Publications by authors named "Nicholas A. Katsanos"

6 Publications

  • Page 1 of 1

Time distribution of adsorption entropy of gases on heterogeneous surfaces by reversed-flow gas chromatography.

J Chromatogr A 2006 Sep 27;1127(1-2):221-7. Epub 2006 Jun 27.

Department of Chemistry, University of Patras, 26504 Patras, Greece.

The reversed-flow gas chromatography (RF-GC) technique has been applied to measure the adsorption entropy over time, when gaseous pentane is adsorbed on the surface of two solids (gamma-alumina and a silica supported rhodium catalyst) at 393.15 and 413.15K, respectively. Utilizing experimental chromatographic data, this novel methodology also permits the simultaneous measurement of the local adsorption energy, epsilon, local equilibrium adsorbed concentration, c(s)(*), and local adsorption isotherm, theta(p, T, epsilon) in a time resolved way. In contrast with other inverse gas chromatographic methods, which determine the standard entropy at zero surface coverage, the present method operates over a wide range of surface coverage taking into account not only the adsorbate-adsorbent interaction, but also the adsorbate-adsorbate interaction. One of the most interesting observations of the present work is the fact that the interaction of n-pentane is spontaneous on the Rh/SiO(2) catalyst for a very short time interval compared to that on gamma-Al(2)O(3). This can explain the different kinetic behavior of each particular gas-solid system, and it can be attributed to the fact that large amounts of n-C(5)H(12) are present on the active sites of the Rh/SiO(2) catalyst compared to those on gamma-Al(2)O(3), as the local equilibrium adsorbed concentration values, c(s)(*), indicate.
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http://dx.doi.org/10.1016/j.chroma.2006.05.067DOI Listing
September 2006

Determination of chemical kinetic properties of heterogeneous catalysts.

J Chromatogr A 2004 May;1037(1-2):125-45

Department of Chemistry, University of Patras, PO Box 1045, GR-265 04 Patras, Greece.

The importance of cooperation of heterogeneous catalysis with surface science is stressed for simultaneous adsorptive and catalytic measurements. Inverse gas chromatography and reversed-flow gas chromatography offer a suitable research ground for such collaboration. After a short introduction, adsorption physicochemical quantities of heterogeneous catalysts with typical recent results, chemical kinetic properties and surface energy of catalysts are described, stressing the important aspect of time-resolved chromatography, due to the heterogeneity of the solid surface of catalysts. Adsorption energies, local monolayer capacities, local isotherms and energy distribution functions are extensively described. Also, lateral molecular interactions, surface diffusion and adsorption rates on heterogeneous catalysts are described.
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http://dx.doi.org/10.1016/j.chroma.2003.11.051DOI Listing
May 2004

Surface energy of solid catalysts measured by inverse gas chromatography.

J Colloid Interface Sci 2004 Feb;270(2):455-61

Department of Chemistry, University of Patras, 26504 Patras, Greece.

The time separation of experimental surface energy on Pt-Rh bimetallic catalysts, together with the time-independent rate constants for adsorption and desorption of O(2), CO, and CO(2) on them, is described, applying the reversed-flow version of inverse gas chromatography. The standard free energy of adsorption DeltaG(z.plims;) and its probability density function over time, together with the geometrical mean of the London parts of the total surface free energy (gamma(L)(1)gamma(L)(2))(1/2) of the adsorbed probe and the solid surface, accompanied by the relevant probability density functions over time are also calculated. The time-resolved phenomena lead to quite varying values of DeltaG(z.plims;), (gamma(L)(1)gamma(L)(2))(1/2), and the distribution functions as time passes, their maximum values being given by the catalyst containing a Pt:Rh = 3:1 weight ratio of the active phase for all adsorbed gases. The conclusion is reached that the surface energy measured as described can be used as a good measure for catalyst characterization.
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http://dx.doi.org/10.1016/j.jcis.2003.07.037DOI Listing
February 2004

Heterogeneous catalysis on solids of gases diffusing through a liquid layer, studied by inverse gas chromatography.

J Chromatogr A 2002 Nov;977(1):107-14

Department of Chemistry, University of Patras, 26504 Patras, Greece.

Physicochemical parameters for heterogeneous catalytic reactions when the catalytic bed was under a liquid phase have been determined, using a non-linear adsorption isotherm by the reversed-flow version of inverse gas chromatography (RF-GC). The mathematical analysis developed in heterogeneous catalysis, mass transfer across gas-liquid boundaries, and diffusion coefficients of gases in liquids was associated with a non-linear adsorption isotherm to find the relevant equations pertaining to the problem. These equations were then used to calculate the adsorption/desorption rate constant, the rate constant for the first-order catalytic reaction and the equilibrium constant for the non-linear adsorption isotherm. The diffusion coefficients of the reactant in the liquid and gaseous phases and the partition coefficients for the distribution of the reactant between the gaseous and liquid phase were also determined.
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http://dx.doi.org/10.1016/s0021-9673(02)01199-8DOI Listing
November 2002

Physicochemical measurements by the reversed-flow version of inverse gas chromatography.

J Chromatogr A 2002 Sep;969(1-2):3-8

Department of Chemistry, University of Patras, Greece.

Since the first publication on the method, reversed-flow gas chromatography has been used to "separate" physicochemical quantities by measuring the value of one in the presence of another. The experimental arrangement consists of a small modification of a commercial gas chromatograph, so that it includes a four- or six-port gas sampling valve, and a simple cell placed inside the chromatographic oven. This cell suppresses the effects of the carrier gas flow on the physicochemical phenomena taking place in the stationary phase. These phenomena pertain to chemical kinetics, diffusion in gases, liquids and surfaces, mass transfer across gas-liquid and gas-solid boundaries, local adsorption on heterogeneous solid surfaces, etc.
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http://dx.doi.org/10.1016/s0021-9673(02)00992-5DOI Listing
September 2002

Interrelations between Adsorption Energies and Local Isotherms, Local Monolayer Capacities, and Energy Distribution Functions, as Determined for Heterogeneous Surfaces by Inverse Gas Chromatography.

J Colloid Interface Sci 2001 Jul;239(1):10-19

Physical Chemistry Laboratory, University of Patras, Patras, 26504, Greece

Physicochemical parameters for adsorption of gases at the submonolayer regions of heterogeneous solid surfaces are measured experimentally as a function of time, and then interrelated as local isotherms θ against adsorption energy varepsilon, fractional changes of adsorption sites f(varepsilon)/c*(max) against varepsilon, θ against f(varepsilon)/c*(max), and distribution functions θ f(varepsilon)/c*(max) over adsorption energy values varepsilon, without using at all the well-known integral equation Theta(p, T)=integral(infinity)(0)θ(p, T, varepsilon)f(varepsilon)dvarepsilon and assumptions concerning the pair f(varepsilon) and θ(p, T, varepsilon). The method uses only chromatographic experimental data obtained by the inverse gas chromatography technique known as reversed-flow gas chromatography. It has been applied to the adsorption of cis-2-butene and trans-2-butene onto particles of Penteli marble at temperatures of 302, 314, 323, and 333 K. The results obtained are comparable with those calculated on the basis of the well-known integral equation. Copyright 2001 Academic Press.
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http://dx.doi.org/10.1006/jcis.2001.7478DOI Listing
July 2001
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