Gas phase catalytic partial oxidation of toluene in a microchannel reactor

Gas phase partial oxidation of toluene over V/Ti oxide catalysts has been successfully performed in a microchannel reactor, which provides very good mass and heat transfer conditions. With the elimination of hot spots, which are known as the most negative factors for partial oxidation of hydrocarbons, steady and uniform reaction conditions can be achieved in the catalyst bed by using, the microreactor. Since the best performance of the catalysts might be exploited, the selectivity of partial oxidation products of toluene has remarkably increased compared to the traditional packed fixed-bed reactor, even without the bother of modifying the catalysts, diluting the reactants or catalysts with inert contents to avoid hot spots or improve the diffusion and mixing. Furthermore, in virtue of its inherent safety features, when using pure oxygen as oxidant, the reactions were handled safety within the explosion limits in the microreactor. With TiO2 carried V2O5 as catalysts, the total selectivity of benzaldehyde and benzoic acid reaches around 60%, and the toluene conversion is about 10%. The conversion can go up without violent decline of selectivity, unlike most fixed bed reactors. Space time yield of 3.12 kg h(-1) L-1 calculated on the basis of the channel volume has been achieved. The influence of operating conditions has been investigated in detail in the microreactor. (c) 2005 Elsevier B.V. All rights reserved.

Fluorescence pH probe based on microstructured polymer optical fiber

A kind of optical pH sensor was demonstrated that is based on a pH-sensitive fluorescence dye-doped (eosin) cellulose acetate (CA) thin-film modified microstructured polymer optical fiber (MPOF). It was obtained by directly inhaling an eosin-CA-acetic acid mixed solution into array holes in a MPOF and then removing the solvent (acetic acid). The sensing film showed different fluorescence intensities to different pH solutions in a pH range of 2.5-4.5. Furthermore, the pH response range could be tailored through doping a surfactant, hexadecyl trimethyl ammonium bromide (CTAB), in the sensing film. (c) 2007 Optical Society of America.

光导纤维pH传感器的光化学pH敏感高分子膜及pH响应性能

pH指示剂在高分子载体上的固定化研究是应光导纤维pH传感器的发展要求而发展起来的新的研究领域。pH指示剂在高分子固态载体上的固定直接决定着光导纤维pH传感器的灵敏度、响应时间、寿命等性能。迄今，吸附、包埋和化学键合三利，固定方法已得到广泛应用。吸附法与包埋法简单易行，但因指示剂易于逸出而无法保证试剂相的使用稳定性及寿命；化学键合法目前仅限于对含氨基等高反应活性基团的指示剂固定。另外，这三种固定技术均存在试剂相与分析对象呈现固／液两相分离的问题，它严重制约了传感器响应性能，成为pH指示剂固定技术发展的“瓶颈”。改善、发展与寻找新的指示剂／载体固定配对体系已成为本领域的研究焦点。本论文针对上述问题，开拓与发展了一系列指示剂固定于固态高分子载体上的新体系。（一）首先开拓与发展了酚红／交联聚乙烯醇与邻甲酚红／交联聚乙烯醇固定对的新体系。在酸性条件下，以甲醛做交联剂，通过在玻璃板上倾涂聚乙烯醇甲醛的凝胶溶液制备了高亲水性的交联聚乙烯醇载体膜；然后采用接枝共聚反应将丙烯酞胺单体与通过酸碱反应接枝有酚红或邻甲酚红的丙烯酞胺混合物接枝固定到交联聚乙烯醇薄膜上，首次将不含氨基的酚红、邻甲酚红在高亲水性的聚乙烯醇载体上固定。利用紫外可见光光谱仪测试了其响应性能。结果表明，固定化指示剂的光谱行为与其相应的水溶液的光谱行为不一致，这可能是固定化过程中新的化学键生成以及载体与指示剂之间的相互作用如氢键的作用等引起的。这也导致了其pH响应范围与相应指示剂水溶液的响应范围的差异。固定酚红交联聚乙烯醇pH敏感膜的pH响应范围为pH=6.72～8.49；固定邻甲酚红交联聚乙烯醇pH敏感膜的两个响应范围分别为［H~+］=0.1mol／L～5mol／L和pH7.97～12.26。这种方式制备的这两种pH敏感薄膜均表现出优异的可重复使用性、可逆性、稳定性及易于制备的特点。更突出的优点在于，与以聚丙烯酰胺为基质直接固定酚红的薄膜（PAM-PR）相比，这种固定技术制备的敏感膜，当其与分析剂溶液接触时，其接枝于表面的水溶性高分子溶解，呈现“液态”，在固态基质表面形成一“液膜”层，从而消除了试剂相与分析剂之间的相界面，克服了指示剂固定化技术中的“瓶颈”问题，大幅度地提高了其响应速度与灵敏度，使响应时间从PAM-PR的数十分钟降至30秒以下。（二）开拓了刚果红醋酸纤维素包埋对的pH敏感膜（CCM）及刚果红／环氧氯丙烷交联聚乙烯醇（PECM）和甲醛交联聚乙烯醇（PFCM）的三种pH敏感膜新体系，测试并比较了三种膜的响应性能。结果表明，固定化刚果红的光谱性质和响应范围与刚果红水溶液不一致，而且用不同载体固定的刚果红的光谱特征与响应范围也各不相同。CCM的响应范围为pH＝2.5～4.5，PECM的响应范围在［H~+］=2mol/L～pH＝6.8之间，PFCM响应范围为pH＝2.90～5.48。这也可能是固定化过程中的氢键效应、空间位阻、指示剂与载体间发生的化学反应不同及载体本身结构的差异等引起的。这三种膜也具有良好的重现性、可逆性及响应迅速（平均响应时间低于25秒）的特点。另外发现醋酸纤维素包埋刚果红的敏感膜具有特殊的稳定性。对这种特殊的稳定性原因的分析表明选择合适尺寸分子的指示剂与载体配对将可能克服包埋技术中指示剂逸出的缺点。（三）对制备的pH敏感膜及对应的水溶液的pH线性响应范围给出了相应的线性回归方程（R＞98.2）。结果表明这些敏感膜对响应范围内的pH均具有良好的线性响应关系。这些结果与思想不仅丰富了光导pH传感器的试剂相内容，也为后续工作提供了一些有益的借鉴。

PH值、氯离子浓度和监酸浓度对于铁的腐蚀电化学行为的影响

本文研究了Armco铁在盐酸溶液中的腐蚀电化学行为，探讨了ψ~-离子和PH值对铁的阳极溶解过程的影响，并进而讨论了ψ~-离子浓度和PH值对铁的腐蚀电化学行为的影响之间是否存在交互效应。在本工作中，作者提出了两个新的研究方法：(a) 从单支弱极化曲线测定腐蚀电流和阴、阳极反应的Tafep斜率；(b)根据交流方波电流扰动的响应函数方程测定极化电阻Rp和界面电容C。设I_c、I_(2c)、I_(3c)及I_(4c)分别为对应于弱极化区内极化电位为ΔE、2ΔE、3ΔE和4ΔE的极化电流，且令a = I_(2c)/I_c, b = I_(3c)/I_c, c = I_(4c)/I_(2c), 而(4b-3a~2)~(1/2)、(3c-2b)~(1/2)、(2c-a~2)~(1/2)则以S_j表示之，则可得到：I_(corr) = I_c/S_j b_c = ΔE/lg((a+s_j)/2) b_a = -ΔE/lg((a-s_j)/2)为了方便，准确地求出动力学参数，可选用一系列的ΔE值，得出相应的极化电流I_λ，求出S_λ，应用统计方法处理数据，可得：I_(corr) = ∑ from i=1 to n I_λ/∑ from i=1 ton S_λ b_c = ∑ form λ to n ΔE_λ/∑ form i=1 to n lg ((a_λ+S_λ)/2) b_a = ∑ form i=1 ton ΔE_λ/∑ form i=1 to n lg ((a_λ-S_λ)/2)在线性极化区间内向腐蚀金属电极体系施加一交流方波电流扰动讯号时，通过Laplace变换分析，得到相应的响应函数方程为：E_1(t) = λ_o(R_s+R_p) - 2λ_oR_p (e~(-(τ-λ)/RpC))/(1+e~(λ/RpC)) (o<τ<λ) E_2(t) = -λ_o(R_s+R_p) + 2λ_oR_p (e~(-(τ-λ)/RpC))/(1+e~(λ/RpC)) (λ<τ<2λ)由此方程可知，它们在E～λ坐标系统中的轨迹为对称兴致勃勃原点的两条直线。由此方程可进一步得到:ΔE = 2λ_oR_p (e~(λ/RpC)-1)/(e~(λ/RpC)+1) = 2λ_oR_p t_(anh)(λ/(2RpC)) Δh = 2λ_o Rs式中ΔE为单支响应直线的长度，Δh则为两条直线最高点之间的距离。上述公式可进一步简化为：Rp =(ΔE)/(2λ_o) λ>>RpC (λ_o)/(ΔE) = C/λ + 1/(2Rp) λ<partial deriv) ψ_(corr))/((partial deriv) PH)]_([ψ~-]) = -55 毫伏 [((partial deriv) ψ_(corr))/((partial deriv) lg[ψ~-])]_(PH) = -15 毫伏 [((partial deriv) lg I_(corr))/((partial deriv) PH)]_([ψ~-]) = -0.4 [((partial deriv) lg I_(corr))/((partial deriv) lg[ψ~-])]_(PH) = 0.13 αψ_(corr)/α lg[Hψ] = -44 毫伏 α lg I_(corr)/α lg[Hψ] = 0.45 b_a = 40 毫伏，b_c = 120 毫伏，为了与弱极化区内得到的数据相比较，又观察了强极化区内的研究结果。由强极化区内Tafel线段的数据分析而得到的离子反应级数和Tafel斜率值与弱极化区得到的结果是一致的。由此，讨论了铁的阳极溶解过程，提出了反应机理，由此机理推论而得出的有关的电化学参数的理论值与实验值符合得很好。最后，对PH值和ψ~-离子浓度对铁的腐蚀电化学行为的影响之间是否存在交互效应进行了探讨。由实验数据的分析得到，PH值和ψ~-离子浓度的效应之间不存在交互效应，或者交互效应不大。

Low-temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe-Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe-Mo/SiO2 catalysts. Iron was loaded on the Mo/SiO2 catalyst by chemical vapor deposition of Fe-3(CO)(12). The catalyst showed good low-temperature activities at 723-823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe-Mo/SiO2 catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO2 decreased with the addition of iron and approached that of the Fe/SiO2. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe-Mo/SiO2 catalyst was proposed: Fe is the center for the C-H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K.

Development and application of oxygen permeable membrane in selective oxidation of light alkanes

In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H-2, oxidative coupling of methane (OCM) to C-2, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.

Liquid phase epitaxy of Al0.3Ga0.7As islands

Self-organized Al0.3Ga0.7As islands generated on the (100) facet are achieved by liquid phase epitaxy. Three particularly designed experimental conditions-partial oxidation, deficient solute and air quenching-result in defect-free nucleation. Micron-sized frustums and pyramids are observed by a scanning electron microscope. The sharp end of the tip has a radius of curvature less than 50 nm. It is proposed that such Al0.3Ga0.7As islands may be potentially serviceable in microscale and nanoscale fabrication and related spheres. (C) 2004 Elsevier B.V. All rights reserved.

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al0.3Ga0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well. (c) 2004 Elsevier B.V. All rights reserved.

Micro-fabricated Al0.3Ga0.7As pyramids for potential SPM applications

A novel technique of manufacturing Al0.3Ga0.7As pyramids by liquid phase epitaxy (LPE) for scanning probe microscopy (SPM) sensors is reported Four meticulously designed conditions-partial oxidation, deficient solute, air quenching and germanium doping result in defect-free homogeneous nucleation and subsequent pyramid formation. Micrometer-sized frustums and pyramids are detected by scanning electron microscopy (SEM). The sharp end of the microtip has a radius of curvature smaller than 50 nm. It is believed that such accomplishments would contribute not only to crystal growth theory, but also to miniature fabrication technology.

Synthesis Gas Generation by Chemical-Looping Reforming Using Ce-Based Oxygen Carriers Modified with Fe, Cu, and Mn Oxides

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H-2 selectivity at above 800 degrees C. As for the Ce-Fe-O oxygen carrier, methane was converted to synthesis gas at a H-2/CO molar ratio close to 2:1 at a temperature of 800-900 degrees C; however, the methane thermolysis reaction was found on Ce-Cu-O and Ce-Mn-O oxygen carriers at 850-900 degrees C. Among the three kinds of oxygen carriers, Ce-Fe-O presented the best performance for methane CLR. On Ce-Fe-O oxygen carriers, the CO and H-2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce-Fe-O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce-Fe-O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce-Fe-O oxides by X-ray diffraction (XRD) analysis.