Spectroscopic studies of the effects of selenate and selenite on cobalt sorption to gamma-Al2O3

The fate and transport of toxic metal ions and radionuclides in the environment is often controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including the presence of cosorbing or complexing ligands. To study the impact of anion cosorption on metal cation sorption behavior, Co(II) sorption to gamma-Al2O3 in the presence of selenium oxyanions was investigated. To aid in the interpretation of macroscopic sorption results, X-ray absorption spectroscopy (XAS) experiments were conducted on single and bisorbate samples where the Co(II) surface coverage of the bisorbate sample was greater than or equal to the single sorbate sample. XAS data for single sorbate Co(II) samples were consistent with reported spectra of Co(II)-Al(III) layered double hydroxides (LDHs), indicating coprecipitates are forming in these samples. Comparison of data from single and bisorbate samples showed a decrease in the number of nearest neighbor cobalt atoms in the presence of Se(IV), irrespective of the order of Se(IV) addition and no change in Co coordination in the presence of Se(VI). The extent of the decrease in cobalt second shell features between single and bisorbate samples with equal Co(II) coverage increased with an increase in the Se:Co surface coverage ratio. This trend suggests that the effect of Se(IV) on Co(II) sorption is a function of the Se(IV) surface coverage. At low ratio values, Co(II)-Al(III) LDH precipitates dominate. Increasing the Se:Co surface coverage ratio results in a progressive conversion of coprecipitate to an unknown, disordered Co(ll)/Se(IV) phase. Based on macroscopic data, this new phase could be an LDH with Se(IV) in the interlayer, an alternative precipitate such as a mixed metal Se(IV) hydrate, or a ternary complex.     

Macroscopic studies of the effects of selenate and selenite on cobalt sorption to gamma-Al2O3

Metal ion sorption can be significantly impacted by the presence of other solutes or complexing species. In this research, macroscopic sorption studies were conducted to evaluate the effect of strongly sorbing Se(IV) and weakly sorbing Se(VI) oxyanions on cobalt(II) sorption to gamma-Al2O3. Se(IV) was found to significantly alter Co(ll) sorption as a function of Co(II) surface coverage, while Se(VI) was found to have no effect on Co(II) sorption. Under low Co(II) surface loadings (<0.1 micromol/m2), Se(IV) increased Co(II) sorption as a function of the Se(IV) coverage. At low Se(IV) surface coverages, no change in Co(II) sorption was detectable, while at high Se(IV) loadings Co(II) sorption was significantly increased. The increase in Co(ll) sorption in the bisorbate systems can be explained by either an electrostatic enhancement mechanism or byternary complex formation. Se(IV) decreased Co(II) sorption at high Co(ll) surface loadings (>0.5 micromol/m2) where coprecipitation of Co(II) and A(III) in the form of layered double hydroxides (LDH) is expected to be the dominant sorption mechanism for the single-sorbate case. The extent of the Co(ll) sorption reduction in Co(III)/Se(IV) bisorbate systems compared to the corresponding single-sorbate systems increased with increasing Co(II) surface coverage. The rate of Co(II) desorption was reduced in the presence of Se(IV) compared to the single-sorbate case, indicating a direct interaction between Co(II) and Se(IV). A reaction between Co(II) and Se(IV) is further supported by an increase in Se(IV) sorption in the same bisorbate samples where Co(II) sorption is decreased. Thus, the macroscopic data indicates Se(IV) may be altering the mechanism of Co(II) sorption, potentially forming a ternary surface complex or different surface precipitate.     

Formation of bromochlorodibenzo-p-dioxins and furans from the high-temperature pyrolysis of a 2-chlorophenol/2-bromophenol mixture

The homogeneous, gas-phase pyrolytic thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a total concentration of 88 ppm, reaction time of 2.0 s, and temperatures from 300 to 1000 degrees C. Observed products included (in decreasing yield) naphthalene, dibenzo-p-dioxin (DD), phenol, dibenzofuran (DF), bromobenzene, chloronaphthalene, 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), bromonaphthalene, benzene, 4,6-dichlorodibenzofuran (4,6-DCDF), chlorobenzene, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), 1-mono-bromodibenzo-p-dioxin (1-MBDD), 2-chloro,4-bromophenol, 2,4-dibromophenol, and 2-bromo-4-chlorophenol. Unlike the case for the pyrolysis of pure 2-chlorophenol, 4,6-DCDF was observed, but the analogous 4,6-DBDF remained undetected similar to the individual results with 2-MBP. This indicates that the presence of bromine increases the concentration of chlorine atoms available for the formation of 4,6-DCDF. Due to bromine atoms acting as better leaving groups than chlorine atoms, the yield of DD was increased over that observed for the pyrolysis of 2-chlorophenol. The addition of bromine to a chlorinated hydrocarbon system results in an increase in the total yield of PCDD/Fs as well as PBDD/Fs and mixed PBCDD/Fs due to the ease of bromine elimination reactions as well as an increase of the chlorine atom concentration.     

Formation of dioxins during the combustion of newspapers in the presence of sodium chloride and poly(vinyl chloride)

Exhaust gases from the combustion of newspaper alone, from branches of London plane tree alone, and from newspapers mixed with sodium chloride (NaCl), polyethylene, or poly(vinyl chloride) (PVC) were collected. The samples were analyzed for dioxins by gas chromatography/mass spectrometry. Total amounts of dioxins found in the samples were 0.186 ng/g from newspapers alone, 1.42 ng/g from the branches of London plane, 102 ng/g from newspapers impregnated with sodium chloride (CI wt % = 3.1), 101 ng/g from newspapers impregnated with sodium chloride mixed with PVC (Cl wt % = 2.6), and 146 ng/g from newspapers mixed with PVC (Cl wt % = 5.1). Samples with a higher chloride content produced more dioxins, and there is a clear correlation between dioxin formation and chloride content. The amount of dioxins formed in the samples according to the number of chlorides was Cl5 > Cl4 > Cl6 > Cl7 > Cl8 in PCDD isomers and Cl4 > Cl5 > Cl6 > Cl7 > Cl8 in PCDF isomers, except in the case of newspapers alone. Benzofurans composed 78-92% of the total dioxins formed in the exhaust gases. The higher the number of the chlorides, the lower the production of benzofuran observed. NaCl vaporized at the temperature of the flame used for combustion of the samples (760-1080 degrees C). The results indicate that NaCl and PVC contribute significantly to dioxin formation from waste materials combusted in incinerators.     

SO2-4 /Al2 O3 催化剂的表征及其在环氧化反应中的催化活性

采用浸渍法制备不同煅烧温度下的固体超强酸SO2-4 /Al2O3。使用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、氨气程序升温脱附(NH3-TPD)和氮气物理吸附(N2-BET)技术表征了固体超强酸的表面性质、晶形,并将其用于催化蓖麻油环氧化反应。结果表明：在蓖麻油质量20 g、催化剂用量2 g、煅烧温度600 ℃、过氧化氢滴加温度40 ℃、反应温度55 ℃、反应时间8 h的条件下,环氧化蓖麻油的碘值（Ⅰ）为48.4 g/100 g,环氧值可达0.551%;催化剂重复使用4次后,仍表现出较好的催化活性。     

Origin of carbon in polychlorinated dioxins and furans formed during sooting combustion

The importance of solid- and gas-phase carbon precursors for the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) during sooting combustion was investigated in an entrained flow reactor (EFR). Experiments were performed at various methane (CH4) flame equivalence ratios with or without gas-phase chlorine (Cl2) and fly ash, to provide a realistic environment for carbon reactions and PCDD/DF formation. Selected experiments were conducted with labeled 13CH4 and 37Cl2 to investigate the relative roles of different carbon and chlorine species for the formation of PCDD/DF. The presence of soot and ash were the two major factors controlling the PCDD/DF yields. The 16 PCDD/DF homologues as well as other analyzed chlorinated aromatics were formed by reaction pathways that varied with degree of chlorination. The mono- and dichlorinated homologues were formed by gas-phase, catalytic, or noncatalytic flame product reactions, occurring during soot formation in the near flame zone and/or at lower reaction temperatures (<650 degrees C) in the postcombustion zone. Meanwhile, the higher (tri- to octa-) chlorinated homologues were mainly formed in the postcombustion zone (<650 degrees C) by fly ash-catalyzed de novo synthesis of the soot. Of these, the PCDD/DFs were formed from high carbon number (>C12) fragments in the solid soot structure, while the PCDDs, at least in part, were also formed by reaction of two C6 fragments. The tri- to hexachlorinated DD/DF homologues were formed via a relatively fast de novo synthesis occurring during the first minutes of reactions on the continuously formed soot particles, whereas de novo synthesis on an aged soot matrix was the major pathway for the hepta- and octachlorinated congeners.     

Effect of pH and aging time on the kinetic dissociation of 243Am(III) from humic acid-coated gamma-Al2O3: a chelating resin exchange study

The chelating resin was studied to assess its influence on metal availability and mobility in the environment. The association of organic-inorganic colloid-borne trace elements was investigated in this work. The radionuclide 243Am(III) was chosen as the representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. The kinetic dissociation behavior of 243Am(III) from humic acid-coated gamma-Al2O3 was studied at pH values of 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2 with a contact time of 2 days after the addition of a chelating cation exchanger resin. The concentrations of the components were: 243Am(III) 3.0 x 10(-7) mol/L, gamma-Al2O3 0.5 g/L, HA 10 mg/L (pH 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2) and 50 mg/L (pH 6.0 +/- 0.2), respectively. The kinetics of dissociation of 243Am(III) after different equilibration time with humic acid-coated gamma-Al2O3 was also investigated at pH 5.0 +/- 0.2. The experiments were carried out in air and at ambient temperature. The results suggest that the fraction of irreversible bonding of radionuclides to HA-coated Al2O3 increases with increasing pH and is independent of aging time. The assumption of two different 243Am(III)-HA-Al2O3 species, with "fast" and "slow" dissociation kinetics, is required to explain the experimental results. 243Am(III) species present on HA-Al2O3 colloids moves from the "fast" to the "slow" dissociating sites with the increase of aging time.     

Formation of bromochlorodibenzo-p-dioxins and dibenzofurans from the high-temperature oxidation of a mixture of 2-chlorophenol and 2-bromophenol

The homogeneous, gas-phase oxidative thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, with a reaction time of 2.0 s, over a temperature range of 300 to 1000 degrees C. Observed products in order of decreasing yield included the following: dibenzo-p-dioxin (DD), 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), phenol, 4,6-dibromodibenzofuran (4,6-DBDF), 2,6-dibromophenol, 4,6-dichlorodibenzofuran (4,6-DCDF), 2-bromo-4-chlorophenol, 2,4-dibromophenol, 2-chloro-4-bromophenol, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), dibenzofuran (DF), 1-monobromodibenzo-p-dioxin (1-MBDD), 1-monochlorodibenzo-p-dioxin (1-MCDD), 2,4,6-tribromophenol, naphthalene, chloronaphthalene, bromonaphthalene, chlorobenzene, bromobenzene, and benzene. The results are compared and contrasted with previous results reported for the oxidations of pure 2-chlorophenol and 2-bromophenol as well as results for the pyrolysis of the mixture of 2-chlorophenol and 2-bromophenol. 4,6-DBDF and 4,6-DCDF were observed in higher yields than under pyrolytic conditions but considerably less than the yields observed for the individual oxidation of 2-chlorophenol and 2-bromophenol. The effect on chlorine and bromine on the concentration of hydroxyl radical is shown to control the dioxin-to-furan ratio.     

Low-temperature complete combustion of a dilute mixture of methane and propane over transition-metal-doped ZrO2 catalysts: effect of the presence of propane on methane combustion

Complete combustion of dilute methane alone or a dilute mixture of methane and propane over transition-metal (viz. Mn, Co, Cr, Fe, and Ni)-doped ZrO2 (cubic) catalysts at different temperatures (523-873 K) and a space velocity of 51,000 cm3 x g(-1) x h(-1) has been investigated for controlling methane and propane emissions from exhaust gases. The catalysts are compared for their catalytic ignition temperature and activity in the combustion of propane and methane in the presence of each other. The methane combustion activity of all the catalysts is strongly influenced by the presence of propane; it is decreased markedly. In the combustion of mixed methane and propane the Mn-doped ZrO2 and Cr-doped ZrO2 catalysts show the highest activity in the combustion of methane and propane, respectively; the Ni-doped ZrO2 shows the lowest activity in both cases. In the combustion of mixed methane and propanethe propane combustion is enhanced butthe methane combustion retarded when the Cr-doped ZrO2 and Mn-doped ZrO2 catalysts in a 1:1 ratio are used together in different ways (mixed or in layers).     

氧化铝载钌催化植物油异构化制备共轭亚油酸的研究

以棉籽油为原料,氧化铝载钌(Ru/AL2O3)为催化剂,对亚油酸异构化制备共轭亚油酸进行了研究。采用GC-MS分析不同温度、搅拌速率、催化剂添加量条件下产物中主要成分含量。通过判断反应前后棉籽油甘三酯Sn-1,2,3位脂肪酸组成的变化,评价金属钌催化剂的选择异构化催化特性。研究结果表明,165℃下Ru/AL2O3用量为棉籽油质量的2.5%,搅拌速率800 r/min, N2环境,反应36 h条件下,亚油酸转化率可达87.78 %,共轭亚油酸的选择性为57.17%,得到产物中共轭亚油酸含量为289.3 mg/g棉籽油。随反应时间,顺、反共轭亚油酸会向双反式共轭亚油酸转化,产物中的反式油酸含量有所增加,并且,Sn-1,3位的共轭亚油酸选择性异构化率高于Sn-2位。     

纳米Al2O3溶胶的稳定性及PVDF/Al2O3杂化膜的性能研究

以异丙醇铝(AIP)为原料,采用溶胶-凝胶法,制备了纳米氧化铝(Al2O3)溶胶。研究了酸解剂、酸铝比[n(H+)/n(Al3+)]、陈化时间等因素对溶胶粒径和稳定性的影响,得到了制备稳定、透明纳米Al2O3溶胶的最佳工艺条件,即酸解剂HNO3;n(H+)/n(Al3+)=0.18~0.25;陈化时间20 h。为了改善聚偏氟乙烯(PVDF)膜的性能,通过PVDF与AIP的原位聚合,制备了不同PVDF含量的PVDF/Al2O3杂化膜。采用扫描电镜(SEM)、原子力显微镜(AFM)、红外光谱(FI-IR)、差示扫描量热法(DSC)、热失重分析(TGA)等手段对膜的结构和性能进行了表征。结果表明:杂化膜的纯水通量随着PVDF浓度的增大呈下降趋势,截留率则随着PVDF浓度的增大逐渐升高;AIP的加入使得杂化膜两相之间存在键合,可以增强Al2O3和PVDF之间的化学连接,从而提高杂化膜的亲水性和机械强度;添加AIP后,杂化膜的热分解温度向低温移动,即杂化膜的热稳定性下降;而AIP对PVDF膜的熔点影响不明显。     

Formation and stabilization of combustion-generated environmentally persistent free radicals on an Fe(III)2O3/silica surface

Previous studies have shown environmentally persistent free radicals (EPFRs) form when chlorine- and hydroxy-substituted benzenes chemisorb on Cu(II)O-containing surfaces under postcombustion conditions. This paper reports the formation of EPFRs on silica particles containing 5% Fe(III)(2)O(3). The EPFRs are formed by the chemisorption of substituted aromatic molecular adsorbates on the metal cation center followed by electron transfer from the adsorbate to the metal ion at temperatures from 150 to 400 °C. Depending on the nature of the adsorbate and the temperature, two organic EPFRs were formed: a phenoxyl-type radical, which has a lower g-value of 2.0024-2.0040, and a second semiquinone-type radical, with a g-value of 2.0050-2.0065. Yields of EPFRs were ～10× lower for iron than copper; however, the half-lives of EPFRs on iron ranged from 24 to 111 h, compared to the half-lives on copper of 27 to 74 min. The higher oxidation potential of Fe(III)(2)O(3) is believed to result in greater decomposition of the adsorbate, resulting in the lower EPFR yields, but increased stabilization of the EPFR once formed, resulting in the longer half-lives.     

Formation and destruction of CH2O in the exhaust system of a gas engine

A computational study of chemical reactions occurring in the exhaust system of natural gas engines has been conducted, emphasizing the formation and destruction of formaldehyde. The modeling was based on a detailed reaction mechanism, developed for describing oxidation of C1-C2 hydrocarbons and formaldehyde. The mechanism was validated against data from laboratory flow reactors and from the exhaust system of a full-scale gas engine. A parametric study of the exhaust system chemistry was performed, investigating the effect of temperature, stoichiometry, pressure, and exhaust gas composition. The results indicate a complex interaction between unburned hydrocarbons (UHC), formaldehyde, and nitrogen oxides. Above 850 K, partial oxidation of unburned hydrocarbons may occur, resulting in net formation or net destruction of CH2O depending on the unburned hydrocarbons/CH2O ratio and the reaction conditions. At the typical unburned hydrocarbons/CH2O ratio of 1.0-1.5% for gas engines, net formaldehyde formation may occur in the exhaust system if temperatures above 850 K are reached.     

K2 O/MgFe2 O4磁性固体碱催化剂的制备、表征 及催化酯交换制备碳酸甘油酯

为了解决生物柴油制备过程中副产物甘油过剩、碳酸甘油酯产率低和催化剂回收困难的问题,以聚乙二醇600（PEG-600）为模板和分散剂,采用溶胶凝胶法制备镁铁氧体（MgFe2O4）,以其为载体,KNO3为活性组分前驱体,采用浸渍法制备K2O/MgFe2O4磁性固体碱催化剂。通过X射线衍射、 X射线光电子能谱、扫描电镜、CO2程序升温脱附(CO2-TPD)和磁性分析对催化剂进行表征,并将催化剂用于甘油与碳酸二甲酯酯交换制备碳酸甘油酯的反应中,考察其催化性能。结果表明：制备的K2O/MgFe2O4形成了K-Fe-Mg键,K2O/MgFe2O4表面呈霉菌状,具有较多的中强碱位点和强碱位点,且具有较好的磁性;在PEG-600加入量10 g（硝酸镁1.5 g、硝酸铁4.71 g）、反应温度105 ℃、反应时间2 h、催化剂用量3%、甘油与碳酸二甲酯物质的量比1∶ 2的条件下,甘油转化率可达到99.53%,碳酸甘油酯产率可达到96.36%,且制备的催化剂重复使用性能良好,在重复使用5次后,碳酸甘油酯产率仍可达80.14%。综上,所制备的催化剂具有高甘油转化率、高碳酸甘油酯产率、重复使用性能高（通过外部磁场即可回收）等优点,有望实现工业化。     

固体超强酸S2O82-/Fe2O3-MoO3催化合成乙酸环己酯

以硝酸铁和钼酸铵为原料,柠檬酸为络合剂,采用溶胶-凝胶法,制备固体超强酸S2O82-/Fe2O3-MoO3.以乙酸和环己醇的酯化反应为探针反应,考察了(NH4)2S2O4浓度、焙烧温度、焙烧时间对催化活性的影响,实验确定的催化剂制备的较佳工艺条件为:浸泡液中c(NH4)2S2O8=0.5 mol/L,焙烧温度350℃,焙烧时间3.5 h.用在该条件下制备的催化剂催化合成乙酸环己酯,正交试验确定的最佳工艺条件为:n(环己醇)∶n(乙酸)=1.2,0.7 g S2O82-/Fe2O3-MoO3(以0.2 mol乙酸为准),带水剂V(环己烷)=12 mL,反应时间2.5 h,在此条件下,酯化率可达96.6%.     

K2O/γ-Al2O3型固体超强碱催化合成芹菜酮的研究

在正丁醛和乙酰乙酸乙酯为原料合成芹菜酮的合成过程中,对其催化方法进行改进.首次采用K2O/γ-Al2O3型固体超强碱催化合成的工艺路线,考察了催化剂的焙烧温度、合成反应温度、催化剂用量、反应物的量比对转化率的影响,确定了最优化的反应条件,缩短了反应时间,提高了产物的收率.该催化剂具有较高的催化活性,易于回收,能够重复利用五次以上.     

Treatment of volatile organic chemicals on the EPA Contaminant Candidate List using ozonation and the O3/H2O2 advanced oxidation process

Seven volatile organic chemicals (VOCs) on the EPA Contaminant Candidate List together with 1,1-dichloropropane were studied for their reaction kinetics and mechanisms with ozone and OH radicals during ozonation and the ozone/ hydrogen peroxide advanced oxidation process (O3/H2O2 AOP) using batch reactors. The three aromatic VOCs demonstrated high reactivity during ozonation and were eliminated within minutes after ozone addition. The high reactivity is attributed to their fast, indirect OH radical reactions with k(OH,M) of (5.3-6.6) x 10(9) M(-1) s(-1). Rates of aromatic VOC degradation are in the order 1,2,4-trimethylbenzene > p-cymene > bromobenzene. This order is caused by the selectivity of the direct ozone reactions (k(O3,M) ranges from 0.16 to 304 M(-1) s(-1)) and appears to be related to the electron-donating or -withdrawing ability of the substituent groups on the aromatic ring. The removal rates for the five aliphatic VOCs are much lower and are in the order 1,1-dichloropropane > 1,3-dichloropropane > 1,1-dichloroethane > 2,2-dichloropropane > 1,1,2,2-tetrachloroethane. The second-order indirect rate constants for the aliphatic VOCs range from 0.52 x 10(8) to 5.5 x 10(8) M(-1) s(-1). The relative stability of the carbon-centered intermediates seems to be related to the relative reactivity of the aliphatic VOCs with OH radicals. Except for 1,3-dichloropropane, ozonation and the O3/H2O2 AOP are not effective for the removal of other aliphatic VOCs. Bromide formation during the ozonation of bromobenzene indicates that bromate can be formed, and thus, ozonation and O3/H2O2 AOP may not be suitable for the treatment of bromobenzene.     

溶胶-凝胶法在金刚石表面涂覆铝-硅-硼氧化物涂层的研究

采用溶胶-凝胶法在金刚石表面涂覆了铝-硅-硼氧化物涂层,并用扫描电子显微镜、综合热分析仪和抗压强度仪对涂层的形貌、结构以及涂膜前后金刚石的氧化行为和单颗粒金刚石的抗压强度进行了表征。结果表明：所制得的涂层在金刚石颗粒表面分布较均匀,结构致密,可将金刚石颗粒的起始氧化温度提高100℃左右,并能有效地延缓金刚石在高温环境下的氧化速度,同时还可以提高金刚石单颗粒抗压强度约22.75%。