Chemical Stability of Ti-Modified MCM-41 Catalysts in the Hydroxylation of Benzene in the Liquid Phase

Ti-substituted MCM-41 and Ti-grafted MCM-41 materials possessing both well-ordered long-range and pore structures have been used as catalysts for the hydroxylation of benzene in the liquid phase. The stability of the catalytic performance and the changes in the structural characteristics of Ti-modified MCM-41 resulting from the hydroxylation reaction have been investigated. It has been found that Ti-grafted MCM-41 exhibits better stability of catalytic performance than Ti-substituted MCM-41. For the Ti-substituted MCM-41, the migration of framework Ti into non-framework sites results in a decrease in the catalytic performance and the partial collapse of the pore structure. For the Ti-grafted MCM-41, the hydroxylation of benzene induces a smaller decrease in the pore volume and specific surface area than that observed for Ti-substituted MCM-41.     

Ethylene epoxidation on Ag catalysts supported on non-porous, microporous and mesoporous silicates

The ethylene epoxidation activity of Ag catalysts supported on non-porous SiO₂, microporous silicalite zeolite and mesoporous MCM-41 and HMS silicates was investigated in the present study in comparison to conventional low surface area -Al₂O₃ based catalysts. The MCM-41 and HMS based catalysts exhibited similar ethylene conversion activity and ethylene oxide (EO) selectivity with the SiO₂ and -Al₂O₃ based catalysts at relatively lower temperatures (up to 230 °C), whereas their activity and selectivity decreased significantly at higher temperatures (≥300 °C). The silicalite based catalyst was highly active for a wide temperature range, similar to the SiO₂ and -Al₂O₃ based catalysts, but it was the less selective amongst all catalysts tested. High loadings of Ag particles (up to ca. 40 wt.%) with medium crystallites size (20–55 nm) could be achieved on the mesoporous materials resulting in very active epoxidation catalysts. The HMS-type silicate with the 3D network of wormhole-like framework mesopores (with average diameter of 3.5 nm), in combination with a high-textural (interparticle) porosity, appeared to be the most promising mesoporous support.     

SO42-/ZrO2/MCM-41催化丙烯和乙酸合成乙酸异丙酯的研究

水热合成了介孔材料MCM-41,并以其为载体负载固体超强酸SO42-/ZrO2,通过XRD和N2吸附/脱附对制备的SO42-/ZrO2/MCM-41催化剂进行了表征。在固定床反应器中,以丙烯和乙酸为原料,研究了该催化剂合成乙酸异丙酯的活性。对反应条件进行了系统考察,得出了最佳的反应条件:反应温度140℃;反应压力1.2 MPa;空速(LHSV)1.0h-1;n(C3H6)∶n(CH3COOH)=3∶1。在此条件下,乙酸异丙酯的产率最高可达68.9%。同时,通过48 h的催化剂寿命实验,结果表明该催化剂具有较好的稳定性。     

无硼体系MCM-22分子筛的合成

以哌啶(PI)为模板剂,在不添加晶化助剂下,采用动态水热晶化法合成MCM-22分子筛,考察了晶化时间、PI和Si O2、OH-和Si O2、Si O2和Al2O3的物质的量之比等对晶化产物的影响,结果表明,PI和Si O2,OH-和Si O2,Si O2和Al2O3的物质的量之比为0.50~0.70,0.09~0.10和30~40,晶化时间48~72 h的条件下,能较好地合成MCM-22分子筛。在苯与乙烯液相烷基化制乙苯反应中,以哌啶为模板剂与采用六亚甲基亚胺为模板剂合成的MCM-22分子筛的催化性能相当。     

双模板剂合成Zr—MCM-41的结构表征及催化性能

以十二烷基硫酸钠（SDS）和辛基酚聚氧乙烯醚（TX～100）为模板剂,正硅酸乙酯（TEOS）为硅源,乙二胺为碱性介质,当n（TEOS）：n（Zr（NO3）4）：n（SDS）：n（H2NCH2CH2NH2）：n（H2O）=1：0．008：0．10：0．05：2．2：120合成Zr-MCM-41介孔分子筛,通过XRD、N2吸附脱附、NH3-TPD等方法对分子筛的晶体结构和表面物性进行了研究。结果表明,合成的分子筛具有典型的六方介孔结构特征,孔径分布较窄,具有较大的比表面积和较强的酸性,在乙氧基化催化反应中具有较高的催化活性。     

Multiwalled carbon nanotubes synthesis with high yield utilizing Pt/Al-MCM-41 via catalytic chemical vapour deposition technique

Multiwalled carbon nanotubes (MWNTs) were synthesized over Pt impregnated Al-MCM-41 catalyst by decomposition of acetylene and characterized by XRD and nitrogen sorption isotherm to study the mesophase nature of the material. The optimum temperature and flow rate of the carbon source for CNTs synthesis are 800 °C and 60 mL/min, respectively, within a short reaction period, typically 10 min. Moreover, longer reaction time (i.e. 30 min) favours the formation of more amorphous carbon. When the reaction time is reduced to less than 10 min, formation of amorphous carbon is greatly suppressed by the high yield of MWNTs (85%). The products obtained from the decomposition of acetylene over these catalysts were characterized by TGA, SEM, TEM and Raman spectroscopy. The TEM analysis reveals that CNTs are free from amorphous carbon, whereas Raman spectrum shows two prominent peaks at 1,327 and 1,594 cm⁻¹ as the tangential modes of CNTs. As a conclusion, Pt/Al-MCM-41 is an effective template for MWNTs synthesis using acetylene as a carbon source.     

MgO/MCM-22催化苯与草酸二乙酯烷基化合成乙苯的研究

实验以MgO/MCM-22为催化剂,在气相连续流动固定床反应器上催化苯与草酸二乙酯(DEO)烷基化,合成乙苯(EB)。考察了MgO负载量变化和工艺条件的影响。以硝酸镁为前驱体通过等体积浸渍法制备了MgO/MCM-22催化剂,并以低温N_2吸附脱附、X射线衍射、NH_3-TPD、吡啶吸附IR等,对催化剂进行了表征。实验结果表明:随MgO负载量的增加,苯的转化率逐渐下降,而乙苯的选择性明显提高,这主要是由于负载MgO后催化剂的酸性位数量下降引起的。以MCM-22为催化剂,在最佳反应条件下:温度653 K,空速为2 h~(-1),原料配比n(苯):n(DEO)=4:1,苯的转化率为37.5%,乙苯选择性为80.3%。     

应用运动控制模块PP41实现位置闭环控制

基于松下FP2-PLC和运动控制模块PP41,采用步进电机和编码器方式实现了位置的闭环控制,将三轴的轴向位置精度控制在0.5μm以内。使位置闭环系统能够在低成本下实现。     

Dark matter searches with H.E.S.S.

WIMP annihilations are required to reproduce the correct dark matter abundance in the Universe. This process can occur in dense regions of our Galaxy such as the Galactic center, dwarf galaxies and other types of sub-haloes. High-energy γ-rays are produced in dark matter particle collisions and can be detected by Cherenkov telescopes such as H.E.S.S. We report here the search for γ-ray signals from the Galactic center and the nearby Sagittarius and Canis Major satellites. In the absence of a convincing signal, modelling the dark matter density within these objects allows to put constraints on the WIMP parameters such as its mass and annihilation cross-section. Beyond these targeted searches, the wide-field survey of the inner Galaxy with H.E.S.S. is used to constrain sub-halo formation models involving intermediate-mass black holes.     

一种基于2.4GHz频段的宽带射频发射机的研制

在现代无线通信系统中,研制宽带无线发射机成为射频无线电的发展趋势。以采用ADI公司的ADF4115和MAXIM公司的MAX2750构成的锁相环路提供2880MHz的射频信号源,以ADI公司的AD9857将基带信号调制为70MHz的QPSK信号,再以MAXIM公司的MAX2671作为直接上变频器,从而可以设计出一款工作在2．4GHz频段的宽带射频发射机,从而满足红外图像信号等大信息量数据的无线传输。