No description available.

Thesis (Doctoral)--Ruhr-Universität Bochum, 1983.

Correlation of adsorption behavior for a gas-surface system to the molecular structure of the gas-phase molecule is necessary to better constrain atmospheric modeling. Despite the variety of compounds emitted into the atmosphere, the role of molecular structure on uptake probability, γ, for a compound adsorbing onto a surface is not well understood. A custom designed flow manifold coupled to a mass spectrometer provides the means to analyze changes in γ for gases at environmentally relevant low ppb concentrations. Studies have focused on the adsorption of two classes of compounds: singly substituted benzene derivatives and several terpenoid compounds for a silica surface composed of hydroxyl groups and bridging oxygen species. Results for benzene derivatives show an enhancement of the initial γ value of all functionalized compounds relative to benzene, with this initial value influenced by both the dipole and volatility of a compound. The time-dependent behavior of γ has been shown to depend on the interactions occurring between the adsorbate and surface with species capable of hydrogen bond interactions exhibiting a greater number of adsorbed species at equilibrium. The initial γ value for terpenoid species was observed to increase from isoprene to sesquiterpenes, with several monoterpene isomers exhibiting distinct adsorption behavior based on structural differences. The sesquiterpene examined, β-caryophyllene, exhibited continuous uptake onto the silica surface and such uptake behavior could contribute in part to the low concentrations of sesquiterpenes observed in the environment. Encapsulation of the hydroxyl groups resulted in decreased uptake of several aromatic and terpenoid species examined and indicates that hydroxyl groups represent the majority of adsorption sites for the systems examined. Comparison between observed uptake behavior to adsorption models exhibited the best agreement with a model depicting monolayer formation with cooperative adsorption due to interactions between adsorbates. Formulations for predicting initial γ values based on the volatility and dipole of the compound are provided. Overall, these results represent the first step towards a better understanding of gas-surface interactions that occur in the environment. Sesquiterpenes represent one class of biogenic emissions not well constrained with regards to SOA influence due to their low volatility and concentrations relative to more abundant terpenoid species. Ambient measurements of sesquiterpenes through the Semi-Volatile Thermal desorption Aerosol Gas chromatography (SV-TAG) instrument presented total sesquiterpene concentrations that ranged from 0.8 to 2 ppt with no isomer dominating. Sesquiterpene contribution towards hydroxyl reactivity is negligible in comparison to more abundant terpenoid species while ozone reactivity was dominated by two isomers and could contribute to atmospheric reactivity during periods of high emissions. These measurements represent the first step in better constraining the contribution of sesquiterpenes towards secondary organic aerosol formation. / Doctor of Philosophy / A large variety of compounds are emitted into the atmosphere from natural and human sources. The molecular structures of these compounds are complex and differences in structure can alter the environmental fate of compounds, which can directly affect human health. While atmospheric modeling provides insight into the fate of compounds, it relies on experimentally determined values for accuracy. The probability that a gas-phase molecule "sticks" to a surface upon collision, defined as the uptake probability, represents one value that is not well understood. My research has primarily focused on the development and testing of an instrument capable of observing gas uptake onto a surface for environmentally relevant gas concentrations. This has included understanding how differences in structure of a molecule affect adsorption for a single surface. For example, α-pinene and β-pinene (both compounds emitted by plants and found in air fresheners!) exhibit distinct adsorption behavior that arises from the location of a single carbon-carbon double bond for the same structure. Similarly, making a "water-loving" surface into a "water-repelling" surface results in less α-pinene adsorbed, despite α-pinene being considered insoluble in water. The developed instrument represents a vital tool in improving the accuracy of atmospheric modeling. In addition to understanding gas adsorption onto a surface, my research has focused on the detection and quantification of one class of naturally emitted compounds in Virginia: sesquiterpenes. These compounds are emitted by plants for a variety of reasons, and their influence on particle formation is not well understood. Measurement of sesquiterpenes at two sites in Virginia provides a better understanding of the abundance of sesquiterpenes in geographic regions not previously analyzed. These measurements contribute to an increased understanding of the role of different compound classes on particle formation in the atmosphere.

Using computational tools ranging from molecular simulations – including both Monte Carlo and molecular dynamics methods – to quantum mechanical (QM) calculations (primarily at density functional theory (DFT) level), this work focuses on addressing some of the challenges faced in molecular simulations of gas adsorption in metal–organic frameworks (MOFs). This work consists of two themes: one concerns gas adsorption in MOFs with coordinatively unsaturated metal sites (cus’s), and the other one deals with predicting and understanding the breathing behaviour of the flexible MOF MIL-53(Sc). It has been shown experimentally that incorporation of cus’s – also known as “open” metal sites or unsaturated metal centres – into MOFs significantly enhances the uptake of certain gases such as CO2 and CH4. As a result of the considerably enhanced, localized guest-molecule interactions with the cus’s, it, however, remains a challenge to predict correctly adsorption isotherms and/or mechanisms in MOFs with cus’s using grand-canonical Monte Carlo (GCMC) simulations based on generic classical force fields. To address this problem, two multi-scale modelling approaches – which combine GCMC simulations with QM calculations – have been proposed in this work. The first approach is based on the direct implementation of a fluid–framework potential energy surface, calculated by a hybrid DFT/ab initio method, in the GCMC simulations. The second approach involves parameterization of ab initio force fields for GCMC simulations of gas adsorption in MOFs with cus’s. This approach focuses on the generation of accurate ab initio reference data, selection of semiempirical model potentials, and force-field fitting through a multi-objective genetic algorithm approach. The multi-scale simulation strategy not only yields adsorption isotherms in very good agreement with experimental data but also correctly captures adsorption mechanisms, including the adsorption on the cus’s, observed experimentally but absent from GCMC simulations based on generic force fields. The second challenge that this work aims to address concerns the “breathing” phenomenon of MOFs, in which the framework structure adapts its pore opening to accommodate guest molecules, for example. The breathing effect gives rise to some exceptional properties of these MOFs and hence promising applications. However, framework flexibility often poses a challenge for computational studies of such MOFs, because suitable flexible force fields for frameworks are lacking and the effort involved in developing a new one is no less a challenge. Here, an alternative to the force-field-based approach is adopted. Ab initio molecular dynamics (AIMD) simulations – which combine classical molecular dynamics simulations with electronic-structure calculations “on the fly” – have been deployed to study structural changes of the breathing MOF MIL-53(Sc) in response to changes in temperature over the range 100–623 K and adsorption of CO2 at 0–0.9 bar at 196 K. AIMD simulations employing dispersion-corrected DFT accurately simulated the experimentally observed closure of MIL-53(Sc) upon solvent removal and the transition of the empty MOF from the closed-pore phase to the very-narrow-pore phase with increasing temperature. AIMD simulations were also used to mimic the CO2 adsorption of MIL-53(Sc) in silico by allowing the MIL-53(Sc) framework to evolve freely in response to CO2 loadings corresponding to the two steps in the experimental adsorption isotherm. The resulting structures enabled the structure determination of the two CO2-containing intermediate and large-pore phases observed by experimental synchrotron X-ray diffraction studies with increasing CO2 pressure; this would not have been possible for the intermediate structure via conventional methods because of diffraction peak broadening. Furthermore, the strong and anisotropic peak broadening observed for the intermediate structure could be explained in terms of fluctuations of the framework predicted by the AIMD simulations. Fundamental insights from the molecular-level interactions further revealed the origin of the breathing of MIL-53(Sc) upon temperature variation and CO2 adsorption. Both the multi-scale simulation strategy for gas adsorption in MOFs with cus’s and the AIMD study of the stimuli-responsive breathing behaviour of MIL-53(Sc) illustrate the power and promise of combining molecular simulations with quantum mechanical calculations for the prediction and understanding of MOFs.

No description available.

Standard catalyst characterisation techniques such as gas adsorption porosimetry and mercury porosimetry only account for some of the physical heterogeneity of the catalyst surface. They completely ignore the chemical heterogeneity present and in most cases consider pores present in the medium to be independent of each other. Thus, most results of characterisation (pore space descriptors such as BET surface area, BJH pore size distribution, mercury porosimetry surface area, etc.) are not accurate. This has been a major issue that remains to be resolved during the characterisation of fresh and coked catalysts. In this thesis, the use of a multi-component adsorption system is recommended as a step-change solution to this limitation. Two approaches are adopted. Firstly, integrated nitrogen-waternitrogen gas adsorption experiments are performed on fresh and coked catalysts. This established the significance of pore coupling by showing the presence of advanced adsorption. The method also helped to determine the location of coke deposits within catalysts and indicated that water vapour adsorption was a good probe to understand the sites responsible for coking. Secondly, coadsorption of immiscible liquids – cyclohexane and water – was performed on fresh and coked catalysts following which the displacement of cyclohexane by water was studied using NMR relaxometry and diffusometry. This novel approach takes the wettability of the surface into consideration, unlike the former methods. It is therefore a method that accounts for the chemical heterogeneity of the surface. It also helped determine the location of coke within catalysts. The different approaches are presented in the context of combustion of heavy oil in bitumen reservoirs, and the use of supercritical conditions that help to dissolve coke precursors in the isomerisation of 1-hexene. Thus, the solutions provided in this thesis are directions in which catalyst characterisation, especially distinguishing fresh and coked catalysts, and other porous materials, must be carried out.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18952号 / 工博第3994号 / 新制||工||1615(附属図書館) / 31903 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 杉野目 道紀, 教授 宮原 稔 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

As supplier and producing company in the adsorption field, we study diffusion phenomena both related to adsorption and in business field development. In the context of pure gas adsorption for texture characterization of porous materials we find phenomena which are easy to explain, e.g., the blockage of narrow micropores in Zeolith 4A dependent on the measuring temperature (see Fig. 1). Fig. 2 shows temperature profiles and breakthrough curves of mixed gas and vapor adsorption studies, measured with the 3P mixSorb dynamic sorption analyzer [3].

Activated carbons as emerging classes of porous materials have gained tremendous attention because of their versatile applications such as gas storage/separations sorbents, oxygen reduction reaction (ORR) catalysts and supercapacitor electrodes. This diversity originates from fascinating features such as low-cost, lightweight, thermal, chemical and physical stability as well as adjustable textural properties. More interestingly, sole heteroatom or combinations of various elements can be doped into their framework to modify the surface chemistry. Among all dopants, nitrogen as the most frequently used element, induces basicity and charge delocalization into the carbon network and enhances selective adsorption of CO2. Transformation of a task-specific and single source precursor to heteroatom-doped carbon through a one-step activation process is considered a novel and efficient strategy. With these considerations in mind, we developed multiple series of heteroatom doped porous carbons by using nitrogen containing carbon precursors. Benzimidazole-linked polymers (BILP-5), benzimidazole monomer (BI) and azo-linked polymers (ALP-6) were successfully transformed into heteroatom-doped carbons through chemical activation by potassium hydroxide. Alternative activation by zinc chloride and direct heating was also applied to ALP-6. The controlled activation/carbonization process afforded diverse textural properties, adjustable heteroatom doping levels and remarkable gas sorption properties. Nitrogen isotherms at 77 K revealed that micropores dominate the porous structure of carbons. The highest Brunauer-Emett-Teller (BET) surface area (4171 m2 g-1) and pore volume (2.3 cm3 g-1) were obtained for carbon synthesized by KOH activation of BI at 700 °C. In light of the synergistic effect of basic heteroatoms and fine micropores, all carbons exhibit remarkable gas capture and selectivity. Particularly, BI and BIPL-5 derived carbons feature unprecedented CO2 uptakes of 6.2 mmol g-1 (1 bar) and 2.1 mmol g-1 (0.15 bar) at 298 K, respectively. The ALP-6 derived carbons retained considerable amount of nitrogen dopants (up to 14.4 wt%) after heat treatment owing to the presence of more stable nitrogen-nitrogen bonds compared to nitrogen-carbon bonds in BILP-5 and BI precursors. Subsequently, the highest selectivity of 62 for CO2/N2 and 11 for CO2/CH4 were obtained at 298 K for a carbon prepared by KOH activation of ALP-6 at 500 °C.