Stereochemistry and mechanism of the hydrogenation of dialkyl cyclohexenes

In order to investigate the steric effect of the substituents to determine the product distribution, disubstituted cyclohexenes were hydrogenated over several transition metal catalysts. Some cyclohexenes which have two large substituents at the vicinal carbon atoms, at least one of which is trigonal, were not hydrogenated over Raney Ni at all but were hydrogenated over Pt catalyst under our experimental conditions. Presumably, the stereoselectivity depends on the competitive operation of the torsional angle strain and the catalyst hindrance with substituents. In the hydrogenation over Pd catalyst, thermodynamically more stable products were dominant at the standard condition but at high substrate to catalyst ratio the less stable products were slightly preferred. No appreciable stereoselectivity was observed in the hydrogenation of 1,4-disubstituted cyclohexenes.     

圆弧齿轮的解析法设计计算

本文对目前在仪器仪表中采用的圆弧齿轮进行了分析,在图解法设计的基础上,推出了一套解析法设计计算方案。     

基于H.264编码域的显著运动检测算法

视频监控中运动目标检测算法易受背景、噪声等因素的影响,导致运动检测准确性降低。针对该问题,提出一种基于H.264编码域的显著运动目标检测改进算法。该算法基于编码过程中帧间运动预测模块输出像素值的绝对差值和,计算其标准差以作为运动判据,同时自适应设置运动判断阈值,以降低背景和噪声的影响。实验结果表明,相比于传统的低复杂度算法,该算法能有效降低背景和噪声等因素的影响,提高显著运动目标的检测准确性。相比于传统的运动检测算法,该算法保持了计算复杂度低的特点,算法复杂度仅为帧间差分法的18.3%,更适用于实时性要求高的监控系统。     

不同煅烧温度下形成的含氟硫A矿对水泥水化性能的影响

为研究不同煅烧温度下，含氟硫熟料中不同性能、形貌特征的A矿与水泥水化形成钙矾石的关系以及A矿对水泥水化性能的影响，采用工业原料并尽量模拟立窑内煅烧状况，对经1350℃和1425℃温度下煅烧的熟料进行了A矿形貌、A矿水化率及A矿与钙矾石形成关系等系列试验。试验结果表明，在传统的煅烧温度下（1400～l425℃）烧成的熟料．其A矿的固溶程度及A矿含量均比低温（1350℃）烧成的高；掺氟硫复合矿化剂烧制的熟料的A矿具有较高的水化速度，熟料强度较高．其制成的水泥在水化时，液相成分受高固溶程度A矿的水化所控制，所形成的钙矾石较低温煅烧的稳定．且A矿水化产物的形成与钙矾石（AFt）的形成较协调，水泥石机械强度更高。     

Preparation and characterization of antibacterial silver-dispersed activated carbon aerogels

Silver-dispersed carbon aerogels (CAs) were obtained by direct immersion of organic aerogels prepared by ambient pressure drying technique in AgNO₃ aqueous solution and then carbonization. The effect of preparation conditions such as the resorcinol/catalyst ratio, the feed AgNO₃ concentration, the ratio of aerogel mass/solution volume, immersion time and carbonization temperature on the bulk density and silver content as well as the BET surface area of the dispersed CAs was studied. The dispersion and structure of silver nanoparticles in obtained materials were investigated by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The Ag-dispersed CAs prepared exhibit strong and long-term antibacterial activity.     

The effect of H2 treatment on the activity of activated carbon for the oxidation of organic contaminants in water and the H2O2 decomposition

In this work, hydrogen peroxide reactions, i.e. H₂O₂ decomposition and oxidation of organics in aqueous medium, were studied in the presence of activated carbon. It was observed that the carbon pre-treatment with H₂ at 300, 500, 700 and 800 °C resulted in an increase in activity for both reactions. The carbons were characterized by BET nitrogen adsorption, thermogravimetric analyses (TG), temperature programmed reduction (TPR), electron paramagnetic resonance (EPR), iodometric titration and determination of the acid/basic sites. TPR experiments showed that activated carbon reacts with H₂ at temperatures higher than 400 °C. The treatment produces a slight increase in the surface area. EPR analyses indicate the absence of unpaired electrons in the carbon. Iodometric titrations and TG analyses suggested that the treatment with H₂ generates reduction sites in the carbon structure, with concentration of approximately 0.33, 0.53, 0.59, 0.65 and 0.60 mmol/g for carbons treated at 25, 300, 500, 700 and 800 °C, respectively. It was also observed the appearance of basic sites which might be related to the reduction sites. It is proposed that these reducing sites in the carbon can activate H₂O₂ to generate HO^* radicals which can lead to two competitive reactions, i.e. the hydrogen peroxide decomposition or the oxidation of organics in water.     

Lipase-catalyzed esterification of lactic acid with straight-chain alcohols

Enzymatic synthesis of esters of lactic acid and straight-chain alcohols with different chain lengths (C₆–C₁₈) were investigated in batch reactions with hexadecanol (C₁₆) as the model alcohol. Cyclohexane was the best solvent for higher ester yields, and the best biocatalyst was the immobilized Candida antarctica lipase B (Novozym 435) as well as the textile-immobilized Candida sp. lipase. A method was established to obtain ester yields in the range of 71 to 82% for the different alcohols, and the most favorable conditions for the esterification reaction using Novozym 435 were an equimolar ratio of lactic acid to alcohol, each at a concentration of 120 mM each; a 50°C reaction temperature; 190 rpm shaking speed; and the addition of 100 mg molecular sieves (4 Å) for drying. The ester yield increased with increasing lipase load, and a yield of 79.2% could be obtained after 24 h of reaction at 20 wt% of Novozym 435. The immobilized Candida sp. lipase prepared in the laboratory also could be used to produce esters of lactic acid and straight-chain alcohols, but it had a much lower activity than Novozym 435 with a temperature optimum of 40°C.     

固体酸催化合成草酸二乙酯的应用研究

以粉煤灰、活化剂、硫酸为主要原料经活化、陈化、浸泡、焙烧等处理制得的固体酸催化剂，应用于草酸二乙酯的合成中取得了良好的催化效果。实验发现，当醇酸摩尔比为3．5、催化剂用量为草酸的5％、反应时间在4h时，酯产率可达81.8％，该催化剂具有贮存稳定性高、可重复使用、制备工艺简单、原料成本低廉等特点，是一种易于工业化应用的环境友好固体酸催化剂。     

化学镀镍-磷合金机理的研究

通过对化学镀Ni—P合金过程中线性极化电阻及沉积速度的测量,得出极化电阻的倒数1/Rp与电流密度i呈线性关系。用阳极极化曲线的方法,较详细地研究了次磷酸钠在镍电极上的氧化过程。提出了化学镀Ni—P合金是按电化学机理进行的。     

Aqueous electrochemical intercalation of bromine into graphite fibers

For the first time, graphite fibers have been electrochemically intercalated with Br⁻ that have the same structure and properties as those intercalated from vapor phase Br₂. This was accomplished by intercalating pitch-based Thornel^® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br⁻ is oxidized to aqueous Br₂ which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br₂ solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br₂ unless a voltage is applied.