The study of the active surface for CO oxidation over supported Pd catalysts

CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programmed reaction.The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones.Model studies were performed to better understand the oxidation state,reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction conditions using an in situ infrared reflection absorption spectrometer(IRAS).Three O/Pd(100)model surfaces,chemisorbed oxygen covered surface,surface oxide and bulk-like surface oxide,were prepared and characterized by low-energy electron diffraction(LEED)and Auger electron spectroscopy(AES).The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface,and is unstable under the reaction conditions with sufficient CO.     

Modification of Pd-CeO2 catalyst by different treatments: Effect on the structure and CO oxidation activity

To investigate the interaction between noble metal and CeO₂, a Pd-doped CeO₂ catalyst was prepared by sol-gel method, and the catalyst was then treated in static air and a H₂/O₂ alternating flow at 800 °C, respectively. It is found by step-scanning XRD that Pd ions migrate out of the ceria lattice during the redox treatment, while the exudation of Pd is not so obvious after the oxidative treatment. For the CO oxidation activity, the redox treated catalyst is seriously weakened compared with the oxidative-treated one. This difference is ascribed to the encapsulation of Pd crystallites by the CeO₂ support during the redox treatment, which is confirmed by XPS and CO-TPR. Based on the activity and FTIR results, it is proposed that, CO oxidation at low temperatures proceeds mainly via the reaction between the adsorbed CO on Pd sites and the lattice oxygen of surface CeO₂ at the Pd-Ce interface.     

微重力下Stewart平台的主动减振系统研究分析

Stewart平台是一种并联减振机构,因其具有承载能力强、刚度大、结构稳定、精度高等优点,广泛应用于航天航空和精密仪器领域。采用Cubic构型Stewart平台并对压电陶瓷的力一位移关系线性化后,可简化成单自由度的线性主动控制系统,对六自由度的Stewart平台分散控制,在随机平稳白噪声的激励下考虑时滞影响,并对其解耦后的Stewart平台进行LQR数值分析,用Adams预测公式进行时滞补偿。分析结果表明：Stewart平台具有较好的减振性能,能有效减小平台在微重力干扰下引起的位移反应;时滞因素会降低LOR的控制作用;可通过Adams预测公式对时滞影响进行较好地补偿。     

一种自适应容错控制方法

提出了一种基于分布估计的自适应容错控制方法．该方法利用随机参数模型，并在建立自适应容错控制算法时将随机参数的概率分布估计引入控制系统性能指标，解决了系统运行模态参数不确定和系统运行模态变化不确定的问题．计算机仿真结果表明该方法可以对故障系统进行有效地容错控制     

The Synthesis of p-Methoxybenzyloxycarbonyl Amino Acids

o-Chlorobenzyloxycarbonylimino-2-phenylacetonitrile (Cl-Z-ON) and p-methoxybenzyloxycarbonylimino-2-phenylacetonitrile (MOZ-ON) have been prepared from 2-hydroxyimino-2-phenylacetonitrile (oxime), phosgene, and the corresponding alcohols. Cl-Z-ON is synthesized for the first time and found to be stable at room temperature. MOZ-ON is utilized for the preparation of MOZ-amino acids under various conditions. The oxime can be recovered and reused. The combination of Cl-Z- and MOZ- for the alternative masking of the N⁴- and N⁴-amino groups of lysine residue has also been studied.     

Development of Nitroreductase-Activatable Fluoroquinolone Prodrugs Exhibiting Attenuated Magnesium Ion Binding

Fluoroquinolones such as levofloxacin and ciprofloxacin are potent antibiotics prescribed to treat various bacterial infections. Recent studies have also identified prominent examples as promising anti-cancer agents. However, significant off-target effects observed in human patients have precluded their wide-spread clinical use. For instance, upon systemic administration, overt toxicity toward eukaryotic organelles (i. e., mitochondria) can result to the destruction of healthy tissue. Moreover, fluoroquinolones feature a β-ketoacid motif which binds to and strips magnesium ions from cartilage, leading to rupture of the Achilles tendon. In this study, we have masked the β-ketoacid of levofloxacin and ciprofloxacin (as well as two quinolones) with a nitroreductase (NTR)-responsive warhead appended through a new self-immolative prodrug linker. The resulting β-ketoester functional group was found to be remarkably resistant toward spontaneous hydrolysis, esterase activity, as well as other ester-cleaving enzymatic systems. Further testing also reveal no cross-reactivity against commonly encountered biologically relevant analytes (e. g., ROS and thiols). Importantly, we demonstrate that upon esterification, the binding toward magnesium ions was attenuated based on an in vitro fluorescent competition assay with the unmodified parent drug.