浆态反应器中铁／活性炭催化剂上还原研究

众所周知，费托合成（Fischer-Tropsch synthesis,FTS)反应是一个有理论与应用价值的研究课题。数十年来，学者们已发现了铁系，钴系和钌系等具有优良FTS反应性能的催化剂体系，铁／活性炭（Fe/Activated Carbon,AC)催化剂是中国科学院大连化学物理研究所八十年代末开发的一类费托合成催化剂，由于活性炭载体发达的孔结构使得该催化剂上FTS反应产物中汽油，柴油选择性高（烃类碳数小于20）和油收率大（C5^ ,112g/m^3 sysgaa)^[1,2]，具有工业放大前景。本文采用1L浆态床反应器，应用不同的还原方法（原位高压还原和反应器外还原）和XRD物相表征手段，了铁／活性炭催化剂在浆态床中的还原与反应问题，得到了一些有用的信息。     

石墨烯的氧化还原法制备及结构表征

采用改进的Hummers法对天然鳞片石墨进行氧化处理制备氧化石墨,经超声分散,然后在水合肼的作用下加热还原制备了在水相条件下稳定分散的石墨烯。用红外光谱、拉曼光谱、扫描探针显微镜和ζ电位仪对样品进行了结构、谱学、形貌和ζ电位分析。结果表明,石墨被氧化后形成以C=O、C-OH、-COOH和C-O-C等官能团形式的共价键型石墨层间化合物;还原氧化石墨后形成的石墨烯表面的官能团与石墨的相似;氧化石墨烯和石墨烯在碱性条件下可形成稳定的悬浮液;氧化石墨烯和石墨烯薄片厚度为1.0nm左右。考察并讨论了还原过程中水合肼用量,体系反应温度、反应时间和pH值对石墨烯还原程度和稳定性的影响,水合肼用量和反应时间是影响石墨烯还原程度的主要因素;pH值对石墨烯稳定性影响较大。     

化学还原法制备纳米铜

以硼氢化钾为还原剂、硫酸铜为氧化剂并添加PVP等辅助材料,采用还原法成功地制备了改性酚醛树脂用纳米铜.通过XRD和TEM对纳米铜进行了表征.结果显示,纳米铜呈球形,粒径为10～50 nm.探讨了BH₄^-与Cu²⁺的反应历程,认为该反应是分三步进行的:第一步是铜的还原反应;第二步是生成的H⁺分别与BH₄^-和OH^-的反应,这是一对竞争反应;第三步是硼的水解反应.在反应过程中,硼氢化钾与硫酸铜消耗的摩尔比为2:1.     

新型还原法脱除苯并噻吩有机硫

新型还原法脱除苯并噻吩有机硫;还原脱硫;苯并噻吩;反应条件;反应机理     

电解还原法合成间苯二胺

在酸性介质中以铜为阴极、石墨为阳极电解还原间二硝基苯制备间苯二胺。考查了温度、电流密度、间二硝基苯用量和盐酸质量百分数对间苯二胺产率的影响及电量对电流效率的影响 ,正交实验确定反应的最佳条件为 :温度 4 0℃ ,电流密度 4A·dm- 2 ,间二硝基苯 0 .2 5g ,HCl质量百分数 15 %。在最佳条件下 ,间苯二胺的产率达 74 .2 %。     

锌-镉还原-分光光度法测定地表水中硝酸盐

提出预先将试样中NO-3用锌-镉还原法还原为NO-2.对还原反应的条件,诸如氯化钠及氯化镉的浓度、溶液的PH值、金属锌(卷状)的加入量以及还原反应所需时间等,进行了研究和优化.还原所得NO-2在酸性溶液中与磺胺进行重氮化后再与萘乙二胺偶合生成红色偶氮化合物.在其吸收峰543 nm波长处测定其吸光度,据此,在校正曲线上间接地查得试样中NO-3的含量.NO-3质量浓度在0～0.400 mg·L-1范围内遵守比耳定律.方法的检出限(S/N=3)为0.008 mg·L-1,在0.1 mg·L-1的浓度水平进行了测定的精密度试验,计算得到相对标准偏差(n=6)为2.1%.在3个浓度水平上作了回收试验,得出回收率在99%～103%之间.     

不同炭载体上碳化钼催化剂的合成

在三种不同炭材料上用程序升温还原法成功制备了负载型Mo2C催化剂,并用X射线衍射和程序升温还原-质谱检测了合成过程中Mo2C的形成历程. 结果显示,炭材料的性质及合成条件均对Mo2C的形成温度及合成过程有着显著的影响. 以纯氢为反应气体时,石墨化程度较高的炭黑载体上钼物种可被还原为金属Mo, 再与碳物种直接碳化生成Mo2C;在碳纳米管载体上Mo2C的生成温度较炭黑上低;在活性炭载体上钼物种只被还原到较低的氧化态,之后与碳反应生成Mo2C. 当氢气不足或在惰性气氛下,炭载体在高于700 ℃时还原钼物种并使之发生碳化生成Mo2C.     

烷基胺为媒介的铜纳米棒的合成及其生长机制研究

以氯化铜为前躯体,葡糖糖为还原剂,烷基胺(十六胺和十八胺的混合物)为络合剂和表面包覆剂,经过络合反应和溶剂热两步反应首先得到形貌均一、直径约为100 nm的铜纳米颗粒, 随后自发生长为五重孪晶铜纳米棒(仍含有部分颗粒)。实验过程中分别对溶剂热反应1 h、3 h和5 h后的还原产物的形貌特征加以表征,可以推断被还原的铜原子首先均匀成核形成初级铜纳米颗粒,经过奥斯特瓦尔德老化过程生长为五重孪晶的次级铜纳米颗粒,由于孪晶结构具有很高的生长活性,在烷基胺的表面包覆作用下生长为各项异性的铜纳米棒。该方法提供了一种有效的铜纳米棒的制备方法并且降低了一维铜纳米材料的合成成本。     

抗氧化剂没食子酸丙酯合成纳米银及其应用

在十六烷基三甲基溴化铵(CTAB)存在下, 硝酸银与没食子酸丙酯在碱性介质中发生还原反应, 制得纳米银; 考察了反应时间、 氢氧化钠浓度、 反应温度以及PG/Ag⁺浓度比等条件对合成纳米银粒子的影响. 利用扫描电子显微镜对纳米银颗粒形貌和尺寸进行了表征, 结果表明获得了分散性良好的球形粒子. 实验中还发现在还原银离子制备纳米银过程中会产生强烈的表面等离子共振峰, 用紫外-可见光谱监测制备过程得到的纳米银紫外吸收带范围为400~450 nm, 最大吸收波长为420 nm, 光谱强度与抗氧化剂的浓度成正比. 将纳米银的这一特性用于定量测定没食子酸丙酯(PG)、 二丁基羟基甲苯(BHT)、 叔丁基对羟基茴香醚(BHA)和叔丁基对苯二酚(TBHQ)等抗氧化剂, 所得检出限分别为0.0752, 0.1242, 0.0693和0.0701 mg/L, 线性范围分别为0.2~1.8, 0.2~3.4, 0.2~3.4和0.2~3.0 mg/L.     

纳米级Ag粉的制备

报道了氧化还原法制备纳米Ａｇ粉，通过对样品的评估，得出此种方法制备的纳米级Ａｇ粉颗粒分散性好，颗粒分布均匀，范围窄，最小粒径为５ｎｍ。     

The diffusion coefficient of Cd2+ ion in different ionic media measured by pulse polarography

The voltammetric reduction behaviors of 12 chlorinated benzenes have been examined in dimethylsulfoxide. Accurate and reproducible reduction potentials were obtained for overlapping reduction peaks by using interrupted sweep voltammetry. Controlled-potential electrolysis and subsequent gas chromatographic product analysis were performed to verify the reduction pathways predicted by the voltammetric reduction potentials.     

Kinetics of calcium phosphate reduction by carbon

A fundamental study was made on the reduction of calcium phosphate by carbon. The mechanism of reduction was presented on applying different additions. Both silica and alumina increased the extent of reduction but with variable rates. The activation energies were calculated on the basis of first-order reactions. The phases formed during reduction were investigated by X-ray analysis.     

Fischer-Tropsch synthesis over ruthenium-promoted Co/Al2O3 catalyst with different reduction procedures

The effect of reduction procedure on catalyst properties, activity and products selectivity of ruthenium-promoted Co/γ-Al2O3 catalyst in Fischer-Tropsch synthesis (FTS) was investigated. Catalyst samples were reduced with different reduction gas compositions and passivated before being characterized by TPR and XRD techniques. Different activity and product selectivity analyses were also performed. These results showed that the catalyst dispersion, particle size, and the degree of reduction changed with different reduction gas compositions, which were resulted from the water partial pressures in reduction process that give varying degrees of interaction with the support. It has been suggested that the FTS activity of cobalt catalyst was directly dependent on the catalyst reducibility. A reduction gas with a molar ratio of H2/He = 1 was used to prevent the formation of Co-support compound during catalyst reduction.     

硝基苯在铜电极上的电还原特性研究

应用循环伏安法和线性扫描伏安法研究水溶液中硝基苯在铜电极上的电还原特性及其电还原为苯胺的中间步骤和反应机理.结果表明:铜电极上硝基苯的还原电位在-0.58V和-1.32V左右(vs.SCE),溶液的酸性和碱性均有益于该还原反应的发生;还原过程伴有反应物吸附现象,当硝基苯浓度较大时,还原过程受传质过程控制;随着厌氧程度的提高,还原速率加快.     

5-硝基-1,4-萘醌在玻碳电极上的电化学行为研究

采用循环伏安法和线性扫描伏安法,研究了5-硝基-1,4-萘醌在玻碳电极上的电化学行为.结果表明,在丙酮的稀硫酸溶液中,5-硝基-1,4-萘醌在0.0V、-0.8V(vs.SCE)处各有一个还原峰,分别为硝基、醌的不可逆电极反应;5-硝基-1,4-萘醌在电极表面的传质为线性扩散,电还原过程由扩散控制,并求得传递系数分别为...     

煤粉着火模式对再燃脱硝效率影响的实验研究

在一维携带流实验台上研究了烟煤煤粉着火模式,包括均相着火和非均相着火,对煤粉再燃还原NO的影响。实验结果表明,温度一定时,随着再燃区氧体积分数的增加,煤粉挥发分首先着火,脱硝效率明显下降;而非均相着火初期造成的颗粒高温有利于异相还原NO,脱硝效率得以回升;氧体积分数进一步提升,再燃区呈现富氧状态,脱硝效率再次下降。提高再燃区温度促进煤粉还原NO,脱硝效率更高,但是也促使挥发分在更低的氧体积分数下着火,着火后脱硝效率下降更多;粒径对煤粉着火以及还原NO的影响较为复杂,粒径在40μm以上,不同氧体积分数下脱硝效率基本上随粒径增大而下降。     

Relationship between the reducibility and selectivity of CeMoxV1-xO4 catalysts by kinetic parameters of TPR

CeVO4, CeMo0.01V0.99O4 and CeMo0.03V0.97O4 were prepared by co-precipitation method. The addition of molybdenum as promoter shows a positive effect on the catalytic behavior of CeVO4 in oxidative dehydrogenation of propane to propylene. The reduction behaviors of the catalysts were characterized by temperature-programmed reduction. The activation energies of reduction process for the catalysts were obtained at different reduction rates by Kissinger method. The addition of Mo to CeVO4 enhances the selectivity to propylene.     

Reduction of nitrobenzene derivatives using sodium borohydride and transition metal sulfides

Reported here is the reduction of aromatic nitro compounds using sodium borohydride and transition metal sulfides as catalysts. The reaction conditions were optimized using the reduction of nitrobenzene as a model reaction. The catalysts studied were iron sulfide (Fe₃S₄), copper sulfide (CuS), zinc sulfide (ZnS), cobalt sulfide (Co₃S₄), and nickel sulfide (NiS). The reduction was monitored using gas chromatography. Quantitative conversions were achieved using Co₃S₄ and NiS, representing a ten-fold increase in reactivity compared to the non-catalyzed reaction. Fe₃S₄ and ZnS had no apparent effect on the reduction of nitrobenzene while the reduction using CuS showed a marginal increase. The reduction method was applied to several aryl-nitro derivatives containing either electron-withdrawing or electron-donating groups. Halogen containing aryl-nitro compounds were reduced without dehalogenation. The reduction had no effect on other functional groups such as carboxylic acids, esters, amides, or alkenes, indicating that the reduction is highly chemoselective.     

Ag改性提高TiO_2对Cr(VI)的光催化还原活性机理

在消除了质子缺乏、光生电子-空穴复合对Cr6 光催化还原负效应影响下,比较了TiO2和Ag/TiO2(Ag质量分数1.0％)光催化还原活性.结果表明,相同条件下Ag/TiO2表现出比TiO2更高的催化活性.EPR分析表明,对于Ag/TiO2,UV照射后Ag表面有活性物种O2生成,在TiO2上有活性中心表相Ti3 生成.光生电子通过表相Ti3 向Cr6 传递电子是cr6 光催化还原的速度控制步骤.较多的表相Ti3 参与还原反应是Ag/TiO2表现出较高催化活性的主要原因,担载Ag上积聚光生电子的较强流动性对反应也起到一定促进作用.     

二氧化碳在P+/P-Si半导体电极上光电化学还原的研究

1870年,Royer使用Zn电极将CO₂还原为HCOOH。近年来,人们对CO₂在几十种金属电极上的电化学还原进行了深入的研究。但普遍存在的问题是CO₂在金属电极上还原的过电位较大,导致耗电较多。