Effect of alkaline earth metal promoter on catalytic activity of MnO2 for the complete oxidation of toluene

Herein, Na⁺ and Ca²⁺ are introduced to MnO₂ through cation-exchange method. The presence of Na⁺ and Ca²⁺ significantly enhance the catalytic activity of MnO₂ in toluene oxidation. Among them, the Ca-MnO₂ catalyst exhibits the best catalytic activity (T₅₀ = 194°C, T₉₀ = 215°C, E_a = 57.2 kJ/mol, reaction rate 8.40 × 10^?10 mol/(sec?m²) at 210°C. T₅₀ and T₉₀: the temperature of 50% and 90% toluene conversion; E_a: apparent activation energy) and possess high tolerance against 2.0 vol.% water vapor. Results reveal that the increased acidic sites of the MnO₂ sample can enhance the adsorption of gaseous toluene, and the mobility of oxygen species and the content of reactive oxygen species in the catalyst are significantly improved due to the formed oxygen vacancy. Thus these two factors result in excellent catalytic performance for toluene oxidation combining with the weak CO₂ adsorption ability.     

Pd/silicalite-1: An highly active catalyst for the oxidative removal of toluene

Catalytic combustion is thought as an efficient and economic pathway to remove volatile organic compounds, and its critical issue is the development of high-performance catalytic materials. In this work, we used the in situ synthesis method to prepare the silicalite-1 (S-1)-supported Pd nanoparticles (NPs). It is found that the as-prepared catalysts displayed a hexagonal prism morphology and a surface area of 390−440 m²/g. The sample (0.28Pd/S-1-H) derived after reduction at 500°C in 10 vol% H₂ showed the best catalytic activity for toluene combustion (T_50% = 180°C and T_90% = 189°C at a space velocity of 40,000 mL/(g·hr), turnover frequency (TOF_Pd) at 160°C = 3.46 × 10⁻³ sec⁻¹, and specific reaction rate at 160°C = 63.8 µmol/(g_Pd·sec)), with the apparent activation energy (41 kJ/mol) obtained over the best-performing 0.28Pd/S-1-H sample being much lower than those (51−70 kJ/mol) obtained over the other samples (0.28Pd/S-1-A derived from calcination at 500°C in air, 0.26Pd/S-1-im derived from the impregnation route, and 0.27Pd/ZSM-5-H prepared after reduction at 500°C in 10 vol% H₂). Furthermore, the 0.28Pd/S-1-H sample possessed good thermal stability and its partial deactivation due to CO₂ or H₂O introduction was reversible, but SO₂ addition resulted in an irreversible deactivation. The possible pathways of toluene oxidation over 0.28Pd/S-1-H was toluene → p-methylbenzoquinone → maleic anhydride, benzoic acid, benzaldehyde → carbon dioxide and water. We conclude that the good dispersion of Pd NPs, high adsorption oxygen species concentration, large toluene adsorption capacity, strong acidity, and more Pd⁰ species were responsible for the good catalytic performance of 0.28Pd/S-1-H.     

Hydrothermal-treated Pt/Al2O3 as an excellent catalyst for toluene total oxidation

The preparation of highly active supported noble metal catalysts with a low noble metal loading has always been the ultimate goal of researchers working on catalysis. Hydrothermally treated Pt/Al₂O₃ (Pt/Al₂O₃-H) exhibits better catalytic activity than that (Pt/Al₂O₃-C) treated via the conventional calcination approach. At the high space velocity of 100,000 mL/(g∙hr), the temperature that correspond to 50% toluene conversion (T₅₀) of Pt/Al₂O₃-H is 115°C lower than that of Pt/Al₂O₃-C, and the turnover frequency (TOF) value can reach 0.0756 sec⁻¹. The mechanism by which the hydrothermal approach enhances Pt/Al₂O₃ activity has been investigated. The structure associated with the high catalytic activity of Pt nanoparticles (NPs) can be retained via hydrothermal treatment. Furthermore, the support is transformed to AlO(OH) with numerous surface hydroxyl groups, which in turn can facilitate the adsorption of toluene. And the synergistic effects of Pt NPs and AlO(OH) increases the contents of Pt in oxidation state and active oxygen, which are beneficial for toluene oxidation.     

Activation of sulfite by metal-organic framework-derived cobalt nanoparticles for organic pollutants removal

Sulfite (SO₃²⁻) activation is one of the most potential sulfate-radical-based advanced oxidation processes, and the catalysts with high efficiency and low-cost are greatly desired. In this study, the cobalt nanoparticles embedded in nitrogen-doped graphite layers (Co@NC), were used to activate SO₃²⁻ for removal of Methyl Orange in aqueous solution. The Co@NC catalysts were synthesized via pyrolysis of Co²⁺-based metal-organic framework (Co-MOF), where CoO was firstly formed at 400℃ and then partially reduced to Co nanoparticles embedded in carbon layers at 800℃. The Co@NC catalysts were more active than other cobalt-based catalysts such as Co²⁺, Co₃O₄ and CoFe₂O₄, due to the synergistic effect of metallic Co and Co_xO_y. A series of chain reaction between Co species and dissolved oxygen was established, with the production and transformation of SO₃^•−, SO₅²⁻, and subsequent active radicals SO₄^•− and HO•. In addition, HCO₃⁻ was found to play a key role in the reaction by complexing with Co species on the surface of the catalysts. The results provide a new promising strategy by using the Co@NC catalyst for SO₃²⁻ oxidation to promote organic pollutants degradation.     

Competing pathways of cresol formation in toluene photooxidation: OH-toluene adducts react with NO2 or with O2?

Methyl-hydroxy-cyclohexadienyl radicals (OTAs) are the key products of the photooxidation of toluene, with implications for the fate of toluene. Hence, we investigated the photooxidation mechanisms and kinetics of three main OTAs (o-OTA, m-OTA, and p-OTA) with NO₂ using quantum chemical calculations as well as the fate of OTAs under the different concentration ratios of NO₂ and O₂. The mechanism results show that the pathway of H-abstraction by NO₂ to anti-HONO (anti-H-abstraction) is more favorable than the syn-H-abstraction pathway, because the strong interaction between OTAs and NO₂ is formed in the transition states of the anti-H-abstraction pathways. The branching ratios of the anti-H-abstraction pathways are more than 99% in the temperature range of 216−298 K. The total rate constant of the OTA-NO₂ reaction is 9.9 × 10⁻¹² cm³/(molecule∙sec) at 298 K, which is contributed about 90% by o-OTA + NO₂, and the main products are o-cresol and anti-HONO. The half-lives of the OTA-NO₂ reaction in some polluted areas of China are 35 times longer than those of the OTA-O₂ reaction. In the atmosphere, the NO₂- and O₂- initiated reactions of OTAs have the same ability to form cresols as [NO₂] is up to 142.1 ppmV, which is impossible to achieve. It implies that under the experimental condition, the [NO₂]/[O₂] should be controlled to be less than 7.8 × 10⁻⁵ to simulate real atmospheric oxidation of toluene. Our results reveal that for the photooxidation of toluene, the yield of cresol is not affected by the concentration of NO₂ under the atmospheric environment.     

Simultaneous removal of gaseous CO and elemental mercury over Cu-Co modified activated coke at low temperature

Cu-Co multiple-oxides modified on HNO₃-pretreated activated coke (AC_N) were optimized for the simultaneous removal of gaseous CO and elemental mercury (Hg⁰) at low temperature (< 200 °C). It was found that 2%CuOx-10%CoOx/AC_N catalyst calcined at 400°C resulted in the coexistence of complex oxides including CuO, Cu₂O, Co₃O₄, Co₂O₃ and CoO phases, which might be good for the simultaneous catalytic oxidation of CO by Co-species and removal of Hg⁰ by Cu-species, benefiting from the synergistic catalysis during the electro-interaction between Co and Cu cations (CoO ? Co₃O₄ and Cu₂O ? CuO). The catalysis removal of CO oxidation was obviously depended on the reaction temperature obtaining 94.7% at 200 °C, while no obvious promoting effect on the Hg⁰ removal (68.3%-78.7%). These materials were very substitute for the removal of CO and Hg° from the flue gas with the conditions of 8–20 vol.% O₂ and flue-gas temperature below 200 °C. The removal of Hg° followed the combination processes of adsorption and catalytic oxidation reaction via Langmuir-Hinshelwood mechanism, while the catalysis of CO abided by the Mars-van Krevelen mechanism with lattice oxygen species.     

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C₅ aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18)  ×  10⁻¹⁰ and (2.07 ± 0.14)  ×  10⁻¹⁰ cm³/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C₅ aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C₅ aldehyde compounds.     

Promotional catalytic activity and reaction mechanism of Ag-modified Ce0.6Zr0.4O2 catalyst for catalytic oxidation of ammonia

Ce_1-xZr_xO₂ composite oxides (molar, x = 0-1.0, interval of 0.2) were prepared by a cetyltrimethylammonium bromide-assisted precipitation method. The enhancement of silver-species modification and catalytic mechanism of adsorption-transformation-desorption process were investigated over the Ag-impregnated catalysts for low-temperature selective catalytic oxidation of ammonia (NH₃-SCO). The optimal 5 wt.% Ag/Ce_0.6Zr_0.4O₂ catalyst presented good NH₃-SCO performance with >90% NH₃ conversion at temperature (T) ≥ 250°C and 89% N₂ selectivity. Despite the irregular block shape and underdeveloped specific surface area (∼60 m²/g), the naked and Ag-modified Ce_0.6Zr_0.4O₂ solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer (SEM-EDS) (mapping), N₂ adsorption-desorption test and X-ray diffraction (XRD). H₂ temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO₂ reducibility and synergistic Ag⁰/Ag⁺ and Ce⁴⁺/Ce³⁺ redox cycles. Besides, Ag⁺/Ag₂O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia. NH₃-temperature programmed desorption (NH₃-TPD) showed more adsorption-desorption capacity to ammonia were provided by physical, weak- and medium-strong acid sites. Diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments revealed the activation of ammonia might be the control step of NH₃-SCO procedure, during which NH₃ dehydrogenation derived from NH_x-species and also internal selective catalytic reduction (i-SCR) reactions were proposed.     

Comparison of UV and UV-LED activated sodium percarbonate for the degradation of O-desmethylvenlafaxine

As an active metabolite of venlafaxine and emerging antidepressant, O-desmethylvenlafaxine (ODVEN) was widely detected in different water bodies, which caused potential harm to human health and environmental safety. In this study, the comparative work on the ODVEN degradation by UV (254 nm) and UV-LED (275 nm) activated sodium percarbonate (SPC) systems was systematically performed. The higher removal rate of ODVEN can be achieved under UV-LED direct photolysis (14.99%) than UV direct photolysis (4.57%) due to the higher values of photolysis coefficient at the wavelength 275 nm. Significant synergistic effects were observed in the UV/SPC (80.38%) and UV-LED/SPC (53.57%) systems and the former exhibited better performance for the elimination of ODVEN. The degradation of ODVEN all followed the pseudo-first-order kinetics well in these processes, and the pseudo-first-order rate constant (k_obs) increased with increasing SPC concentration. Radicals quenching experiments demonstrated that both ·OH and CO₃·⁻ were involved in the degradation of ODVEN and the second-order rate constant of ODVEN with CO₃·⁻ (1.58 × 10⁸ (mol/L)⁻¹ sec⁻¹) was reported for the first time based on competitive kinetic method. The introduction of HA, Cl⁻, NO₃⁻ and HCO₃⁻ inhibited the ODVEN degradation to varying degrees in the both processes. According to quantum chemical calculation, radical addition at the ortho-position of the phenolic hydroxyl group was confirmed to be the main reaction pathways for the oxidation of ODVEN by ·OH. In addition, the oxidation of ODVEN may involve the demethylation, H-abstraction, OH-addition and C-N bond cleavage. Eventually, the UV-LED/SPC process was considered to be more cost-effective compared to the UV/SPC process, although the UV/SPC process possessed a higher removal rate of ODVEN.     

Enhanced catalytic complete oxidation of 1,2-dichloroethane over mesoporous transition metal-doped γ-Al2O3

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℃. The catalytic activity and product selectivity were strongly dependent on the presence and the type of dopant ion. While Cu²⁺- and Cr³⁺-containing catalysts showed 100% conversion at 300℃ and 350℃, 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.     

国际化学危险品分类体系简介

介绍了当前国际化学危险品的各种分类体系,对比了GHS与TDG、EU_CLP、DOT、WHMIS等对化学危险品的具体分类。有助于GHS的理解与掌握,全面推进GHS在我国的实施。     

土壤整体质量的生态毒性评价

土壤样品采自沈阳西部污灌区 .进行了污染物 (重金属和矿物油 )含量分析和生态毒性试验 .重金属采用原子吸收分光光度仪测定 ,矿物油采用紫外分光光度计测定 .生态毒性试验分别参照国际标准组织 (ISO)和OECD指南 ,进行了植物毒性试验、蚯蚓毒性试验和蚕豆根尖微核试验 .植物试验以小麦种子发芽根伸长抑制率为试验终点 ,试验周期50h ,蚯蚓毒性试验以蚯蚓死亡率、体重增长抑制率为试验终点 ,试验周期28d .土壤中矿物油含量在145mg/kg～1121mg/kg ,重金属Cd为0.34mg/kg～1.81mg/kg .土壤对植物和蚯蚓显示不同程度的毒性效应 ,土壤的蚕豆根尖微核率明显高于对照 .种子发芽根伸长抑制率为2.0%至-35.1% ,蚯蚓死亡率为0%～40%.体重增长抑制率由14d的-2.3%～-19.4%在28d增加到-2.1%～10.7% ,蚕豆根尖微核率最高达6.62/100.研究表明 ,土壤中的污染物积累较低 ,但具有明显的生态毒性 .     

多目标规划在预测区域总产值-排污-水质协调解中的应用研究

以某区域水环境－经济系统为研究实例，寻求值－排污－水质综合协调解方法，寻求净收益最大时的总体规划方案。建立目标参数规划模型，寻求不同生产规模条件下的产值－排污－水质协调解，又探讨了水环境标准约束下的某化工区废水治理费用的计算方法，提出了以供决策者选择的方案。     

滇池富营养化特性评价

介绍了滇池水质状况,对滇池富营养化特性进行了分析和评价,并提出了对策.     

生态保护地协同管控成效评估

分区分类管理是我国生态保护的重要管控制度,生态保护地是事关国家生态安全的关键区域,开展生态保护地保护成效评估及不同类型生态保护地之间的协同管控成效评估具有重要意义。以吉林省自然保护地和重点生态功能区等生态保护地(即禁止开发区和限制开发区)为研究对象,以重要生态空间、植被生态、水源涵养功能为主要内容,基于"禁止开发区—限制开发区—省域"的管控梯度差异,评估分析了生态保护地的协同管控成效。结果表明:(1)从重要生态空间协同管控成效来看,自然保护地的重要生态空间面积比例最高、人类活动干扰指数最低,这与生态保护管控严格程度呈现很好地正相关。但是1980—2015年间重要生态空间面积比例均有所减少,减少幅度与管控严格程度没有表现出正相关。(2)从植被生态协同管控成效来看,植被覆盖总体呈现出自东向西逐步降低的特点,与东部分布有重点生态功能区和森林类自然保护区、西部分布较多的湿地类自然保护地的空间特征一致。但是,由于湿地及水域类型自然保护地面积占比较高,且分布在吉林西部草原和平原区的面积比例较高,自然保护地的年际变化较大、且植被覆盖稳定度低于重点生态功能区。(3)从水源涵养功能协同管控成效来看,水源...     

乌海市城区环境噪声现状分析

对乌海市《城市区域环境噪声标准》适用区域进行了划分,以乌海市2011年城区环境噪声监测统计数据为基础,分析了乌海市暴露在不同等效声级下的城区面积分布状况和达标情况。     

后勤装备防腐涂层加速试验环境谱研究

结合后勤装备服役特点,综合考虑亚热带沿海地区湿热、紫外光照、盐雾等主要腐蚀因素的影响,建立了适用于后勤装备表面涂层的加速试验环境谱,给出了各环境块的具体确定方法,并且提出了建立加速谱与装备实际使用环境的当量加速关系的方法。为后勤装备外露关键部位涂层使用寿命评定、涂层有效性检验和腐蚀修理方案制定提供了重要的依据。     

烟气脱硫副产物的综合利用

通过分析烟气脱硫石膏的性能 ,介绍了脱硫石膏的利用情况和研究进展 ,利用脱硫石膏生产建筑材料 ,如 β石膏和α石膏的工艺日臻成熟 ,利用脱硫石膏生产水泥辅料已进入工业化 ,而利用脱硫石膏生产充填尾砂胶结剂已经完成试验阶段 ,脱硫石膏在农业上也有很广泛的用途。     

氯苯类化合物的生物降解

经过2个月的驯化,从某染料厂和某毛纺厂活性污泥中分离出能够生长于1,4-二氯苯、1,2,4-三氯苯和六氯苯的4种微生物.通过测定该混合菌降解氯苯类化合物过程中的累积好氧量、微生物生长曲线及降解产物Cl^-的释放,证明在好氧条件下该混合菌能够以1,4二氯苯和1,2,4-三氯苯为唯一碳源和能源,降解产物Cl^-浓度的变化与微生物生长周期有关.通过好氧振荡瓶培养法测得3种氯苯的生物降解顺序为:1,4-二氯苯[356.7μg/(L·d)]>1,2,4-三氯苯[110.4μg/(L·d)]>六氯苯[～6μg/(L·d)],说明氯取代数越多,氯苯类化合物越难被好氧降解.     

哈尔滨松北区城市湿地的生态安全分析

以哈尔滨松北区城市湿地为研究对象,选择10个指标,采用因子分析法和聚类分析法,研究了松花江发生污染事故前后城市湿地的生态安全状况.结果表明:发生污染前哈尔滨松北区城市湿地东区的生态安全程度最高,发生污染后中区的生态安全程度最低;西区的抗干扰能力较差.各主因子中以水因子的下降幅度最大,说明水污染直接影响了哈尔滨松北区城市湿地的生态安全.最后有针对性地提出了哈尔滨松北区城市湿地的生态安全对策.