纳米级Fe3O4-Pd/Fe复合材料催化脱氯2,4-D研究

采用共沉淀法制备纳米级Fe_3O_4,将其包覆在纳米Pd/Fe颗粒表面制成纳米级Fe_3O_4-Pd/Fe复合材料,并用于2,4-二氯苯氧乙酸(2,4-D)的催化脱氯.同时,采用透射电镜(TEM)、扫描电镜(SEM)等方法对复合材料的结构进行分析,并考察了初始pH、钯化率、反应温度、纳米Fe_3O_4投加量等实验参数对n Fe_3O_4-Pd/Fe复合材料催化脱氯2,4-D的影响.结果发现,纳米Fe_3O_4粒径小于Pd/Fe纳米颗粒,具有一定的磁性,包覆于纳米Pd/Fe表面,提高了纳米材料的稳定性及分散性,并有利于复合材料的回收和循环利用.此外,纳米Fe_3O_4具有一定的导电性,可作为良好的电子通道为纳米Pd/Fe颗粒传递电子,促进反应的进行,增强2,4-D的去除效果.实验结果表明,较高的钯化率、反应温度、Fe_3O_4∶Fe质量比及中性pH条件均有利于反应的进行.当纳米Fe投加量为1.0 g·L-1,m(Fe_3O_4)∶m(Fe)为1∶1,初始pH为7.0,钯化率为0.15%,反应温度为25.0℃时,反应90 min后,40.0 mg·L-1的2,4-D的去除率达到100%,苯氧乙酸(PA)的生成率达99.8%.     

Pd/CeO2-Al2O3对烟气中多环芳烃的催化氧化性能研究

采用浸渍法制备了不同负载量及不同钯铈比(Pd:Ce)的Pd/CeO2-Al2O3催化剂,并结合XRD、BET、SEM、O2-TPD和H2-TPR等方法对催化剂的性质进行了表征,研究了所制备的催化剂对燃煤烟气中多环芳烃(PAHs)的催化转化效率.XRD和SEM结果表明,Ce和Pd在Al2O3表面呈高度分散状态,有利于PAHs的催化氧化.BET测试表明,Ce的引入改变了催化剂表面孔径结构,提高其比表面积.O2-TPD和H2-TPR测试表明,适当钯铈比条件下制备的催化剂有较强的储氧能力和活性.催化氧化实验结果表明,所制备的Pd/CeO2-Al2O3催化剂对PAHs具有较高的转化效率,其平均转化率均在80%以上,且PAHs的毒性当量显著降低,钯铈比对PAHs的催化氧化性能影响较大,当催化剂的钯铈比为1:1时,PAHs的转化率最高,可达90%以上.     

In situ adsorption-catalysis system for the removal of o-xylene over an activated carbon supported Pd catalyst

An activated carbon (AC) supported Pd catalyst was used to develop a highly efficient in situ adsorption-catalysis system for the removal of low concentrations of o-xylene. In this study, three kinds of Pd/AC catalysts were prepared and tested to investigate the synergistic efficiency between adsorption and catalysis for o-xylene removal. The Pd/AC catalyst was first used as an adsorbent to concentrate dilute o-xylene at low temperature. After saturated adsorption, the adsorbed o-xylene was oxidized to CO2 and H2O by raising the temperature of the catalyst bed. The results showed that more than 99% of the adsorbed o-xylene was completely oxidized to CO2 over a 5% Pd/AC catalyst at 140℃. Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), and temperature-programmed oxidation (TPO) were applied to investigate the physical properties of o-xylene adsorption-desorption and the in situ adsorption-catalysis activity of the AC support and Pd/AC catalyst. A synergistic relationship between the AC support and the active Pd species for the removal of low concentrations of o-xylene was established.     

酸性体系中Pd/PPy/foam-Ni电极电化学还原三氯甲烷

在沉积电流密度5 mA·cm^-2,沉积时间40 min条件下,通过电沉积方法制备Pd/PPy/泡沫镍(foam-Ni)电极,以Pd/PPy/foam-Ni电极为阴极研究酸性体系中三氯甲烷的电化学还原脱氯,实验在室温条件下进行.采用循环伏安法对电极进行测试,Pd/PPy/foam-Ni电极在-500 mV (vs Hg/Hg₂SO₄)左右获得很大的氢吸附峰电流值,峰电流值为－100 mA.扫描电镜(SEM)分析表明,聚吡咯的引入改变了Pd在电极表面的沉积形态,使电极表面具有很好的空间延伸性.在酸性体系中进行Pd/PPy/foam-Ni电极对三氯甲烷的电化学还原脱氯实验,结果表明,综合考虑三氯甲烷去除率及脱氯过程电流效率,在保证脱氯过程电流效率为44.17%的条件下,三氯甲烷的去除率为49.23%,此时最佳脱氯电流密度为0.05 mA·cm^-2,最佳脱氯时间为180 min,实现了在酸性水溶液体系中,低初始浓度三氯甲烷较好的脱氯效果.     

树脂D001负载纳米Pd/Fe双金属脱溴2,2＇,4,4＇-四溴联苯醚（BDE-47）的研究

采用大孔树脂D001交换吸附Pd2＋、Fe2＋并在厌氧条件下以硼氢化钠溶液还原吸附的钯铁离子制备成负载纳米Pd/Fe双金属树脂。利用该树脂对2,2＇,4,4＇-四溴联苯醚（BDE-47）进行脱溴反应,探讨了该法的可行性和特性。结果表明：当大孔树脂D001、氯化钯、硫酸亚铁用量分别为0.75 g、2μg和0.2 g时所制备的双金属树脂脱溴水-乙醇溶液中的BDE-47效果最佳,反应遵循准一级动力学,速率常数k约为0.161 d-1,半减期为1.21 d。负载Pd/Fe的D001连续3次脱溴反应都有较好的效果,水-乙醇溶液中超过90%以上的BDE-47在反应6 d后被降解。负载Pd/Fe双金属的树脂可以重复活化再生,但再生2次后其脱溴效率变差,反应6 d只有47.3%的BDE-47被降解。用气相色谱-质谱联用仪和离子色谱仪跟踪Pd/Fe双金属树脂脱溴BDE-47反应,可知产物包括溴离子、三溴联苯醚、二溴联苯醚、一溴联苯醚和联苯醚。     

Pd/Fe及纳米Pd/Fe对氯酚的脱氯研究

采用化学沉淀法制备得到了纳米Fe和纳米Pd/Fe(20～100nm),利用制备的纳米催化剂对氯酚进行了催化脱氯研究,并与常规的零价铁和Pd/Fe进行了对比分析.结果表明,纳米颗粒具有较高的比表面积和表面反应活性,所制备的纳米Pd/Fe双金属BET比表面积达到12.4m²/g,而商用铁颗粒(<10m)的比表面积只有0.49m²/g;当钯化率为0.0666%,纳米Pd/Fe用量在6g/L时,氯酚脱氯率达到90%以上,在相同的处理效果下,常规Pd/Fe的使用量为纳米Pd/Fe的20倍左右,纳米Pd/Fe催化氯酚的脱氯降解遵循一级反应动力学.     

铈改性Al2O3担载Pd催化剂的CO氧化性能研究

浸渍法制备了Al2O3＋CeO2为载体的Pd催化剂,对制备中各因素对催化剂效果的影响作了初步研究。考察了活性组分含量与催化剂性能的关系以及焙烧温度、水蒸气对催化剂活性的影响。结果表明,稀土Ce元素的存在使催化剂的性能得到明显改善。制备过程中焙烧步骤对催化剂的活性影响很大,催化剂制备必须高于600℃焙烧。     

功能微生物对污染农田土壤中铅锌的溶出实验

用微生物修复重金属污染的土壤是当今的研究热点之一。试图寻找一类可以增加土壤中重金属铅、锌的可溶态的功能微生物,并研究该微生物在不同土壤含水率和不同投菌比条件下对铅、锌溶出作用的影响。最终筛选出符合条件的菌JK3,并发现当土壤含水率为35%,投菌比为0.15 mL/g土(菌液OD=1)时,土壤中铅和锌的可溶态增加量最多。其中,可溶态铅的含量由原来的0.49 mg/kg增加到了5.04 mg/kg,可溶态锌的含量由原来的2.23 mg/kg增加到了22.44mg/kg。该方法为后续用植物提取或化学淋洗等方法将土壤中的重金属彻底去除提供了可能。     

液相催化加氢法去除Cr（Ⅵ）

采用浸渍法合成出Pd/Al2O3催化剂,通过ICP、XRD、TEM和Zeta电位等表征手段对催化剂的组成和形貌进行了表征.在液相催化加氢还原Cr（Ⅵ）的反应中,分别研究了催化剂加入量、Cr（Ⅵ）初始浓度、pH值、Pd负载量等因素的影响.结果表明,该催化剂表面酸性影响催化还原效果,此反应属于吸附抑制型.     

Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solid electrode

Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solidelectrode was studied. As solid electrodes, carbon cloth (CC), carbon felt (CF) and titanium mesh were used, and palladium was plated on solid electrodes by either electrolytic or electroless method. On each electrode with Pd, chlorophenols were qualitatively dechlorinated to phenol, while they were entirely intact on electrodes without Pd. Moreover, neither base electrode nor plating method significantly affected the activity of Pd as far as it was sufficiently loaded on the electrode. Based on the results in the experiments using one electrode repeatedly, Pd catalyst proved to possess a satisfactory duarability under the present condition. It was suggested that the reactive species responsinble for the dechlorination of chlorophenols could be formed during preliminary electrolysis. Thus, (Pd)_x-H resulting from the adsorption of electrogenerated hydrogen on metallic Pd might be assumed most probable.