under the action of pyridinic N on Fe@N-C cathode. Overall, various pollutants degradation on Fe@N-C cathode performed with good stability with low leaching iron (0.12 mg L~(-1)) and low energy consumption (<0.3 kWh·log~(-1)·m~(-3)). This study sheds light on different mechanisms of reactive species production on M@N-C cathode, thus providing guidance for the selectivity between M@N-C via active species and pollutants.
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