Wei Peng,Jianmei Xie,Junying Zhang,Xia Yang,Aihua He
The isoprene polymerization kinetics by using TiCl 4 /MgCl 2 type Ziegler-Natta catalysts (TMC) with different titanium contents were studied for better understanding the possible active-specie structures of heterogeneous Ziegler-Natta (Z-N) catalysts for conjugated diene polymerizations. The catalytic features including the catalytic activity (CA), number of active centers ([C*]/[Ti]), rate constant for polymerization (k p ), stereoregularity of these TMC catalysts were studied. The low titanium content catalyst TMC-1 (Ti = 0.09 wt.%) with more isolated mononuclear titanium species showed higher CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with low molecular weight ( M w ) in the initial polymerization stage. The medium high titanium content catalyst TMC-2 (Ti = 2.38 wt.%) with more clustered mononuclear titanium species showed lower CA and yielded cis-1,4-/trans-1,4- mixed microstructure polyisoprene with high M w in the early stage of polymerization. The high titanium content catalyst TMC-3 (Ti = 3.76 wt.%) presented lowest CA and yielded high trans-1,4- polyisoprene with higher M w .
Guojun Lv,Xuyang Zou,Yan Chen,Qing Zhang,Xubin Zhang,Fumin Wang
The successful one-pot synthesis of MCM-41/MFI composite is mainly concentrated on the trivalent heteroatom of Al 3+ and Fe 3+ , however there are almost no reports about the one-pot synthesis of Ti-MCM-41/MFI composite. In this work, we reported the one-pot synthesis of Ti-MCM-41/MFI composite with a temperature-gradient hydrothermal strategy using hexadecyl trimethylammonium bromide CTAB and silicalite-1 seed as structure directing agents as well as ammonia solution as alkali source, and its application as heterogeneous catalyst in the cyclohexene epoxidation reactions. The impact of Si/Ti molar ratio and ammonia dosage as well as CTAB amount on the formation and property of Ti-MCM-41/MFI composite were systematically investigated. In addition, a possible partial transformation mechanism of Ti-MCM-41/MFI composite sample was proposed. The synthesized Ti-HMZ-50-N3.77-Se0.05 sample with ordered mesoporous structure and high content of framework titanium active centers revealed the eminent cyclohexene epoxidation performance, achieving a 32.51 % of cyclohexene conversion and a 61.27 % selectivity of cyclohexene oxide within 5 h of reaction.
Yu Liu,Meng Huang,Fangyu Xiong,Jiexin Zhu,Qinyou An
Zinc-ion batteries (ZIBs) using zinc metal as anode materials suffer from Zn dendrite formation and hydrogen evolution during the stripping/plating process, which will lead to performance degradation and hinder practical application. Herein, the 1,4,5,8-naphthalene diimide (NI) is proposed as a promising dendrite-free organic anode material for ZIBs . Moreover, the effect of different binders on electrochemical performance of NI electrode is investigated. Compared NI electrode with polyvinylidene fluoride (PVDF) binder, the NI electrode with the polytetrafluoroethylene (PTFE) binder shows highly enhanced rate capability (122.2 mA h g – 1 at 5 A g – 1 ) and cycling performance (123.3 mA h g – 1 at 3 A g – 1 after 2200 cycles). The improvement cycling stability of NI is attributed to PTFE binder, which effectively maintains electrode structure and inhibits dissolution of organic molecules during the cycling process. In addition, the ion kinetics analyses reveal that the superior rate capability is provided by the capacitive charge storage. And the carbonyl group of NI is active center of electrochemistry, which is revealed by in-situ attenuated total reflection–Fourier transform infrared (ATR-FTIR) and ex-situ Raman. Besides, the aqueous Zn-ion full cell based on metal-free NI anode and Prussian blue analogues (PBAs) cathode exhibits excellent rate capability (113.9 mA h g – 1 at 10.0 A g – 1 ), high operation voltage of ~ 1.2 V (at 1.0 A g – 1 ) and energy density of 50.2 Wh kg total – 1 . This work may provide a new design inspiration to develop organic dendrite-free zinc anodes for high-performance aqueous ZIBs batteries.
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