The gas-phase reaction of O3 with H2CO

Explosions occur when O₃ and H₂CO are mixed in a fresh vessel, even in the presence of several hundred torr of N₂ or O₂. However, in an aged vessel the reaction is well behaved. The reaction between O₃ and H₂CO was studied at room temperature in an aged vessel in the presence of about 400 torr of either N₂ or O₂. The initial rate of O₃ decay in the presence of N₂ is about 10³ times faster than in the presence of O₂, and very small amounts of O₂ quickly reduce the initial rate of O₃ decay in the N₂ case. A chain mechanism is postulated to account for the results in which chain initiation can occur both by thermal decomposition of O₃, followed by reaction of O(³P) with H₂CO to produce HO and HCO, as well as by which may occur both homogeneously and heterogeneously. The rate coefficient k₁ ? 2.1 × 10^?24 cm³/molec · sec represents an upper limit (to within a factor of 2 uncertainty) to the direct gas-phase reaction between O₃ and H₂CO.     

Photocatalytic Oxidation of CO on TiO2: Chemisorption of O2, CO,and H2

On the surface : Adsorption of O₂ at the surface oxygen vacancy (SOV) sites of TiO₂ reconstructs the lattice oxygen (healing SOVs), resulting in a decrease of the photocatalytic activity of oxidizing CO over vacuum‐pretreated TiO₂ with increasing temperature (see scheme). Adsorption of H₂ produces new SOVs at the TiO₂ surface and stabilizes the photocatalytic activity.

     

O2/CO2气氛下CO2和H2O气化反应对煤及煤焦燃烧特性的影响

利用热天平对比研究了大同煤及煤焦在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的燃烧行为,探讨CO₂和H₂O气化反应对其富氧燃烧特性的影响。结果表明,在5%氧气浓度下,煤粉在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的燃烧速率按顺序依次降低。氧气浓度降低到2%,由于CO₂和H₂O气化反应的作用,煤粉在高温区的整体反应速率按顺序依次增大。当氧气浓度为5%时,煤焦在O₂/CO₂中的燃烧速率要低于O₂/N₂中的燃烧速率,但燃烧反应推迟后气化反应的参与使得煤焦在O₂/H₂O/CO₂中的整体反应速率显著升高。当氧气浓度降低到2%后,随着温度的升高,在CO₂气化反应的作用下,煤焦在O₂/CO₂中的整体反应速率逐渐高于O₂/N₂中的燃烧速率。在O₂/H₂O/CO₂中,由于H₂O在共气化中起主要作用,煤焦在O₂/H₂O/CO₂高温区的整体反应速率进一步升高。动力学分析表明,在5%氧浓度时,煤焦在O₂/N₂、O₂/CO₂和O₂/H₂O/CO₂中的表观活化能依次升高。随着氧气浓度的降低,在不同反应气氛中的表观活化能均有所下降。     

·C2H3+O2→HC·O+H2CO 的密度泛函理论研究

应用密度泛函理论研究了@C2H3+O2→HC@O+H2CO的反应机理.在DFT(B3LYP/6-31G*)水平上对反应过程中所有反应物、中间体、过渡态和产物的几何构型进行优化,通过频率振动分析确认中间体和过渡态.计算IRC反应路径的能量,分析了中间体的异构化过程和各主要原子的自旋密度.     

Flow reactor studies and kinetic modeling of the H2/O2/NOX and CO/H2O/O2/NOX reactions

Flow reactor experiments were performed over wide ranges of pressure (0.5–14.0 atm) and temperature (750–1100 K) to study H₂/O₂ and CO/H₂O/O₂ kinetics in the presence of trace quantities of NO and NO₂. The promoting and inhibiting effects of NO reported previously at near atmospheric pressures extend throughout the range of pressures explored in the present study. At conditions where the recombination reaction H + O₂ (+M) = HO₂ (+M) is favored over the competing branching reaction, low concentrations of NO promote H₂ and CO oxidation by converting HO₂ to OH. In high concentrations, NO can also inhibit oxidative processes by catalyzing the recombination of radicals. The experimental data show that the overall effects of NO addition on fuel consumption and conversion of NO to NO₂ depend strongly on pressure and stoichiometry. The addition of NO₂ was also found to promote H₂ and CO oxidation but only at conditions where the reacting mixture first promoted the conversion of NO₂ to NO. Experimentally measured profiles of H₂, CO, CO₂, NO, NO₂, O₂, H₂O, and temperature were used to constrain the development of a detailed kinetic mechanism consistent with the previously studied H₂/O₂, CO/H₂O/O₂, H₂/NO₂, and CO/H₂O/N₂O systems. Model predictions generated using the reaction mechanism presented here are in good agreement with the experimental data over the entire range of conditions explored. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 705–724, 1999     

Adsorption of H2O, CO2 and Xe on Soft Surfaces

The interactions of water, carbon dioxide, and Xe with octadecanethiol (C(18)H(37)SH, ODT) self-assembled monolayers (SAMs) were studied under ultrahigh vacuum conditions employing temperature-programmed desorption and optical diffraction measurements. The ODT layer was grown on a 1 nm thick gold film deposited over a Ru(001) single-crystal substrate. The gases used in this report differ in their lateral interactions while adsorbed on ODT-SAM being either repulsive (Xe) or attractive (H(2)O, CO(2)). The activation energies for desorption of the first layer from ODT are E(a) = 3.6 +/- 0.9, 4.1 +/- 0.5, and 8.5 +/- 0.9 kcal/mol for Xe, CO(2), and H(2)O, respectively. Sticking probabilities of the three gases on the soft ODT surface are S(0) = 0.7 +/- 0.1, 0.8 +/- 0.1, and 0.95 +/- 0.05 for xenon, CO(2), and water, respectively, derived from the respective adsorption curves. Optical diffraction studies from multilayer coverage grating of Xe on ODT-SAM have demonstrated that sublimation is a thermodynamically more favorable process over diffusion and wetting. The significantly lower binding energy of the first layers of H(2)O and CO(2) adsorbed on the soft surface of ODT compared to that on clean metals and oxides, reflects generally weak (CO(2)) and hydrophobic (H(2)O) interactions that are important for understanding the behavior of these molecules on interfaces that are found in biological systems.     

Marked adsorption irreversibility of graphitic nanoribbons for CO2 and H2O

Graphene and graphitic nanoribbons possess different types of carbon hybridizations exhibiting different chemical activity. In particular, the basal plane of the honeycomb lattice of nanoribbons consisting of sp(2)-hybridized carbon atoms is chemically inert. Interestingly, their bare edges could be more reactive as a result of the presence of extra unpaired electrons, and for multilayer graphene nanoribbons, the presence of terraces and ripples could introduce additional chemical activity. In this study, a remarkable irreversibility in adsorption of CO(2) and H(2)O on graphitic nanoribbons was observed at ambient temperature, which is distinctly different from the behavior of nanoporous carbon and carbon blacks. We also noted that N(2) molecules strongly interact with the basal planes at 77 K in comparison with edges. The irreversible adsorptions of both CO(2) and H(2)O are due to the large number of sp(3)-hybridized carbon atoms located at the edges. The observed irreversible adsorptivity of the edge surfaces of graphitic nanoribbons for CO(2) and H(2)O indicates a high potential in the fabrication of novel types of catalysts and highly selective gas sensors.     

湿气源吸附碳捕集: CO2/H2O共吸附机制及应用

大型湿气源排放中普遍存在的水汽是制约吸附碳捕集规模化发展的重要挑战之一。H₂O的极性往往会导致吸附材料的CO₂捕集率降低甚至出现失效,也会造成捕集系统产生温降、压降等寄生损失,甚至形成设备腐蚀、吸附剂中毒等不利影响,最终额外能耗和成本大幅提高。为解决上述挑战,深入理解CO₂与H₂O共吸附过程的作用机制,据此开发成本合理、再生能耗低且对水气不敏感的高效CO₂吸附剂及吸附技术是实现湿气源下高效吸附碳捕集的重要途径。目前,由于分散在多个领域且各有侧重,关于H₂O对CO₂吸附影响的机制分析缺乏汇总与概括,难以形成相对统一的观点。本文针对CO₂与H₂O共吸附过程,从宏观与微观层面进行了详细综述。首先,基于共吸附机制的基础研究,依次介绍了竞争吸附、变湿吸附和呼吸效应领域的研究进展并进行了简要评价。其次,基于共吸附的应用研究,阐述了湿气源CO₂捕集技术的吸附剂研发与工艺改进两部分的现状及进展,也对不同湿气源下CO₂捕集水平进行了简要评价。最后,总结了目前研究中的不足之处并展望了未来的研究方向。本文将分散于各领域的CO₂与H₂O共吸附过程进行集中归纳、分析和对比,或可为湿气源碳捕集技术提供有效的指导。     

Mechanism of phototransfer of hydrogen atom in the model H2CO + H2O system

A system modelling the photochemical abstraction of a hydrogen atom by ketones in alcohols is calculated by the semiempirical INDO and MINDO/3 methods with allowance for the configuration interaction in the singly and doubly excited states. The states participating in the elimination reaction and the electronic rearrangement taking place in the course of the reaction are traced on the basis of an analysis of the wave functions and the electron and spin densities. It is established that the state of the ketone which participates in hydrogen abstraction is a lowest triplet state of the n^* type, which is formed through the avoidance of intersections of several states of different orbital type ^3*, ³n^* and the charge-transfer state.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 476–480, July–August, 1989.     

Selective oxidation of CO in the presence of H2, H2O and CO2 via gold for use in fuel cells

An Au/Fe2O3 catalyst prepared using a two-stage calcination procedure achieves target conversion and selectivity for the competitive oxidation of dilute CO in the presence of moist excess H2 and CO2.     

CuOx/TiO2光催化水蒸气还原CO2

以商品TiO2-P25为原料,通过浸渍法负载一定量过渡金属Cu,得到一系列不同含量的CuOx/TiO2光催化剂。利用X射线衍射（XRD）,X－射线光电子能谱（XPS）,BET,高分辨率透射镜（HRTEM）,X射线荧光光谱（XRF）和光致发光光谱（PL）等方法对催化剂进行了详细表征,在自建的光催化反应器中评价了气态水光催化还原CO2反应的活性和CH4收率。结果表明负载CuOx后的TiO2纳米材料光催化性能显著提高,其中1%CuOx/TiO2样品紫外光照72 h后,CH4生成量达到了24.86 µmol•gTi-1。同时,CuOx负载量、反应温度、反应时间等因素对CH4收率均有显著影响。     

芳香硝基物CO选择还原—环境友好芳胺合成新路线

含有羰基、氯、氰基和双键的芳胺类化合物是染料、颜料、医药和农药等领域的重要中间体［1］.然而,它们难以从相应的芳香硝基物与金属氢化物试剂的催化加氢直接制得,因为在这些还原条件下,羰基、氯、氰基和双键也能发生还原反应［2］ .目前,工业上通常还只能用经典的铁粉还原法或硫化碱还原法生产这些芳胺衍生物,但用铁粉还原法,产生的大量铁泥严重污染环境;硫化碱还原法,则存在合成路线复杂、成本高、收率低和废液量大等不足之处［3］ .近年来,一种以CO为还原剂还原芳香硝基物的反应,以其对硝基的高选择性而日益引起人们的兴趣,因而有望成为合成含有羰基、氯和氰基的芳香胺类衍生物的一条环境友好新途径［4］.     

Deuterium exchange in the systems of H2O+/H2O and H3O+/H2O

The reactions of H₂O⁺, H₃O⁺, D₂O⁺, and D₃O⁺ with neutral H₂O and D₂O were studied by tandem mass spectrometry. The H₂O⁺ and D₂O⁺ ion reactions exhibited multiple channels, including charge transfer, proton transfer (or hydrogen atom abstraction), and isotopic exchange. The H₃O⁺ and D₃O⁺ ion reactions exhibited only isotope exchange. The variation in the abundances of all ions involved in the reactions was measured over a neutral pressure range from 0 to 2 × 10⁻⁵ Torr. A reaction scheme was chosen, which consisted of a sequence of charge transfer, proton transfer, and isotopic exchange reactions. Exact solutions to two groups of simultaneous differential equations were determined; one group started with the reaction of ionized water, and the other group started with the reactions of protonated water. A nonlinear least-squares regression technique was used to determine the rate coefficients of the individual reactions in the schemes from the ion abundance data. Branching ratios and relative rate coefficients were also determined in this manner.A delta chi-squared analysis of the results of the model fitted to the experimental data indicated that the kinetic information about the primary isotopic exchange processes is statistically the most significant. The errors in the derived values of the kinetic information of subsequent channels increased rapidly. Data from previously published selected ion flow tube (SIFT) study were analyzed in the same manner. Rigorous statistical analysis showed that the statistical isotope scrambling model was unable to explain either the SIFT or the tandem mass spectrometry data. This study shows that statistical analysis can be utilized to assess the validity of possible models in explaining experimentally observed kinetic behaviors.     

Surface chemistry of Cu in the presence of CO2 and H2O

The chemical nature of copper and copper oxide (Cu 2O) surfaces in the presence of CO 2 and H 2O at room temperature was investigated using ambient pressure X-ray photoelectron spectroscopy. The studies reveal that in the presence of 0.1 torr CO 2 several species form on the initially clean Cu, including carbonate CO 3 (2) (-), CO 2 (delta-) and C (0), while no modifications occur on an oxidized surface. The addition of 0.1 ML Zn to the Cu results in the complete conversion of CO 2 (delta-) to carbonate. In a mixture of 0.1 torr H 2O and 0.1 torr CO 2, new species are formed, including hydroxyl, formate and methoxy, with H 2O providing the hydrogen needed for the formation of hydrogenated species.