Chemical deactivation of V2O5-WO3/TiO2 SCR catalyst by combined effect of potassium and chloride

V₂O₅-WO₃/TiO₂ catalyst was poisoned by impregnation with NH₄Cl, KOH and KCl solution, respectively. The catalysts were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), N₂ physisorption, Raman, UV-vis, NH₃ adsorption, temperature-programmed reduction of hydrogen (H₂-TPR), temperature-programmed oxidation of ammonia (NH₃-TPO) and selective catalytic reduction of NO _x with ammonia (NH₃-SCR). The deactivation effects of poisoning agents follow the sequence of KCl>KOH?NH₄Cl. The addition of ammonia chloride enlarges the pore size of the titania support, and promotes the formation of highly dispersed V = O vanadyl which improves the oxidation of ammonia and the high-temperature SCR activity. K⁺ ions are suggested to interact with vanadium and tungsten species chemically, resulting in a poor redox property of catalyst. More importantly, potassium can reduce the Brønsted acidity of catalysts and decrease the stability of Brønsted acid sites significantly. The more severe deactivation of the KCl-treated catalyst can be mainly ascribed to the higher amount of potassium resided on catalyst.     

Solar photocatalytic degradation of the herbicide isoproturon on a Bi–TiO2/zeolite photocatalyst

The photocatalytic degradation of the herbicide isoproturon under solar light was investigated in aqueous solution containing a Bi–TiO₂/zeolite photocatalyst. The catalysts were characterized using X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, Fourier transform-infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The effect of Bi–TiO₂ loading onto the zeolite support and influence of the parameters such as catalyst amount, pH, and initial concentration of isoproturon on the degradation rate were evaluated. The recycling ability of the catalyst was found to be sustainable for elongated periods. The high activity of the Bi–TiO₂/zeolite was attributed to its absorptivity of visible light and its high adsorption capacity for the pollutant molecules.     

Photocatalytic mineralization of a water pollutant,Sunset Yellow dye by an advanced oxidation process using a modified catalyst

ZnS-loaded TiO₂ (ZnS–TiO₂) was synthesized by a sol–gel method. The catalyst was characterized by using different techniques (XRD, HR-SEM, EDS, DRS, PL, XPS, and BET methods). The photocatalytic activity of ZnS–TiO₂ was investigated for the degradation of Sunset Yellow FCF (SY) dye in an aqueous solution using ultraviolet light. ZnS–TiO₂ is found to be more efficient than prepared TiO₂, TiO₂–P25, TiO₂ (Merck), and ZnS at pH 7 for the mineralization of SY. The effects of operational parameters such as the amount of photocatalyst, dye concentration, and initial pH on photo mineralization of SY have been analyzed. The mineralization of SY has been confirmed by chemical oxygen demand measurements. The catalyst is found to be reusable.     

Effect of K and Ca on catalytic activity of Mn-CeO x /Ti-PILC

Mn-CeO _x /Ti-pillared clay (PILC) is an attractive catalyst for selective catalytic reduction of NO _x at low temperature because of its low cost. The poisoning of K and Ca on the catalyst of Mn-CeO _x /Ti-PILC is an important problem because K and Ca are always in presence in flue gas. To investigate the effect of K and Ca on the physicochemical characters of the catalysts, the techniques of NH₃-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) were used to analyze the fresh and deactivated catalysts of Mn-CeO _x /Ti-PILC. (Ca)Mn-CeO _x /Ti-PILC and (K)Mn-CeO _x /Ti-PILC are denoted for the dopes of the catalyst of Mn-CeO _x /Ti-PILC with Ca and K, respectively. The activities of Mn-CeO _x /Ti-PILC, (Ca)Mn-CeO _x /Ti-PILC and (K)Mn-CeO _x / Ti-PILC for NH₃-selective catalytic reduction (SCR) reaction at low temperature were investigated. The results showed that with the dopes of K and Ca on the catalysts, the SCR activities of the catalysts decreased greatly, and K exhibited more poisoning effect than Ca. With the dopes of K and Ca, the acidity, the redox property and chemisorbed oxygen on the surfaces of the catalysts were decreased, which resulted in a decreasing in SCR activity.     

Catalytic ozonation performance and surface property of supported Fe3O4 catalysts dispersions

Fe₃O₄ was supported on mesoporous Al₂O₃ or SiO₂ (50 wt.%) using an incipient wetness impregnation method, and Fe₃O₄/Al₂O₃ exhibited higher catalytic efficiency for the degradation of 2,4-dichlorophenoxyacetic acid and para-chlorobenzoic acid aqueous solution with ozone. The effect and morphology of supported Fe₃O₄ on catalytic ozonation performance were investigated based on the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, BET analysis and Fourier transform infrared spectroscopy. The results indicated that the physical and chemical properties of the catalyst supports especially their Lewis acid sites had a significant influence on the catalytic activity. In comparison with SiO₂, more Lewis acid sites existed on the surface of Al₂O₃, resulting in higher catalytic ozonation activity. During the reaction process, no significant Fe ions release was observed. Moreover, Fe₃O₄/Al₂O₃ exhibited stable structure and activity after successive cyclic experiments. The results indicated that the catalyst is a promising ozonation catalyst with magnetic separation in drinking water treatment.     

Factors influencing the photodegradation of N-nitrosodimethylamine in drinking water

In order to provide basic data for practical application, photodegradation experiment of N-nitrosodimethylamine (NDMA) in aqueous solution was carried out with a low-pressure Hg lamp. Effects of the initial concentration of NDMA, solution pH, dissolved oxygen, and the presence of humic acid on NDMA photodegradation were investigated. NDMA at various initial concentrations selected in this study was almost completely photodegraded by UV irradiation within 20 min, except that at 1.07 mmol/L, NDMA could be photodegraded almost completely in the acidic and neutral solutions, while the removal efficiency decreased remarkably in the alkaline solution. Dissolved oxygen enhanced the NDMA photodegradation, and the presence of humic acid inhibited the degradation of NDMA. Depending on the initial concentration of NDMA, NDMA photodegradation by UV obeyed the pseudo-first-order kinetics. Dimethylamine, nitrite, and nitrate were detected as the photodegradation products of NDMA. ¹O₂ was found to be the reactive oxygen species present in the NDMA photodegradation process by UV, based on the inhibiting experiments using tert-butanol and sodium azide.     

Characteristics and mechanisms of 4A zeolite supported nanoparticulate zero-valent iron as Fenton-like catalyst to degrade methylene blue

4A zeolite supported nanoparticulate zero-valent iron (nZVI/4A zeolite), synthesized through borohydride reduction method, was used as a catalyst with H₂O₂ to build Fenton-like reaction system to degrade methylene blue (MB) in model wastewater. The characteristics and primary mechanisms of the catalyst were investigated. The results show that nZVI/4A zeolite has the potential as a Fenton-like catalyst, and (about 30 mg/L) MB was degraded completely in 3 h with 10 mM H₂O₂, 0.2 g/L catalyst, and initial pH of 3.0. The MB degradation rates were obtained at least 70% in the tests with initial pH ranged from 2.0 to 9.0 and the catalyst dose rose from 0.2 to 5.0 g/L. Importantly, the catalyst also has a distinctive ability to increase the solution pH value from its initial acidic pH and then maintain the value at close to neutrality. This ability was controlled by both the initial pH and the catalyst dose. MB degradation clarified that hydroxyl radical was the dominated active oxidative specie in the tests with initial acidic pH and low catalyst dose (less 2.5 g/L); otherwise, Fe(VI) oxidation was the main mechanism for MB degradation; and the two processes shared synergistic effect in MB degradation in the present test. The catalyst has high operational stability in both of the composites with low iron leaching (less 2%) and catalyzing ability. Therefore, nZVI/4A zeolite has great potential as a Fenton-like catalyst and is used with H₂O₂ to build Fenton-like system which could be used to degrade MB efficiently.     

Removal of cyanide in aqueous solution by oxidation with hydrogen peroxide in presence of activated alumina

This work is dedicated to the removal of free cyanide from aqueous solution by oxidation with hydrogen peroxide H₂O₂ catalyzed by neutral activated alumina. Effects of initial molar ratio [H₂O₂]₀/[CN^?]₀, catalyst amount, pH, and temperature on cyanide removal have been examined. The presence of activated alumina has increased the reaction rate showing thus, a catalytic activity. The rate of removal of cyanides increases with rising initial molar ratio [H₂O₂]₀/[CN^?]₀ but decreases at pH 10 to 12. Increasing the alumina amount from 1.0 to 30 g/L has a beneficial effect, and increasing the temperature from 20 °C to 35 °C improves cyanide removal. The kinetics of cyanide removal has been found to be of pseudo-first-order with respect to cyanide and the rate constants have been determined.     

Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/γ-Al2O3 to oxidize gaseous ammonia

This work describes the environmentally friendly technology for oxidation of ammonia (NH₃) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al₂O₃ catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H₂PtCl₆) and rhodium (III) nitrate (Rh(NO₃)₃) with γ-Al₂O₃ in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), threedimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic lightscattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH₃ was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al₂O₃ catalyst. N₂ was the main product in NH₃-SCO process. Further, it reveals that the oxidation of NH₃ was proceeds by the over-oxidation of NH₃ into NO, which was conversely reacted with the NH₃ to yield N₂. Therefore, the application of nanosized Pt-Rh/γ-Al₂O₃ catalyst can significantly enhance the catalytic activity toward NH₃ oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al₂O₃ catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.     

Effect of nitrogen supply on nitrogen uptake,accumulation and assimilation in Porphyra perforata (Rhodophyta)

Porphyra perforata J. Ag. was collected from a rocky land-fill site near Kitsilano Beach, Vancouver, British Columbia, Canada and was grown for 4 d in media with one of the following forms of inorganic nitrogen: NO ₃ ^- , NH ₄ ⁺ and NO ₃ ^- plus NH ₄ ⁺ and for 10 d in nitrogen-free media. Internal nitrogen accumulation (nitrate, ammonium, amino acids and soluble protein), nitrate and ammonium uptake rates, and nitrate reductase activity were measured daily. Short initial periods (10 to 20 min) of rapid ammonium uptake were common in nitrogen-deficient plants. In the case of nitrate uptake, initial uptake rates were low, increasing after 10 to 20 min. Ammonium inhibited nitrate uptake for only the first 10 to 20 min and then nitrate uptake rates were independent of ammonium concentration. Nitrogen starvation for 8 d overcame this initial suppression of nitrate uptake by ammonium. Nitrogen starvation also resulted in a decrease in soluble internal nitrate content and a transient increase in nitrate reductase activity. Little or no decrease was observed in internal ammonium, total amino acids and soluble protein. The cultures grown on nitrate only, maintained high ammonium uptake rates also. The rate of nitrate reduction may have limited the supply of nitrogen available for further assimilation. Internal nitrate concentrations were inversely correlated with nitrate uptake rates. Except for ammonium-grown cultures, internal total amino acids and soluble protein showed no correlation with uptake rates. Both internal pool concentrations and enzyme activities are required to interpret changes in uptake rate during growth.     

Thermal treatment of plasma-synthesized goethite improves Fenton-like degradation of orange II dye

Various iron oxides are used for Fenton reactions to degrade organic pollutants. The degradation efficiency may be improved by transforming an iron oxide phase to another. Here, we report on the transformation of goethite into hematite by thermal treatment at 400 °C. The products were analyzed by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and N₂-physisorption. The catalytic activities were measured for orange II bleaching at initial concentration of 25 mg L^?1, pH 3, catalyst concentration of 0.2 g L^?1; 5 mM H₂O₂, 30 °C. Results show that the synthesized goethite was successfully transformed into hematite, and the specific surface area of the material increased from 134 to 163 m² g^?1. The bleaching efficiency of the orange II dye reached 100 % for the hematite product, versus 78 % for goethite. Therefore, a moderate thermal treatment of a plasma-synthesized goethite improves the catalytic oxidation of organic pollutants.     

Ce0.7Zr0.3O2纳米棒的制备及其对柴油车尾气碳颗粒的催化净化性能

本研究以硝酸铈、硝酸锆为原料使用溶剂热合成法,制备了CeO₂-ZrO₂纳米棒催化剂(Ce_0.7Zr_0.3O₂(NR)),并用于柴油车尾气碳颗粒催化净化.催化活性检测证实:Ce_0.7Zr_0.3O₂(NR)纳米棒催化剂可有效净化柴油车尾气碳烟颗粒.在Ce_0.7Zr_0.3O₂(NR)存在下,碳颗粒净化率为10%、50%和90%时,所需温度分别仅为375℃、414℃和455℃,比商用Ce_0.7Zr_0.3O₂和Ce0.3Zr0.7O2催化剂性能更优.采用氮吸附-脱附、X射线光电子能谱(XPS)、H2程序升温还原(H₂-TPR)、X射线衍射(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等技术对催化剂进行表征.XRD和Raman结果证实,Ce_0.7Zr_0.3O₂(NR)主要由立方相CeO₂构成,并掺杂了少量四方相氧化锆.SEM和TEM结果则显示,Ce_0.7Zr_0.3O₂(NR)催化剂颗粒明显由纳米棒堆积而成,特定的纳米形貌会影响其对碳颗粒的催化氧化活性.XPS结果证明Ce_0.7Zr_0.3O₂(NR)催化剂主要具有晶格氧、化学氧和表面吸附氧等氧物种;晶格氧是碳颗粒氧化的活性氧物种,其溢流到催化剂表面可与碳颗粒接触从而提高反应活性;化学氧和表面吸附氧均为表面氧物种,极易与表面固体碳颗粒直接接触,从而可在较低温度下促进碳颗粒的净化.H₂-TPR结果进一步证实了XPS结果,Ce_0.7Zr_0.3O₂(NR)催化剂的低温还原温度比商用Ce_0.7Zr_0.3O₂催化剂更低,且含有更多的易还原氧物种,这些低温易还原氧物种可以在较低温度下参与催化反应,促进柴油车尾气颗粒物的低温催化净化.     

Solar photocatalytic decomposition of two azo dyes on multi-walled carbon nanotubes (MWCNTs)/TiO<Subscript>2</Subscript> composites

Multi-walled carbon nanotubes (MWCNTs)/TiO₂ composite photocatalysts with high photoactivity were prepared by sol-gel process and further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and UV-vis absorption spectra. Compared to pure TiO₂, the combination of MWCNTs with titania could cause a significant absorption shift toward the visible region. The photocatalytic performances of the MWCNTs/TiO₂ composite catalysts were evaluated for the decomposition of Reactive light yellow K-6G (K-6G) and Mordant black 7 (MB 7) azo dyes solution under solar light irradiation. The results showed that the addition of MWCNTs enhanced the adsorption and photocatalytic activity of TiO₂ for the degradation of azo dyes K-6G and MB 7. The effect of MWCNTs content, catalyst dosage, pH, and initial dye concentration were examined as operational parameters. The kinetics of photocatalytic degradation of two dyes was found to follow a pseudo-first-order rate law. The photocatalyst was used for seven cycles with photocatalytic degradation efficiency still higher than 98%. A plausible mechanism is also proposed and discussed on the basis of experimental results.     

Promotion of transition metal oxides on the NH<Subscript>3</Subscript>-SCR performance of ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> catalyst

Chromium oxide and manganese oxide promoted ZrO₂-CeO₂ catalysts were prepared by a homogeneous precipitation method for the selective catalytic reduction of NO _x with NH₃. A series of characterization including X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), Brunauer–Emmett–Teller (BET) surface area analysis, H₂ temperatureprogrammed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the influence of the physicochemical properties on NH₃-SCR activity. Cr-Zr-Ce and Mn-Zr-Ce catalysts are much more active than ZrO₂-CeO₂ binary oxide for the low temperature NH₃-SCR, mainly because of the high specific surface area, more surface oxygen species, improved reducibility derived from synergistic effect among different elements. Mn-Zr-Ce catalyst exhibited high tolerance to SO₂ and H₂O. Cr-Zr-Ce mixed oxide exhibited>80% NO _x conversion at a wide temperature window of 100°C–300°C. In situ DRIFT studies showed that the addition of Cr is beneficial to the formation of Bronsted acid sites and prevents the formation of stable nitrate species because of the presence of Cr^{6 +}. The present mixed oxide can be a candidate for the low temperature abatement of NO _x .

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1株贫营养好氧反硝化菌的分离鉴定及其脱氮特性

从水库底泥样品中,以硝酸盐为唯一氮源进行驯化、分离筛选出1株能在贫营养及好氧条件下进行高效反硝化的菌株PY8,经过电镜形态学观察、生理生化和16S rDNA序列分析,并基于16SrDNA序列结果,构建了该菌株的系统发育树,最终确定菌株PY8为根瘤菌Rhizobiumsp.。考察了初始pH值、温度、C/N、初始硝酸钠质量浓度、投菌量对菌株PY8硝酸盐还原活性的影响,以及该菌株的异养硝化性能。结果表明,在pH6.0～10.0,温度25～30℃,C/N1.0～9.0,初始硝酸钠质量浓度0.01～0.50g·L-1,投菌量1%～15%时,菌株PY8培养72h后的硝氮去除率可达到95%以上。另外,该菌株具有同时硝化-反硝化作用,在培养过程中氨氮去除率可达到58%左右。实验结果表明,菌株PY8在微污染水体生物脱氮领域中具有很大的应用潜力。     

Competition for electrons between reductive dechlorination and denitrification

It is common that 2,4,6-trichlorophenol (TCP) coexists with nitrate or nitrite in industrial wastewaters. In this work, simultaneous reductive dechlorination of TCP and denitrification of nitrate or nitrite competed for electron donor, which led to their mutual inhibition. All inhibitions could be relieved to a certain degree by augmenting an organic electron donor, but the impact of the added electron donor was strongest for TCP. For simultaneous reduction of TCP together with nitrate, TCP’s removal rate value increased 75% and 150%, respectively, when added glucose was increased from 0.4 mmol?L^–1 to 0.5 mmol?L^–1 and to 0.76 mmol?L^–1. For comparison, the removal rate for nitrate increased by only 25% and 114% for the same added glucose. The relationship between their initial biodegradation rates versus their initial concentrations could be represented well with the Monod model, which quantified their half-maximum-rate concentration (K _S value), and K _S values for TCP, nitrate, and nitrite were larger with simultaneous reduction than independent reduction. The increases in K _S are further evidence that competition for the electron donor led to mutual inhibition. For bioremediation of wastewater containing TCP and oxidized nitrogen, both reduction reactions should proceed more rapidly if the oxidized nitrogen is nitrite instead of nitrate and if readily biodegradable electron acceptor is augmented.

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氯代芳烃催化氢转移脱氯的研究

本文以甲酸钠为氢源,对聚乙烯吡咯烷酮锚定的ＰｄＣｌ２催化氯代芳烃脱氯进行了研究,考察了反应条件对反应的影响,研究了脱氯的选择性。结果表明;该方法具有卓越的脱氯选择性,催化剂用量少,反应条件温和,操作简便。本文并对其脱氯反应机理进行了初步探讨。     

Catalytic activity of cerium-doped Ru/Al2O3 during ozonation of dimethyl phthalate

In this paper, factors influencing the mineralization of dimethyl phthalate (DMP) during catalytic ozonation with a cerium-doped Ru/Al₂O₃ catalyst were studied. The catalytic contribution was calculated through the results of a comparison experiment. It showed that doping cerium significantly enhanced catalytic activity. The total organic carbon (TOC) removal over the doped catalyst at 100 min reached 75.1%, 61.3% using Ru/Al₂O₃ catalyst and only 14.0% using ozone alone. Catalytic activity reached the maximum when 0.2% of ruthenium and 1.0% of cerium were simultaneously loaded onto Al₂O₃ support. Results of experiments on oxidation by ozone alone, adsorption of the catalyst, Ce ion’s and heterogeneous catalytic ozonation confirmed that the contribution of heterogeneous catalytic ozonation was about 50%, which showed the obvious effect of Ru-Ce/Al₂O₃ on catalytic activity.     

Fe-pillared bentonite,a stable Fenton catalyst for treatment of petroleum refinery wastewater

Fe-pillared bentonite (Fe-Bent) was prepared by ion exchange as heterogeneous catalyst for degradation of organic contaminants in petroleum refinery wastewater. X-ray diffraction analysis showed the existence of α-Fe₂O₃. The effects of pH, H₂O₂ concentration, and catalyst dosage on the rate of lowering the chemical oxygen demand (COD) were investigated in detail. Removal efficiency of COD can be up to 92% under the following conditions: dosage of Fe-Bent 7 g L^?1, pH value 3, and H₂O₂ concentration 10 mmol L^?1. Fe-Bent showed good stability for the degradation of organics in petroleum refinery wastewater for five cycles. The adsorption of organics in wastewater onto Fe-Bent could be well described by a pseudo-second-order kinetic model.     

Catalytic activities and mechanism of formaldehyde oxidation over gold supported on MnO<Subscript>2</Subscript> microsphere catalysts at room temperature

MnO₂ microspheres with various surface structures were prepared using the hydrothermal method, and Au/MnO₂ catalysts were synthesized using the sol-gel method. We obtained three MnO₂ microspheres and Au/MnO₂ samples: coherent solid spheres covered with wire-like nanostructures, solid spheres with nanosheets, and hierarchical hollow microspheres with nanoplatelets and nanorods. We investigated the properties and catalytic activities of formaldehyde oxidation at room temperature. Crystalline structures of MnO₂ are the main factor affecting the catalytic activities of these samples, and γ-MnO₂ shows high catalytic performance. The excellent redox properties are responsible for the catalytic ability of γ-MnO₂. The gold-supported interaction can change the redox properties of catalysts and accelerate surface oxygen species transition, which can account for the catalytic activity enhancement of Au/MnO₂. We also studied intermediate species. The dioxymethylene (DOM) and formate species formed on the catalyst surface were considered intermediates, and were ultimately transformed into hydrocarbonate and carbonate and then decomposed into CO₂. A proposed mechanism of formaldehyde oxidation over Au/MnO₂ catalysts was also obtained.