Preparation and characterization of Fe2O3-CeO2-TiO2/γ-Al2O3 catalyst for degradation dye wastewater

In order to develop a catalyst with high activity for catalytic wet oxidation (CWO) process at room temperature and atmospheric pressure, Fe2O3-CeO2-TiO2/γ-Al2O3 catalyst was prepared by consecutive impregnation method and the prepared parameters were optimized. The structure of the catalyst was characterized by BET, XRF, SEM and XPS technologies, and the actual wastewater was used to investigate the catalytic activity of Fe2O3-CeO2-TiO2/γ-Al2O3 in CWO process. The experimental results showed that the prepared catalyst exhibited good catalytic activity when the doping amount of Ti was 1.0 wt% (the weight ratio of Ti to carriers), and the middle product, CeO2-TiO2/γ-Al2O3, was calcined in 450℃ for 2 h. The CWO experiment for treating actual dye wastewater indicated that the COD, color and TOC of actual wastewater were decreased by 62.23%, 50.12% and 41.26% in 3 h,respectively, and the ratio of BOD5/COD was increased from 0.19 to 0.30.     

Au − Pd/mesoporous Fe2O3: Highly active photocatalysts for the visible-light-driven degradation of acetone

Three-dimensionally ordered mesoporous Fe_2O_3(meso-Fe_2O_3) and its supported Au, Pd,and Au-Pd alloy(xA uP dy/meso-Fe_2O_3; x = 0.08–0.72 wt.%; Pd/Au molar ratio(y) = 1.48–1.85)photocatalysts have been prepared via the KIT-6-templating and polyvinyl alcohol-protected reduction routes, respectively. Physical properties of the samples were characterized, and their photocatalytic activities were evaluated for the photocatalytic oxidation of acetone in the presence of a small amount of H_2O_2 under visible-light illumination. It was found that the meso-Fe_2O_3 was rhombohedral in crystal structure. The as-obtained samples displayed a high surface area of 111.0–140.8 m~2/g and a bandgap energy of 1.98–2.12 eV. The Au, Pd and/or Au–Pd alloy nanoparticles(NPs) with a size of 3–4 nm were uniformly dispersed on the surface of the meso-Fe_2O_3 support. The 0.72 wt.% AuP d1.48/meso-Fe_2O_3 sample performed the best in the presence of 0.06 mol/L H_2O_2 aqueous solution, showing a 100% acetone conversion within4 hr of visible-light illumination. It was concluded that the good performance of 0.72 wt.%AuPd_(1.48)/meso-Fe_2O_3 for photocatalytic acetone oxidation was associated with its ordered mesoporous structure, high adsorbed oxygen species concentration, plasmonic resonance effect between AuPd_(1.48) NPs and meso-Fe_2O_3, and effective separation of the photogenerated charge carriers. In addition, the introduction of H_2O_2 and the involvement of the photo-Fenton process also played important roles in enhancing the photocatalytic activity of 0.72 wt.%AuPd_(1.48)/meso-Fe_2O_3.     

Steady-state kinetics and osillation phenomena for complete oxidation of benzene over Pt/Al_2O_3 catalyst

The steady-state kinetics for complete oxidation of benzene over has been investigated by the external recycling reactor. The kinetics equation was described by the L-H model of adsorption of benzene and oxygen with the inhibition of carbon dioxide. The parameters of the kinetics model were estimated by the method of orthogonal design. The heats of adsorption of benzene, oxygen and carbon dioxide were determined by the method of gas-adsorption chromatography. The details of oscillations of complete oxidation of benzene were investigated.     

Coating of γ-Al2O3 on the stainless steel substrate by electrophoretic deposition method

γ-Al₂O₃ coatings were prepared on aluminum-free stainless steel (SUS304) by electrophoretic deposition method. Both X-ray diffraction and scanning electron microscopy were used to study the crystalline structure and morphological features of the coatings. Themo gravimetry-differential termal analysis (TG-DTA) is used to study the thermo-chimerical reaction behavior of coatings. Catalytic activity of coatings is determined by degrading of NO_x. The results indicated that the thickness of the coatings onto SUS304 could reach 5 μm without any exfoliation at optimized conditions. Catalytic properties of samples coated by electrophoretic deposition method were highly enhanced as compared with that of samples prepared by the dip coating method.     

Investigation in the sorption mechanism and behavior of nano γ-Al2O3 for the removal of fluorine ions

研究了纳米γ-Al2O3吸附剂对氟离子的吸附行为,考查了吸附平衡时间、温度、溶液的pH等对吸附过程的影响.结果表明,在室温下,纳米γ-Al2O3对氟离子的吸附在3min基本达到平衡;在pH3～9范围内,吸附率达95%以上;吸附过程符合准二级反应动力学模型,其反应的表观活化能（Ea）为10.99kJ.mol-1;颗粒内扩散过程是吸附的主要控制步骤,而颗粒外扩散过程对吸附也有影响;吸附过程符合Langmuir、D-R等温模型,常温下,纳米γ-Al2O3对氟离子的平均吸附能为11.15kJ.mol-1.吸附反应的ΔGθ〈0,ΔHθ〉0,说明该吸附过程是自发的吸热反应.共存阴离子HCO3-和PO43-、阳离子Cu2＋对氟离子的吸附影响较大.纳米γ-Al2O3在动态和静态吸附实验中的除氟效果相近.     

Promoting effect of vanadium on catalytic activity of Pt/Ce–Zr–O diesel oxidation catalysts

A series of Pt–V/Ce–Zr–O diesel oxidation catalysts was prepared using the impregnation method. The catalytic activity and sulfur resistance of Pt–V/Ce–Zr–O were investigated in the presence of simulated diesel exhaust. The effect of vanadium on the structure and redox properties of the catalysts was also investigated using the Brunauer–Emmett–Teller method,X-ray diffraction, H2temperature-programmed reduction, CO temperature-programmed desorption, X-ray photoelectron spectroscopy, and Energy Dispersive Spectroscopy. Results showed that the Pt particles were well dispersed on the Ce–Zr–O carrier through the vanadium isolation effect, which significantly improved the oxidation activity toward CO and hydrocarbons. An electron-withdrawing phenomenon occurred from V to Pt, resulting in an increase in the metallic nature of platinum, which was beneficial to hydrocarbon molecular activation.     

Novel CeO2@TiO2 core–shell nanostructure catalyst for selective catalytic reduction of NOx with NH3

The CeO₂@TiO₂ core–shell nanostructure catalyst prepared by a two-step hydrothermal method was used for selective catalytic reduction (SCR) of NOx with NH₃ in this study. The catalyst presented the obvious core–shell structure, and the shell was amorphous TiO₂ which could protect the active center from the SO₂ erosion. The catalyst showed high activity and stability, excellent N₂ selectivity and superior SO₂ resistance and H₂O tolerance. Characterizations such as TEM, HR-TEM, XRD, BET, XPS, NH₃-TPD, and H₂-TPR were carried out. The results indicated that the catalyst had large surface area and the active sites were well dispersed on the surface. The NH₃-TPD, H₂-TPR and XPS results implied that its increased SCR activity might be due to the enhancement of NH₃ chemisorption and the increase of active oxygen species, both of which were conductive to NH₃ activation. The excellent catalytic performance suggests that it is a promising candidate for SCR catalyst.     

Mechanism of Hg oxidation in the presence of HCl over a commercial V2O5–WO3/TiO2 SCR catalyst

Experiments were conducted in a fixed-bed reactor containing a commercial V₂O₅/WO₃/TiO₂ catalyst to investigate mercury oxidation in the presence of HCl and O₂. Mercury oxidation was improved significantly in the presence of HCl and O₂, and the Hg⁰ oxidation efficiencies decreased slowly as the temperature increased from 200 to 400°C. Upon pretreatment with HCl and O₂ at 350°C, the catalyst demonstrated higher catalytic activity for Hg⁰ oxidation. Notably, the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O₂, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg⁰ were first adsorbed onto the catalyst and then reacted with O₂ following its adsorption, which indicates that the oxidation of Hg⁰ over the commercial catalyst followed the Langmuir–Hinshelwood mechanism. Several characterization techniques, including Hg⁰ temperature-programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS), were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O₂. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury.     

Effect of SiO2 addition on NH4HSO4 decomposition and SO2 poisoning over V2O5–MoO3/TiO2–CeO2 catalyst

The deposition of NH₄HSO₄ and the poisoning effect of SO₂ on SCR catalyst are the main obstacles that restrict the industrial application of CeO₂-doped SCR catalysts. In this work, deposited NH₄HSO₄ decomposition behavior and SO₂ poisoning over V₂O₅–MoO₃/TiO₂ catalysts modified with CeO₂ and SiO₂ were investigated. By the means of characterization analysis, it was found that the addition of SiO₂ into VMo/Ti–Ce had an impact on the interaction existed between catalyst surface atoms and NH₄HSO₄. Temperature-programmed methods and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments indicated that the doping of SiO₂ promoted the decomposition of deposited NH₄HSO₄ on VMo/Ti–Ce catalyst surface by reducing the thermal stability of NH₄HSO₄ and enhancing the NH₄HSO₄ reactivity with NO in low temperature. And this improvement may be the reason for the better catalytic activity than VMo/Ti–Ce in the case of NH₄HSO₄ deposition. Accompanied with cerium sulfate species generated over catalyst surface, the conversion of SO₂ to SO₃ was inhibited in SiCe mixed catalyst. The addition of SiO₂ could promote the decomposition of cerium sulfate, which may be a potential strategy to enhance the resistance of SO₂ poisoning over CeO₂-modifed catalysts.     

Role of NO in Hg~0 oxidation over a commercial selective catalytic reduction catalyst V_2O_5–WO_3/TiO_2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst,V_2O_5–WO_3/TiO_2,to investigate mercury oxidation in the presence of NO and O_2.Mercury oxidation was improved by NO,and the efficiency was increased by simultaneously adding NO and O_2.With NO and O_2 pretreatment at 350°C,the catalyst exhibited higher catalytic activity for Hg~0 oxidation,whereas NO pretreatment did not exert a noticeable effect.Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O_2.Although NO promoted Hg~0 oxidation at the very beginning,excessive NO counteracted this effect.The results show that NO plays different roles in Hg~0oxidation; NO in the gaseous phase may directly react with the adsorbed Hg~0,but excessive NO hinders Hg~0 adsorption.The adsorbed NO was converted into active nitrogen species(e.g.,NO_2) with oxygen,which facilitated the adsorption and oxidation of Hg~0.Hg~0 was oxidized by NO mainly by the Eley–Rideal mechanism.The Hg~0 temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O_2.     

Promoting effect of FeOx addition on the mechanochemically prepared vanadium-based catalyst for real PCDD/Fs removal and mechanism insight

Industrial-use VOx-based catalysts usually have a higher active temperature window (>250-300℃),which becomes a“bottleneck”for the practical application of PCDD/Fs catalytic degradation technology.In this work,VOx-FeOx/TiO₂catalyst prepared via mechanochemically method was investigated for the catalytic removal of PCDD/Fs.The removal efficiency of 1,2-DCBz,pure PCDD/Fs gas generated in the lab,PCDD/Fs from actual fue gas,long-term were studied,and the degradation mechanism was explo...     

Insights into the interface of NiCo2O4 spinel/LaCoO3 perovskite nano-composite for CO and soot oxidation

In the quest for the development of thermally stable, highly active and low-cost catalysts for use in catalyzed diesel particulate filter, nano-composites are new areas of research. Therefore, we reported the easy synthesis of spinel NiCo₂O₄/perovskite LaCoO₃ nano-composite,and its individual oxides NiCo₂O₄and LaCoO₃ for comparison. The detailed insights into the physio-chemical characteristics of formed NiCo₂O₄     

Pd Pt VOx/CeO2-ZrO2:Highly efficient catalysts with good sulfur dioxide-poisoning reversibility for the oxidative removal of ethylbenzene

The PdPtVO_x/CeO₂-ZrO₂(PdPtVO_x/CZO) catalysts were obtained by using different approaches,and their physical and chemical properties were determined by various techniques.Catalytic activities of these materials in the presence of H₂O or SO₂were evaluated for the oxidation of ethylbenzene (EB).The PdPtVO_x/CZO sample exhibited high catalytic activity,good hydrothermal stability,and reversible sulfur dioxide-poisoning perfo...     

Preparation and characterization of Fe2O3-CeO2-TiO2/γ-Al2O3 catalyst for degradation dye wastewater

In order to develop a catalyst with high activity for catalytic wet oxidation （CWO） process at room temperature and atmospheric pressure, Fe2O3-CeO2-TiO2/γ-Al2O3 catalyst was prepared by consecutive impregnation method and the prepared parameters were optimized. The structure of the catalyst was characterized by BET, XRF, SEM and XPS technologies, and the actual wastewater was used to investigate the catalytic activity of Fe2O3-CeO2-TiO2/γ-Al2O3 in CWO process. The experimental results showed that the prepared catalyst exhibited good catalytic activity when the doping amount of Ti was 1.0 wt% （the weight ratio of Ti to carriers）, and the middle product, Fe2O3-CeO2-TiO2/γ-Al2O3, was calcined in 450℃ for 2 h. The CWO experiment for treating actual dye wastewater indicated that the COD, color and TOC of actual wastewater were decreased by 62.23%, 50.12% and 41.26% in 3 h, respectively, and the ratio of BOD5/COD was increased from 0.19 to 0.30.     

Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe3O4: Inhibitor or stabilizer?

The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe₃O₄ catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H₂O₂. This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H₂O₂. In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H₂O₂ and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe₃O₄ catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H₂O₂ stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.     

Role of NO in Hg oxidation over a commercial selective catalytic reduction catalyst V2O5–WO3/TiO2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst, V₂O₅–WO₃/TiO₂, to investigate mercury oxidation in the presence of NO and O₂. Mercury oxidation was improved by NO, and the efficiency was increased by simultaneously adding NO and O₂. With NO and O₂ pretreatment at 350°C, the catalyst exhibited higher catalytic activity for Hg⁰ oxidation, whereas NO pretreatment did not exert a noticeable effect. Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O₂. Although NO promoted Hg⁰ oxidation at the very beginning, excessive NO counteracted this effect. The results show that NO plays different roles in Hg⁰ oxidation; NO in the gaseous phase may directly react with the adsorbed Hg⁰, but excessive NO hinders Hg⁰ adsorption. The adsorbed NO was converted into active nitrogen species (e.g., NO₂) with oxygen, which facilitated the adsorption and oxidation of Hg⁰. Hg⁰ was oxidized by NO mainly by the Eley–Rideal mechanism. The Hg⁰ temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O₂.     

The effect of freezing on the composition of supercooled droplets—I. Retention of HCl,HNO3, NH3 and H2O2

Experiments were done to check on the possibility that cloud droplets might, during freezing, lose acidity by evolution of HCl or HNO₃, lose NH₃ or lose dissolved H₂O₂. A spray of droplets with average diameter 39μm was produced by an ultrasonic transducer. The droplets acquired a temperature between −8 and −12°C and fell onto an ice surface, where they froze. Appropriate analytical techniques were applied to compare the composition of the frozen droplets with that of the sprayed liquid. It was found that the four chemical species studied were totally retained in the ice after freezing.     

Synthesis, characterization, and photocatalytic activity of porous La–N–co-doped TiO2 nanotubes for gaseous chlorobenzene oxidation

The photocatalytic oxidation of gaseous chlorobenzene(CB) by the 365 nm-induced photocatalyst La/N–Ti O2, synthesized via a sol–gel and hydrothermal method, was evaluated. Response surface methodology(RSM) was used to model and optimize the conditions for synthesis of the photocatalyst. The optimal photocatalyst was 1.2La/0.5N–Ti O2(0.5) and the effects of La/N on crystalline structure, particle morphology, surface element content, and other structural characteristics were investigated by XRD(X-ray diffraction), TEM(Transmission Electron Microscopy), FTIR(Fourier transform infrared spectroscopy), UV–vis(Ultraviolet–visible spectroscopy), and BET(Brunauer Emmett Teller). Greater surface area and smaller particle size were produced with the co-doped Ti O2 nanotubes than with reference Ti O2. The removal of CB was effective when performed using the synthesized photocatalyst,though it was less efficient at higher initial CB concentrations. Various modified Langmuir-Hinshelwood kinetic models involving the adsorption of chlorobenzene and water on different active sites were evaluated. Fitting results suggested that competitive adsorption caused by water molecules could not be neglected, especially for environments with high relative humidity. The reaction intermediates found after GC–MS(Gas chromatography–mass spectrometry) analysis indicated that most were soluble, low-toxicity, or both. The results demonstrated that the prepared photocatalyst had high activity for VOC(volatile organic compounds) conversion and may be used as a pretreatment prior to biopurification.     

Pd/ZrO【sub】2【/sub】-Al【sub】2【/sub】O【sub】3【/sub】催化剂加氢脱硫性能的研究

采用等体积浸渍法制备了一系列不同Zr含量的ZrO2-Al2O3复合载体和Pd/ZrO2-Al2O3催化剂,利用连续流动微反装置考察了Pd/ZrO2-Al2O3催化剂的噻吩加氢脱硫(HDS)性能,并运用程序升温还原(TPR),程序升温脱附(H2-TPD,NH3-TPD)和N2物理吸附等技术对载体及催化剂进行了表征.结果表明:ZrO2-Al2O3复合载体中Zr含量对Pd基催化剂的HDS性能有较大影响,加入适量Zr可增大Pd/Al2O3催化剂的分散度及H2吸附量和酸量,减弱活性组分与载体的相互作用,使活性中心和噻吩吸附位增多以及活化能降低,从而有利于Pd基催化剂HDS反应活性的提高,w(Zr)为9%时Pd/ZrO2-Al2O3催化剂的活性最好.