Degradation of phenolic aqueous solutions by high frequency sono-Fenton systems (US–Fe2O3/SBA-15–H2O2)

The aim of this work is to establish the influence of different ultrasonic frequencies ranging from 20 to 1142 kHz on the efficiency of the US/Fe₂O₃/SBA-15/H₂O₂ (sono-Fenton) system. The frequency of 584 kHz has been established as the optimum ultrasonic irradiation for the degradation of aqueous phenol solutions by the sono-Fenton system and the effect of different variables, such as hydrogen peroxide concentration or catalyst loadings in the reaction was studied by factorial design of experiments. Catalyst loadings of 0.6 g/L and hydrogen peroxide concentration, close to the stoichiometric amount, show high organic mineralization, accompanied by excellent catalyst stability in a wide range of concentrations of aqueous phenol solutions (0.625–10 mM). Additionally, the catalyst can be easily recovered by filtration for reuse in subsequent reactions without appreciable loss of activity. The coupling of US (584 kHz)/Fe–SBA-15/H₂O₂ at room temperature is revealed as a promising technique for wastewater treatment. Additionally, a new sono-Fenton variant, the so-called latent remediation has also been studied, using ultrasonic irradiation only as pretreatment for 15 min in an attempt at reducing the cost of the degradation process. It has been observed that latent remediation provides TOC degradation of around 21% after 15 min sonication followed by 6 h silent reaction while the typical sono-Fenton reaction affords 29% TOC reduction after 6 h sonication.     

Catalytic wet peroxide oxidation of phenolic solutions over a LaTi1−xCuxO3 perovskite catalyst

LaTi_1−xCu_xO₃ perovskites are efficient catalysts for the oxidation of aqueous solutions of phenol using hydrogen peroxide as precursor of free radicals. The catalytic results have shown that under mild reaction conditions and oxidant contents lower than stoichiometric, phenol was rapidly removed with a final total organic carbon (TOC) conversion of ca. 90%. Initial rate of TOC removal depends dramatically on temperature, catalyst loading and peroxide concentration. Perovskite catalyst after reaction is completely regenerated by calcination and retains a similar catalytic performance. Finally, the catalytic results demonstrate that leaching of active species during the catalytic oxidation seems to proceed by a complex mechanism in which the presence of hydrogen peroxide in combination with phenol plays an essential role.     

Catalytic property of Fe-Al pillared clay for Fenton oxidation of phenol by H2O2

Clay pillared with Fe-Al was synthesized as a catalyst for Fenton oxidation of phenol by hydrogen peroxide (H₂O₂). The pillaring process altered the basal space of clay, which is related to the amounts of aluminium and iron in the pillaring solution. The catalytic activity of the pillared clay was attributed to the accessible iron species, whose amount is regulated not only by the introduced iron species but also by the basal space that subsequently depends on the introduced aluminium species. The heterogeneous Fenton reaction exhibited an induction period followed by an apparent first order oxidation of phenol by H₂O₂. The induction period was proposed as an activation process of the surface iron species, which is thus enabled to complex with the reactants. The induction time (t_I) depended on temperature (T) and pH condition but irrelevant to the concentrations of phenol and H₂O₂ and the amount of catalyst. The rate of the oxidation process was evaluated with respect to the concentrations of phenol and H₂O₂, the amount of catalyst, pH and temperatures. During the catalytic reaction the trend of iron leaching showed an ascending period and a descending period, which was related to the presence of ferrous ions and ferric ions. The Fe-Al pillared was recovered through two procedures, dry powder and slurry, which have different effect on the induction period.     

Fe/Al_2O_3催化剂催化氧化兰炭废水

采用浸渍法制备Fe/Al_2O_3催化剂,采用BET、XRD和穆斯堡尔谱等进行结构和性能表征。以自制Fe/Al_2O_3为催化剂,应用催化湿式过氧化氢氧化技术处理COD为6 742 mg·L-1的兰炭废水,通过建立正交实验确定最佳实验条件,结果表明,在p H=4、过氧化氢添加量9.6 m L、反应时间150 min和反应温度80℃条件下,兰炭废水COD去除率达66.30%。对催化氧化后的废水进行GC-MS分析,确定最终氧化产物主要为乙酸。表明自制Fe/Al_2O_3催化剂具有优良的催化效果,并使大分子难降解有机污染物分解为易生化的小分子污染物,甚至被完全分解矿化。     

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

Preparation of nanosized Mn3O4/SBA-15 catalyst for complete oxidation of low concentration EtOH in aqueous solution with H2O2

A new heterogeneous Fenton-like system consisting of nano-composite Mn₃O₄/SBA-15 catalyst has been developed for the complete oxidation of low concentration ethanol (100 ppm) by H₂O₂ in aqueous solution. A novel preparation method has been developed to synthesize nanoparticles of Mn₃O₄ by thermolysis of manganese (II) acetylacetonate on SBA-15. Mn₃O₄/SBA-15 was characterized by various techniques like TEM, XRD, Raman spectroscopy and N₂ adsorption isotherms. TEM images demonstrate that Mn₃O₄ nanocrystals located mainly inside the SBA-15 pores. The reaction rate for ethanol oxidation can be strongly affected by several factors, including reaction temperature, pH value, catalyst/solution ratio and concentration of ethanol. A plausible reaction mechanism has been proposed in order to explain the kinetic data. The rate for the reaction is supposed to associate with the concentration of intermediates (radicals: OH, O₂⁻ and HO₂) that are derived from the decomposition of H₂O₂ during reaction. The complete oxidation of ethanol can be remarkably improved only under the circumstances: (i) the intermediates are stabilized, such as stronger acidic conditions and high temperature or (ii) scavenging those radicals is reduced, such as less amount of catalyst and high concentration of reactant. Nevertheless, the reactivity of the presented catalytic system is still lower comparing to the conventional homogenous Fenton process, Fe²⁺/H₂O₂. A possible reason is that the concentration of intermediates in the latter is relatively high.     

Water delignification by advanced oxidation processes: Homogeneous and heterogeneous Fenton and H2O2 photo-assisted reactions

The oxidation of lignin in synthetic aqueous solutions as well as in the biologically treated pulp-and-paper mill wastewater with hydrogen peroxide was studied in various methods: hydrogen peroxide UV-photolysis, homogeneous, heterogeneous and UV-assisted heterogeneous Fenton reactions, catalysed by FeZSM-5 zeolite. Contrasting the low-molecular organic contaminants, the oxidation of lignin in aqueous solutions was drastically slowed down in presence of heterogeneous FeZSM-5 zeolite, showing the superior performance of acidic homogeneous Fenton and hydrogen peroxide photolysis. This is explained by steric hindrance in oxidation of lignin with OH radicals on the catalyst surface and possible deactivation of lignin molecules adsorbed on the zeolite. The hydrogen peroxide photolysis among the studied delignification methods appeared to be the most efficient one in a wide range of pH.     

Ca_(0.16)MnO_2·2H_2O催化氧化乙醇制乙醛

研究了低成本和环保的层状锰氧化物对乙醇氧化的催化作用,通过X射线衍射、N2吸附和扫描电镜等对催化剂进行表征,考察溶剂、反应温度、氧化剂用量、催化剂用量、溶剂用量和反应时间等对乙醇催化氧化制乙醛的影响。结果表明,制备的Ca_(0.16)MnO_2·2H_2O呈疏松多孔的层状结构,在氧化剂过氧化氢用量4 m L、催化剂用量0.01 g、溶剂乙腈用量5 m L、反应温度55℃和冷凝回流60 min条件下,乙醇转化率最高,为85.5%。     

Co/γ-Al2O3催化乙酰丙酸加氢合成γ-戊内酯的研究

采用等体积浸渍法制备一系列Co负载量不同的Co/Al₂O₃催化剂,用于乙酰丙酸液相催化加氢制γ-戊内酯反应。采用X射线衍射仪和透射电镜对Co/Al₂O₃催化剂进行表征,考察Co负载量、反应温度、反应压力和催化剂用量等对乙酰丙酸液相催化加氢反应的影响。结果表明,在Co负载质量分数15%、反应温度140 ℃、反应压力4.0 MPa和催化剂用量为反应物总质量的20%条件下,以甲醇为溶剂,反应6 h,乙酰丙酸转化率100%,γ-戊内酯选择性80.4%。催化剂重复使用6次仍具有较好的催化性能。     

Performance and deactivation of Ir/γ-Al2O3 catalyst in the hydrogen peroxide monopropellant thruster

The performance of Ir/γ-Al₂O₃ catalyst for the decomposition of high concentration hydrogen peroxide was investigated in a monopropellant thruster. The changes of ignition delay (t₀), chamber pressure (P_c) and catalyst bed temperature (T_c) with the numbers of startup–shutdown cycles were proved to be effective indicators of catalyst bed efficiency. The fresh catalyst and the deactivated catalyst were characterized with H₂-TPR, XRD and XPS. It was found that catalyst oxidation and surface Sn poisoning are the major reasons of catalyst deactivation.     

铜铁复合层柱粘土的制备及其在含酚废水处理中的应用

以蒙脱石为原料，利用共聚法合成了铜铁复合层柱粘土催化剂。通过XRD、FTIR和N₂吸附-脱附等检测方法对其结构进行了表征。结果证实，交联剂成功插入到蒙脱石层间，所得催化材料具有较大的比表面积。将其作为催化剂，采用催化湿式过氧化物氧化处理含酚废水,实验结果表明，与铁、铁铝等层柱粘土相比，铜铁复合层柱粘土在苯酚处理浓度、催化剂用量、反应时间以及初始pH适用范围等方面都有较大的改善。在最佳工艺条件下，苯酚去除率可达99%，pH＝3~9都具有较高的去除效果，平均去除率达97%以上，循环使用四次后去除率仍大于90%。     

Comparison of supports for the direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using a range of supported Au–Pd alloy catalysts is compared for different supports using conditions previously identified as being optimal for hydrogen peroxide synthesis, i.e. low temperature (2 °C) using a water–methanol solvent mixture and short reaction time. Five supports are compared and contrasted, namely Al₂O₃, -Fe₂O₃, TiO₂, SiO₂ and carbon. For all catalysts the addition of Pd to the Au only catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Of the materials evaluated, the carbon-supported Au–Pd alloy catalysts give the highest reactivity. The results show that the support can have an important influence on the synthesis of hydrogen peroxide from the direct reaction. The effect of the methanol–water solvent is studied in detail for the 2.5 wt% Au–2.5 wt% Pd/TiO₂ catalyst and the ratio of methanol to water is found to have a major effect on the rate of hydrogen peroxide synthesis. The optimum mixture for this solvent system is 80 vol.% methanol with 20 vol.% water. However, the use of water alone is still effective albeit at a decreased rate. The effect of catalyst mass was therefore also investigated for the water and water–methanol solvents and the observed effect on the hydrogen peroxide productivity using water as a solvent is not considered to be due to mass transfer limitations. These results are of importance with respect to the industrial application of these Au–Pd catalysts.     

Heterogeneous photo-Fenton degradation of phenolic aqueous solutions over iron-containing SBA-15 catalyst

A novel iron-containing mesostructured material has been successfully tested for the heterogeneous photo-Fenton degradation of phenolic aqueous solutions using near UV–vis irradiation (higher than 313 nm) at room temperature and close to neutral pH. This catalyst is a composite material that contains crystalline hematite particles embedded into the mesostructured SBA-15 matrix in a wide distribution of size (30–300 nm) and well dispersed ionic iron species within the siliceous framework. The outstanding physico-chemical properties make this material a promising photocatalyst leading to better activity than other unsupported iron oxides. An experimental design model has been applied to assign the weight of catalyst and hydrogen peroxide concentrations in the photo-Fenton processes over this particular material. The catalytic performance has been monitored in terms of aromatics and total organic carbon (TOC) conversions, whereas the catalyst stability was evaluated according to the metal leached into the aqueous solution. Hydrogen peroxide concentration plays an important role in the stability of the iron species, preventing their leaching out into the solution, in contrast to the effect shown in typical dark-Fenton reaction. The homogeneous leached iron species result in very little contribution to the overall photocatalytic process. Catalyst loadings of 0.5 g/L and concentration of hydrogen peroxide close to the stoichiometric amount have yielded a total abatement of phenol and a remarkable organic mineralization.     

Phenol photodegradation with oxygen and hydrogen peroxide over TiO2 and Fe-doped TiO2

Photodegradation of phenol was investigated with two types of oxidant agents in water, oxygen and hydrogen peroxide, at two different reaction pH with a series of nanosized iron-doped anatase TiO₂ catalysts with different iron contents. The catalysts have been prepared by a sol–gel/microemulsion method. Firstly, iron-doped titania catalysts were studied with respect to their activity behavior when oxygen was used as oxidant agent in the photocatalytic degradation of aqueous phenol in comparison with un-doped reference catalysts. Secondly, two catalysts (TiO₂ and 0.7 wt.% Fe-doped TiO₂) were selected to extend the study for the employment of hydrogen peroxide as oxidant at different concentrations and two initial reaction pHs. An enhancement of the photocatalytic activity is observed only for relatively low doping level (ca. 0.7 wt.%) in catalyst calcined at 450 °C preferably using hydrogen peroxide as oxidant agent which is attributable to the partial introduction of Fe³⁺ cations into the anatase structure. Nevertheless, it has been demonstrated that catalyst surface properties can play an important role during phenol photodegradation process on the basis of the analysis of differences found in the photoactivity as a function of reaction pH.     

Phenol oxidation over CuO/Al2O3 in supercritical water

Phenol was oxidized in supercritical water at 380–450°C and 219–300 atm, using CuO/Al₂O₃ as a catalyst in a packed-bed flow reactor. The CuO catalyst has the desired effects of accelerating the phenol disappearance and CO₂ formation rates relative to non-catalytic supercritical water oxidation (SCWO). It also simultaneously reduced the yield of undesired phenol dimers at a given phenol conversion. The rates of phenol disappearance and CO₂ formation are sensitive to the phenol and O₂ concentrations, but insensitive to the water density. A dual-site Langmuir–Hinshelwood–Hougen–Watson rate law used previously for catalytic SCWO of phenol over other transition metal oxides and the Mars–van Krevelen rate law can correlate the catalytic kinetics for phenol disappearance over CuO. The supported CuO catalyst exhibited a higher activity, on a mass of catalyst basis, for phenol disappearance and CO₂ formation than did bulk MnO₂ or bulk TiO₂. The CuO catalyst had the lowest activity, however, when expressed on the basis of fresh catalyst surface area. The CuO catalyst exhibited some initial deactivation, but otherwise maintained its activity throughout 100 h of continuous use. Both Cu and Al were detected in the reactor effluent, however, which indicates the dissolution or erosion of the catalyst at reaction conditions.     

The kinetics of phenol decomposition under UV irradiation with and without H2O2 on TiO2, Fe–TiO2 and Fe–C–TiO2 photocatalysts

H₂O₂ used in the photo-Fenton reaction with iron catalyst can accelerate the oxidation of Fe²⁺ to Fe³⁺ 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 H₂O₂ predominantly produces highly hydrophilic products and catechol, which can accelerate the rate of phenol decomposition. However, while H₂O₂ under UV irradiation could decompose phenol to highly hydrophilic products and dihydroxybenzenes in a very short time, complete mineralization proceeded rather slowly. When H₂O₂ is used for phenol decomposition in the presence of TiO₂ and Fe–TiO₂, decrease of OH radicals formed on the surface of TiO₂ and Fe–TiO₂ has been observed and photodecomposition of phenol is slowed down. In case of phenol decomposition under UV irradiation on Fe–C–TiO₂ photocatalyst in the presence of H₂O₂, marked acceleration of the decomposition rate is observed due to the photo-Fenton reactions: Fe²⁺ is likely oxidized to Fe³⁺, which is then efficiently recycled to Fe²⁺ by the intermediate products formed during phenol decomposition, such as hydroquinone (HQ) and catechol.     

Kinetics of propylene epoxidation using H2 and O2 over a gold/mesoporous titanosilicate catalyst

The oxidation of propylene to propylene oxide (PO) with hydrogen–oxygen mixtures was studied on gold supported on the mesoporous titanium silicate, Ti-TUD. The catalyst gave stable activity at low conversions of propylene (<6%) and high selectivity to PO (>95%). Kinetic data were fit to a power-rate law and gave the following expression: r_PO = k(H₂)^0.54(O₂)^0.24(C₃H₆)^0.36. The fractional orders in hydrogen, oxygen, and propylene indicated that these reactants interacted with the catalyst to form species that led to the final PO product. The catalyst likely operated by the commonly accepted mechanism of hydrogen peroxide production on gold sites, and epoxidation on titanium centers. Carbon dioxide was formed primarily from further oxidation of PO rather than the oxidation of propylene, while water was produced from the reaction of hydrogen and oxygen.     

Assessment of Fe2O3/SiO2 catalysts for the continuous treatment of phenol aqueous solutions in a fixed bed reactor

Different iron-containing catalysts have been tested for the oxidation of phenol aqueous solutions in a catalytic fixed bed reactor in the presence of hydrogen peroxide. All the catalysts consist of iron oxide, mainly crystalline hematite particles, over different silica supports (mesostructured SBA-15 silica and non-ordered mesoporous silica). The immobilization of iron species over different silica supports was addressed by direct incorporation of metal during the synthesis or post-synthesis impregnation. The synthesis conditions were tuned up to yield agglomerated catalysts with iron loadings between 10 and 15 wt.%. The influence of the preparation method and the type of silica support was evaluated in a catalytic fixed bed reactor for the continuous oxidation of phenol in terms of catalysts activity (phenol and total organic carbon degradation) as well as their stability (catalyst deactivation by iron leaching). Those catalysts prepared by direct synthesis, either in presence of a structure-directing agent (Fe₂O₃/SBA-15(DS)) or in absence (Fe₂O₃/SiO₂(DS)), achieved high catalytic performances (TOC reduction of 65% and 52%, respectively) with remarkable low iron leaching in comparison with their silica-based iron counterparts prepared by impregnation. Catalytic results have demonstrated that the synthesis method plays a crucial role in the dispersion and stability of active species and hence resulting in superior catalytic performances.     

Si-FeOOH/H2O2类芬顿降解盐酸四环素废水的效能及其机理

采用碱沉法制备的Si-FeOOH作为非均相类芬顿催化剂,研究其催化降解盐酸四环素废水的效能,考察了催化剂投量、pH、过氧化氢加入量对盐酸四环素降解效能和反应速率的影响。实验结果表明:在催化剂投加量3.0 g·L^-1、H₂O₂投加量9.9 mmol·L^-1、pH为3、室温[(25±1)℃]的条件下,盐酸四环素降解率为90%,一级反应速率常数为0.0504 min^-1。与催化剂FeOOH相比,类芬顿催化剂Si-FeOOH性能更卓越。同时采用探针化合物正丁醇、苯醌,证明了Si-FeOOH /H₂O₂ 催化体系中的氧化活性种主要为羟基自由基(·OH)和超氧自由基(HO₂·), 并推测了其催化反应机理。     

Phenol degradation by Fenton's process using catalytic in situ generated hydrogen peroxide

The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6 h corresponding to the termination of 100 mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300 ppm H₂O₂ displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45 °C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts.