Liquid-phase hydrodechlorination of chlorinated benzenes over active carbon supported nickel catalysts under mild conditions

Liquid phase hydrodechlorination of chlorinated benzenes was studied over Ni/active carbon (Ni/AC), Ni/gamma-Al2O3, Ni/SiO2 and Raney Ni. The complete dechlorination of chlorobenzene (ClBz) was realized at 333-343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Dichloro- and trichlorobenzenes were also hydrodechlorinated with 50-95% yields of benzene under the similar conditions, as above. The reaction follows zero-order to ClBz concentration and 1.9 order to hydrogen pressure. The reaction does not proceed in the absence of alkaline hydroxide, suggesting the complete coverage of active nickel surface with produced chlorine and the removal of the chlorine ion with hydroxide ion as a rate-limiting step. The active catalysts were characterized by H-2 chemisorption and transmission electron microscopy techniques. The apparent activity strongly depends on the active area of nickel on catalyst surface. (C) 2004 Published by Elsevier B.V.

Highly Active Carbon-supported PdSn Catalysts for Formic Acid Electrooxidation

PdSn/C catalysts with different atomic ratios of Pd to Sn were synthesised by a NaBH4 reduction method. Electrochemical tests show that the alloy catalysts exhibit significantly higher catalytic activity and stability for formic acid electrooxidation (FAEO) than the Pd/C catalyst prepared with the same method. XRD and TEM indicate that a particle-size effect is not the main cause for the high performance. XPS confirms that Pd is modified by Sn through an electronic effect which can decrease the adsorption strength of poisonous intermediates on Pd and thus promote the FAEO greatly.

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase immobilized on active carbon

For the first time horseradish peroxidase (HRP) immobilized on the surface of active carbon powder modified at the surface of a glassy carbon electrode has been shown to undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E-o/, is -0.363 V in phosphate buffer solution (pH 6.8) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 50-700 mV/s. The dependence of E-o/ on the pH of the buffer solution indicated that the conversion of HRP-Fe(III)/HRP-Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized HRP retained its bioelectrocatalytic activity to the reduction of H2O2. Furthermore, the HRP adsorbed oil the surface of the active carbon powder can be stored at 4 degreesC for several months without any loss of the enzyme activity. The method presented for immobilizing HRP can be easily extended to immobilize and obtain the direct electrochemistry of other enzymes.

Direct electrochemical reaction of horseradish peroxidase immobilized on the surface of active carbon powders

It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction. In addition, the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2.

Immobilization and direct electrochemistry of copper-containing enzymes on active carbon

Two typical and important copper-containing enzymes, laccase (Lac) and tyrosinase (Tyr), have been immobilized on the surface of active carbon with simple adsorption method. The cyclic voltammetric results indicated that the active carbon could promote the direct electron transfer of both Lac and Tyr and a pair of well-defined and nearly symmetric redox peaks appeared on the cyclic voltammograms of Lac or Tyr with the formal potential, E-0', independent on the scan rate. The further experimental results showed that the immobilized copper-containing oxidase displayed an excellent electrocatalytic activity to the electrochemical reduction of O-2. The immobilization method presented here has several advantages, such as simplicity, easy to operation and keeping good activity of enzyme etc., and could be further used to study the direct electrochemistry of other redox proteins and enzymes and fabricate the catalysts for biofuel cell.

Effect of properties of active carbon supports on performance of Pt/C catalysts in polymer electrolyte membrane fuel cell

The Pt/C catalysts were prepared with pine active carbon and Vulcan XC-72 active carbon as the supports. The performances of the Pt/C catalysts in polymer electrolyte membrane fuel cell were compared. The result indicates that the performance of Pt/Vulcan XC-72 is better than that of Pt/pine. The physical and chemical properties of the two active carbons were measured using several analysis techniques. It was found that the pore size, specific conductivity and the surface function group significantly influence the performance of the electrocatalyst.

Influences of acid treatments of active carbons on no reduction over carbon-supported copper oxides

Active carbon supported copper oxides were used in NO reduction. The conversions of NO reduction depends strongly on surface oxygen-containing groups on the active carbons, among them the carboxyls and lactones favored remarkably the NO reduction. However, hydrochloric acid treatment led to the decomposition of the carboxyls and lactones on C2 and C3, decreasing their reactivities for NO reduction. Concentrated HNO3 treatment of active carbon produced higher conversions of NO reduction at relatively low temperatures due to the marked increase in the amounts of the carboxyls and lactones.

A novel form of carbon micro-balls from coal

A novel form of ball-like carbon material with its size in micrometer range was prepared from coal with nickel as catalyst by arc plasma method. The carbon material has been systematically studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and ultraviolet laser Raman spectroscopy. The SEM observation shows that the novel carbon material exists in various forms such as individual balls, net-like and plate-like forms, all of which have a quite smooth surface. The diameters of these carbon spheres are quite uniform and in a narrow range of 10-20 mum. The EDS analysis reveals that the ball-like carbon material contains more than 99.5% of carbon and a little amount of other elements such as nickel, silicon and aluminum, The XRD and UV-Raman results reveal that the novel carbon material is a kind of highly graphitized carbon. The growth mechanism of the ball-like carbon material was proposed and discussed in terms of arc plasma parameters and the chemical structure of coal-based carbon. (C) 2002 Elsevier Science Ltd. All rights reserved.

Hydrogenation of cinnamaldehyde over Pt/RHCs in supercritical carbon dioxide - Influence of support pretreatment and phase behavior

The selective hydrogenation of cinnamaldehyde (CAL) was investigated using rice husk-based porous carbon (RHCs) supported platinum catalysts in supercritical carbon dioxide (SCCO2). The effects of surface chemistry treatment of the support and the reaction phase behavior have been examined. The Pt/H-RHCs (HNO3-pretreated) was more active for CAL hydrogenation compared with Pt/NH3 - RHCs (NH3 center dot H2O-pretreated). The Pt/RHCs catalyst exhibited a higher selectivity to cinnamyl alcohol (COL) compared with commercial catalyst of Pt/C, which is relative to the micro - mesoporosity structure of the RHCs.

Soil organic carbon storage and soil CO2 flux in the alpine meadow ecosystem

High-resolution sampling, measurements of organic carbon contents and C-14 signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of C-14 tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12x10(4) kg C hm(-2) to 30.75x10(4) kg C hm(-2) in the alpine meadow ecosystems, with an average of 26.86x10(4) kg C hm(-2). Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m(-2) a(-1) to 254.93 gC m(-2) a(-1), with an average of 191.23 g C m(-2) a(-1). The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m(-2) a(-1) to 181 g C m(-2) a(-1). More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%. 81.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research.

应用负载型纳米铁去除饮用水中砷的研究

砷是毒性最强的元素之一，水体中砷的污染己经引起人们广泛的关注。我国的新疆、内蒙、山西和台湾等省和地区地下水砷含量严重超标。全球共有5,000多万人遭受高砷饮用水的威胁，其中中国有1,500多万，是饮用水砷污染最严重的国家之一。WHO推荐饮用水砷的最高允许浓度从原来的50 µg•L-1已降至10 µg•L-1。更为严格的砷卫生标准的颁布，对作为饮用水源的地下水中的砷去除工艺提出了更高的要求。吸附法除砷比膜法、混凝法和离子交换法更安全、简便，是砷去除工艺中最有效的方法之一。 首先，本研究通过优化制备条件（包括炭种类的选择、炭的粒径大小、还原剂的浓度及滴定速率、反应温度、铁盐的种类及浓度、分散剂的比例及浓度），制备了负载型纳米铁。考虑到砷的去除效率、工程应用的可行性以及经济性，最优的制备条件如下：选用粒径为20~40目煤质炭，在室温、一定的分散剂比例及浓度，0.2 M KBH4滴速为20 d•min-1时所制备的Fe/炭为82.0 mg•g-1；纳米铁在活性炭孔内呈针状，其直径为30~500 nm，长度为1,000~2,000 nm。绝大多数的铁都负载到活性炭内部，这在处理水时铁不流失很重要。 其次，利用制备的负载型纳米铁作吸附载体，进行了饮用水中As(Ⅴ)的吸附去除实验。研究了该吸附剂对As(Ⅴ)的吸附等温线、动力学以及影响动力学的各种因素（包括As(Ⅴ)的不同初始浓度、吸附剂用量、pH值、共存离子和不同温度）、pH值、共存离子等环境条件对As(Ⅴ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现在前12 h内吸附较快，72 h时达到了平衡。用Langmuir 吸附等温式估算出As(Ⅴ)的吸附量为12.0 mg•g-1。该吸附剂在pH 6.5， (25±2)℃， As(Ⅴ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时，As(Ⅴ)的去除率为75.2%；当把吸附剂的用量增加到1.5 g•L-1时，As(Ⅴ)的去除率可达99.9%以上。吸附剂可以用0.1M的NaOH浸泡12 h后即可再生，再生效率较高。常见的阴离子中PO43-、SiO32-对As(Ⅲ)的去除抑制较大，而SO42-、CO32-、C2O42-等离子对砷的去除影响较小。Fe2+对As(Ⅲ)的吸附抑制作用较大而其它阳离子影响不大。吸附剂可用0.1 M NaOH 有效再生，并且具有良好的机械性能。实验室初步实验数据表明，该吸附剂对饮用水除砷具有较好的应用前景。 第三，利用实验室制备的负载型纳米铁对饮用水中As(Ⅲ)的吸附去除也进行了研究。考察了吸附等温线、动力学以及影响动力学的各种因素、pH值、共存离子等环境条件对As(Ⅲ)去除的影响；以及吸附剂的再生及再生后的吸附效率等。研究发现，该吸附剂在pH 6.5， (25±2)℃， As(Ⅲ)初始浓度为2 mg•L-1，吸附剂用量为1.0 g•L-1时， 对As(Ⅲ)的去除率为99.8%；其吸附容量为1.996mg•g-1。吸附过程中部分As(Ⅲ)被氧化。与As(Ⅴ)的吸附相比，该吸附剂对As(Ⅲ)的效率比较高-而常见的其它除砷吸附剂如载铁纤维棉等，对As(Ⅴ)的效率比As(Ⅲ)高，为有效去除As(Ⅲ)，常常需要专门加上氧化这一过程。 最后，利用负载型纳米铁对饮用水中As(Ⅲ) 的氧化性能进行考察，发现该吸附剂不但能够有效吸附去除饮用水中的砷，而且还能把As(Ⅲ)有效地氧化为As(Ⅴ)。经过对吸附剂的构成组分分析发现，活性炭表面因富含多种官能团而对三价砷的氧化作用最大；其次是纳米铁也能把As(Ⅲ)氧化为As(Ⅴ)。