共查询到20条相似文献,搜索用时 15 毫秒
1.
The use of hydrogen peroxide (H 2O 2) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO 2 powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H 2O 2/UV, TiO 2/UV, and H 2O 2/TiO 2/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 H 2O 2 concentrations on photodegradation process were examined. It was shown that photodegradation using H 2O 2/TiO 2/UV process was much more effective than using either H 2O 2/UV or TiO 2/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 H 2O 2/TiO 2/UV process. The role of H 2O 2 on such enhanced photodegradation of phenol in aqueous solution was finally discussed. 相似文献
2.
To get the low temperature sulfur resistant V 2O 5/TiO 2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V 2O 5/TiO 2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V 2O 5/TiO 2 catalysts showed high catalytic activity for NH 3 selective catalytic reduction (NH 3-SCR) of NO x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V 2O 5/TiO 2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V 2O 5/TiO 2 for maximum NO x conversion, which also showed high resistance to SO 2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V 2O 5/TiO 2 and compared with commercial W(10%)V 2O 5/TiO 2 catalyst. High electrical conductivity difference (Δ G) for Sb(2%)/V 2O 5/TiO 2 catalyst with temperature was observed. SO 2 deactivation experiments were carried out for Sb(2%)/V 2O 5/TiO 2 and W(10%)/V 2O 5/TiO 2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V 2O 5/TiO 2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V 2O 5/TiO 2 than Sb(2%)/V 2O 5/TiO 2 catalyst. 相似文献
3.
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
4.
The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al 2O 3, TiO 2 and SiO 2 have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al 2O 3 supported catalyst, while the activity of the TiO 2 and SiO 2 supported catalysts increased. However, at high concentrations of water both the SiO 2 and TiO 2 supported catalyst deactivated. Common for all catalysts was an increase in C 5+ selectivity and a decrease in the CH 4 selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H 2 chemisorption and X-ray diffraction (XRD). 相似文献
5.
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
6.
The effect of tungsten and barium on the thermal stability of V 2O 5/TiO 2 catalyst for NO reduction by NH 3 was examined over a fixed bed flow reactor system. The activity of V 2O 5/sulfated TiO 2 catalyst gradually decreased with respect to the thermal aging time at 600 °C. The addition of tungsten to the catalyst surface significantly enhanced the thermal stability of V 2O 5 catalyst supported on sulfated TiO 2. On the basis of Raman and XRD measurements, the tungsten on the catalyst surface was identified as suppressing the progressive transformation of monomeric vanadyl species into crystalline V 2O 5 and of anatase into rutile phase of TiO 2. However, the NO removal activity of V 2O 5/sulfated TiO 2 catalyst including barium markedly decreased after a short aging time, 6 h at 600 °C. This may be due to the transformation of vanadium species to inactive V–O–Ba compound by the interaction with BaO which was formed by the decomposition of BaSO 4 on the catalyst surface at high reaction temperature of 600 °C. The addition of SO 2 to the feed gas stream could partly restore the NO removal activity of thermally aged V 2O 5/sulfated TiO 2 catalyst containing barium. 相似文献
7.
The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C 2 hydrocarbons and by-products were CO and H 2. Methane conversion and the yield of C 2 hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C 2 hydrocarbons decreased. The synergism of La 2O 3/γ-Al 2O 3 and plasma gave methane conversion of 24.9% and C 2 hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C 2 hydrocarbons changed by using Pd-La 2O 3/γ-Al 2O 3 catalyst, the major C 2 product was ethylene. 相似文献
8.
研究了不同物相TiO 2对H 2O 2/O 3氧化效能的影响,目标有机物为羟基自由基探针化合物乙酸。结果表明,在初始pH为7.0和10.0时,加入TiO 2反而降低了H 2O 2/O 3的氧化效率,其中锐钛矿TiO 2比金红石TiO 2的减弱作用更为明显。当初始pH为3.0时,金红石TiO 2能显著提高H 2O 2/O 3的氧化效率,但锐钛矿TiO 2影响不明显。机理分析表明,H 2O 2浓度及其衰减速率与乙酸的去除效率有很大的相关性。在pH为7.0和10.0时,两种物相TiO 2均能加快H 2O 2的分解,其中锐钛矿TiO 2作用更为显著。此条件下HO 2-能有效引发臭氧分解产生羟基自由基,故H 2O 2过快分解反而降低了乙酸的去除效果。在pH为3.0时,H 2O 2去质子化反应困难,故O 3/H 2O 2氧化效率极低,H 2O 2浓度也几乎不变。加入TiO 2能明显提高H 2O 2的分解速率,相比金红石TiO 2,锐钛矿TiO 2使H 2O 2在5 min内基本分解完毕,但其对H 2O 2/O 3氧化效率几乎没有影响。饱和臭氧水分解速度的批处理实验也有相似的结果。由此可见,合适引发剂浓度可能是保证臭氧类高级氧化技术较高效率的关键,否则只会导致氧化剂的无效过快分解。利用氯化硝基四氮唑蓝法对比分析了酸性条件下H 2O 2/O 3、锐钛矿TiO 2/H 2O 2/O 3和金红石TiO 2/H 2O 2/O 3体系产生超氧自由基(·O 2-)的量,其大小顺序为:H 2O 2/O 3< 金红石TiO 2/H 2O 2/O 3< 锐钛矿TiO 2/H 2O 2/O 3,这与前面结果吻合很好。 相似文献
9.
The effects of cobalt and manganese oxides-doping on surface and catalytic properties of Cr 2O 3/MgO system have been investigated. The dopant concentration was changed between 1 and 5 mol% cobalt and manganese oxides. Pure and variously doped solids were subjected to heat treatment at 400 and 700 °C. The techniques employed were X-ray diffraction (XRD), nitrogen adsorption at –196 °C, catalytic conversion of iso-propanol at 200–400 °C using flow technique and catalytic decomposition of H 2O 2 at 20–40 °C. The results revealed that the doping process of the system investigated followed by calcinations at 400 or 700 °C, enhanced the solid–solid interactions between catalyst constituents yielding (-MgCrO 4, β-MgCrO 4) and MgCr 2O 4, respectively. Furthermore, manganese and cobalt oxide-doping for Cr 2O 3/MgO system increased its catalytic activity much towards H 2O 2-decomposition. The increase was, however, more pronounced in the case of manganese-doping. Opposite results have been observed in the case of iso-propanol conversion, which proceeds via dehydrogenation and dehydration reaction. The SBET of the investigated system was found to decrease by increasing the dopant concentration. The doping process did not modify the activation energy of the catalyzed reaction, but rather changed the concentration of the catalytically active constituents without changing their energetic nature. 相似文献
10.
二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。 相似文献
11.
High surface area (>300 m 2 g −1) nano-structured TiO 2 oxides (ns-T) were used as CoMo hydrodesulfurization catalyst support. Cylindrical extrudates were impregnated by incipient wetness with Mo (2.8 Mo at. nm −2) and Co (atomic ratio Co/(Co + Mo) = 0.3). Characterization of impregnated precursors was carried out by N 2 physisorption, XRD and atomic absorption and laser-Raman spectroscopies. Sulfided catalysts (400 °C, H 2S/H 2) were studied by X-ray photoelectronic spectroscopy. As indicated by XRD and after various preparation steps (extrusion, Mo and Co impregnation and sulfiding) the nano-structured material was well preserved. XPS analyses showed that Co and Mo dispersion over the ns-T support was much higher than that on alumina. Very high surface S concentration suggested that even ns-T was partially sulfided during catalyst activation. Dibenzothiophene hydrodesulfurization activity (5.73 MPa, 320 °C, n-hexadecane as solvent) of CoMo/ns-T was two-fold to that of an alumina-supported commercial CoMo catalyst. The improvement was even more remarkable in intrinsic pseudo kinetic constant basis. No important differences in selectivity over the catalysts supported on either Al 2O 3 or ns-T were observed, where direct desulfurization to biphenyl was favored. Both Mo dispersion and sulfidability were enhanced on the ns-T support where Mo 4+ fraction was notably increased (100%) as to that found on CoMo/Al 2O 3. 相似文献
12.
The effect of the TiO 2–Al 2O 3 mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO 2 into the support, and particularly over rich- and pure-TiO 2-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO 2. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO 2 content and large differences are observed between the catalysts supported on pure Al 2O 3 and pure TiO 2. In contrast, in the case of the thiophene test, the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al 2O 3- and pure TiO 2-based catalysts is relatively small and dependent on the H 2 pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H 2 partial pressure on the thiophene HDS, and on the effect of H 2S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking. 相似文献
13.
TiO 2/epoxy composite thick films containing the TiO 2 powders doped with 4 and 10 vol% Nb 2O 5 heat treated under vacuum at 1050 and 1150 °C, were prepared by the screen printing and curing steps. The Nb 2O 5-doped TiO 2 ceramic bulks demonstrated a higher effective dielectric constant at different densification environments, as compared with pure TiO 2. The dielectric properties of the TiO 2/epoxy thick films were improved if the heat-treated 4 vol% Nb 2O 5-doped TiO 2 powder was incorporated instead of the un-doped and heat-treated 10 vol% Nb 2O 5-doped TiO 2 powders. The disadvantage of the doped TiO 2 having higher dielectric loss tangent could be minimized after its powder was properly treated and mixed with epoxy to form the TiO 2/epoxy composite. A best result with the dielectric constant of 23 and the loss tangent of 0.046 was obtained for the 40 vol% TiO 2/epoxy composite thick films, where the TiO 2 powder was doped with 4 vol% Nb 2O 5 followed by calcination at 1000 °C in air and heat treatment at 1150 °C under vacuum. 相似文献
14.
In situ Raman spectroscopy was used for studying the ternary 2% CrO 3–6% V 2O 5/TiO 2 catalyst, for which a synergistic effect between vanadia and chromia leads to enhanced catalytic performance for the selective catalytic reduction (SCR) of NO with NH 3. The structural properties of this catalyst were studied under NH 3/NO/O 2/N 2/SO 2/H 2O atmospheres at temperatures up to 400 °C and major structural interactions between the surface chromia and vanadia species are observed. The effects of oxygen, ammonia, water vapor and sulfur dioxide presence on the in situ Raman spectra are presented and discussed. 相似文献
15.
Combined effect of H 2O and SO 2 on V 2O 5/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2, H 2O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2O and reactants (NO and/or NH 3). Although SO 2 promotes the SCR activity of the V 2O 5/AC catalyst in the absence of H 2O, it speeds the deactivation of the catalyst in the presence of H 2O. The dual effect of SO 2 is attributed to the SO 42− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C. 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.
A magnetically separable nitrogen-doped photocatalyst TiO 2−xN x/SiO 2/NiFe 2O 4 (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO 2/NiFe 2O 4 (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO 2−xN x were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO 2/NiFe 2O 4 (SN) nanoparticles adhere to the surface of TiO 2−xN x congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO 2 coating round the surface of NiFe 2O 4 nanoparticles prevents effectively the injection of charges from TiO 2 particles to NiFe 2O 4, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity. 相似文献
18.
研究者在苯胺模拟废水高级氧化处理方面开展了很多研究,但针对炼化企业苯胺装置废水含盐高、色度高、COD降解难等问题尚未开展工程应用。为解决苯胺生产废水的实际问题,本研究开展了TiO 2/UV-H 2O 2氧化降解苯胺废水(1~2m 3/h)的现场试验研究。考察了苯胺废水在单独TiO 2/UV、单独H 2O 2氧化及TiO 2/UV-H 2O 2协同作用下的处理效果,提出了苯胺废水的最佳处理工艺方案,并进行了成本核算。结果表明,单独TiO 2/UV和单独H 2O 2氧化对苯胺废水的脱色率和COD去除率偏低,而TiO 2/UV-H 2O 2协同作用时苯胺废水脱色率和COD去除率可达95%以上。协同氧化体系中,H 2O 2的氧化降解作用显著,H 2O 2投加量1%~2%;酸性条件利于苯胺废水的降解,特别是pH=3.8~4.2时;TiO 2/UV和H 2O 2协同作用一段时间后,停止UV而凭借残余H 2O 2可以将体系中的中间产物继续降解直至矿化成CO 2。TiO 2/UV- H 2O 2协同处理炼化企业苯胺生产废水,出水COD≤60mg/L,色度≤20倍,单位能耗约18.44kW·h/m 3,明显低于文献报道值,具有显著的技术性与经济性。 相似文献
19.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
20.
Alachlor, atrazine and diuron dissolved in water at 50, 25 and 30 mg/L, respectively were photodegraded by Fe 2+/H 2O 2, Fe 3+/H 2O 2, TiO 2 and TiO 2/Na 2S 2O 8 treatments driven by solar energy at pilot-plant scale using a compound parabolic collector (CPC) photoreactor. All the advanced oxidation processes (AOPs) employed mainly compared the TOC mineralisation rate to evaluate treatment effectiveness. Parent compound disappearance, anion release and oxidant consumption are discussed as a function of treatment time. The use of Fe 2+ or Fe 3+ showed no influence on the reaction rate under illumination and the reaction using 10 or 55 mg/L of iron was quite similar. TiO 2/Na 2S 2O 8 showed a quicker reaction rate than TiO 2 and a similar rate compared to photo-Fenton. The main difference found was between TiO 2/Na 2S 2O 8 and photo-Fenton, detected during atrazine degradation, where pesticide transformation into cyanuric acid was confirmed only for TiO 2/Na 2S 2O 8. 相似文献
|