Heat of adsorption and density distribution in slit pores with defective walls: GCMC simulation studies and comparison with experimental data

The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid-fluid interaction, sites with varying degree of affinity), (ii) fluid-fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å.     

Electrocatalytic reduction of alkyl iodides in tetrahydrofuran at silver electrodes

Recent interest in the electrocatalytic activity of silver towards the reduction of alkyl iodides has led us to investigate whether the effect is observed in tetrahydrofuran (THF) at room temperature. Using platinum electrodes in THF for the reduction of alkyl halides at 298 K has been hampered by the solvent window, which ‘obscures’ the voltammetric signals of interest. In order to overcome these problems, voltammetry has been performed at low temperature and was shown to extend the voltammetric window, leading to accurate electrochemical analyses and even novel changes in mechanism(s) of the reactive species following electron‐transfer (ET). Herein, it is shown that for a primary and tertiary alkyl iodide in THF, electroreduction at silver leads to a significant shift in the reduction potential to more positive values compared to platinum. In addition, following reduction, a characteristic series of oxidation peaks are observed and are shown to be due to the specific activity of iodide ions towards silver following reductive cleavage of the parent alkyl iodide. This characteristic feature is not observed with other halide ions: bromide and chloride. Preparative electrolyses at controlled‐potential have suggested that the reduction of the above alkyl iodides is a one‐electron concerted process. The ‘free’ iodide ions act as a monitor of reaction progression, and the carbon‐centred radical either dimerises and/or abstracts a hydrogen atom from the electrolyte/solvent; 1‐iodoadamantane giving percentage yields of 58% adamantane and 39% 1,1'‐biadamantane, the primary alkyl iodide, prepared in‐house, giving 67% R‐H and 25% R‐R. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of adsorption of oxygen on β-Al2O3 + Au and β-Al2O3 + Pt: Work function measurements—proposition of a model

To improve the understanding of the electrochemical effects observed on an original potentiometric gas sensor, interactions of oxygen with the device were investigated. This gas sensor is made of a solid electrolyte (treated Na-β-alumina) associated with two metallic electrodes (gold and platinum) located in the same gas mixture. Adsorption of charged oxygen species, considered responsible for the electrical response developed by the sensor, was investigated by work function measurements. Results showed that charged oxygen species only form on partially gold or platinum covered solid electrolyte. Comparison of these results with those obtained in a previous calorimetric study of interactions between oxygen and the same materials suggests the existence of at least two different oxygen species adsorbed on the surface of the sensitive element. The first one, located on the solid electrolyte surface, is neutral and characterized by an endothermal reaction of formation. The second one is charged and probably produced at the gas/solid electrolyte/metallic electrode interface. A mechanism based on the concept of “three phase boundary” and similar to the “reverse spillover” phenomenon is proposed to account for the adsorption of these oxygen species.     

Theoretical investigation of CO adsorption on TM-doped (MgO)12 (TM = Ni, Pd, Pt) nanotubes

CO adsorption on TM-doped magnesia nanotubes (TM = Ni, Pd and Pt) have been studied by using density functional theory. Our calculation results show that CO favors adsorption on TM-doped magnesia nanotubes in the form of C atom bonding with TM atom. Fukui indices analysis clearly exhibits that doping of impurity TM atom allows for a noticeably enhancement of nucleophilic reactivity ability of magnesia nanotube. The adsorption energies demonstrate that CO molecule is more strongly bound on the 3-fold TM atoms than the 4-fold TM atoms. This finding is well confirmed by TM-C bond length, charge transfer and C-O vibrational frequency. The high adsorption energy of 2.55 eV is found when CO adsorbs on 3-fold Pt in Pt-doped magnesia nanotubes, implying the kind of the doping TM atom has a significant influence on the chemical reactivity.     

Thermodynamics of nitrogen adsorption on the zeolite H-FER

Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-FER results in hydrogen bonding of the adsorbed N₂ molecules with the zeolite Si(OH)Al Brønsted acid groups. This hydrogen bonding interaction leads to activation, in the IR, of the fundamental NN stretching mode, which appears at 2331 cm⁻¹. From the infrared spectra taken over a temperature range, while simultaneously recording integrated IR absorbance, temperature and nitrogen equilibrium pressure, the thermodynamics of the adsorption process was studied. The standard adsorption enthalpy and entropy resulted to be ΔH° = −20(±1) kJ mol⁻¹ and ΔS° = −131(±10) J mol⁻¹ K⁻¹, respectively.     

Interaction of Alkali Blue 6B with Cetyltrimethylammonium Bromide

The microsurface adsorption–spectral correction (MSASC) technique has been applied to investigate the interaction of alkali blue 6B (AB6B) with cetyltrimethylammonium bromide (CTAB). The aggregation of AB6B on CTAB obeys the Langmuir isothermal adsorption. The aggregate was characterized by MSASC. For the monomer aggregate AB6B₂CTAB formed, its binding constant is calculated to be K = 3.01·10⁵ and its molar absorptivity to be 2.45·10⁶ liters·cm^–1 at = 690 nm. The adsorption has been used to carry out quantitative detection of cationic surfactant in samples.     

等离子体-吸附SO2转化机理研究

本文对SO2在等离子体和分子筛吸附联合作用下的转化现象进行了研究,开展了实验、模型建立、机理研究和理论计算等工作。研究表明,二者共同作用下可有效的将SO2转化,等离子体在转化反应中起着决定性的作用,其主要反应为OH SO2→HOSO2。理论计算和实验数据基本吻合。     

Photochemistry in ordered physisorbed monolayers of dinitrogen tetroxide

The effects of physisorption and two-dimensional ordering on the photochemistry of N₂O₄ were investigated. Ordered monolayers were prepared by adsorption of NO₂ at 100 K on a water-ice surface. Irradiation with a continuous light source in the wavelength region 300–400 nm or with pulsed laser radiation at 355 nm resulted in exclusive desorption of NO₂. This desorption was induced by electronic absorption directly in the adsorbate via a transition corresponding to the ( )¹B_2u←( )¹A_g transition in N₂O₄, as in the gas phase. However, the subsequent dynamics in the excited state were markedly different from the gas-phase counterpart. Time-of-flight mass spectrometry of NO₂ photodesorbed at 355 nm revealed a most probable fragment translational energy of ca. 17 meV; and the angular distribution of the nascent NO₂ was peaked sharply in a direction around 10° from the normal. It is apparent that, despite the weak interaction with the substrate, significant energy transfer occurs in the ordered physisorbed monolayer to yield nascent NO₂ with very low translational energy and a constrained angle of escape which is consistent with a high degree of adsorbate order and alignment.     

Surface chemistry of alkyl and perfluoro ethers: a FTIR and ab initio study of adsorption and decomposition of CF3OCF3 on an Al2O3 surface

The adsorption and thermal decomposition of perfluorodimethyl ether, (CF₃)₂O, on a high-surface-area Al₂O₃ surface was investigated by FTIR under both vacuum and pressure conditions. IR spectra in the 4000-1050 cm⁻¹ range were collected and the spectral assignments were assisted by quantum chemical ab initio calculations. The spectral evidence indicated that (CF₃)₂O decomposed to form adsorbed fluoroformate, FCOO (ads). Increases of temperature (up to 525 K) caused the FCOO (ads) to convert to hydrogen formate, HCOO (ads). Surface hydroxyl groups participated in the decomposition of (CF₃)₂O and the conversion of FCOO (ads) to HCOO (ads). A decomposition mechanism is proposed.     

固体吸附式制冷中热波循环的分析研究

1引言由Tehernev博士和S．V．Shelton教授提出的热波循环，是吸附式制冷中引起广泛兴趣的一种循环方式。其特点是高效回热，Shelton采用斜波法［‘］和方波法［‘］分析了热波循环，回热率达70％，热泵工况COP超过1．6。其它学者作了改进研究［‘并热波循环的模拟效果很好，但实验方面进展相当缓慢。采用螺旋板式换热器作吸附器，也发现热波循环的运行效果很不理想问。目前，相关的文献主要是系统模拟，而对其关键，热波的形成、特性研究较少。另外，研究侧重于系统性能（COP），对能量密度（SPD）考虑较少。本文将从传热的角度分析热…