查看更多>>摘要：High-efficient and long-cycle air cathodes are crucial for the development of rechargeable zinc-air batteries (ZABs). Herein, we develop a strategy of micro-spherical cobalt-doped Fe5(PO4)4(OH)3 center dot H2O (Co-FPOH), synthesized by a novel water-oil two-phase hydrothermal method, which was used as ORR/OER bifunctional electrocatalyst for ZABs. The change of local electronic distribution is identified by doping of Co into Fe5(PO4)4(OH)3 center dot H2O (FPOH), effectively improving the electrocatalytic performance of the resulted Co-FPOH. The OER overpotential of Co-FPOH (290 mV) far outperforms state-of-the-art RuO2 (350 mV); the ORR catalytic reaction of Co-FPOH is near 4e-, almost reaching the theoretical value of Pt/C (n = 4.00). The ZAB assembled with Co-FPOH as an air electrode exhibits an ultralong cycling lifetime of 450 h at 5 mA cm-2, a super high peak power density of 167.8 Wh cm- 2, a high open circuit voltage of about 1.42 V and a large discharge specific capacity of 817 mAh gZn- 1 at 10 mA cm-2. The proposed Co-FPOH is expected to outperform precious metal electrocatalysts as a potential bifunctional electrocatalyst for advanced ZABs. Also, this work offers a novel strategy to synthesize excellent bifunctional electrocatalysts for this kind of energy-related electrocatalytic reactions.
查看更多>>摘要：For Fe-based Fischer-Tmpsch synthesis catalyst, how to decrease CO2 formation is a big challenge. In this work, a capsule catalyst (FeMn@HZSM-5) with FeMn as core and HZSM-5 as shell was prepared and used for Fischer-Tropsch to olefins (FTO) reaction, compared with bare FeMn catalyst and several hybrid catalysts by physically mixing FeMn and HZSM-5 in different ways. Among these catalysts, the FeMn@HZSM-5 capsule catalyst showed the best catalytic performance with the highest light olefins selectivity and the lowest CO2 selectivity. Compared with FeMn catalyst, the CO2 selectivity of FeMn@HZSM-5 catalyst decreased more than 10%. However, the CO2 selectivity of other physically mixing catalysts was similar to that of bare FeMn catalyst, indicating that randomly adding HZSM-5 had no effect on depressing the CO2 formation. Benefiting from the HZSM-5 shell, the FeMn@HZSM-5 capsule catalyst could effectively affect the diffusion of H2O and thus suppress the water-gas shift reaction in FTO reaction.
查看更多>>摘要：The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H-2 and O-2 on a model Mn4O8 cluster. DFT calculations indicate that Mn (IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H-2 oxidation. Accordingly, a MnCeOx catalyst (Mn-at/Ce-at, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T >= 293 K and no H-2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H-2 oxidation rate, although different activation energies favor the preferential oxidation (PROX) pattern of the studied catalyst (353-423 K). Conversion-selectivity of 100%, high stability during 72 h reaction time and moderate inhibiting effects of water and CO2 feeding reveal the potential of MnO2 materials as efficient, low-cost and robust PROX catalysts.
查看更多>>摘要：Fischer-Tropsch synthesis of light olefins plays a vital role in the production of major chemical building blocks from non-petroleum resources, having great academic and commercial importance. Herein, Na and S modulated FeMnOx catalysts were employed to systematically investigate the influence of additives, which not only enhanced the CO conversion but also facilitated the olefin formation and suppressed the undesired methane formation. Multiple characterizations confirmed that the existence of promoters would enhance the formation of active species of Fe5C2 at FTO conditions because of the promoted carbon insertion into the iron species from the intermediates dissociation. Combined the steady-state isotopic transient kinetic analysis with dynamic calculation, it confirmed that the promoters indeed had the ability to lower CO activation energy, as well as increase the carbon chain growth activity and the energy barrier to hydrogenation. This study provides a practical strategy for exploring the highly active and stable FTO catalysts.
查看更多>>摘要：Regulating the surface states distribution on the photoanode/electrolyte interface is crucial to photo electrochemical (PEC) water splitting. Here we develop a CdIn2S4/InOx/NiFe-LDH adaptive junction to improve the PEC performance and stability of bare CdIn2S4, which achieves a photocurrent density of 5.47 mA cm(-2) at 1.23 V-RHE as well as good durability under AM 1.5G illumination without sacrificial reagent. The experimental characterizations evidence that both the charge carrier density (N-d) and surface states distribution (N-ss) alter along with the interfacial structural regulation in the CdIn2S4/InOx/NiFe-LDH photoanode, and a proper ratio of N-ss/N-d guarantee the optimal photocurrent. Meanwhile, a strained surface states distribution and negative shifted N-ss center facilitate the charge transfer and interfacial water oxidation kinetics as well. This work highlights the influence of interfacial structural regulation on the entangled surface states distribution and charge carrier density and may inspire more excellent work on designing other efficient photoanodes.
查看更多>>摘要：N-doped hierarchical porous carbon nanosheets-supported copper catalysts (Cu/NCNS-x) were fabricated to solve the problem of deactivation caused by the leaching, agglomeration and oxidation of Cu nanoparticles (NPs) in the dimethyl carbonate (DMC) synthesis. The optimal Cu/NCNS-12 exhibited superb activity and stability without obvious deactivation after 10 cycles. The nanosheet structure produced new defects resulting in Cu reconstruction during the reaction process, while the strong interaction between Cu-0 and N atoms greatly inhibited the oxidation of Cu-0. The reconstruction of Cu was stimulated at above 100 degrees C, regardless of atmosphere, solvent types, pressure and rotation speed. The mechanism was elaborated that the initial Cu NPs (11 nm) migrated and then was trapped into newly created defects, finally formed into clusters (0.91 nm) as well as single-atom sites. This work provides profound potential in understanding metal reconstruction and developing a promising synthetic strategy of metal cluster catalysts.
查看更多>>摘要：Efficient solar energy-driven conversion of CO2 to valuable chemicals is challenging. Here we design an imidazolium-based ionic conjugated microporous polymer (ImI-CMP), which unblocks readily intramolecular charge transfer and triggers CO2 photoreduction. Under visible light irradiation, ImI-CMP incorporated with Co (II) species exhibits a high CO production rate of 2953 mu mol g-1 h-1 and a turnover frequency of 30.8 h-1; these numbers are competitive to that of the best porous organic polymers. The mechanism studies reveal that two factors play key roles in the outstanding photocatalytic performance. First, the imidazolium motifs on the ImICMP enhance the activation of CO2. Second, pi-conjugation structure and the built-in electric field allow ultrafast intramolecular photoinduced electron transfer in the ImI-CMP. This work provides a new strategy for designing high-performance organic photocatalysts for CO2 reduction by combining cationic imidazolium motifs and pi-conjugation structures.
De Coster, ValentijnSrinath, Nadadur VeeraraghavanTheofanidis, Stavros AlexandrosPirro, Laura...
13页
查看更多>>摘要：The evolution of the constituents of an 8 wt%Ni-5 wt%Fe/MgAl2O4 catalyst for dry reforming of methane (DRM) is monitored by in situ quick X-ray absorption spectroscopy (QXAS) and Fe-57 Mossbauer spectroscopy. In as prepared state, Fe is present as NiFe2O4 at the surface and as MgFex3+Al2-xO4 within the support, whereas Ni is mainly present as NiO. During H-2-TPR, NiFe2O4 and NiO form an alloy from 500 degrees C on and (MgFex+Al2-xO4)-Al-3 is partially reduced to MgFex2+Al2-xO4, such that Ni-Fe alloy, MgFex2+Al2-xO4 and MgFex3+Al2-xO4 are the prevalent phases in the reduced catalyst. During DRM, dominantly oxidizing environments (CH4/CO2 = 1/2, 1/1.5) lead to formation of FeOx nanoparticles at the surface of the Ni-Fe alloy, thereby affecting the DRM activity, and possibly to some reincorporation of Fe into the support. For CH4/CO2 = 1/1, no significant changes occur in the catalyst's activated state, as a consequence of reduction by CH4 dissociation species counteracting oxidation by CO2. However, Mossbauer analysis detects continued extraction of Fe from the support, sustaining ongoing NiFe alloying.
查看更多>>摘要：Utilizing CuxO nanoparticles supported on carbon nanotube as catalyst, visible-light could efficiently transform Glaser homo-coupling into Sonogashira cross-coupling. The isolated Sonogashira product yield is up to 0.58 mmol (sel. 97%) under visible-light irradiation while the Glaser product achieves 0.45 mmol (sel. 92%) in the dark for phenylacetylene and iodobenzene. We also discover that the active species under light irradiation is different from that in the dark. The visible light-driven adsorption of aromatic iodides on CuxO nanoparticles and light-excited copper(I) phenylacetylide intermediates together enables the high selectivity of Sonogashira product. The synergistic effect between Cu(II) and Cu(I) acetylide dimer complex enhances the Glaser product yield in the dark.
查看更多>>摘要：The overlooked role of high-valent cobalt-oxo species (Co(IV)) in the Co(II)/peroxymonosulfate (PMS) process was uncovered recently using methyl phenyl sulfoxide (PMSO) as the probe. Herein, we further interestingly found that Co(IV) could trigger hydroxyl radical (center dot OH) formation, resulting in the oxidized products distribution of PMSO heavily relied on the relative concentration of PMSO. More significantly, the generation of a series of 18O-labeled hydroxylated products (i.e., hydroxylated methyl phenyl sulfone, nitrobenzene and 4-nitrobenzoic acid) in H218O conclusively verified that center dot OH was triggered by Co(IV) species. Density functional theory calculation demonstrated that Co(IV) initiated center dot OH formation via oxo ligand protonation-induced valence tautomerization. Moreover, the oxidative contribution of Co(IV) and center dot OH on organic degradation was specifically dependent on the type and concentration of the substrate. This study provided deeper insights into the evolution pathway of center dot OH mediated by Co(IV) species and enriched the understandings on the collaborative oxidation mechanism in Co(IV)-involved processes.
NSTL
Elsevier