H2O2、金属离子等对Cr（Ⅵ）离子光催化还原及对敌敌畏农药光催化氧化的影响

以Cr(Ⅵ）离子、敌敌畏农药作为污染物的代表，研究了H2O2、金属离子等对Cr(Ⅵ）离子光催化还原及对敌敌畏农药光催化氧化的影响。结果表明，加入少量的H2O2对Cr(Ⅵ）离子的光催化还原起阻碍作用，对敌敌畏农药的光催化氧化起促进作用；加入少量的Cu^2 对Cr(Ⅵ）离子光催化还原及对敌敌畏农药的光催化氧化均起促进作用；加入Zn^2 ,Na^ 对Cr(Ⅵ）离子及敌敌畏农药的光催化降解均无明显的影响；加入甲醇、甲苯对Cr(Ⅵ）离子的光催化还原起促进作用，对敌敌畏农药的光催化氧化起阻碍作用。探讨了H2O2、金属离子等对Cr(Ⅵ）离子光催化还原及对敌敌畏农药光催化氧化影响的机理。     

间苯二酚的生产技术现状

介绍了间苯二酚的主要用途和国内外生产现状 ,并对主要的生产方法磺化法和氧化法从环境效应上进行了比较 ,对今后我国间苯二酚的生产发展提出了建议     

氧气法合成乙醛酸的中试研究

中试结果表明 ,在复合催化剂作用下 ,用低压氧气氧化乙二醛水溶液 ,可成功合成乙醛酸。电位滴定跟踪反应过程 ,可满意监控乙二醛反应程度。此反应乙二醛转化率 99% ,乙醛酸收率(以乙二醛为基准 ) 94 %。优化工艺为 :介质 pH <1,釜内氧气、水气等混合气体总压 0 12～ 0 13MPa ,w(乙二醛 ) =15 5 6 % ,反应温度 4 5～ 6 0℃ ,时间 4h。     

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH₄ to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH₄ into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl₂O₄ spinel phase had a positive effect on the stability of the catalyst.     

Preparation, Characterisation and Catalytic Behaviour of a New TeVMoO Crystalline Phase

TeM_xMo_1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N₂. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb₄Mo₁₀O₃₁ and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene.     

The role of water in the oxidation process of extra virgin olive oils

Different emulsifying techniques were used to study the influence of water on the oxidative degradation of extra virgin olive oil. The emulsions of water/extra virgin olive oil, oxidized with O₂, UV radiation, and Air, were prepared by dispersing water under different conditions. Oil oxidation, monitored by measuring the PV and polyphenolic content, was greater for emulsions obtained with low dispersing power. A linear model was used to correlate the PV and the polyphenolic content with dispersing energy. An important result was that the dispersed water exerted a positive antioxidant effect on the oil.     

Some aspects of the electrochemistry of the flotation of pyrrhotite

The iron sulfide mineral, pyrrhotite (Fe_(1–x)S), has long been known to be more difficult to recover by flotation from alkaline slurries than many other base metal sulfide minerals. This paper summarizes the results of an electrochemical study of the surface reactions that occur during the flotation of nickeliferous pyrrhotite in the recovery of nickel and the platinum group metals. Mixed potential measurements conducted with natural pyrrhotite electrodes in various stages of an operating flotation plant showed that the mineral potential is positive to the equilibrium potential of the xanthate/dixanthogen couple. Similar results were obtained during batch flotation experiments and in synthetic solutions in the laboratory. Cyclic voltammetric and potentiostatic current/time transient experiments were used to investigate the oxidation of pyrrhotite under various conditions. In addition, the reduction of oxygen, the reaction of copper ions and the oxidation of xanthate ions at the mineral surface were investigated. The formation of dixanthogen on pyrrhotite surfaces is thermodynamically favourable in plant flotation slurries. However the interaction with xanthate at pH values above 7 is inhibited by a surface species formed during the conditioning prior to xanthate addition. In acidic solutions copper ions react readily with pyrrhotite to form a species, possibly CuS that can be oxidized at potentials above 0.4 V. At pH 9 this species does not form and there is no electrochemical reaction between pyrrhotite and copper ions. The beneficial effects of copper ions to flotation performance appear to be related to an enhancement of the oxidation of xanthate.     

Propene Oxidation on Ag(111): Spectroscopic Evidence of Facile Abstraction of Methyl Hydrogen

Reactions of propene on an oxygen-modified Ag(111) surface were investigated by means of temperature-programmed reaction spectra and reflection--adsorption infrared spectroscopy (RAIRS) at 100 K. In the presence of oxygen adatoms, interactions of propene with the substrate are strengthened. The reaction between propene and oxygen adatoms (0.086 monolayer) produces not only total oxidation products (CO₂ and H₂O), but also partial oxidation products (CO and acetone). The formation of chemisorbed hydroxyl groups is identified by RAIRS when coadsorbed propene and oxygen adatoms are annealed to 200 K. The formation of hydroxyl is ascribed to the abstraction of methyl hydrogen by oxygen adatoms.     

New Reaction Engineering Concepts for Selective Oxidation Reactions

In order to enhance product yields in selective oxidation reactions, numerous reaction engineering concepts are being studied worldwide. Periodic operation has been investigated for decades, yet its application is limited to a few examples, such as the butane oxidation after DuPont or reverse-flow reactors for VOC removal. The use of microchannel reactors is a younger field, but it has already yielded promising results for process optimization. Catalytic wall reactors have proved to be a helpful tool for kinetic studies. On the laboratory scale, membrane reactors have displayed favorable behavior in selective oxidation. The Na vapor-catalyzed dehydrogenation of methanol to formaldehyde is a final example of an unusual new concept for selective oxidation.     

Formation of 4-hydroxynonenal, a toxic aldehyde, in soybean oil at frying temperature

The formation of 4-hydroxy-2-trans-nonenal (HNE), a mutagenic and cytotoxic product of the peroxidation of linoleic acid, was monitored in soybean oil that was heated at 185°C for 2, 4, 6, 8, and 10 h. Unheated soybean oil contained no HNE and a relatively low concentration of polar lipophilic secondary oxidation products (aldehydes and related carbonyl compounds), measured as 2,4-dinitrophenylhydrazine derivatives by HPLC. An increase in the concentration of both HNE and total lipophilic polar oxidation products was observed with increased exposure to frying temperature. A considerable concentration of HNE had already formed at 2 h and the concentration continued to increase at 4 and 6 h of heating. After 6 h the concentration of HNE decreased, possibly due to degradation of the aldehyde with further exposure to high temperature. The loss of endogenous tocopherols was also monitored in the heated oil, and the tocopherol concentration decreased as the secondary lipid oxidation products increased.