基于零价铁的双金属体系对六氯苯还原脱氯研究

利用Ag、Pb和Cu作为催化金属与微米级铁粉制成不同的双金属体系还原脱氯六氯苯(hexachlorobenzene,HCB),探讨不同催化金属种类、不同双金属添加量以及不同离子强度3种因素对HCB脱氯效率的影响,并剖析双金属催化条件下HCB的脱氯规律.结果表明,微米级铁粉对HCB几乎无还原脱氯效果,添加Ag、Pb和Cu对HCB均具有良好的催化脱氯能力,当Ag/Fe、Pb/Fe和Cu/Fe的最佳比例分别为0.2%、0.5%和1%时,反应2 h后HCB的脱氯率分别达到93.5%、88.5%和49.6%;同时,由于催化金属均匀附着在零价铁表面可以形成更多的微型原电池,故增加双金属投加量可有效提高HCB脱氯速率,0.1 g Pb/Fe对HCB脱氯率为38.3%,而0.8 g Pb/Fe对HCB脱氯率可达到88.6%;另外,离子强度增大对HCB的脱氯也有一定促进作用,在Na2SO4浓度分别为0、0.05和0.5 mol·L-1的3个反应器中,反应2 h后HCB脱氯率分别达到93.5%、98.0%和98.9%.     

Ni/Fe双金属降解四氯化碳和四氯乙烯的对比试验

以四氯化碳(CT)和四氯乙烯(PCE)为目标污染物,以批试验方法研究Ni/Fe双金属对CT和PCE的还原性脱氯.结果表明:Ni/Fe双金属可有效去除水中的CT和PCE;Ni/Fe双金属对CT和PCE的降解反应均符合准一级反应动力学方程;在相似的反应条件下,Ni/Fe双金属对CT和PCE脱氯的反应速率常数(kobs)之比为1.48和1.67,说明Ni/Fe双金属对CT的脱氯速率要快于对PCE的脱氯速率;Ni/Fe双金属可对PCE完全脱氯,但对CT脱氯过程中产生少量三氯甲烷(TCM).     

生物炭负载纳米铁镍双金属去除水中1,1,1-三氯乙烷

以小麦秸秆为原料制备生物炭,再通过液相还原法制备了生物炭负载纳米铁镍双金属材料(Ni/Fe/BC),运用FTIR,SEM,XRD技术进行了表征,并将该材料用于水中1,1,1-三氯乙烷(TCA)的去除。表征结果显示,生物炭具有良好的空隙结构和较大的比表面积,能有效负载纳米铁镍双金属,防止纳米铁镍双金属颗粒的团聚。实验结果表明:Ni/Fe/BC的最佳制备条件为生物炭、Fe、Ni的质量比1∶1∶0.01;在TCA质量浓度200 mg/L、Fe加入量1 g/L的条件下,反应60 min时,Ni/Fe/BC对TCA的去除率达99.2%,与未经生物炭负载时的39.1%相比显著提高;生物炭通过吸附TCA使TCA与双金属的接触增多,而铁腐蚀产生的氢被吸附在镍金属表面形成活性氢自由基,促进了TCA的去除。     

铁基双金属强化降解地下水中四氯化碳

采用沉积置换法制备了微米级的Ni-Fe、Cu-Fe、Ag-Fe双金属颗粒，应用扫描电镜（SEM）、X射线光电子能谱（XPS）分析了其表面特征，考察了负载金属类型、金属负载量对铁基双金属降解四氯化碳（CCl₄）的影响.结果表明：Ni、Cu、Ag等催化金属非均匀地负载在铁基体上，双金属颗粒表面发生了氧化.CCl₄的降解速率对催化金属的负载量比较敏感，双金属体系Ni、Cu、Ag的适宜负载量分别为1.0wt%、0.8wt%和0.4wt%.CCl₄在双金属体系中的降解途径为零价铁颗粒表面的直接还原及催化金属表面的催化加氢还原，以催化加氢还原为主.Ni-Fe、Cu-Fe、Ag-Fe对CCl₄的还原降解速率大小顺序与其电偶电池电动势的大小顺序一致，即Ag-Fe对CCl₄的降解速率最快，Cu-Fe次之，Ni-Fe最慢.     

Degradation and fate of 2,4-dinitroanisole (DNAN) and its intermediates treated with Mg/Cu bimetal: Surface examination with XAS, DFT, and LDI-MS

A novel Mg-based bimetal reagent (Mg/Cu) was used as an enhanced reductive system to degrade insensitive munition 2,4-dinitroanisole (DNAN), a contaminant found in energetic-laden waste. Degradation of DNAN was significantly impacted by dissolved oxygen and studied in anoxic and oxic bimetal systems (i.e., purging with N₂, air, or O₂ gas). Degradation occurred through sequential nitroreduction: first one nitro group was reduced (ortho or para) to form short-lived intermediates 2-amino-4-nitroanisole or 4-amino-2-nitroanisole (2-ANAN or 4-ANAN), and then subsequent reduction of the other nitro group formed 2,4-diaminoanisole (DAAN). The nitro-amino intermediates demonstrated regioselective reduction in the ortho position to 2-ANAN; Regioselectivity was also impacted by the anoxic/oxic environment. Under O₂-purging DNAN degradation rate was slightly enhanced, but most notably O₂ significantly accelerated DAAN generation. DAAN also further degraded only in the oxygenated Mg/Cu system. Adsorption of DNAN byproducts to the reagent occurred regardless of anoxic/oxic condition, resulting in a partition of carbon mass between the adsorbed phase (27%-35%) and dissolved phase (59%-72%). Additional surface techniques were applied to investigate contaminant interaction with Cu. Density functional theory (DFT) calculations identified preferential adsorption structures for DNAN on Cu with binding through two O atoms of one or both nitro groups. X-ray absorption spectroscopy (XAS) measurements determined the oxidation state of catalytic metal Cu and formation of a Cu-O-N bond during treatment. Laser desorption ionization mass spectrometry (LDI-MS) measurements also identified intermediate 2-ANAN adsorbed to the bimetal surface.     

纳米Pd/Fe双金属对2,4-二氯酚的脱氯机理及动力学

采用纳米Pd Fe双金属对2,4 二氯酚(2,4 DCP)进行了催化还原脱氯处理.结果表明,纳米Pd Fe双金属具有较高的比表面积和反应活性,对2,4 DCP具有较好的脱氯效率.当纳米Pd Fe用量在6g·L-1时,2,4 DCP脱氯率达到90%以上;脱氯效率与pH值、温度、钯化率、Pd Fe投加量等因素有关.2,4 DCP在脱氯过程中先生成邻氯酚和对氯酚,而后继续脱氯生成苯酚,或由2,4 DCP直接降解成苯酚.2,4 DCP降解符合拟一级反应动力学.2,4 DCP催化还原脱氯反应的活化能为139 7kJ·mol-1.     

球形氧化铝负载Ni-Co双金属催化剂上沼气重整制氢——操作条件的影响

前期研究开发出了活性、稳定性和抗积碳性能都较好的沼气重整制氢Ni-Co/La2O3-Al2O3催化剂。在此基础上选用商业球形氧化铝作为载体(4~5 mm)并掺杂La2O3,用浸渍法制备了Ni-Co/La2O3-Al2O3球形催化剂,以CH4/CO2体积比为1的混合气模拟沼气,考察了操作条件对工业尺度催化剂沼气重整反应性能的影响。结果表明:负载活性组分的γ-Al2O3球形催化剂的沼气重整活性基本达到小试的水平。反应温度升高有利于提高催化剂的重整活性,850℃以上催化剂的活性趋于稳定。反应温度升高有利于减少催化剂的表面积碳,却加速了金属颗粒的团聚。随着空速的增加,催化剂的活性显著降低。较好的催化剂还原方式为用纯H2在700℃下还原2 h,用该方式还原的催化剂反应后金属粒径较小,平均积碳速率较低。     

Catalytic reductive dechlorination of p–chlorophenol in water using Ni/Fe nanoscale particles

Nanoscale bimetallic Ni/Fe particles were synthesized from the reaction of sodium borohydride （NaBH4） with reduction of Ni^2＋ and Fe^2＋ in aqueous solution. The obtained Ni/Fe particles were characterized by TEM （transmission electron microscope）, XRD （X-ray diffractometer）, and N2-BET. The dechlorination activity of the Ni/Fe was investigated using p-chlorophenol （p-CP） as a probe agent. Results demonstrated that the nanoscale Ni/Fe could effectively dechlorinate p-CP at relatively low metal to solution ratio of 0.4 g/L （Ni 5 wt%）. The target with initial concentration ofp-CP 0.625 mmol/L was dechlorinted completely in 60 rain under ambient temperature and pressure. Factors affecting dechlorination efficiency, including reaction temperature, pH, Ni loading percentage over Fe, and metal to solution ratio, were investigated. The possible mechanism of dechlorination ofp-CP was proposed and discussed. The pseudo-first- order reaction took place on the surface of the Ni/Fe bimetallic particles, and the activation energy of the dechlorination reaction was determined to be 21.2 kJ/mol at the temperature rang of 287-313 K.     

Pd/Fe0双金属复合催化纤维降解水中痕量亚硝基二甲胺

存在于环境水体中的亚硝基二甲胺(NDMA)是一种强致癌性有机物,采用零价铁催化还原技术可以将其降解转化为低毒性物质,针对水中痕量NDMA的去除,需要深入开展基于高效零价铁材料、还原性能及还原机制方面的研究.以聚丙烯(PP)纤维为基材,采用紫外辐射接枝-金属离子配位-化学还原方法制备了含Pd/Fe~0双金属的复合催化纤维(Pd/Fe~0-PP-gAA),开展水中亚硝基二甲胺的去除研究.通过SEM、ICP-AES和XPS分析等对Pd/Fe~0/PP-g-AA进行表征.研究了不同制备条件和反应条件下,复合催化纤维对NDMA的降解性能.结果表明,丙烯酸单体质量分数为20%时,通过配位还原制备的复合催化纤维对NDMA的催化降解效果最佳,降解过程符合准一级反应动力学模型.在痕量浓度范围,NDMA初始浓度和溶液pH对复合纤维还原NDMA的性能影响不大.CO_3~(2-)和NO_3~-的存在显著抑制NDMA的降解,SO_4~(2-)、HCO_3~-和腐殖酸的存在对NDMA降解影响较小.     

金属催化还原技术对p-二氯苯的脱氯

研究了Pd/Fe双金属体系对p-二氯苯(p-DCB)的快速催化还原脱氯处理. 结果表明, 在Pd的催化作用下,零价Fe对p-DCB具有较好的还原脱氯效率. 当Pd/Fe双金属的钯化率为0.02%,催化还原剂的用量为4g/75mL,反应90min p-DCB脱氯率达到90%以上;p-DCB的脱氯效率与溶液初始pH值、反应温度、钯化率、Pd/Fe投加量等因素有关;p-DCB在催化还原脱氯过程中先生成氯苯,而后继续脱氯生成苯.