Effect of iridium loading on HZSM-5 for isomerization of n-heptane

The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.     

关于高含量组分光度测定中吸收池误差的消除

对高含量组分的测定,采用高吸收差示分析法可提高吸光度测定的准确度和精密度。但在测定中由于吸收池光程的不匹配而引起的误差往往重视不够。本文研究了吸收池不匹配所引起的误差的消除方法,并应用于陶瓷结合剂中高含量二氧化硅的测定,取得较好效果,测定结果的相对标准偏差小于0.3％。 1 方法原理 在进行一次光度测定中,所测得的吸光度值包括被测物质的吸收、溶液体系的背景吸收以及试剂空白的吸收。在吸收池完全匹配的情况下,按Lambert-Beer定律可得:     

Transition to Film Boiling in Microgravity： Influence of Subcooling

The transition process to film pool boiling in microgravity is studied experimentally aboard the Chinese recoverable satellite S J-8. A quasi-steady heating method is adopted, in which the heating voltage is controlled to increase exponentially with time. Small, primary bubbles are formed and slid on the surface, which coalesce with each other to form a large coalesced bubble. Two ways are observed for the transition from nucleate to film boiling at different subcoolings. At high subcooling, the coalesced bubble with a smooth surface grows slowly. It is then difficult for the coalesced bubble to cover the whole heater surface, resulting in a special region of transition boiling in which nucleate boiling and local dry areas can coexist. In contrast, strong oscillation of the coalesced bubble surface at low subcooling may cause rewetting of local dry areas and activation of more nucleate sites, resulting in an abrupt transition to film boiling.     

解读吉利财务实践

无论是“资本链、融资线、现金池”还是三链协同,吉利的财务创新理论如何才能真正落地？本期客座总编辑吉利控股集团副总裁、财务总监尹大庆和对外经贸大学国际商学院的执行院长汤谷良教授如是点评。     

ICP-MS测定开口箭根茎中的27种金属元素

采用电感耦合等离子体-质谱(ICP-MS)法测定了湖北省长阳县乐园镇产开口箭根茎中27中金属元素的含量.其中13中金属元素V、Cr、Mn、Fe、Cu、Zn、As、Se、Mo、Ag、Cd、Tl、Pb等采用普通模式检测,14种金属元素Li、Be、B、Mg、Al、Co、Ni、Ga、Rb、Sr、Te、Ba、Bi、U等采用碰撞/反应池技术(CCT)模式测定,以消除样品溶液中潜在的干扰.实验条件下,Co、Ni、Cr、Zn、Se、Mo、Ag、Pb等8种金属元素未检出.方法检出限Fe为9.789ng/mL、Cr为2.691ng/mL,Zn为1.803ng/mL,B为2.076ng/mL,Mg为1.977ng/mL,Al为3.024ng/mL,Ni为1.824ng/mL,其它元素为0.003-0.921ng/mL,精密度的RSD为0.164％-9.933％,加标回收介于90.0％-110.0％之间.     

基于可调谐半导体激光吸收光谱技术的逃逸氨在线监测研究

可调谐半导体激光吸收光谱技术(TDLAS)具有高选择性、高准确性的优点,为逃逸氨的在线检测提供了可靠的技术手段。首先研究了温度对NH3浓度检测的影响,表明在25³00℃之间,浓度随温度的升高而降低;然后在室温为25℃时,利用TDLAS系统对浓度为10300℃之间,浓度随温度的升高而降低;然后在室温为25℃时,利用TDLAS系统对浓度为10¹00ppm的NH3进行检测,采集得到其二次谐波光谱。比较了单光程和多光程样品池测量结果,得到单光程样品池最低检出限为22.9ppm,多光程样品池的检测限为1.21ppm,多光程样品池能够明显地提高检测精度。结果表明,该系统能够适应现场测量环境。     

钼改性页硅酸镍催化剂催化顺酐加氢性能

通过蒸氨法合成了一系列钼改性的页硅酸镍催化剂, 考察了钼含量对催化剂结构及其催化顺酐液相加氢性能的影响. 采用氮气物理吸附-脱附、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)、 透射电子显微镜(TEM)、 氢气程序升温还原(H₂-TPR)、 氨气程序升温脱附(NH₃-TPD)、 吡啶吸附红外光谱(Py-IR)和原位X射线光子能谱(XPS)等手段对催化剂的结构和形貌等进行了表征. 结果表明, 助剂Mo的引入对催化剂结构形貌及其催化性能影响显著. Mo的引入提高了活性金属Ni的还原度, 增加了催化剂表面金属Ni⁰的数量, 金属Ni在还原过程产生氢溢流, 溢流氢将部分MoO₃还原为具有酸性的MoO_x物种, 由于金属Ni⁰与具有Lewis酸(L酸)特性的MoO_x及Ni^σ+的协同效应, 显著提高了催化剂对顺酐C≡C和C≡O的加氢活性. 当Mo含量(质量分数)为3%时, 其催化活性最高, 在160 ℃和5 MPa H₂气条件下, 反应3 h顺酐的转化率为100%, 产物γ-丁内酯的选择性为27%.     

超急速爆发沸腾的傅立叶与小波分析

采用快速瞬态微型压力测量系统对脉冲激光加热下无水乙醇超急速爆发沸腾过程中液池内压力变化进行了测量,利用傅立叶变换、小波分析等理论工具对该过程的能量与频率特性进行了分析,并对汽泡群行为进行了理论推测.结果发现,爆发沸腾过程中压力信号频率处于MHz量级;在不同阶段气泡群行为具有不同特点.     

原位电化学与核磁共振联用新技术及其应用进展

电极表面微观的电化学反应动力学机制无法通过孤立的传统电化学方法直接揭示,核磁共振技术能在分子水平上提供待测样品的化学位移和J耦合产生的微小分裂等信息,它可以更容易地鉴定同分异构体、分子构象和电子变化。因此,原位电化学与核磁共振联用技术可以从分子层面上对物质反应机理和反应动力学过程进行原位无损实时研究,发现非原位技术无法监测的短寿命中间体,揭示反应机理和构效关系等相关信息,是一种非常有发展前途的原位谱学技术。但是由于电化学池和核磁共振的不兼容性,对原位电化学与核磁共振的研究及应用相对较少,为了让更多的人了解原位电化学与核磁共振联用这一新技术,文章分别阐述了该技术的国内外进展、工作原理、面临的挑战及其在电化学催化及物质反应机理、燃料电池和药物研究等方面的应用,并对今后需要解决的关键性问题进行了展望。     

Lewis酸催化纤维素制乳酸机理研究

Because fossil fuels are continuously depleted, valorization of biomass into valuable liquid products and chemicals is of great significance yet it remains challenging. Among many biomass-derived products, lactic acid is one of the most important renewable monomers for preparing the degradable polymer polylactic acid. The use of raw biomass to produce lactic acid through catalytic conversion is an attractive approach. In this work, the catalytic reaction performance and mechanism of different Lewis acids (Y³⁺, Sc³⁺, and Al³⁺) for the production of lactic acid from cellulose were investigated in detail by isotopic nuclear magnetic resonance (NMR) and mass spectrometry. The production of lactic acid from cellulose includes tandem and competing reactions. The order of catalytic activity for the one-pot conversion of cellulose into lactic acid is as follows: Y³⁺ > Al³⁺ > Sc³⁺. The main tandem reactions involve the hydrolysis of cellulose into glucose, the isomerization of glucose into fructose (the order of catalytic activity, the same below: Y³⁺ > Al³⁺, Y³⁺ > Sc³⁺), the cleavage of fructose via a retro-aldol reaction to glyceraldehyde (GLY) and 1, 3-dihydroxyacetone (DHA) (Sc³⁺ > Y³⁺ > Al³⁺), and the conversion of DHA or GLY to the final product lactic acid (Al³⁺ > Y³⁺ > Sc³⁺). It was found that the process of glucose isomerization to fructose was the key step to the final selectivity of the tandem reaction of cellulose conversion to lactic acid, and it was clarified that the production of lactic acid from DHA underwent a keto-enol (K-E) tautomerization process rather than a classical 1, 2-shift process. First, DHA was transformed into GLY via the isomerization process, then the adjacent hydroxyl group of GLY was removed in the form of water to produce an α, β-unsaturated species. After that, the α, β-unsaturated species underwent K-E tautomerization to generate unsaturated aldehyde-ketone intermediates. Meanwhile, a molecule of water was added to aldehyde-ketone intermediates to obtain a diol product, the hydrogen atom at the methine position was transferred and the lactic acid was finally obtained through the K-E tautomerization process. The in-depth understanding of the reaction mechanism presented in this work will help to design more selective catalysts for cellulose conversion into value-added oxygen-containing small molecule chemicals.