甲醛在TiO_2颗粒物表面的非均相反应

使用漫反射红外傅里叶变换光谱(DRIFTS)原位反应器研究了甲醛在TiO2颗粒物表面的非均相反应,结合离子色谱定量分析了反应的主要产物甲酸盐,甲酸盐是由中间产物二氧亚甲基进一步氧化生成.研究了温度和紫外光照对反应的影响,结果表明升高温度和紫外光照可提高反应速率,推测了暗反应和紫外光照下甲醛在TiO2表面的非均相反应机制.结果表明常温下甲醛在TiO2颗粒物表面的反应级数接近2级,初始反应摄取系数为(0.5～5)×10-8([HCHO]:1×1013～2×1014molecule·cm-3),是甲醛浓度的一次函数,同时测定了表观活化能.     

SO2与Fe2O3生成Fe（Ⅱ）（aq）和硫酸盐的复相反应机理

使用DR IFTS,XPS,HPLC和IC考察了常温、常压和氧气存在下SO2与Fe2O3的复相反应,结果表明,SO2在Fe2O3表面的反应活性与Fe2O3表面含水量密切相关,表面含水量增加有助于Fe(Ⅱ)(aq)和硫酸盐的生成.室温下(T=291 K,相对湿度68%),每毫克Fe2O3在30 m in内可消耗53.6μg SO2,生成12.6 ngFe(Ⅱ)(aq)和56.2μg SO42-.反应产物SO42-的浓度比Fe(Ⅱ)(aq)的浓度高3个数量级,表明在生成硫酸盐的复相反应中铁对SO2氧化具有非常高的催化活性.提出了Fe(Ⅱ)(aq)和硫酸盐的生成机理.     

SO_2在TiO_2颗粒物表面的非均相反应

使用漫反射红外傅里叶变换光谱(DRIFTS)原位反应器研究了SO2在TiO2颗粒物表面的非均相反应.研究了氧气浓度、相对湿度(RH)及紫外光光照对反应的影响.结果表明,SO2在TiO2颗粒物上可转化为亚硫酸盐或被氧化为硫酸盐.水汽或者紫外光照可促进SO2在TiO2颗粒物表面的非均相氧化反应,在两者都存在的情况下,对促进硫酸盐的生成有协同效应.在干态无光照条件下和一定湿度(RH=40%)紫外光照条件下,以硫酸盐的生成来计算,SO2在TiO2颗粒物表面的反应级数分别为二级和一级;反应摄取系数γBET分别为1.94×10-6和1.35×10-5.TiO2颗粒物表面的羟基参与了反应,在紫外光照下表面生成的活性氧物种在反应中起重要作用.     

NO_2和HSO反应的机理及动力学研究

本文采用CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ方法构建了NO_2+HSO反应的单、三重态势能面,并对主通道速率常数进行了计算。结果表明,该反应在单[R1(HN(O)O+~1SO)、R2 (cis-HONO+~1SO)和R3 (trans-HONO+~1SO)]、三重态[R6 (HN (O)O+~3SO)、R7 (cis-HONO+~3SO)和R8 (trans-HONO+~3SO)]均存在3条抽氢反应通道,在单[R4(NO+HS(O)O)和R5(H+SO_2+NO)]、三重态[R9(HS(O) O+NO)和R10(H+SO_2+NO)]均存在两条抽氧通道,其中单重态抽氢通道R2(cis-HONO+~1SO)是NO_2+HSO反应主通道。利用传统过渡态理论(TST)并结合Wigner校正,计算了上述10条通道在200K～1000K温度范围内的速率常数。计算结果表明,NO_2+HSO反应主通道在298K时的速率常数(7.78×10-13cm3·molecule-1·s-1)与实验值(9.6×10-12cm3·molecule-1·s-1)相近。此外,水分子影响主通道R2(cis-HONO+~1SO)经历了NO_2+H_2O…HSO和NO_2+H_2O…HSO(HSO+NO_2…H_2O)两条反应通道,且两条通道的能垒分别比R2升高了49.97和20.67 kcal·mol-1,说明在实际大气环境中水分子对NO_2+HSO反应几乎没有影响。     

稀土氧化物的掺杂量对SO42-/ZrO2/Al2O3催化剂催化性能的影响

采用浸渍-沉淀法制备负载型纳米ZrO2/Al2O3,复合载体,并将不同量的氧化钕、氧化镨掺杂到负载型纳米ZrO2/Al2O3复合载体中以调变ZrO2的表面性能.同时以此复合载体负载SO42-制备SO42-/REXOY-ZrO2/Al2O3催化剂.运用XHD、BET、NH3-TPD、原位红外技术对催化剂的晶相结构、比表面积、孔径分布、酸中心种类等进行表征,并以α-蒎烯异构化为探针反应考察了催化剂的活性.结果表明,适量的稀土掺杂会增加催化剂的比表面积,降低ZrO2的粒径,从而增加催化剂表面SO42-的配位吸附量,提高表面酸中心数和酸强度,增强催化剂的活性.     

稀土氧化物掺杂对SO4^2-／ZrO2／Al2O3催化剂催化性能的影响

采用浸溃-沉淀法在具有较大比表面积的Al2O3上直接合成纳米ZrO2制备负载型纳米ZrO2/Al2O3复合载体,并将氧化钪、氧化钕、氧化错等稀土氧化物(RExOy)分别掺杂到负载型纳米ZrO2/Al2O3复合载体中以改善ZrO2的表面性能.同时以此复合载体负载SO42-制备SO42-/RExOy-ZrO2/Al2O3催化剂.运用XRD,BET,NH3-TPD,原位红外等技术与方法对催化剂的晶相结构、比表面积、孔径分布、酸中心种类等进行表征,并以α-蒎烯异构化反应为探针考察了催化剂的催化性能.结果表明,掺杂的稀土氧化物没有改变ZrO2的晶相结构,但ZrO2粒度有所减小,催化剂的比表面积增加,同时稀土氧化物的存在还会改变催化剂表面SO42-的配位方式,提高表面酸中心数和酸强度,增强催化剂的活性.催化剂的孔结构对选择性有较大的影响.     

MaterialSO2与Fe2O3生成Fe(Ⅱ)(aq)和硫酸盐的复相反应机理

使用DRIFTS, XPS, HPLC和IC考察了常温、常压和氧气存在下SO2与Fe2O3的复相反应, 结果表明, SO2在Fe2O3表面的反应活性与Fe2O3表面含水量密切相关, 表面含水量增加有助于Fe(Ⅱ)(aq)和硫酸盐的生成.室温下(T=291 K, 相对湿度68%), 每毫克Fe2O3在30 min内可消耗53.6 μg SO2, 生成12.6 ng Fe(Ⅱ)(aq)和56.2 μg SO2-4.反应产物 SO2-4的浓度比Fe(Ⅱ)(aq)的浓度高3个数量级, 表明在生成硫酸盐的复相反应中铁对SO2氧化具有非常高的催化活性.提出了Fe(Ⅱ)(aq) 和硫酸盐的生成机理.     

海盐颗粒物表面的NO_2非均相反应

为了深入理解沿海城市大气环境中NO2和海盐颗粒物的非均相反应规律,本研究使用漫反射红外傅立叶变换光谱(DRIFTS)比较研究了0%和20%相对湿度(relative humidty,RH)下NO2在湿海盐颗粒物表面的非均相反应.动力学测量表明硝酸盐的生成对NO2是二级反应,并且0%和20%相对湿度条件下,NO2分子浓度为1.96×1015molcules·cm-3时,反应增长阶段反应摄取系数分别为(5.51±0.19)×10-7和1.26×10-6.结果还显示相对湿度在30%以下时,海盐表面MgCl2·6H2O、CaCl2·2H2O所在点位通过释放结合水和吸附水汽,在海盐表面形成液态水的斑点,增强了反应持续能力.因此氯化钠表面非均相反应的研究可能会低估海盐颗粒物的非均相反应活性.     

SO2在Fe2O3颗粒表面不同温度下非均相反应的实验模拟

使用漫反射Fourier变换红外光谱(DFTIRS)、离子色谱(IC)及透射电子显微镜(TEM)对不同温度条件下SO2在α-Fe2O3颗粒表面的非均相反应过程进行实验模拟和监测,并分析了反应剧烈波段(8.7μm)的产物硫酸盐以及颗粒吸收和后向散射光学系数的变化.结果表明,在15-45℃内,硫酸盐生成量、生成速率以及吸收系数、后向散射系数都随反应温度的升高而呈现先增加后减少的趋势;同一反应温度下,硫酸盐生成速率随时间呈现先增大后减小,最后逐渐趋于稳定的演变;光学系数变化与硫酸盐生成量之间存在较好的指数关系.在当前全球气候变暖背景下,研究结果将对深入了解真实大气中SO2与矿尘非均相反应造成的气溶胶光学特性演变,以及定量评估其辐射强迫影响具有一定意义.     

甲醛在α-Al2O3颗粒物表面的非均相反应研究

使用漫反射傅里叶变换红外光谱(DRIFTS)原位反应器研究了273~333 K下甲醛与α-Al2O3颗粒物表面的非均相反应. 结果表明, 甲醛在α-Al2O3颗粒物表面生成产物主要为甲酸盐、二氧亚甲基以及少量多聚甲醛和吸附态甲醛, 甲酸盐是由中间产物二氧亚甲基进一步氧化生成的. 在293 K下, 甲醛在α-Al2O3颗粒物表面的反应级数为0.81±0.05, 以样品池几何面积计算的初始摄取系数γ0GEO为(2.3±0.5)×10-5, 以颗粒物BET面积计算的初始摄取系数γ0BET为(9.4±1.7)×10-9, 表观活化能为33.5 kJ/mol.     

Heterogeneous reactions of sulfur dioxide on typical mineral particles

The heterogeneous reaction of SO2 on Al2O3, CaO, TiO2, MgO, FeOOH, Fe2O3, MnO2, and SiO2, as well as authentic aerosol sample, was investigated by using a White Cell coupled with in situ-FTIR and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). Simultaneous observations of reactants and products were performed to obtain full information on the mechanism and kinetics of the reactions. SO2 was irreversibly adsorbed to form surface sulfite (SO3(2-)), bisulfite (HSO3(-)), and sulfate (SO4(2-)). The reactivity order of these particles is the following: FeOOH >Al2O3 > mixture > MgO > Fe2O3 > SiO2. Field-collected aerosol showed significant activity for the oxidation of SO2. The uptake coefficient of SO2 on Al2O3 with different acidity varied in the order of basic Al2O3 > neutral Al2O3 > acidic Al2O3. The surface-active oxygen and hydroxyl might be the key factors for the conversion of SO2 to SO4(2-). The faster reaction rate could be achieved with greater surface area on particles with the same mass. On the basis of the same surface area Fe2O3 could be most reactive in the reaction with SO2 compared with all other particles. The apparent rate constants were determined to be 1.35 x 10(-2) and 9.4 x 10(-3) for uptake on Al2O3 and MgO, respectively, which are the same as the results of other scientists.     

Synergistic reaction between SO2 and NO2 on mineral oxides: a potential formation pathway of sulfate aerosol

Sulfate is one of the most important aerosols in the atmosphere. A new sulfate formation pathway via synergistic reactions between SO(2) and NO(2) on mineral oxides was proposed. The heterogeneous reactions of SO(2) and NO(2) on CaO, α-Fe(2)O(3), ZnO, MgO, α-Al(2)O(3), TiO(2), and SiO(2) were investigated by in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) at ambient temperature. Formation of sulfate from adsorbed SO(2) was promoted by the coexisting NO(2), while surface N(2)O(4) was observed as the crucial oxidant for the oxidation of surface sulfite. This process was significantly promoted by the presence of O(2). The synergistic effect between SO(2) and NO(2) was not observed on other mineral particles (such as CaCO(3) and CaSO(4)) probably due to the lack of the surface reactive oxygen sites. The synergistic reaction between SO(2) and NO(2) on mineral oxides resulted in the formation of internal mixtures of sulfate, nitrate, and mineral oxides. The change of mixture state will affect the physicochemical properties of atmospheric particles and therefore further influence their environmental and climate effects.     

NaCl与Fe2O3混合物对SO2的有效吸收

采用DRIFTS和XPS等方法研究了SO2在NaCl和α-Fe2O3混合物表面的复相反应, 并计算了反应的吸附常数. 结果表明, 反应生成物主要为硫酸盐、硫酸氢盐以及少量的亚硫酸(氢)盐; SO2与NaCl和α-Fe2O3混合物的反应符合零级反应动力学规律; NaCl的含量对反应有影响, 随着混合物中NaCl含量的增加, BET吸附常数呈现先上升而后再下降的变化规律, 当NaCl的质量分数达到70%左右时, BET吸附常数达到最大(4.62×10-6), 是纯α-Fe2O3(5.72×10-7)的8.08倍; 反应生成的FeCl2-SO3-中间体作为SO2的储存库, 促进了更多的硫酸盐生成.     

Mechanism of heterogeneous oxidation of carbonyl sulfide on Al2O3: an in situ diffuse reflectance infrared fourier transform spectroscopy investigation

Heterogeneous reaction of carbonyl sulfide (OCS) on the surface of different types of alumina (Al(2)O(3)) at 298 K was investigated in a closed system and a flowed system using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The effects of calcination temperature of the Al(2)O(3) on its catalyzed reactivity were studied. The crystal structure and surface area of the Al(2)O(3) were characterized using X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method. This paper revealed that adsorbed OCS could be catalytically oxidized on the surface of Al(2)O(3) to form gas-phase CO(2) and surface hydrogen carbonate (HCO(3)(-)) and sulfate (SO(4)(2-)) species at 298 K. The surface hydroxyl (OH) species on the Al(2)O(3) had been found to be the key reactant for the heterogeneous oxidation of OCS. Furthermore, the surface hydrogen thiocarbonate (HSCO(2)(-)) species, an intermediate formed in the reaction of OCS with OH, can be observed on the thermal-treated Al(2)O(3). On the basis of these results, the reaction mechanism of heterogeneous oxidation of OCS on Al(2)O(3) is discussed.     

Preparation of mesostructured barium sulfate with high surface area by dispersion method and its characterization

The spherical and cubic mesoporous BaSO(4) particles with high surface area were successfully produced via one-step process through precipitation reaction in aqueous solution of Ba(OH)(2) and H(2)SO(4) with ethylene glycol (n-HOCH(2)CH(2)OH) as a modifying agent. The BaSO(4) nanomaterial revealed that the high surface area and the mesoporous was stable up to 400 degrees C. Agglomerate mesoporous barium sulfate nanomaterials were obtained by the reaction of Ba(2+) and SO(2-)(4) with ethylene glycol aqueous solution. The ethylene glycol was used to control the BaSO(4) particle size and to modify the surface property of the particles produced from the precipitation. The dried and calcined mesoporous BaSO(4) nanomaterials were characterized by X-ray diffraction (XRD), BET surface area and N(2) adsorption-desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared resonance (FTIR) and thermogravimetric analysis (TGA). The as-prepared mesoporous dried BaSO(4) possesses a high BET surface area of 91.56 m(2) g(-1), pore volume of 0.188 cm(3) g(-1) (P/P(0)=0.9849) and pore size of 8.22 nm. The SEM indicates that the morphology of BaSO(4) nanomaterial shows shell like particles up to 400 degrees C, after that there is drastically change in the material due to agglomeration. Synthesis of mesoporous BaSO(4) nanomaterial is of significant importance for both sulphuric acid decomposition and oxidation of methane to methanol.     

S-oxygenation of thiocarbamides IV: Kinetics of oxidation of tetramethylthiourea by aqueous bromine and acidic bromate

The kinetics and mechanism of oxidation of tetramethylthiourea (TTTU) by bromine and acidic bromate has been studied in aqueous media. The kinetics of reaction of bromate with TTTU was characterized by an induction period followed by formation of bromine. The reaction stoichiometry was determined to be 4BrO(3)(-) + 3(R)(2)C═S + 3H(2)O → 4Br(-) + 3(R)(2)C═O + 3SO(4)(2-) + 6H(+). For the reaction of TTTU with bromine, a 4:1 stoichiometric ratio of bromine to TTTU was obtained with 4Br(2) + (R)(2)C═S + 5H(2)O → 8Br(-) + SO(4)(2-) + (R)(2)C═O + 10H(+). The oxidation pathway went through the formation of tetramethythiourea sulfenic acid as evidenced by the electrospray ionization mass spectrum of the dynamic reaction solution. This S-oxide was then oxidized to produce tetramethylurea and sulfate as final products of reaction. There was no evidence for the formation of the sulfinic and sulfonic acids in the oxidation pathway. This implicates the sulfoxylate anion as a precursor to formation of sulfate. In aerobic conditions, this anion can unleash a series of genotoxic reactive oxygen species which can explain TTTU's observed toxicity. A bimolecular rate constant of 5.33 ± 0.32 M(-1) s(-1) for the direct reaction of TTTU with bromine was obtained.     

Kinetics of the sulfur oxidation on palladium: a combined in situ x-ray photoelectron spectroscopy and density-functional study

We studied the reaction kinetics of sulfur oxidation on the Pd(100) surface by in situ high resolution x-ray photoelectron spectroscopy and ab initio density functional calculations. Isothermal oxidation experiments were performed between 400 and 500 K for small amounts (~0.02 ML) of preadsorbed sulfur, with oxygen in large excess. The main stable reaction intermediate found on the surface is SO(4), with SO(2) and SO(3) being only present in minor amounts. Density-functional calculations depict a reaction energy profile, which explains the sequential formation of SO(2), SO(3), and eventually SO(4), also highlighting that the in-plane formation of SO from S and O adatoms is the rate limiting step. From the experiments we determined the activation energy of the rate limiting step to be 85 ± 6 kJ mol(-1) by Arrhenius analysis, matching the calculated endothermicity of the SO formation.     

SO_2在ZnO颗粒物表面的非均相反应

使用原位漫反射红外傅里叶变换光谱(DRIFTS)研究了SO2在ZnO颗粒物表面的非均相反应,考察了相对湿度(RH)及紫外光光照对反应的影响.结果表明:无紫外光光照条件下,SO2在ZnO颗粒物表面反应的主要产物为亚硫酸盐,RH与生成的亚硫酸盐量呈负相关关系;有紫外光光照条件下,SO2在ZnO颗粒物表面反应的主要产物为亚硫酸盐和硫酸盐,随着相对湿度和紫外光照强度的增加,亚硫酸盐向硫酸盐转化.光照和水汽对SO2在ZnO颗粒物上的氧化反应起到协同促进作用.以亚硫酸盐生成量计算,干态无光条件下反应对SO2的级数为1.6,接近二级反应;在RH为40%且紫外光光照条件下,反应对SO2的级数为0.91,接近一级反应;使用BET比表面积作为反应有效面积,反应初始摄取系数在干态无光照条件和RH=40%且紫外光照条件下分别为4.87×10-6和2.29×10-5.