Fani Roubani-Kalantzopoulou

Diffusion, adsorption and catalytic studies by gas chromatography

Three topics important in many areas of physical chemistry, namely measurements of diffusion coefficients, adsorption kinetics and adsorption isotherms, as well as rates and conversions in heterogeneous catalysis, are reviewed from the gas chromatography viewpoint. After a general introduction, various theoretical sections include synopses of important mathematical models and developments, followed by experimental sections describing basic instrumentation and set-ups, and sections exemplifying the main results with brief discussions. The article is concluded with a methodology embracing simultaneous determination of all three properties (diffusion, adsorption and catalytic rates) in a single experiment by GC.

Measurement of adsorption energies on heterogeneous surfaces by inverse gas chromatography

Abstract Inverse gas chromatography methods, like the reversed-flow gas chromatography technique, offer a new pathway to the determination of adsorption energies of gaseous substances on heterogeneous solid adsorbents, as a function of time. The theoretical development was based on the local isotherm model of Jovanovic, and the experimental arrangement was a simple gas chromatograph, slightly modified. The method was applied to four gas–solid systems, at 323.2 K, namely, gaseous C2H4 and ZnO, PbO, TiO2, Fe2O3, the solids also being γ-irradiated with 8.2 Mrad before adsorption experiments. The results obtained point to the conclusion that a time transition period with respect to the adsorption energy exists, consisting of maxima and minima in the values of energy with time. It ends by levelling off at long times. The kinetic physicochemical quantities of adsorption have also been measured.

Chromatographic study of the influence of nitrogen dioxide on the reactions between volatile hydrocarbons and inorganic pigments

Abstract Deposition velocities, V d , reaction probabilities, γ , and local adsorption parameters, k 1 , describing the isotherms of ethane, ethene, ethyne, propene and 1-butene onto three solid pigments (PbO, Fe 2 O 3 , CdS) have been determined in the absence and in the presence of NO 2 , together with the surface reaction rate constant, k 2 , and the desorption rate constant, k −1 . The calculations are based on experimental adsorption isotherms, since the linear adsorption model is not a very good approximation for inorganic solids like those mentioned above. The important result found is the effect of NO 2 on the values of the parameters V d , γ , k 1 , k −1 and k 2 in most cases.

Development and characterization of ZnO, Au/ZnO and Pd/ZnO thin films through their adsorptive and catalytic properties.

In this paper, we report (a) the development of ZnO thin films prepared by pulsed laser deposition and partially covered with nano-particles Pd or Au and (b) their physicochemical study, in order to investigate their catalytic and/or adsorptive properties. It is the first time where two different and popular methods, namely pulsed laser deposition and reversed flow-inverse gas chromatography, are combined. The inverse gas chromatographic technique with the corresponding time-resolved analysis is used for the first time in order to characterise compounds in the nano-scale domain. We focus on the determination of physicochemical quantities mainly concerning the adsorption in thin films, with (Pd/ZnO) or without (Au/ZnO) catalytic behaviour. Thus, entropy and other important physicochemical quantities are calculated which reveal the mechanism of adsorption as well as of isomerization-hydrogenation of 1-butene and contribute to the study of heterogeneity of thin film surfaces. The programs used have been written in Fortran. An important achievement is also the determination of the standard deviations of the kinetic constants.

Gas chromatographic determination of binary adsorption isotherms

Abstract Reversed-flow gas chromatography is a dynamic method useful for measuring adsorption isotherms at low concentrations. This method based on the mass-balance equations is useful for evaluating the adsorption isotherms because it gives model-independent results. The method is described and evaluated for the determination of the adsorption isotherms of two components in gas–solid systems. The following adsorbents were included in the study: iron oxide, zinc oxide, chromium oxide, lead oxide and titanium oxide. The adsorption of two significant aromatic hydrocarbons (benzene and toluene) was investigated in the presence of an inorganic gas (nitrogen dioxide).

A differential method for the analysis of chemical kinetics results based on reversed-flow gas chromatography

SummaryThe reversed-flow gas chromatographic technique has been applied to the determination of the apparent rate constant and the reaction order of a reaction between two gases or vapors. For seven hydrocarbons (ethane, ethene, ethyne, propene, butene, benzene and toluene) reacting with nitrogen dioxide, the above mentioned kinetic parameters have been determined. For these determinations, the necessary mathematical formulation of the problem has been written and solved, leading to simple expressions which describe the height of the chromatographic sample peaks as a function of time.

Experimental adsorption isotherms based on inverse gas chromatography

A new chromatographic perturbation method is used for studying the adsorption-desorption equilibrium in various gas-solid heterogeneous systems. It is the reversed-flow method giving accurate and precise values of many physicochemical constants including the basic and necessary adsorption isotherm values. For four inorganic oxides, namely, Cr2O3, Fe2O3, TiO2 and PbO, and two aromatic hydrocarbons (benzene, toluene) these adsorption isotherms have been determined through a non-linear model.

Hydrogenation of 1-butene on nanosized Pd/ZnO catalysts

The reaction concerning the hydrogenation of 1-butene has occupied the researchers conducting research based on the method of reversed-flow inverse gas chromatography (RF-IGC), for extended time periods. This work aims to define and record, with the utmost accuracy, the phenomena and their possible parallel reactions. It was a challenge for the RF-IGC, which was met. The venture consisted of many parts. Answers had to be provided to the following questions: (a) Can RF-IGC deal with issues of catalysis? (b) Can RF-IGC be applied to thin films? (c) Can RF-IGC identify peaks? (d) Can RF-IGC define the gnostic regions of adsorption, desorption, surface diffusion, surface reaction, the existence of more than one reaction? (e) Can it kinetically follow the above? The answer is certainly yes. The effort made is presented in this work and aims to answer all the above questions.

Study of the Adsorption of Ozone on the Surface of Ferric Oxide by Reversed-Flow Inverse Gas Chromatography

Abstract In this work, in order to describe the impact of ozone on ferric oxide – a common constituent of building materials – in purely scientific terms, a novel methodology that of Reversed Flow–Inverse Gas Chromatography (RF–IGC or RF–GC) is proposed. Five important physicochemical quantities concerning adsorption of ozone on the solid surface of ferric oxide are determined, in five temperatures, in a time-resolved way. By means of a simple PC-program, the values of local adsorption energy, local adsorption isotherm, local monolayer capacity, probability density function for adsorption energy, and energy from lateral interactions are calculated. Thus, the role of surface heterogeneity, lateral interactions and different distributions of active sites (surface topography) on the adsorption of ozone on the surface of ferric oxide is analyzed in the way the RF–IGC method has it developed.

Contribution of Adsorption Phenomena to the Degradation Study of Marble Statues in the Archaeological Museum of Philippi, Greece

A description is provided of the contribution of time-resolved analysis in understanding adsorption phenomena and its contribution to an examination of the overall degradation mechanism of authentic marble pieces brought about by air pollution. As a consequence, a scientific answer has been provided to the question “how are materials of cultural heritage affected by air pollution?” The use of reversed-flow inverse gas chromatography (RF-IGC) has allowed the determination of important local physicochemical quantities relating to the influence of three light hydrocarbons, either in the presence or absence of sulphur dioxide. A detailed analysis of the results as well as a correlation study is given.