Activity and hydrothermal stability of CeO2–ZrO2–WO3 for the selective catalytic reduction of NOx with NH3

A series of CeO_2–ZrO_2–WO_3(CZW)catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction(SCR)of NO with NH_3 over a wide temperature of 150–550°C.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H_2O.The fresh catalyst showed above 90% NO_x conversion at 201–459°C,which is applicable to diesel exhaust NO_x purification(200–440°C).The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures(below 300°C),while the activity was notably enhanced at high temperature(above 450°C).The aged CZW catalyst(hydrothermal aging at 700°C for 8 hr)showed almost 80% NO_x conversion at 229–550°C,while the V_2O_5–WO_3/TiO_2 catalyst presented above 80% NO_x conversion at 308–370°C.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO_2–ZrO_2 solid solution,amorphous WO_3 phase and optimal acidity.In addition,the formation of WO_3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.     

The balance of acidity and redox capability over modified CeO2 catalyst for the selective catalytic reduction of NO with NH3

The effect of acidity and redox capability over sulfuric acid-modified CeO_2 catalysts were studied for the selective catalytic reduction of NO_x with NH_3(NH_3-SCR). The deposition of sulfate significantly enhanced the catalytic performance over CeO_2. NO_x conversion over4H_2SO_4/CeO_2 at 230–440 °C was higher than 90%. The strong redox capability of CeO_2 could result in unselective NH_3 oxidation and decrease high temperatures catalytic activity and N_2 selectivity. The deposition of sulfate increased the acidity and weakened the redox capability, and then increased the high temperature NO_x conversion and N_2 selectivity. An appropriate level of acidity also promoted the activity at 190–250 °C over ceria-based catalysts, and with further increase in the acidity, the SCR activity decreased slightly. Weak redox capability lowered the low-temperature catalytic activity. Excellent SCR activity requires a balance of acidity and redox capability on the catalysts.     

Choice of precipitant and calcination temperature of precursor for synthesis of NiCo2O4 for control of CO–CH4 emissions from CNG vehicles

Compressed natural gas(CNG)is most appropriate an alternative of conventional fuel for automobiles.However,emissions of carbon-monoxide and methane from such vehicles adversely affect human health and environment.Consequently,to abate emissions from CNG vehicles,development of highly efficient and inexpensive catalysts is necessary.Thus,the present work attempts to scan the effects of precipitants(Na_2CO_3,KOH and urea)for nickel cobaltite(Ni Co_2O_4)catalysts prepared by co-precipitation from nitrate solutions and calcined in a lean CO-air mixture at 400°C.The catalysts were used for oxidation of a mixture of CO and CH_4(1:1).The catalysts were characterized by X-ray diffractometer,Brunauer–Emmett–Teller surface-area,X-ray photoelectron spectroscopy;temperature programmedreductionandScanningelectronmicroscopycoupledwith Energy-Dispersive X-Ray Spectroscopy.The Na_2CO_3was adjudged as the best precipitant for production of catalyst,which completely oxidized CO-CH_4mixture at the lowest temperature(T_(100)=350°C).Whereas,for catalyst prepared using urea,T_(100)=362°C.On the other hand the conversion of CO-CH_4mixture over the catalyst synthesized by KOH limited to 97%even beyond 400°C.Further,the effect of higher calcination temperatures of 500 and600°C was examined for the best catalyst.The total oxidation of the mixture was attained at higher temperatures of 375 and 410°C over catalysts calcined at 500 and 600°C respectively.Thus,the best precipitant established was Na_2CO_3and the optimum calcination temperature of 400°C was found to synthesize the Ni Co_2O_4catalyst for the best performance in CO-CH_4oxidation.     

Enhanced catalytic complete oxidation of 1,2-dichloroethane over mesoporous transition metal-doped γ-Al_2O_3

High-surface-area mesoprous powders of γ-Al2O3 doped with Cu2+, Cr3+, and V3+ions were prepared via a modified sol–gel method and were investigated as catalysts for the oxidation of chlorinated organic compounds. The composites retained high surface areas and pore volumes comparable with those of undoped γ-Al2O3 and the presence of the transition metal ions enhanced their surface acidic properties. The catalytic activity of the prepared catalysts in the oxidation of 1,2-dichloroethane(DCE) was studied in the temperature range of 250–400°C. The catalytic activity and product selectivity were strongly dependent on the presence and the type of dopant ion. While Cu2+- and Cr3+-containing catalysts showed100% conversion at 300°C and 350°C, V3+-containing catalyst showed considerably lower conversion. Furthermore, while the major products of the reactions over γ-alumina were vinyl chloride(C2H3Cl) and hydrogen chloride(HCl) at all temperatures, Cu- and Cr-doped catalysts showed significantly stronger capability for deep oxidation to CO2.     

NH3-SCR denitration catalyst performance over vanadium-titanium with the addition of Ce and Sb

Selective catalytic reduction technology using NH3 as a reducing agent(NH3-SCR) is an effective control method to remove nitrogen oxides. TiO2-supported vanadium oxide catalysts with different levels of Ce and Sb modification were prepared by an impregnation method and were characterized by X-ray diffractometer(XRD), Brunauer–Emmett–Teller(BET), Transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FT-IR), UV–Vis diffuse reflectance spectroscopy(UV–Vis DRS), Raman and Hydrogen temperature-programmed reduction(H2-TPR). The catalytic activities of V5 CexS by/TiO2 catalysts for denitration were investigated in a fixed bed flow microreactor. The results showed that cerium, vanadium and antimony oxide as the active components were well dispersed on TiO2, and the catalysts exhibited a large number of d–d electronic transitions, which were helpful to strengthen SCR reactivity. The V5 CexS by/TiO2 catalysts exhibited a good low temperature NH3-SCR catalytic activity. In the temperature range of 210 to 400℃, the V5 CexS by/TiO2 catalysts gave NO conversion rates above 90%. For the best V5Ce35Sb2/TiO2 catalyst, at a reaction temperature of 210℃, the NO conversion rate had already reached 90%. The catalysts had different catalytic activity with different Ce loadings. With the increase of Ce loading, the NO conversion rate also increased.     

Effect of water vapor on NH3-NO/NO2 SCR performance of fresh and aged MnOx-NbOx-CeO2 catalysts

A MnOx–NbOx–CeO2 catalyst for low temperature selective catalytic reduction(SCR) of NOx with NH3 was prepared by a sol–gel method, and characterized by NH3–NO/NO2 SCR catalytic activity, NO/NH3 oxidation activity, NOx/NH3 TPD, XRD, BET, H2-TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy(DRIFTS). The results indicate that the Mn Ox–Nb Ox–CeO2 catalyst shows excellent low temperature NH3-SCR activity in the temperature range of 150–300℃. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NOx adsorption. As the NO2 content increases in the feed, water vapor does not affect the activity in NO2 SCR. Meanwhile, water vapor significantly enhances the N2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH4NO3 into N2O.     

Cu-Mn-Ce ternary mixed-oxide catalysts for catalytic combustion of toluene

Cu–Mn, Cu–Mn–Ce, and Cu–Ce mixed-oxide catalysts were prepared by a citric acid sol–gel method and then characterized by XRD, BET, H_2-TPR and XPS analyses. Their catalytic properties were investigated in the toluene combustion reaction. Results showed that the Cu–Mn–Ce ternary mixed-oxide catalyst with 1:2:4 mole ratios had the highest catalytic activity, and 99% toluene conversion was achieved at temperatures below 220°C. In the Cu–Mn–Ce catalyst, a portion of Cu and Mn species entered into the Ce O_2 fluorite lattice, which led to the formation of a ceria-based solid solution. Excess Cu and Mn oxides existed on the surface of the ceria-based solid solution. The coexistence of Cu–Mn mixed oxides and the ceria-based solid solution resulted in a better synergetic interaction than the Cu–Mn and Cu–Ce catalysts, which promoted catalyst reducibility, increased oxygen mobility, and enhanced the formation of abundant active oxygen species.     

Fe2O3 particles as superior catalysts for low temperature selective catalytic reduction of NO with NH3

Fe203 particle catalysts were experimentally studied in the low temperature selective catalytic reduction （SCR） of NO with NH3. The effects of reaction temperature, oxygen concentration, [NH3]/[NO] molar ratio and residence time on SCR activity were studied. It was found that Fe203 catalysts had high activity for the SCR of NO with NH3 in a broad temperature range of 150-270℃, and more than 95% NO conversion was obtained at 180℃ when the molar ratio [NH3]/[NO] = 1, the residence time was 0.48 seconds and 02 volume fraction was 3%. In addition, the effect of SO2 on SCR catalytic activity was also investigated at the temperature of 180℃. The results showed that deactivation of the Fe2O3 particles occurred due to the presence of SO2 and the NO conversion decreased from 99.2% to 58% in 240 min, since SO2 gradually decreased the catalytic activity of the catalysts. In addition, X-ray diffraction, Thermogravimetric analysis and Fourier transform infrared spectroscopy were used to characterize the fresh and deactivated Fe2O3 catalysts. The results showed that the deactivation caused by SO2 was due to the formation of metal sulfates and ammonium sulfates on the catalyst surface during the de-NO reaction, which could cause pore plugging and result in suppression of the catalytic activity.     

A comparative study of Mn/CeO2, Mn/ZrO2 and Mn/Ce-ZrO2 for low temperature selective catalytic reduction of NO with NH3 in the presence of SO2 and H2O

Ce-ZrO2 is a widely used three-way catalyst support.Because of the large surface area and excellent redox quality,Ce-ZrO2 may have potential application in selective catalytic reduction(SCR) systems.In the present work,Ce-ZrO2 was introduced into a low-temperature SCR system and CeO2 and ZrO2 supports were also introduced to make a contrastive study.Mn/CeO2,Mn/ZrO2 and Mn/Ce-ZrO2 were prepared by impregnating these supports with Mn(NO3)2 solution,and have been characterized by N2-BET,XRD,TPR,TPD,XPS,FT-IR and TG.The activity and resistance to SO2 and H2O of the catalysts were investigated.Mn/Ce-ZrO2 and Mn/CeO2 were proved to have better low-temperature activities than Mn/ZrO2,and yielded 98.6% and 96.8% NO conversion at 180°C,respectively.This is mainly because Mn/Ce-ZrO2 and Mn/CeO2 had higher dispersion of manganese oxides,better redox properties and more weakly adsorbed oxygen species than Mn/ZrO2.In addition,Mn/Ce-ZrO2 showed a good resistance to SO2 and H2O and presented 87.1% NO conversion,even under SO2 and H2O treatment for 6 hours,and the activity of Mn/Ce-ZrO2 was almost restored to its original level after cutting off the injection of SO2 and H2O.This was due to the weak water absorption and weak sulfation process on the surface of the catalyst.     

Iron-doped Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO with NH3

The catalysts of iron-doped Mn-Ce/TiO 2(Fe-Mn-Ce/TiO 2) prepared by sol-gel method were investigated for low temperature selective catalytic reduction(SCR) of NO with NH 3.It was found that the NO conversion over Fe-Mn-Ce/TiO 2 was obviously improved after iron doping compared with that over Mn-Ce/TiO 2.Fe-Mn-Ce/TiO 2 with the molar ratio of Fe/Ti = 0.1 exhibited the highest activity.The results showed that 96.8% NO conversion was obtained over Fe(0.1)-Mn-Ce/TiO 2 at 180°C at a space velocity of 50,000 hr 1.Fe-Mn-Ce/TiO 2 exhibited much higher resistance to H 2 O and SO 2 than that of Mn-Ce/TiO 2.The properties of the catalysts were characterized using X-ray diffraction(XRD),N 2 adsorption,temperature programmed desorption(NH 3-TPD and NOx-TPD),and Xray photoelectron spectroscopy(XPS) techniques.BET,NH3-TPD and NOx-TPD results showed that the specific surface area and NH3 and NOx adsorption capacity of the catalysts increased with iron doping.It was known from XPS analysis that iron valence state on the surface of the catalysts were in Fe3+ state.The doping of iron enhanced the dispersion and oxidation state of Mn and Ce on the surface of the catalysts.The oxygen concentrations on the surface of the catalysts were found to increase after iron doping.Fe-Mn-Ce/TiO2 represented a promising catalyst for low temperature SCR of NO with NH3 in the presence of H2 O and SO2.     

铁屑/焦炭/H_2O_2法预处理焦化废水的试验研究

采用铁屑/焦炭/H2O2法对焦化废水进行处理,通过单因素试验法考察了铁炭比、铁炭用量、H2O2用量、废水pH以及反应时间对处理效果的影响,并确定了最适工艺条件。结果表明,铁屑/焦炭/H2O2法与常规的铁屑内电解法相比,可显著提高焦化废水的预处理效果,并缩短反应时间。铁屑/焦炭/H2O2法处理焦化废水的最适条件为:铁炭比为4,铁炭用量为300mg/L铁屑+75mg/L焦炭,H2O2用量为1000mg/L,pH为3,反应时间20min。在此条件下,COD、色度、NH3-N和CN-的去除效率分别可达61.2%、74.0%、56.2%和74.3%,B/C比由处理前的0.189提高到0.387,处理水可生化性良好。铁屑/焦炭/H2O2可作为焦化废水的一种有效的预处理方法。     

孔石莼（Ulva pertusa）对铅、铜、镉的吸收

研究了大型藻孔石莼对铅、铜和镉的吸收动力学和热力学过程。结果表明,暴露于不同浓度的重金属体系中的孔石莼对铅、铜和镉的积累量随着水相中的游离态浓度的增加而增加,可以用Langmuir吸附等温式从热力学平衡角度加以描述,铅和镉饱和结合量分别为：0．715mg/g干重,Cd^2＋为0．037mg／g干重;在孔石莼对铜（0．056mg／L）吸收动力学浓度的实验中,第4天达到了吸收平衡,蓄积量为对照组的9．01倍;在镉暴露浓度为0．028mg／L的实验中,第5天达吸收平衡,蓄积量为对照组的5．06倍。     

O3/H2O2降解Atrazine效能研究

利用O3/H2O2降解莠去津,对氧化产物进行了色谱分析,以评价该体系降解莠去津效能.莠去津初始浓度2 mg/L,7.5mg/L的O3单独氧化去除率为27.2%;相同O3投量下,H2O2/O3摩尔比0.75时,5 min莠去津的去除率最高可达96.5%,表明H2O2/O3体系对莠去津的去除效果良好,降解速度快.以离子色谱对产物的离子进行分析,莠去津浓度下降的同时,硝酸根和氯离子浓度增高.GC-MS检测的产物和对LC-MS谱图的分析表明,有机产物中存在脱乙基、脱异丙基和脱氯莠去津,说明H2O2/O3并不能彻底氧化莠去津,因此工程中作为主要去除单元或突发性污染事件的应急手段可能还需要与活性炭等单元联用.     

VUV/TiO2/H2O2法去除水中微量硝基苯

研究了过氧化氢(H₂O₂)强化的真空紫外光催化(VUV/TiO₂/H₂O₂)方法对水中微量硝基苯(NB)的去除效果,同时考察了H₂O₂ 投加量、NB 初始浓度、重碳酸盐和腐殖酸对NB 降解的影响.采用负载在钛片上的二氧化钛(TiO₂)薄膜为光催化剂,以能发射185nm 真空紫外线(VUV)的紫外灯为光源.结果表明,去离子水中50µg/L 的NB 反应60s 后去除率即达到97.9%.随H₂O₂ 投加量的增加, VUV/TiO2/H₂O₂ 对NB的降解速率先增后减;初始浓度低于170µg/L 时,初始浓度对NB 降解影响不大;重碳酸盐和腐殖酸对硝基苯降解有显著的抑制作用.VUV/TiO₂/H₂O₂能快速有效地去除地表水(含碳酸盐和天然有机物)中的微量NB,5min 内初始浓度为90µg/L的NB去除率达到94.1%, UV₂₅₄在4min 内也降低了53.3%.     

2-酮基-L-古龙酸的高效液相色谱测定方法和条件

为了快速准确的检测维生素C(VC)生产工艺中VC的重要前体物2-酮基-L-古龙酸(2-KLG)浓度,采用高效液相色谱法进行测定,选用6×250 mm Carbohydrate分析柱,乙腈:磷酸二氢钾=60∶40的流动相,在波长210 nm处紫外光检测,控制流速为1 mL/min和温度45℃。结果表明2-KLG在6 min左右出峰,与VC具有较好分离度;2-KLG标准曲线的回归方程为y=0.776x-13.46,相关系数达到99.9%,检出限为0.5 mg/L;回收率为96.3%~104%,RSD为6.28%(n=5)     

Inactivation of SARS-CoV-2 by Ozonated Glycerol

We evaluated the SARS-CoV-2-inactivation activity of ozonated glycerol (OG). When a viral solution with 1% fetal bovine serum (FBS) was mixed with test solutions at a ratio of 1:19 and incubated for 20 s, OG with ozone concentrations of over 1000 ppm inactivated ≥ 94.38% of the virus. Extension of the reaction time to 1 h led to the inactivation of ≥ 99.82% of the virus (the viral titer was below the detection limit). Extension to 24 h resulted in concentrations over 200 ppm OG inactivating ≥ 99.87% of the virus (the viral titers were below the detection limit). Next, viral solutions with 1, 20, and 40% FBS were mixed with test solutions at a ratio of 1:19 and incubated for 5 min. Whereas the virucidal activity of 500 ppm OG was very limited in the presence of 1% FBS (79.47% inactivation), it increased in the presence of 20 and 40% FBS (95.13 and 97.95% inactivation, respectively; the viral titers were not below the detection limit). Meanwhile, over 1000 ppm OG inactivated ≥ 99.44% of the virus regardless of the FBS concentration (the viral titers were below the detection limit). Extension of the reaction time to 1 h led to 500 ppm OG inactivating ≥ 99.91 and ≥ 99.95% of the virus with 20 and 40% FBS, respectively (the viral titers were below the detection limit). These results suggested that OG might be useful as a virucidal agent against SARS-CoV-2.

     

MnO2/TiO2改性沸石去除矿井水中Fe2+和Mn2+的试验研究

针对矿井水中Fe2+、Mn2+浓度超标及处理效果不稳定等问题,通过溶胶-凝胶法将纳米MnO₂和纳米TiO₂负载于天然斜发沸石表面制备出MnO₂/TiO₂改性沸石滤料,并分析了沸石改性前后的微观形貌和孔隙结构. 采用单因素动态吸附试验和Thomas模型拟合探究了MnO₂/TiO₂改性沸石对模拟矿井水水样中Fe2+、Mn2+的去除效果及机理,并考察水流速度、滤层厚度、溶液pH及硬度对去除效果的影响. 结果表明:较天然沸石而言,MnO₂/TiO₂改性沸石的比表面积、孔径、孔体积和阳离子交换量明显增大. 当水流速度为7 m/h、进水pH为9.5、水质硬度为350 mg/L、滤层厚度为110 cm时,改性沸石对Fe2+、Mn2+的最大吸附量分别为44.810、6.549 mg/g,且Thomas模型能较好地拟合改性沸石对Fe2+、Mn2+的吸附动力学特征. 反冲洗试验结果表明,反冲洗强度为13 L/(m2·s),反冲洗时间大于7 min时,改性沸石的再生效果良好,可重复使用. 研究显示,本文制备的MnO₂/TiO₂改性沸石吸附滤料可为同步去除矿井水中Fe2+、Mn2+污染提供一种解决办法.      

催化剂对H2O2降解苯酚废水的影响研究

通过实验研究了Fe2+对H2O2降解苯酚废水的影响.结果表明,Fe2+作催化剂时CODCr去除率随Fe2+浓度增大先升高后降低,当废水中Fe2+浓度为6.4mmol/L时,CODCr去除率高达91.25%;有Cu2+或PO3-4存在时,会对H2O2氧化苯酚废水产生不利影响.     

Modification of CeO2-ZrO2 catalyst by potassium for NOx-assisted soot oxidation

Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method.The ageing treatment was performed in static air at 800°C for 20 hr to evaluate the thermal stability of the catalyst.The catalysts were characterized by X-ray diffraction,BET surface area,oxygen storage capacity,NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements.By introduction of potassium,the maximum soot oxidation rate temperature(Tm) of the ceria-zirconia based catalyst de...     

SiO-TiO2纳米管的制备及其光催化性能的研究

文章采用水热法制备SiO2-TiO2纳米管,通过扫描电镜(SEM)和透射电镜(TEM)考察了该纳米管的结构形态,并用X-射线衍射考察其晶体结构.实验结果表明所制得的纳米管是锐钛晶型,其两端开口,具有多层管壁;管径为8 nm左右,管壁厚1～2 nm.光催化降解酸性橙Ⅱ实验表明:SiO2-TiO2纳米管光催化速率比TiO2纳米管高出10%.这可能是因为Si元素的存在增大了钛纳米管的比表面积,同时SiO2的存在能降低光生电子和空穴的复合率.