气相存在下CO在Pd上非线性脱附动力学的研究

利用同位素技术测定了预吸附在Pd表面上的CO在单一及混合同位素气氛下的脱附动力学．实验发现CO的脱附动力学是非线性的，在饱和表面上为一级加二级．在易位化学吸附模型和协同交换机理的基础上，对表面吸附物种的动态结构进行了深入分析讨论，并推导出了非线性脱附动力学的解析表达式．     

ZrO_2/TiO_2载体协同作用下Fe_2O_3(104)与CO化学链燃烧特性

在表面形貌控制增强铁基载氧体Fe_2O_3(104)化学链燃烧反应活性研究的基础上,进一步研究了TiO_2,ZrO_2载体协同作用下Fe_2O_3(104)与CO化学链燃烧的反应特性.采用X射线衍射(XRD),扫描电子显微镜(SEM)和比表面积(BET)等方法对所制备的载氧体Fe_2O_3(104)/TiO_2和Fe_2O_3(104)/ZrO_2进行表征.研究了700,800和900℃下载氧体与CO化学链燃烧反应特性.结果表明,不同载体对Fe_2O_3(104)与CO发生化学链燃烧反应活性的影响程度不同,ZrO_2作为载体明显促进Fe_2O_3(104)与CO的反应速率.动力学分析结果显示,Fe_2O_3(104)/TiO_2与CO反应模型属于一级反应,反应活化能为153.6 k J/mol;Fe_2O_3(104)/ZrO_2与CO反应模型属于抽缩球体模型,反应活化能为118.9 k J/mol.     

CO在Ag掺杂的氧化锰八面体分子筛上吸附的TAP研究

利用产物瞬时分析反应器中进行的单脉冲实验, 考察了393～493 K温度范围内CO在Ag掺杂的氧化锰八面体分子筛上的吸附行为. 实验表明: CO在催化剂表面发生化学吸附, 并与晶格氧反应生成CO₂. 通过对该过程反应物及产物脉冲响应曲线的模拟, 得到了各基元反应的动力学参数. CO和CO₂在该催化剂表面的脱附活化能分别为83和31 kJ/mol, CO与晶格氧的反应活化能为116 kJ/mol.     

焦炭催化CO还原NO的反应机理研究

利用密度泛函理论,研究了焦炭催化作用下CO还原NO的化学反应机理,优化得到了均相反应路径以及在Zigzag和Armchair型焦炭表面上的异相反应路径中所有驻点的几何构型与能量,并对三条反应路径进行了动力学分析。结果表明,均相NO还原反应的活化能为254.06 kJ/mol,而Zigzag型与Armchair型焦炭表面NO异相还原反应的活化能分别为86.94与52.16 kJ/mol,说明焦炭在NO还原反应中能够起到催化作用。在焦炭表面进行的CO还原NO的反应路径经历N_2形成、N_2释放及两步CO_2释放四个阶段,最终生成一个N_2分子与两个CO_2分子。此外,通过对比不同路径下异相反应的能量变化与动力学参数可知,焦炭表面结构对NO还原反应特性存在较大影响;与Zigzag型焦炭表面相比,基于Armchair型焦炭表面的NO还原反应决速步能垒值更低且反应速率更快,表明在Armchair型焦炭表面上的NO还原反应更易进行。     

K改性的Pt/Al2O3催化剂上CO氧化反应：反应动力学和红外光谱研究

CO氧化不仅具有重要的实用价值,而且在基础研究中被用于考察反应机理及催化剂结构敏感性等一些重要问题,因此,该反应在催化领域中具有重要意义. Pt基催化剂被广泛应用于CO氧化反应.其催化活性取决于催化剂的制备方法.其中,碱金属如Na、K等助剂的添加可有效促进催化活性,红外光谱证据表明,其促进作用在于碱金属的添加可降低CO与表面Pt原子的相互作用.尽管如此,催化剂上反应动力学证据却十分缺乏.反应动力学的研究可以提供一些本证反应信息如反应基元步骤、反应速率表达式以及反应机理等.通过对比不同催化剂之间的反应动力学行为,可以进一步解释碱金属对催化剂结构以及反应行为的影响.因此在本工作中,我们制备了一系列以K为助剂的Pt/Al2O3催化剂,并进行了CO氧化的反应动力学研究,考察了助剂对CO反应级数和反应活化能的影响.结合原位红外光谱表征,进一步揭示了助剂在反应中的作用.通过对比不同Pt和K含量的催化剂上CO氧化反应活性,我们发现, K的添加能促进反应活性,且随着催化剂中K含量的增加,促进程度越明显.例如,0.42K-2Pt/Al2O3上T50温度比对应的2Pt/Al2O3降低了30oC.不同催化剂上CO氧化的反应动力学实验表明,反应速率随着CO的分压的增加而降低;但随着O2分压的增加而增大.幂函数反应速率表达式推导得到的反应级数发现,对于含K的催化剂其CO的反应级数(约为–0.2)明显比不含K的催化剂(约为–0.5)中高,说明K的添加减弱了CO与表面Pt原子之间的吸附能力.但对O2的反应级数影响较小.例如：在0.42K-2.0Pt/Al2O3上反应速率表达式为r =6.55′10–7pco–0.22po20.63;而在2.0Pt/Al2O3上为r =2.56′10–7pco–0.53po20.70.表观反应活化能的计算表明,含K的催化剂上表观反应活化能较低,进一步说明K的添加有利于反应进行.根据反应速率表达式,我们进行了基元步骤的推导,并计算了反应动力学参数.结果发现,与不含K的催化剂相比,含K的催化剂中本征反应速率常数明显增加,而CO吸附平衡常数降低了一半,表明K的存在使CO在Pt表面上的覆盖度降低.我们还通过原位红外光谱对比了催化剂上CO吸附行为的差异.数据表明,与不含K的催化剂相比, K的添加一方面降低了CO在催化剂表面的吸附量(峰面积变小);另一方面显著降低了CO在Pt表面上的脱附温度,说明两者之间的相互作用力减弱.综上所述,通过反应动力学和红外光谱实验,我们认为K助剂与表面Pt原子相互作用后生成了较为稳定的Pt–O–K物种.尽管该物种的具体结构目前还不明确,但我们的实验证据表明,该物种的存在可以有效减弱CO与表面Pt原子之间的相互作用,降低CO的表面覆盖度并有利于O2在Pt表面的竞争吸附,从而降低了表面吸附的CO与O2之间反应的能垒,促进了反应性能.     

可逆型化学振荡器

该文给出了可逆型化学振荡器的定义、意义和可能存在的类型。这些类型包括：（1）自发乳化，通电破乳；（2）乳液中自发产生的甘油三酯水解振荡反应及通电逆向酯化反应；（3）用表面活性剂有机溶液代替盐桥，形成新型的电化学振荡，通电逆向电解。文章对这3种类型可逆型化学振荡器的来源、组成、实验方法、理论分析方法和应用前景进行了深入的讨论和分析。它们还可以进一步组合，形成更多的类型。其主要的研究方法为用正交实验确定最佳配方，由相关分析确定影响因素。这些可逆型化学振荡器的关键组分都是表面活性剂，是表面活性剂在非线性化学动力学研究中的又一应用。对可逆型化学振荡器的研究必将大大促进远离平衡态的复杂反应动力学研究及新型交流蓄电池的开发设计。     

富氧条件下Au/γ-Al2O3催化剂上的CO氧化反应

用脉冲反应研究了Au／γ-Al2O3催化剂上的CO氧化反应，结果表明在催化剂的表面首先发生CO和O2的吸附，然后吸附态的CO和O2之问反应生成CO2；在催化剂的表面CO的吸附强度大于O2的吸附强度，O2单独存在时不能在催化剂表面发生吸附．升高反应温度和提高含氧量都能提高CO的转化活性．     

Au/CeO2催化剂上CO2选择加氢为CO反应及其中间物种研究

CO2的化学转化具有环境及科学双重研究意义.CO2具有很高的化学稳定性,加氢还原是一种有效的转化途径.其中将CO2选择性还原为CO,即逆水汽变换(RWGS)反应(CO2+H2→CO+H2O),具有重要的理论意义和应用价值:(1)CO作为合成气的重要原料,可以通过F-T合成生产更有价值的液体燃料;(2)H2可通过可再生能源电解水制取,实现了全过程的零排放碳循环利用.从热力学角度分析,RWGS反应是一个吸热反应,高温有利于平衡转化率的提高.从动力学角度,一个对正反应有活性的催化剂可同时催化逆反应进行.可还原性载体负载贵金属催化剂,如Pt/CeO2,Au/FeOx,Au/CeO2等,具有很好的低温WGS催化活性,但它们在RWGS反应上的研究较少.我们制备了CeO2负载纳米Au催化剂(HRTEM表征结果表明金高度分散于CeO2载体表面,粒径为4-5 nm),其在常压CO2加氢还原为CO反应中表现出优异的低温活性,分别在450℃,CO2/H2=1,WHSV=12000 mL/(h·g),及400℃,H2/CO2=1,WHSV=6000 mL/(h·g)条件下,CO2转化率接近平衡转化率,且CO的选择性为100%.随着H2/CO2比例增加,CO2转化率明显提高,且维持H2/CO2为1的化学计量比反应.通过原位漫反射红外光谱与质谱相结合的技术,研究了Au/CeO2催化剂上的RWGS反应路径:Au/CeO2催化剂表面形成了甲酸盐中间物种,它的消耗伴随着CO和H2O产物的生成.说明Au/CeO2催化剂遵循中间体机理,这应该是其具有优异低温RWGS反应性能的微观机制.     

碳质表面异相还原NO2的反应机理

基于量子化学密度泛函理论（DFT），研究了碳质表面异相还原NO₂的反应机理，针对Zigzag与Armchair两种碳质表面，采用M06-2X方法与6-311G （d）基组联用，优化得到了不同反应路径下所有驻点的几何构型与能量，并对各路径进行了热力学与动力学分析，重点探究了CO在NO₂异相还原反应中的作用规律，同时考察了碳质表面与反应温度对异相反应的影响。计算结果表明，NO₂在碳质表面的异相还原过程主要分为两个阶段，即NO₂还原阶段与碳氧化物释放阶段。通过对比无CO分子参与的反应可知，参与反应的CO分子可以降低各阶段的反应能垒并且加快各阶段的反应速率；CO分子存在时，NO₂还原阶段的反应能垒被降低，促进了NO₂还原成NO的异相反应过程，同时参与反应的CO分子与碳质表面剩余氧原子结合，形成CO₂分子并释放，使碳氧化物释放阶段的反应能垒降低，从而促进了整体还原反应的进行。此外，与Armchair型相比，基于Zigzag型碳质表面的NO₂异相还原反应能垒更低且反应速率更快，说明NO₂异相还原反应更容易在Zigzag型碳质表面进行。最后，由反应动力学分析可知，随着温度上升，各阶段的反应速率均增大，说明提高温度对碳质表面的NO₂异相还原能够起到促进作用。     

焙烧温度对Au/Fe2O3选择性氧化富氢气体中CO催化性能的影响

甲醇重整在线制氢作为质子交换膜燃料电池的燃料成为当前研究的热点。受重整反应动力学及热力学的限制，使得甲醇重整气(富氢气体)中除含有大量的氢气外还含有少量的CO，CO极易吸附在燃料电池阳极催化剂表面，使电池性能下降，因而必须去除重整气中的CO，选择性氧化脱除富氢气     

O2和CO表面催化反应的活性位分布模型

对于O_2和CO表面催化反应，建立了一个新的不可逆Monte Carlo模拟模型。在 二维格子中，引进了表面活性位和非活性位的要领。模型假设，一定浓度的活性位 随机分布在非活性位上，形成了活性位分布的二维格子模型反应器，并在ZGB模型 的基础上，考虑了氧原子和CO分子的表面扩散，特别是引进了吸附粒子的定向表面 扩散。其中，活性位和活性位最近邻是表面吸附物质反应的活性中心，而非活性位 的作用是通过表面扩散传质。当活性位浓度C_a = 1且考虑扩散时，模型还原为增 加了扩散的ZGB模型。当活性位浓度C_a = 1且只考虑氧的扩散时，模拟结果表明， 扩散几率达到某一数值（0.3）时，二级相变点完全消失。当活性位浓度C_a逐渐减 小时，单位活性位产生的CO_2的速率不断增大，这表明活性位的利用率提高了。     

A+B2表面催化反应相变及自振荡的蒙特卡罗模拟

用MonteCarlo法研究了脱附和E－R机理对不可逆催化氧化反应A＋1／2B2→AB的相交和自振荡的影响、结果表明，（1）催化剂表面A的脱附使ZGB模型中的一级相变点消失，但对二级相交点的影响很小；当有E－R机理参与时，二级相交点消失，且E－R过程的几率对一级相交点的影响较大；当A的脱附和E－R过程同时起作用时，上述反应不存在相交（2）在ZGB模型中的二级相变点附近，反应速率随时间的变化具有明显的振荡现象，在其它位置主要表现为噪音。引入A的脱附后在二级相交点附近明显的自振荡现象依然存在；当E-R过程起作用时，随着二级相交点的消失，明显的振荡现象亦随之消失．（3）A的脱附和E－R过程对上述反应相变的影响与A的表面扩散对相变的影响有着本质的区别，因为后者只能改变相变点的位置而不能改变相变点的存在状况．     

In situ ATR-IR spectroscopic and reaction kinetics studies of water-gas shift and methanol reforming on Pt/Al2O3 catalysts in vapor and liquid phases

Reaction kinetics measurements of the water-gas shift reaction were carried out at 373 K on Pt/Al2O3 in vapor phase to investigate the effects of CO, H2, and H2O partial pressures. Results of in situ ATR-IR studies conducted in vapor phase under similar conditions suggest that the Pt surface coverage by adsorbed CO is high (approximately 90% of the saturation coverage), leading to a negligible effect of the CO pressures on the rate of reaction. The negative reaction order with respect to the H2 pressure is caused by the increased coverage of adsorbed H atoms, and the fractional positive order with respect to the water pressure is consistent with non-equilibrated H2O dissociation on Pt. Results of in situ ATR-IR studies carried out at 373 K show that the presence of liquid water leads to a slight decrease in the Pt surface coverage by adsorbed CO (approximately 80% of the saturation coverage) when the CO partial pressure is the same as in the vapor-phase studies. The rate of the WGS reaction in the presence of liquid water is comparable to the rate under complete vaporization conditions when other factors (such as CO partial pressure) are held constant. Reaction kinetics measurements of methanol reforming were carried out at 423 K over a total pressure range of 1.36-5.84 bar. In situ ATR-IR studies were conducted at 423 K to determine the Pt surface coverage by adsorbed CO in completely vaporized methanol feeds and in aqueous methanol solutions. The decomposition of methanol is found to be slower during the reforming of methanol in liquid phase than in vapor phase, which leads to a lower rate of hydrogen production in liquid phase (0.08 min(-1) at 4.88 bar) than in vapor phase (0.23 min(-1) at 4.46 bar). The lower reaction order with respect to methanol concentration observed for vapor-phase versus liquid-phase methanol reforming (0.2 versus 0.8, respectively) is due to the higher extent of CO poisoning on Pt for reforming in vapor phase than in liquid phase, based on the higher coverage by adsorbed CO observed in completely vaporized methanol feeds (55-60% of the saturation coverage) than in aqueous methanol feed solutions (29-40% of the saturation coverage).     

Probe of NH3 and CO adsorption on the very outermost surface of a porous TiO2 adsorbent using photoluminescence spectroscopy

We report the first measurements of the kinetics of adsorption on the very outermost surface sites of a porous material compared to measurements made of adsorption on the interior sites. NH(3) and CO were employed in this study as representative of slow diffusion and fast diffusion, respectively, through porous TiO(2). Adsorption of NH(3) at 200 K occurs mainly at the very near surface (~20 nm) region as observed by photoluminescence (PL) spectroscopy, and its distribution by surface diffusion through the powder is highly retarded as judged by transmission IR spectroscopy. In contrast, the adsorption of CO in the near-surface region at 120 K is followed by the fast distribution of CO by surface diffusion into TiO(2) powder, causing the near-surface CO coverage to lag behind the coverage in the bulk. In the desorption process, the near-surface region delivers adsorbed CO molecules into the gas phase, accompanied by the supply of diffusing CO molecules from the interior. As a result, the adsorption/desorption processes for CO in the near-surface region of porous TiO(2) show a pronounced hysteresis effect. As surface diffusion is retarded at lower temperatures, the hysteresis effect gradually disappears.     

原位红外光谱研究Ni/Al2O3催化剂上CO的吸附态:Ⅰ.CO的倒式吸附态

CO在过渡金属上的吸附方式一般认为可分成三类:线式吸附态,桥式吸附态和多重键吸附态.这些吸附态的C—O伸缩振动具有红外活性,共振动频率分别位于～2050,～1950和～1700cm~(-1).但也有人认为CO在过渡金属表面上可能会形成倒式吸附态,即C—O键向表面倾斜,甚至平行于表面.例如,Dijk等曾推测在Ni/SiO_2催化剂上CO可能形成倒式双点吸附态(即C,O原子同时与表面成键).Krasser等用喇曼光谱研究CO在Ni/SiO_2上的吸附态时发现在330cm~(-1)处有一喇曼峰,认为这个峰可能来自倒式     

First-order phase transitions in repulsive rigid k-mers on two-dimensional lattices

In a previous paper [F. Roma?, A. J. Ramirez-Pastor, and J. L. Riccardo, Phys. Rev. B 72, 035444 (2005)], the critical behavior of repulsive rigid rods of length k (k-mers) on a square lattice at half coverage has been studied by using Monte Carlo (MC) simulations. The obtained results indicated that (1) the phase transition occurring in the system is a second-order phase transition for all adsorbate sizes k; and (2) the universality class of the transition changes from 2D Ising-type for monomers (k = 1) to an unknown universality class for k ≥ 2. In the present work, we revisit our previous results together with further numerical evidences, resulting from new extensive MC simulations based on an efficient exchange algorithm and using high-performance computational capabilities. In contrast to our previous conclusions (1) and (2), the new numerical calculations clearly support the occurrence of a first-order phase transition for k ≥ 2. In addition, a similar scenario was found for k-mers adsorbed on the triangular lattice at coverage k/(2k+1).     

An NMR determination of CO diffusion on platinum electrocatalysts

We report the first direct measurement of CO diffusion on nanoparticle Pt electrocatalysts at the solid/liquid interface, carried out using 13C nuclear magnetic resonance (NMR) with a spin-labeling pulse sequence. Diffusion parameters were measured in the temperature range of 253-293 K for CO adsorbed on commercial Pt-black under saturation coverage. 2H NMR of the same system indicates that the electrolyte remains in the liquid state at temperatures where the CO diffusion experiments were performed. The CO diffusion parameters follow typical Arrhenius behavior with an activation energy of 6.0 +/- 0.4 kcal/mol and a pre-exponential factor of (1.1 +/- 0.6) x 10-8 cm2/s. Exchange between different CO populations, driven by a chemical potential gradient, is suggested to be the main mechanism for CO diffusion. The presence of the electrolyte medium considerably slows down the diffusion of CO as compared to that seen on surfaces of bulk metals under UHV conditions. This work opens up a new approach to the study of surface diffusion of adsorbed molecules on nanoparticle electrode catalysts, including the possibility of correlating diffusion parameters to catalytic activity in real world applications of broad general interest.     

Liposome fluidization and melting point depression by pressurized CO2 determined by fluorescence anisotropy

The influence of CO2 on the bilayer fluidity of liposomes, which are representative of model cellular membranes, was examined for the first time at the elevated pressures (up to 13.9 MPa) associated with CO2-based processing of liposomes and microbial sterilization. Fluidization and melting point depression of aqueous dipalmitoylphosphatidylcholine (DPPC) liposomes by pressurized CO2 (present as an excess phase) were studied by steady-state fluorescence anisotropy using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Isothermal experiments revealed reversible, pressure-dependent fluidization of DPPC bilayers at temperatures corresponding to near-gel (295 K) and fluid (333 K) phases at atmospheric pressure, where the gel-to-fluid phase transition (Tm) occurs at approximately 315 K. Isobaric measurements (PCO2 =1.8, 7.0, and 13.9 MPa) of DPH anisotropy demonstrate substantial melting point depression (DeltaTm = -4.8 to -18.5 K) and a large broadening of the gel-fluid phase transition region, which were interpreted using conventional theories of melting point depression. Liposome fluidity is influenced by CO2 accumulation in the hydrocarbon core and polar headgroup region, as well as the formation of carbonic acid and/or the presence of buffering species under elevated CO2 pressure.     

DRIFTS studies on the photosensitized transformation of gallic acid by iron(III) chloride as a model for HULIS in atmospheric aerosols

Little is known about the interfacial photochemistry of transition metal cations and chromophores relevant to atmospheric aerosols. We report herein water uptake and in situ surface-sensitive spectroscopic studies on the photosensitized transformation of solid gallic acid (GA), externally mixed with FeCl(3) as a photosensitizer, under dry and humid conditions of <1% and 30% relative humidity (RH), respectively. GA is a hydrolysis product of tannic acid, a model macromolecule for humic-like substances (HULIS) in aerosols and aged polyaromatic hydrocarbons (PAH). Water uptake on GA and GA/FeCl(3) mixture films was quantified using a quartz crystal microbalance (QCM) as a function of %RH (<1-60%). Results indicate continuous multilayer formation of adsorbed water with no phase transitions, with a monolayer of adsorbed water forming around 30 and 12%RH, respectively. Photochemical studies were conducted using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Spectra were collected as a function of irradiation time (4 h), mass fraction of FeCl(3) (0.5-3%) using irradiance of simulated solar light equivalent to 120 Wm(-2) at 555 nm. Difference absorbance spectra show changes to GA functional groups suggesting the formation of organochlorine compounds in the condensed phase with their signature v(C=C) at 1601 cm(-1), and release of CO(2). Potential halogenation pathways of GA in the presence of Fe(3+) are discussed based on well-known aqueous phase chemistry. These pathways along with our results also suggest the release of volatile organochlorine compounds and Cl(2) gas. Apparent first order rate constants, k(s), of the photosensitized reactions were derived from kinetic curves of the most intense positive and negative spectral features at 1601 and 1381 cm(-1), respectively. Values of k(s) at 120 Wm(-2) are found to be higher than those reported from UV photo-Fenton reactions of GA in bulk aqueous phases containing H(2)O(2), Fe(2+) or Fe(3+). The implication of our studies on the aging of multicomponent aerosols containing organic matter, transition metals and halide ions due to heterogeneous photochemistry is discussed.     

Pressure and temperature dependence of the recombination of p-fluorobenzyl radicals

The rate constants of the recombination reaction of p-fluorobenzyl radicals, p-F-C6H4CH2 + p-F-C6H4CH2 (+M) --> C14H12F2 (+M), have been measured over the pressure range 0.2-800 bar and the temperature range 255-420 K. Helium, argon, and CO2 were employed as bath gases (M). At pressures below 0.9 bar in Ar and CO2, and 40 bar in He, the rate constant k1 showed no dependence on the pressure and the nature of the bath gas, clearly indicating that it had reached the limiting high-pressure value of the energy-transfer (ET) mechanism (k(1,infinity)ET). A value of k(1,infinity)ET(T) = (4.3 +/- 0.5) x 10(-11) (T/300 K)(-0.2) cm3 molecule(-1) s(-1) was determined. At pressures above about 5 bar, the k1 values in Ar and CO2 were found to gradually increase in a pressure range where according to energy-transfer mechanism, they should remain at the constant value k(1,infinity)ET. The enhancement of the recombination rate constant beyond the value k(1,infinity)ET increased in the order He < Ar < CO2, and it became more pronounced with decreasing temperature. The dependences of k1 on pressure, temperature, and the bath gas were similar to previous observations in the recombination of benzyl radicals. The effect of fluorine-substitution of the benzyl ring on k1 values is discussed. The present results confirm the significant role of radical complexes in the recombination kinetics of benzyl-type radicals in the gas-liquid transition range. The observations on a rate enhancement beyond the experimental value of k(1,infinity)ET at elevated densities up to the onset of diffusion-control are consistently explained by the kinetic contribution of a "radical-complex" mechanism which is solely based on standard van der Waals interaction between radicals and bath gases.