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1.
Phosphate of transition elements A 3M 4(PO 4) 6 (A=Fe, Ni, Zn, Mg, Cu, Cr and M=Fe, V, Cr) are prepared by solid methods, at 1223 K. Their activity in H 2S selective oxidation are compared. In spite of their low specific area, the catalysts develop a good activity (up to 17% of H 2S conversion for surface area lower than 1 m 2 g −1) and an excellent sulphur selectivity (always higher than 95%). Screening experiments show that the best systems always contain Fe as element and, in these cases, Mössbauer characterisations evidence the establishment of Fe 2+/Fe 3+ mixed valency during the reaction. As shown by XANES and XRD results, the ability of the element in the divalent A site to promote the redox mechanism between M 2+/M 3+and H 2S/S 0 and to prevent sulphidation determines the catalytic activity. 相似文献
2.
利用嗜酸性氧化亚铁硫杆菌将含硫酸亚铁废溶液中的Fe 2+氧化成Fe 3+后用于脱除H 2S,同时实现了含硫酸亚铁废溶液的循环利用和H 2S的脱除。而溶解性Fe 3+较高的生成量是保证该处理系统连续高效运行的关键因素。但在充足氮源和K +条件下大量Fe 3+以黄铁矾沉淀形式存在。因此,本文通过控制氮源种类及投加浓度,减少沉淀生成,增大溶解性Fe 3+生成量,以期提高H 2S的去除效率。结果表明(NH 4) 2HPO 4可替代以往研究中的(NH 4) 2SO 4作为氮源,确定适宜菌体生长的氮源浓度范围为0.33~1 g·L -1。在1 g·L -1 (NH 4) 2HPO 4条件下细菌生长无明显停滞期、Fe 2+平均氧化速率为0.221~0.229 g·(L·h) -1,Fe 3+生成量为7.62~7.72 g·L -1,沉淀量为1.17 g·L -1,因此确定(NH 4) 2HPO 4为1 g·L -1时最能保证H 2S的脱除效率。为降低工艺成本,最低可采用0.33 g·L -1为运行浓度。该优化方案不仅保证了菌体的Fe 2+氧化活性,而且有效地减少了菌体培养过程中沉淀的产生,获得了较高的Fe 3+生成量和增速,为使用含硫酸亚铁废溶液处理H 2S的工艺条件优化提供了依据。 相似文献
3.
Ferric sulfate is used in water purification. The oxidation of ferrous sulfate, FeSO 4, to ferric sulfate in acidic aqueous solutions of H 2SO 4 over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and two kinds of catalysts were utilized: active carbon, doped active carbon. Both active carbon and doped active carbon catalysts enhanced the oxidation rate considerably. Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60–100°C and 4–10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe2+ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe2+ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe2+ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe2+ over pure active carbon and doped active carbon catalysts. 相似文献
4.
Ta 3N 5 was synthesized by nitridation of Ta 2O 5 under NH 3 flow at 700 °C. The catalyst was pure Ta 3N 5 according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m 2/g. When Ta 3N 5 was added to Fe 3+/H 2O 2 solution (known as Fenton-like system), most Fe 3+ were adsorbed on the Ta 3N 5 surface and could not react with H 2O 2 in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe 3+ ions were reduced to Fe 2+ rapidly and Fe 2+ were reoxidized by H 2O 2 on the Ta 3N 5 surface, thus a fast Fe 3+/Fe 2+ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta 3N 5/Fe 3+/H 2O 2 system could efficiently decompose H 2O 2 to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N, N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results. 相似文献
5.
Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H 2S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O 3.1 oxygen type with BE 536.8–537.7 eV) present on the carbons surface. Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H2S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300 °C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups. The KAU samples treated in flow of inert gas at 900–1000 °C were very active in H2S oxidation to elemental sulfur transforming up to 51–57 mmol H2S/g catalyst at 180 °C with formation of 1.7–1.9 g Sx/g catalyst. 相似文献
6.
The catalytic behavior of the Fe 3+/Fe 2+ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O 2-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na 2SO 4 as supporting electrolyte and Fe 3+ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe 2+ + H 2O 2, both of them generated at the cathode). The catalytic behavior of the Fe 3+/Fe 2+ system mainly depends on the cathode tested. In the cells with an O 2-diffusion cathode, H 2O 2 is largely accumulated and the Fe 3+ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe 3+ concentration, because this leads to a higher quantity of Fe 2+ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H 2O 2 is electrogenerated in small extent, whereas Fe 2+ is largely accumulated because the regeneration of this ion from Fe 3+ reduction at the cathode is much faster than its oxidation to Fe 3+ at the anode. In this case, an Fe 3+ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O 2 diffusion cell because the final Fe 3+–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe 3+, because oxalic acid and its Fe 2+ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution. 相似文献
7.
A lost of culturability of bacteria Escherichia coli K12 was observed after exposition to a solar simulator (UV–vis) in a laboratory batch photoreactor. The bacterial inactivation reactions have been carried out using titanium dioxide (TiO 2) P25 Degussa and FeCl 3 as catalysts. At the starting of the treatment, the suspensions were at their “natural” pH. An increase in the efficiency in the water disinfection was obtained when some advanced oxidation processes such as UV–vis/TiO 2, UV–vis/TiO 2/H 2O 2, UV–vis/Fe 3+/H 2O 2, UV–vis/H 2O 2 were applied. The presence of H 2O 2 accelerates the rate of disinfection via TiO 2. The addition of Fe 3+ (0.3 mg/l) to photocatalytic system decreases the time required for total disinfection (<1 CFU/ml), for TiO 2 concentrations ranging between 0.05 and 0.5 g/l. At TiO 2 concentrations higher than 0.5 g/l the addition of Fe 3+ does not significantly increase the disinfection rate. The systems: Fenton (H 2O 2/Fe 3+/dark), H 2O 2/dark, H 2O 2/TiO 2/dark showed low disinfection rate. The effective disinfection time (EDT 24) was reached after 60 and 30 min of illumination for the Fe 3+ and TiO 2 photoassisted systems, respectively. EDT 24 was not reached for the system in the absence of catalyst (UV–vis). The effect on the bacterial inactivation of different mixture of chemical substance added to natural water was studied. 相似文献
8.
Decolorization of reactive brilliant red X-3B was studied by using an Fe–Ce oxide hydrate as the heterogeneous catalyst in the presence of H 2O 2 and UV. The decolorization rate was in the order of UV–Fe–Ce–H 2O 2 > UV–Fe 3+–H 2O 2 > UV–H 2O 2 > UV–Fe–Ce ≥ Fe–Ce–H 2O 2 > Fe–Ce. Under the conditions of 34 mg l −1 H 2O 2, 0.500 g l −1 Fe–Ce, 36 W UV and pH 3.0, 100 mg l −1 X-3B could be decolorized at efficiency of more than 99% within 30 min. The maximum dissolved Fe during the reaction was 1 mg l −1. From the fact that the decolorization rate of the UV–Fe–Ce–H 2O 2 system was significantly higher than that of the UV–Fe 3+–H 2O 2 system at Fe 3+ = 1 mg l −1, it is clear that the Fe–Ce functioned mainly as an efficient heterogeneous catalyst. UV–vis, its second derivative spectra, and ion chromatography (IC) were employed to investigate the degradation pathway. Fast degradation after adsorption of X-3B is the dominant mechanism in the heterogeneous catalytic oxidation system. The first degradation step is the breaking down of azo and CN bonds, resulting in the formation of the aniline- and phenol-like compounds. Then, the breaking down of the triazine structure occurred together with the transformation of naphthalene rings to multi-substituted benzene, and the cutting off of sulphonic groups from the naphthalene rings. The last step includes further decomposition of the aniline structure and partial mineralization of X-3B. 相似文献
9.
H 2O 2 used in the photo-Fenton reaction with iron catalyst can accelerate the oxidation of Fe 2+ to Fe 3+ under UV irradiation and in the dark (in the so called dark Fenton process). It was proved that conversion of phenol under UV irradiation in the presence of H 2O 2 predominantly produces highly hydrophilic products and catechol, which can accelerate the rate of phenol decomposition. However, while H 2O 2 under UV irradiation could decompose phenol to highly hydrophilic products and dihydroxybenzenes in a very short time, complete mineralization proceeded rather slowly. When H 2O 2 is used for phenol decomposition in the presence of TiO 2 and Fe–TiO 2, decrease of OH radicals formed on the surface of TiO 2 and Fe–TiO 2 has been observed and photodecomposition of phenol is slowed down. In case of phenol decomposition under UV irradiation on Fe–C–TiO 2 photocatalyst in the presence of H 2O 2, marked acceleration of the decomposition rate is observed due to the photo-Fenton reactions: Fe 2+ is likely oxidized to Fe 3+, which is then efficiently recycled to Fe 2+ by the intermediate products formed during phenol decomposition, such as hydroquinone (HQ) and catechol. 相似文献
10.
在工业二氧化碳加氢制甲醇过程中,硫化氢气体的引入将对该过程中使用的催化剂活性及稳定性带来负面的影响。基于此,采用微反应合成法成功制备了InZrO x和ZnZrO x锆基催化剂,并研究了在二氧化碳加氢反应中,硫化氢气体对锆基催化剂的结构性质及其催化性能的影响规律。结果表明,在T=573 K、p=3.0 MPa和GHSV=18 000 mL/(g cat·h)条件下,仅通入二氧化碳/氢气反应气时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择性分别为7.2%、9.3%和93%、92%。在二氧化碳/氢气原料气中通入体积分数为5×10 -3硫化氢气体时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择性都降为0,这主要是因为硫化氢气体占据了氧空位,导致锆基双金属氧化物催化剂硫中毒失活。当停止通硫化氢气体时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择... 相似文献
11.
Highly ordered iron-containing mesoporous material, Fe-MCM-41, with 0.5–4 Fe/Si mol% loading was prepared and characterization was performed using XRD, SEM/TEM, EDS, N 2-sorption, and FT-IR and UV–vis spectroscopies. Fe-MCM-41 exhibited high catalytic activity in phenol hydroxylation using H 2O 2 as oxidant, giving phenol conversion of ca. 60% at 50 °C [phenol:H 2O 2 = 1:1, water solvent]. Effects of Fe contents in Fe-MCM-41 and catalyst concentration, temperature, solvent used, phenol/H 2O 2 mole ratios and H 2O 2 feeding method, and catalyst calcination temperature on conversion profiles were examined. Catalyst recycling was performed to investigate the extent of potential metal leaching. Comparisons in performance were also made using nano-sized Fe 2O 3 particles and Fe-salt impregnated MCM-41 as catalyst. Catechol to hydroquinone in product ratio was close to 2:1 in accordance with a free radical reaction scheme involving Fe 2+/Fe 3+ redox pair and the larger amount of Fe species always achieved the given phenol conversion at a shorter reaction time. As the calcination temperature increases from 400 to 800 °C increasing amount of Fe species came out from the MCM-41 framework. Both tetrahedral Fe and extra-framework Fe species were found catalytically active, but high dispersion of Fe species achieved in Fe-MCM-41 was an advantage. 相似文献
12.
The catalytic behavior in N 2O reduction by propane in the presence of O 2, H 2O and SO 2 of Fe/ZSM-5 catalysts prepared by ion exchange and chemical vapour deposition (CVD) is reported. The catalyst prepared by CVD shows a lower dependence of the rate of selective N 2O reduction on the decrease in C 3H 8 to N 2O ratio in the feed and a higher resistance to deactivation by SO 2 in accelerated durability tests with high SO 2 concentration (500 ppm). This catalyst shows stable catalytic behavior in the presence of SO 2 for more than 600 h of time-on-stream. Characterization of the catalysts by UV–VIS–NIR diffuse reflectance indicates that the poor performances of the sample prepared by ion exchange could be related to the presence of highly clustered Fe 3+ species, in this catalyst. On the other hand, Fe 2O 3 particles are not present in the sample prepared by CVD while mainly isolated Fe 3+ ions and iron-oxide nanoclusters are present. 相似文献
13.
采用实验方法研究了低成本环境友好型添加剂抗坏血酸(AA)对Fe 2+/H 2O 2体系氧化NO气体及其对体系内H 2O 2分解的影响,分析了AA对体系氧化NO能力及H 2O 2分解的影响机制。研究结果表明:AA通过加速Fe 3+向Fe 2+的转化而促进Fe 2+/H 2O 2体系对NO的氧化。[AA] 0:[Fe 2+] 0对体系氧化NO的能力及H 2O 2的分解具有重要影响。综合考虑NO氧化脱除量及H 2O 2消耗量,合理的[AA] 0:[Fe 2+] 0为1/3~1/2。AA的分次添加方式可大幅度提升体系氧化NO气体的能力。研究结果可望为发展基于H 2O 2为氧化剂的烟气NO绿色氧化技术提供理论基础。 相似文献
14.
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H 2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO 2/SiO 2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H 2S. Steam reforming Ni catalyst was effective for the tar removal without H 2S addition, however, the addition of H 2S deactivated drastically. In contrast, Rh/CeO 2/SiO 2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H 2S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO 2/SiO 2, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis. 相似文献
15.
Pt supported on CeO 2 and 10 wt.% La 3+-doped CeO 2 catalysts have been prepared, characterised and tested for soot oxidation by O 2 in TGA. The reaction mechanism has been studied in a TAP reactor with labelled O 2. Isotopic oxygen exchange between molecular O 2 and ‘O’ on the support/catalyst was observed and soot oxidation is being carried out by lattice oxygen. TAP studies further show that Pt improves O 2 adsorption and, therefore, 5 wt.% Pt-containing catalysts are more active for soot oxidation than the counterpart supports. In addition, CeO 2 doping by La 3+ leads to an improved support, since La 3+ stabilises the structure of CeO 2 when calcined at high temperature (1000 °C) and minimises sintering. In addition, La 3+ improves the Ce 4+/Ce 3+ reduction as deduced from H 2-TPR experiments and favours oxygen mobility into the lattice. A synergetic effect of Pt and La 3+ is observed, Pt-containing La 3+-doped CeO 2 being the most active catalyst for soot oxidation by O 2 among the samples studied. 相似文献
16.
Field disinfection of water in a large solar compound parabolic collector (CPC) photoreactor (35–70 l) was conducted at 35 °C by different photocatalytic processes: sunlight/TiO 2, sunlight/TiO 2/Fe 3+, sunlight/Fe 3+/H 2O 2 and compared to the control experiment of direct sunlight alone. Experiments were carried out using a CPC and natural water spiked with E. coli K 12. Under these conditions, total disinfection by bare sunlight irradiation was not reached after 5 h of treatment; and bacterial recovery was observed during the subsequent 24 h in the dark. The addition of TiO2, TiO2/Fe3+ or Fe3+/H2O2 to the water accelerates the bactericidal action of sunlight, leading to total disinfection by solar-photocatalysis. No bacterial regrowth was observed during 24 h after stopping sunlight exposure. For some samples, the decrease of bacteria continues in the dark. A “residual disinfection effect” was observed for these samples before reaching the total inactivation. The effective disinfection time (EDT24), defined as the treatment time required to prevent any bacterial regrowth during the subsequent 24 h in the dark, after stopping the phototreatment, was reached in the presence but not in the absence of different photocatalytic systems. EDT24 was 2 h 30 min, 2 h and 1 h 30 min for sunlight/TiO2, sunlight/TiO2/Fe3+ and sunlight/Fe3+/H2O2 systems, respectively. The post irradiation events observed when the phototreated water is poured into an optimal growth medium are also discussed. 相似文献
17.
The H 2-TPR (temperature-programmed reduction) study was performed for supported copper oxide catalysts with low loading (0.5 wt% as copper). Among the various kinds of support materials (γ-Al 2O 3, TiO 2, ZrO 2, SiO 2, ZSM-5), alumina-supported copper oxide indicated a one-electron reduction behavior of Cu 2+ into Cu + ions in the presence of H 2. The reduction of the isolated Cu 2+ species in a tetragonally distorted octahedral symmetry into the low coordinated Cu + ions was identified by means of X-ray absorption spectroscopy (XANES and EXAFS). The isolated Cu + ions hosted by γ-Al 2O 3 surface were prevented from further reduction into metallic Cu 0 state under reducing condition with H 2 at 773 K. Less dispersed supported copper oxide species were easily reduced to Cu 0 metal particles with H 2 at 573 K regardless of the kinds of support materials. It is suggested that the one-electron redox behavior of the isolated copper oxide species over γ-Al 2O 3 promotes the catalytic reduction of NO with CO in the presence of oxygen on the basis of redox-type mechanism between Cu 2+ and Cu + in atomically dispersed state. 相似文献
18.
Zeolite LTL in the potassic form (
-LTL) was used as support of iron. The precursor was characterized by temperature programmed reduction (TPR) and Mössbauer spectroscopy (MS) at 298 and 15 K. The catalyst was obtained reducing the precursor with H 2 and its structural properties were studied by H 2 chemisorption, volumetric oxidation and MS under controlled conditions at 298 and 15 K. Measurements of activity and selectivity were carried out at 1 and 20 bar in the CO hydrogenation. Two different types of active sites were detected: Fe 0 inside the zeolite channels and carburized iron on its external surface. The solid showed a high activity and selectivity towards light alkenes in comparison with other iron supported systems (Fe/SiO 2, Fe/Al 2O 3 and Fe/C). This behavior can be attributed to the high percentage of metallic iron promoted by potassium ions, located inside the zeolite channels. The external carbide crystals generate hydrocarbons in the diesel oil range. 相似文献
19.
采用等体积浸渍法制备了1% AuCl 3/AC催化剂,探究了硫化氢(H 2S)为毒物对乙炔氢氯化反应中催化剂催化活性的影响及失活机理。催化活性测试结果表明,以H 2S为毒物可导致乙炔氢氯化反应中的AuCl 3/AC催化剂的失活,且是一个不可逆过程;程序升温还原(TPR)和X射线光电子能谱(XPS)分析结果表明,H 2S的加入可有效地加快Au 3+还原为Au 0;透射电镜能谱(TEM-EDX)观测分析形成的Au-S化合物也可导致催化剂失活,即随着H 2S量的增大,更多的Au 3+被还原为Au 0,且形成的Au-S化合物覆盖在活性位点,使有效的活性组分降低进而导致AuCl 3/AC催化剂失活。 相似文献
20.
Degradation of 4-chloro-2-methylphenol (PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H 2O 2, produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe 2+]/[PCOC] 0 and the effect of replacing Fe 2+ by Mn 2+ ion have been examined. It was found that degradation rate was increased with increasing [Fe 2+]/[PCOC] 0 ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn 2+ was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval, has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% TOC decay and complete dechlorination were observed by consuming only 141.4 C electrical charge during a 300 min photoelectron-Fenton treatment. In the case of electro-Fenton system, 280.7 C electrical charge was consumed during 450 min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions. 相似文献
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