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A Condensation/Reductive Alkylation/Hydrogenation Cascade for Facile Synthesis of Chiral 2,3-Disubstituted Indolines
No full textA divergent and enantioselective procedure for synthesis of 2,3-disubstituted indolines was developed through Bronsted acid/palladium-complex promoted condensation/reductive alkylation/ hydrogenation cascade reactions from simple amino ketones and aldehydes in one operation. Five Bronsted acid-promoted steps and two Pd-catalyzed hydrogenation steps were involved in this process. This strategy provides facile synthesis of structurally diverse multi-substituted chiral indolines
Molybdenum-Catalyzed Oxidative Cleavage of Raw Poplar Sawdust into Mono-Aromatics and Organic Acid Esters
No full textConversion of non-edible lignocellulosic biomass into value-added chemicals is of great significance and also particularly attractive. However, owing to the complexity and inertness, valorization of native lignocellulose remains to be quite challenging. Herein, catalytic oxidative cleavage of raw poplar sawdust was studied, mono-aromatics and organic acid esters with 34.8 wt% and 27.4 wt% yield respectively were achieved over MoO2(acac)(2) with molecular oxygen, which was suggested to be attributed to a prior cleavage of the carbohydrate fractions. This catalytic oxidation approach demonstrates the feasibility of transformation of raw woody biomass into valuable chemicals
Advanced Porous Membranes with Tunable Morphology Regulated by Ionic Strength of Nonsolvent for Flow Battery
No full textA simple salt-induced phase separation method is presented to prepare porous polybenzimidazole (PBI) membranes with tunable morphology for vanadium flow batteries (VFBs). This method is based on the traditional nonsolvent-induced phase separation (NIPS) method where salt is introduced into the coagulation bath to change the ionic strength of the nonsolvent. The change of ionic strength will affect the phase separation rate, and finally, the morphology of porous membranes is well tuned from finger-like voids to spongelike pores in site. The membrane with sponge-like pores created multiple barriers to the transfer of vanadium ions, offering the membrane with superhigh selectivity; meanwhile, spongy cells filled with sulfuric acid could provide the membrane with high proton conductivity. As a result, the membrane with sponge-like pores demonstrated a much better performance than that with finger-like voids. The resultant sponge-like porous PBI membrane exhibited a very impressive VFB performance with an energy efficiency of 89.9% at a current density of 80 mA cm(-2), which was close to the highest values ever reported. The battery kept very stable performance even after continuously running for more than 10000 cycles at 160 mA cm(-2), showing excellent stability. This paper provides an easy to scale up and environment-friendly method to fabricate high-performance porous membranes with tunable morphology
Scalable and Economic Synthesis of High-Performance Na3V2(PO4)(2)F-3 by a Solvothermal-Ball-Milling Method
No full textNa3V2(PO4)(2)F-3 has been emerging as one of the most promising cathodes for sodium-ion batteries due to its stable NASICON structure and fast Na+ diffusion. However, present methods for preparation of Na3V2(PO4)(2)F-3 suffer from either high energy consumption or generating poor rate performance. Herein, a cost-effective solvothermal ball-milling method is proposed to solve the problem. In the solvothermal process, the morphology of Na3V2(PO4)(2)F-3 varies from OD to 3D with changing pH, in which 3D Na3V2(PO4)(2)F-3 at pH = 3 shows optimal purity due to the fastest growth rate. With Ketjenblack (KB) coating by short-time ball-milling, the Na3V2(PO4)(2)F-3 can be further nanosized with a highly graphited carbon coating layer. The purest Na3V2(PO4)(2)F-3@KB from pH = 3 exhibited an initial capacity of 138 mAh g(-1) 0.5 C and 122 mAh g(-1) @ 40 C. Moreover, ultrahigh dosage over an 80 mmol of V source in one 100 mL Teflon-lined autoclave has been achieved for the first time
Surface and Subsurface Structures of the Pt-Fe Surface Alloy on Pt(111)
No full textPt-Fe bimetallic alloys are important model catalysts for a number of catalytic reactions. Combining scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we have studied the structures of Pt-Fe surface alloys prepared on Pt(111) under a variety of conditions. Although the surface and subsurface structures of the Pt-Fe surface alloy could be varied with the deposition amount of Fe atoms and the annealing temperature, a characteristic alloy surface with a bright striped pattern could be identified, which consists of a Pt-dominant surface layer with a small percentage of Fe atoms in the form of isolated atoms or clusters in the surface lattice and a subsurface layer with an ordered Pt3Fe alloy structure. The bright stripes observed in STM were surface dislocations caused by stress relaxation owing to the lattice mismatch between the surface and subsurface layers. This characteristic alloy surface could be prepared on Pt(111) by depositing sub-monolayer Fe at similar to 460 K to facilitate Fe diffusion in the near surface region, or annealing multilayer Fe at similar to 700 K, to enhance bulk diffusion of Fe atoms. The synthesis of this Pt-Fe alloy surface with well-defined structures could allow for further model catalytic studies
Alkaline-earth metallacyclic complexes bearing a diborane-bridged tetraamide ligand: synthesis, structure and fluorescence property
No full textA series of alkaline-earth (Mg, Ca, and Sr) metallacyclic complexes bearing a diborane-bridged tetraamide ligand were achieved for the first time through a clean one-step approach. All of these metallacycles were characterized by single-crystal X-ray diffraction analyses. UV-Vis absorption/emission spectroscopy showed deep blue fluorescence of these complexes
Zeolite-supported metal catalysts for selective hydrodeoxygenation of biomass-derived platform molecules
No full textIncreasing demand for renewable chemicals and fuels has stimulated the search for alternative feedstocks and is driving the ongoing transition to a more renewables-based society. Considerable academic efforts have been directed at the valorisation of biomass sources and derived intermediates, so called platform molecules, to produce value-added chemicals and fuels. In this contribution, opportunities are discussed for the application of zeolite-supported bifunctional catalysts in the conversion of biomass sources into chemicals and fuels via hydrodeoxygenation (HDO). Such metal/zeolite catalyst systems play a prominent role in many of these biomass HDO routes. Emphasis is put on the current progress in metal/zeolite-catalysed HDO of three selected, promising routes involving biomass-derived platform molecules and the model compounds that mimic more complex feeds. Four key concepts of metal/zeolite catalysts, such as combining metal and Bronsted acid sites, site-ratio balancing, proximity between metal and acid functions and shape selectivity are discussed in order to provide a comprehensive overview. In addition, two challenges related to the accessibility of the active sites and catalyst stability in the liquid phase, typically a hot, highly polar, and protic reaction medium, are discussed. Finally, the open challenges and perspectives regarding the development of metal/zeolite catalysts for biomass HDO reactions are examined
Ultrafast decay dynamics of water molecules excited to electronic (D)over-tilde' and (D)over-tilde '' states: a time-resolved photoelectron spectroscopy study
No full textThe ultrafast decay dynamics of water molecules excited to (D) over tilde'B-1(1) and (D) over tilde ''(1)A(2) states is studied by combining two-photon excitation and time-resolved photoelectron imaging methods. The lifetime of the (D) over tilde'B-1(1)(000) state of H2O (D2O) is determined to be 1.54 +/- 0.1 (22.6 +/- 1.6) ps, consistent with a previous high-resolution spectroscopic study. The H2O (D) over tilde ''(1)A(2)(000) state decays with a lifetime of 4.1 +/- 0.2 ps, while in the D2O (D) over tilde ''(1)A(2)(000) state, two independent decay pathways are observed, with time constants of 0.55 +/- 0.1 and 13 +/- 1 ps, respectively. The former is proposed to be associated with a hitherto undocumented (D) over tilde '' -> (C) over tilde pathway, induced by Coriolis interaction