Showing papers by "Weizhong Qian published in 2009"

Energy-Absorbing Hybrid Composites Based on Alternate Carbon-Nanotube and Inorganic Layers

Abstract: [*] Prof. A. Cao Department of Advanced Materials & Nanotechnology Peking University Beijing 100871 (PR China) E-mail: anyuan@pku.edu.cn Prof. Y. F. Lu Departments of Chemical Engineering and Materials Science Engineering University of California Los Angeles, CA 90095 (USA) E-mail: luucla@ucla.edu Prof. F. Wei, Prof. Y. F. Lu, Dr. Q. Zhang, M. Q. Zhao, Y. Liu, Prof. W. Z. Qian Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering, Tsinghua University Beijing 100084 (PR China) E-mail: wf-dce@tsinghua.edu.cn

Gas-Phase Catalytic Hydrochlorination of Acetylene in a Two-Stage Fluidized-Bed Reactor

Abstract: Production of vinyl chloride monomer (VCM) by the hydrochlorination of acetylene with HCl was investigated in both a single-stage fluidized bed (SSFB) and a two-stage fluidized bed (TSFB) at different reaction temperatures and space velocities of acetylene. The conversion of acetylene increases with increasing temperature and decreases with increasing space velocity. Over a wide range of operating conditions, a higher conversion of acetylene was achieved in the TSFB than in the SSFB, with the selectivity of VCM being almost 100%. This process can be described by a two-dimensional dispersion and reaction model. A new catalyst, HgCl2 supported on a coconut-shell-type activated carbon, which has a much higher mechanical strength than the industrial catalyst (HgCl2 supported on a coal-based activated carbon), was employed in the fluidized beds. Evaluation of the catalyst lifetime in a fast sublimation experiment at high temperature showed that the new catalyst has a longer lifetime than the industrial catalys...

Synthesis of High‐Quality, Double‐Walled Carbon Nanotubes in a Fluidized Bed Reactor

Abstract: Double-walled carbon nanotubes (DWCNTs) were synthesized in a packed bed reactor (PBR) and a fluidized bed reactor (FBR) by cracking CH4 on a Fe/MgO catalyst. It is observed that the dominant carbon product changes drastically from DWCNTs to multi-walled CNTs along the axial direction of PBR. The studies indicated that the high concentration of H2 from the high conversion of CH4 causes the quick reduction and sintering of the iron catalyst and inhibits the nucleation of DWCNTs. Based on these results, the batch or continuous feeding mode of small amounts of catalyst was adopted in a FBR to maintain a high space velocity of CH4 and to inhibit the negative effect of excess H2. Finally, a DWCNT product with a specific surface area of 950 m2/g and a purity of 98 %, was obtained.

Modulating the diameter of carbon nanotubes in array form via floating catalyst chemical vapor deposition

Abstract: Based on the analysis of catalyst particle formation and carbon nanotube (CNT) array growth process in floating catalyst chemical vapor deposition (CVD), delicately controlled gaseous carbon sources and catalyst precursors were introduced into the reactor for the controllable growth of CNT array. The low feeding rate of ferrocene was realized through low-temperature sublimation. With less ferrocene introduced into the reactor, the collision among the in situ formed iron atoms decreased, which led to the formation of smaller catalyst particles. The mean diameter of the CNT array, grown at 800oC, decreased from 41 to 31 nm when the ferrocene-sublimed temperature reduced from 80 to 60oC. Furthermore, low growth temperature was adopted in synthesis, through the modulation of the CNT diameter, by controlling the sintering of catalyst particles and the collision frequency. When the growth temperature was 600oC, the as-grown CNTs in the array were with a mean diameter of 10.2 nm. If propylene was used as carbon source, the diameter can be modulated in similar trends. The diameter of CNT can be modulated by the parameter of the operation using the same substrate and catalyst precursor without other equipment or previous treatment. Those results provide the possibility for delicately controllable synthesis of CNT array via simple floating catalyst CVD.

Very High-Quality Single-Walled Carbon Nanotubes Grown Using a Structured and Tunable Porous Fe/MgO Catalyst

Abstract: Fe/MgO nanoparticle catalysts were prepared and used to grow single-walled carbon nanotubes (SWCNTs) from the decomposition of methane. The porous structure of the catalyst can be tailored by an ethanol−thermal treatment and calcination. Catalysts with sufficiently large pores (50 nm to 5 μm) can produce very high-quality SWCNTs that had an intensity ratio of D band to G band in their Raman spectra of less than 0.02−0.03. These SWCNTs had fewer defects than any other SWNT products from the chemical vapor deposition process previously reported.