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Applied Surface Science (v.252, #3)

Fifth International Symposium by Władysław Rudziński (Guest Editor); Małgorzata Witko (Guest Editor) (pp. 501-504).

Generalized statistical description of adsorption of polyatomics by J.L. Riccardo; F. Rom�; A.J. Ramirez-Pastor (pp. 505-511).

Multisite-occupancy adsorption is described as a fractional statistic problem, based on Haldane’s statistics. Site exclusion is characterized by a statistical exclusion parameter, g, which relates to the molecular size and lattice geometry. A general adsorption isotherm is obtained and comparisons with experiments indicate that the spatial configuration of adsorbed molecules and lateral interactions may accurately be assessed from this theory. In addition, the theoretical framework developed in this paper allows to describe orientational transitions occurring in adlayers of polyatomics.

Keywords: PACS; 05.30.Pr; 05.70.Ce; 05.70.Np; 68.35.Md; 68.43.De; 68.43.FgAdsorption isotherms; Multisite occupancy; Quantum fractional statistics; Monte Carlo simulations; Equilibrium thermodynamics and statistical mechanics

Prediction of thermodynamic properties from pure compound information: Characterization of fullerenes by G. Sch�rer; W. Peukert (pp. 512-518).

Fullerenes are widely studied not only in material, but also in life science due to their special properties. Their surface properties determine their interaction with the environment and influence adsorption as well as biodistribution. In this work, the surfaces of a series of fullerenes and polyhydroxylated C₆₀-fullerenes were investigated using density functional theory (DFT)/conductor-like screening model (COSMO)-calculations. The dependence of the screening charge density from the curvature of a carbon hexagon and its effect on the adsorption behavior was studied. The estimation of thermodynamic properties of multiply functionalized C₆₀-molecules gives promising qualitative results using only properties of the pure compounds.

Keywords: Fullerenes; DFT; Functionalization; Adsorption

New insights into the adsorption isotherm interpretation by a coupled molecular simulation—experimental procedure by M.J. S�nchez-Montero; C. Herdes; F. Salvador; L.F. Vega (pp. 519-528).

We present here Grand Canonical Monte Carlo (GCMC) simulation results of nitrogen adsorption at 77K on a crude model of activated carbon. The material is modeled as slit-like pores of different widths, with smooth surfaces. The individual adsorption isotherms serve as the basis to check the success and limitations of the assumptions made when using the BET model to characterize adsorbent materials, in particular to calculate the monolayer capacity and the C parameter. As done in our previous work with several experimental adsorption isotherms, different linearizations of the BET equation are used. The aim of this work is to quantify, using statistical mechanics tools, the changes in the C factor with surface coverage, showing that C is an intrinsically energetic meaningful quantity. The amount of molecules adsorbed at each pressure is calculated in the first and subsequent layers. We also keep track of the adsorbent–adsorbate and adsorbate–adsorbate energy along the simulations. The C factor is obtained following two different routes: as directly derived from the BET equation, once the monolayer capacity is known, and from the heat of adsorption obtained directly from the simulations. Results from simulations confirm the changes in the C values with surface coverage. In addition, molecular simulations provide independent and consistent ways of calculating the monolayer capacity.

Keywords: Nitrogen adsorption isotherms; Activated carbons; BET theory; Molecular simulations; Energetic heterogeneity; Monolayer capacity

Surface topography problem and argon adsorption on crystalline faces: Monte-Carlo and lattice-gas model simulations by J.P. Prates Ramalho; Alexander B. Rabinovich; Denis V. Yeremich; Yuriy K. Tovbin (pp. 529-537).

The lattice-gas model in the quasi-chemical approximation (QCA) was used for adsorption isotherms and heats of adsorption calculations. The theory considers the surface topography, taking into account the atomic surface structure and the occupancy correlation of different adsorption sites. A comparison between Monte-Carlo and QCA simulations of the adsorption isotherms for argon atoms on three faces (110), (100) and (101) of rutile shows that both techniques give rather similar results with the advantage of QCA calculations being performed in a fraction of the time necessary for the Monte-Carlo simulation.

Keywords: PACS; 82.20.Wt; 82.65.−i; 05.50.+qQuasi-chemical approximation; Grand canonical Monte-Carlo; Rutile

Search for a reliable methodology for PSD determination based on a combined molecular simulation–regularization–experimental approach by C. Herdes; M.A. Santos; S. Abell�; F. Medina; L.F. Vega (pp. 538-547).

We present here a methodology for searching a robust pore size distribution (PSD) for adsorbent materials. The method is based on a combination of individual adsorption isotherms, obtained from Grand Canonical Monte Carlo simulations, a regularization procedure to invert the adsorption integral equation (Tikhonov regularization solved by singular value decomposition), and the needed experimental adsorption isotherm. The selection of several parameters from the available choices to start the procedure are discussed here: the size of the kernel (number of individual pores and number of experimental adsorption points to be included), the fulfillment of the Discrete Picard condition, and the L-curve criteria, all leading to find a reliable and robust PSD. The procedure is applied to plugged hexagonal templated silicas (PHTS), synthesized, and characterized in our laboratory.

Keywords: PACS; 02.70.Uu, 68.43.De, 68.43.Fg, 61.46.+wPlugged hexagonal templated silica; Nitrogen adsorption; Molecular simulations; Regularization procedure; Singular value decomposition; Discrete Picard condition

Application of density functional theory to equilibrium adsorption of argon and nitrogen on amorphous silica surface by E.A. Ustinov; D.D. Do; M. Jaroniec (pp. 548-561).

We present a new version of non-local density functional theory (NL-DFT) adapted to description of vapor adsorption isotherms on amorphous materials like non-porous silica. The novel feature of this approach is that it accounts for the roughness of adsorbent surface. The solid–fluid interaction is described in the same framework as in the case of fluid–fluid interactions, using the Weeks–Chandler–Andersen (WCA) scheme and the Carnahan–Starling (CS) equation for attractive and repulsive parts of the Helmholtz free energy, respectively. Application to nitrogen and argon adsorption isotherms on non-porous silica LiChrospher Si-1000 at their boiling points, recently published by Jaroniec and co-workers, has shown an excellent correlative ability of our approach over the complete range of pressures, which suggests that the surface roughness is mostly the reason for the observed behavior of adsorption isotherms. From the analysis of these data, we found that in the case of nitrogen adsorption short-range interactions between oxygen atoms on the silica surface and quadrupole of nitrogen molecules play an important role. The approach presented in this paper may be further used in quantitative analysis of adsorption and desorption isotherms in cylindrical pores such as MCM-41 and carbon nanotubes.

Keywords: Density functional theory; Adsorption; Isotherms; Non-porous silica

Adsorption characterization of surfactant-templated ordered mesoporous silicas synthesized with and without hydrothermal treatment by Jerzy Choma; Stanisław Pikus; Mietek Jaroniec (pp. 562-569).

This work reports a systematic study of ordered mesoporous silicas (OMSs) synthesized with and without hydrothermal treatment at 373K for a series of surfactants of different alkyl chain length (from C10 to C18). For these samples nitrogen adsorption and small angle X-ray scattering (SAXS) data were measured to characterize their adsorption and surface properties. Namely, nitrogen adsorption isotherms were used to evaluate their specific surface area, pore volume and pore size distribution, whereas SAXS data provided information about their structural ordering. It is shown that while the room temperature synthesis afforded OMS samples with cubic MCM-48 structure, an additional 5-day hydrothermal treatment of these samples at 373K caused their transformation to MCM-41 (two-dimensional hexagonal structure) and improved their pore uniformity, which was manifested by reducing the width of pore size distribution.

Keywords: Small angle X-ray scattering; Ordered mesoporous silicas; Nitrogen adsorption isotherms

Evaluation of adsorption energy distribution of microporous materials by a multivariant identification by Jan T. Duda; Janina Milewska-Duda; Mirosław Kwiatkowski (pp. 570-581).

The applicability of new BET-like adsorption models (uLBET and LBET formulas) for the examination of microporous materials of irregular structure is discussed. The models are intended to handle the main effects of random pore geometry on the adsorption isotherm shape. They are based on a generalized BET theory and employ simple (but realistic) adsorption energy–pore geometry relationships. To overcome numerical problems inherent in fitting any more advanced adsorption model, a multivariant identification procedure is proposed with a subset of parameters being fixed in each variant. The reliability assessment of the system parameters evaluation is stressed. The paper outlines formal and numerical bounds for adsorption measurements-based identifiability of irregular porous structures. The LBET-type formulas are recommended for the examination of such materials, as a relatively simple alternative versus DFT-based techniques. Numerous simulation results and exemplary examinations of an empirical isotherm are discussed.

Keywords: Adsorption energy distribution; Microporous materials; Adsorption isotherm

Theoretical study of the influence of laser-induced defects on the adsorption of gases on solid surfaces by Paweł Szabelski; Tomasz Pańczyk; Władysław Rudziński (pp. 582-590).

Laser treatment of a solid surface was modeled by applying an analytical theory as well as by using Monte Carlo simulations. The crystalline surface was assumed to be initially smooth and chemically uniform, that is free of impurities built into the structure. Creation of surface defects by a laser beam was assumed to have entirely random nature. In particular, the surface was assumed to have been scanned by the beam focused successively on randomly chosen points. In the course of the ablation process, the beam produces a pyramidal crater whose dimensions are proportional to the applied laser power. According to the assumed nature of the scanning procedure, the craters formed by the beam are allowed to overlap. The influence of the number of laser pulses and the crater dimensions on the structural and adsorptive properties of the surface were examined by analysis of the variation of the mean surface depth and the surface width. Changes in the adsorptive properties were also estimated by the calculation of the thermally programmed desorption (TPD) spectra of monomolecular adsorbates desorbed from laser-treated surfaces. Additionally, equilibrium adsorption isotherms were calculated for the obtained surfaces.

Keywords: PACS; 68.45.D; 61.72.C; 61.80.BLaser ablation; Surface defects; Monte Carlo simulation; Adsorption isotherms; Thermal desorption

Vapour–liquid coexisting curves and hysteresis of simple adsorbate in complex porous systems by Yu.K. Tovbin; D.V. Yeremich; L.K. Zhidkova (pp. 591-601).

A unified approach for simulation of the vapour–liquid coexisting curves on phase diagrams and hysteresis phenomena for simple adsorbates in various type porous adsorbents was developed on the basis of the lattice–gas model. The ideas of this model in complex porous systems were used twice: for a construction of the over-molecular structure for high-dispersed bodies and for a description of the molecular distribution within the complex porous space. The supramolecular structure of these systems is modelled by sections with a simple regular geometry (slit-like, cylindrical and spherical) with additional inclusion of junctions between different pore sections. At the description of the adsorbate distribution, the lateral interactions between the fluidic molecules were included through the quasi-chemical approximation (QCA) that takes into account direct pair correlations between interacting molecules. The knowledge of phase diagrams allows improving a description of the adsorption hysteresis phenomena. The lattice–gas model enables explaining the experimental data for MCM-41 like sample in which the hysteresis is absent, when the pore size is narrowed more than ∼4nm.

Keywords: PACS; 64.60.−i; 66.20.+d; 68.36.RhMolecular theory; Lattice–gas model; Narrow pores; Phase transition; Argon–carbon system; Hysteresis

An example of chemistry–morphology interaction: making up for the geometric and energetic heterogeneities of the (1 0 0) surface of single crystalline silicon by high-temperature treatments in H₂ by G.F. Cerofolini; C. Galati; S. Reina; L. Renna; D. Jones; V. Palermo (pp. 602-611).

A lot of work has been carried out to prepare chemically homogeneous (1 0 0) silicon surfaces. The hydrogen-terminated (1 0 0) silicon surfaces are the most promising ones, especially in view of their remarkable environmental stability. The simplest way to produce hydrogen-terminated surfaces (attack in water solution of HF of a sacrificial, thermally grown, oxide) results in strongly heterogeneous rough surfaces (although with prevailing dihydride terminations). These surfaces can, however, be flattened and homogenized by treating them inH2 at high temperature (>850°C). The morphological and chemical changes undergone by the surface during the treatment are studied X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunnelling microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, reflection high energy electron diffraction and thermal programmed desorption, and the mechanisms responsible for them are discussed.

Keywords: Thermal programmed desorption; Infrared absorption spectroscopy; X-ray photoelectron spectroscopy

Structural characteristics of porous polymers treated by freezing with water or acetone by V.M. Gun’ko; R. Leboda; J. Skubiszewska-Zięba; B. Gawdzik; B. Charmas (pp. 612-618).

The pore structure of nine polymers of different origin initial and treated in water and acetone for 24h and then frozen by liquid nitrogen for 2h was studied using low-temperature nitrogen adsorption. An average increase in pore volume and surface area is approximately 16 and 8%, respectively, after freezing with water and 19 and 8%, respectively, after treatment with acetone. However, for some samples, this effect is negative but for others, structural changes are significantly greater (up to 106%) than the average one. Certain treated polymers are characterized by shifted pore size distribution which is also accompanied by displacement of nitrogen adsorption energy distribution.

Keywords: PACS; 61.43.Gt powders; Porous materials; 68.35.Bs surface structure and topography; 68.35.Md surface energy; Thermodynamic propertiesPorous polymers; Wetted polymer freezing; Texture; Pore size distribution; Nitrogen adsorption energy

Surface modification of low cost carbons for their application in the environmental protection by A. Arenillas; F. Rubiera; J.B. Parra; C.O. Ania; J.J. Pis (pp. 619-624).

In this work, the CO₂ capture capacity of a series of activated carbons derived from recycled polyethylene terephtalate (PET) was tested, facing two problems at the same time: minimising plastic waste and developing an adsorbent for CO₂ capture. The PET raw material, obtained from post-consumer soft-drink bottles, was chemically activated with KOH. In addition, a series of nitrogen-enriched activated carbons was obtained by mixing the raw material with different nitrogen compounds (i.e., acridine, carbazole and urea). The influence of temperature on the CO₂ capture capacity of the adsorbents was evaluated in a thermogravimetric system. The CO₂ uptake was also related to the chemical and textural characteristics of the samples.

Keywords: CO; ₂; capture; Carbon materials; Plastic waste; Adsorption

The effect of aging temperature on structure characteristics of ordered mesoporous silicas by A. Deryło-Marczewska; A.W. Marczewski; I. Skrzypek; S. Pikus; M. Kozak (pp. 625-632).

A series of mesoporous silica materials were synthesized by applying Pluronic type polymers as pore creating agents. In order to differentiate the characteristics of porous structure of the obtained sorbents the temperature of aging process was changed in the synthesis. The parameters characterizing the pore structure were estimated from nitrogen adsorption/desorption isotherms. The changes of pore arrangement of the obtained materials being a result of different synthesis conditions were investigated by using a small angle X-ray scattering method. Correlations between the values of structure parameters and aging temperature were found.

Keywords: PACS; 61.43.Gt; 67.70.+n; 82.70.−Dd; 82.70.−GgMesoporous silicas; Structure characteristics; SAXS

The use of direct recoil spectrometry (DRS) for the study of water vapor interactions on polycrystalline metallic surfaces—the H₂O/U and H₂O/Ti systems by M.H. Mintz; N. Shamir (pp. 633-640).

Using direct recoil spectrometry (DRS), the shadowing of surface H atoms by neighboring O atoms can differentiate between full and partial dissociation routes of water molecules on the surface as well as point to the geometrical arrangements of hydroxyl surface groups. The H₂O/U and H₂O/Ti systems were compared. It has been found that different mechanisms control the water–surface interactions in these systems.For the H₂O/U system, a simple direct-collision (Langmuir-type) dissociative chemisorption controls the process. Two consecutive stages were identified: (i) below ∼70% monolayer coverage, a complete dissociation of water into oxygen ion and two H atoms, which chemisorb on the remaining unreacted metallic surface and (ii) above about 70% of a full layer coverage, three dimensional oxide islands start to form, causing partial dissociation of water and the formation of surface hydroxyls.For the H₂O/Ti system, a more complicated mechanism, which involves a precursor state, seems to control the process. In that case, two concurrent routes act simultaneously. In addition to the simple direct-collision mechanism, water precursor clusters (bound by hydrogen bonds), which partly dissociate, result in chemisorbed tilted hydroxyl clusters (even at low-coverage). The relative contributions of the precursor route and the direct-collision route are pressure dependent, with the former being dominant at higher exposure pressures.

Keywords: DRS; H; ₂; O/U system; H; ₂; O/Ti system; H shadowing

Study of the energetic heterogeneity of the adsorption of phenol onto activated carbons by TPD under supercritical conditions by F. Salvador; M.J. S�nchez-Montero; A. Salvador; M.J. Mart�n (pp. 641-646).

The Temperature Programmed Desorption (TPD) technique with liquid and supercritical water was used to study the heterogeneity of the adsorption of phenol onto different activated carbons. The presence of several desorption peaks in the spectra clearly indicated that phenol was adsorbed onto the activated carbon with different interaction energies. Calculation of the desorption activation energies revealed that most of the phenol was physisorbed, although a small part was always chemisorbed. The study of the textural characteristics of the carbons suggests that the width of the micropores governs the thermal desorption of the physisorbed phenol.

Keywords: Heterogeneity; Adsorption; Activated carbon; TPD

Heat of adsorption on heterogeneous adsorbents by Shivaji Sircar (pp. 647-653).

The isosteric heat of adsorption is a critical design variable in estimating the performance of an adsorptive gas separation process. The heats can be strong and complex functions of adsorbate loadings when the adsorbent is energetically heterogeneous. Ignoring these characterisitics in process design can lead to serious errors.Only calorimetric heat measurements (pure and multi-component gas) can reveal the complex nature of the adsorbent heterogeneity. Examples of calorimetrically measured heats for adsorption of pure SF₆ and CO₂ on a silicalite sample bonded with alumina, and those for binary CO₂–C₂H₆ mixtures on NaX zeolite are cited to demonstrate the complexity of the subject. The loading dependence of the binary heats is found to be counter-intuitive.A simple analytic thermodynamic model of patchwise heterogeneity is proposed to describe the isosteric heat of adsorption of a single gas and those for the components of a binary gas mixture.

Keywords: Isosteric heat; NaX zeolite; Calorimetric heat

Heats of displacement of hydrogen from palladium by noble gases by Aleksander J. Groszek; Erwin Lalik; Jerzy Haber (pp. 654-659).

It has been observed that noble gases, such as helium, neon and argon produce heat evolution when contacted with Pd powder partially saturated with hydrogen. These phenomena have been studied with flow-through adsorption microcalorimetry. The observed exothermic effects are comparable to those usually associated with the heat of sorption of hydrogen in palladium. It is suggested that the noble gases displace the adsorbed H species from the surface of Pd, causing their reabsorption in the Pd lattice with the exothermic heat of PdH bonds formation, or the formation of H₂, both heat evolutions being observed with a flow-through microcalorimeter.

Keywords: Palladium; Palladium hydride; Noble gases; Heat of sorption; Flow microcalorimetry

Dynamics of CO₂ molecules confined in the micropores of solids as studied by¹³C NMR by Hironori Omi; Takahiro Ueda; Keisuke Miyakubo; Taro Eguchi (pp. 660-667).

The pressure and temperature dependence of¹³C NMR of CO₂ adsorbed in several porous materials was measured. For CO₂ in activated carbon fiber (ACF), the spectrum observed in the pressure range from 0 to 10MPa consisted of two lines. A very sharp peak at δ=126ppm was attributed to free CO₂ gas and a broad peak at δ=123ppm was attributed to confined CO₂ molecules in the micropores of ACF, although CO₂ in microporous materials such as zeolites and mesoporous silica, gave only a single peak attributed to free CO₂ gas. In the low-pressure region, the peak at δ=123ppm shifted to 118ppm and a very broad peak with a line width of about 200ppm appeared. This indicates that there are two kinds of CO₂ molecules confined in ACF with different rates of molecular motion: one is undergoing isotropic rotation and the other is undergoing anisotropic motion, which rotates around an axis tilted by 30° from the molecular axis. This implies that small pockets with a characteristic diameter exist on the surface of the ACF micropore.

Keywords: PACS; 82.75.Mj; 68.43.Fg¹³; C NMR; Adsorption; Carbon dioxide; Nano-space; Microporous materials; Dynamics

Diffusion of particles on a heterogeneous surface by N. Tarasenko; A. Tarasenko; L. Jastrabik (pp. 668-677).

The influence of surface reconstruction on diffusion of particles adsorbed on the surface is investigated in the framework of symmetrical four-position model. The analytical expressions for free energy and diffusion coefficients are obtained assuming the lateral interaction between particles is negligibly small.The critical behavior of the system is described by the Ising spin model. The coverage dependencies of the tracer, jump and chemical diffusion coefficients are calculated for some representative temperatures. The dependencies show clearly strong influence of the surface reconstruction on the thermodynamic and kinetic phenomena: diffusion coefficients become anisotropic on the reconstructed surface. To check the analytical results we have used Monte Carlo simulations of the diffusion on this lattice.

Keywords: PACS; 68.35.F; 68.35.RDiffusion at solid surfaces and solid–solid interfaces; Phase transitions at surfaces and interfaces

On the ways of generalization of adsorption kinetic equations for the case of energetically heterogeneous surfaces by Tomasz Panczyk; Wladyslaw Rudzinski (pp. 678-686).

In this work, we present three different ways of incorporation of the effects of surface energetic heterogeneity in the Statistical Rate Theory kinetic equation. These ways are critically discussed and finally, we come to the conclusion that the most consistent method is based on the assumption that the adsorbing surface should not be considered as composed from independent subsystems but it should be treated as one physical entity. As an illustration, we show the numerical analysis of the experimental data concerning the adsorption of CO₂ on scandia. The estimated best-fit parameters are physically correct and consistent with the results of calorimetric measurements.

Keywords: Statistical Rate Theory; Adsorption/desorption; Kinetics; Energetic heterogeneity

The influence of a small amount of active sites on the adsorption kinetics of nitrogen on ruthenium by Tomasz Panczyk (pp. 687-698).

Recently, Dahl et al. [S. Dahl, A. Logadottir, R.C. Egeberg, J.H. Larsen, I. Chorkendorff, E. T�rnqvist, J.K. N�rskov, Phys. Rev. Lett. 83 (1999) 1814; S. Dahl, E. T�rnqvist, I. Chorkendorff, J. Catal. 192 (2000) 381] have proposed very interesting hypothesis that the rate of dissociation and adsorption of nitrogen on Ru(0001) facet is totally dominated by the presence of a small amount of step sites on Ru(0001) terraces. Following this idea, a kinetic model, based on applying the Statistical Rate Theory approach, was developed in order to explain if such mechanism is able to explain the observed features of the system N₂/Ru(0001). As a result, it was stated that the activation barrier for adsorption on the active (step) sites is equal to 36kJ/mol; in turn, the adsorption energy of nitrogen atoms on the active sites is 43kJ/mol. It implies that the rate of adsorption via the active sites is much faster than direct adsorption on the three-fold hollow sites; moreover, the occupation of the active sites is always close to zero at the investigated temperatures, so they are not blocked and may act as an indirect channel for adsorption. Thus, the rate of nitrogen adsorption on Ru(0001) surface is governed by the rate of diffusion of nitrogen atoms from the active sites into the three-fold hollow sites. The analysis of thermodesorption spectra revealed an important role of repulsive interactions between the N atoms adsorbed on the hollow sites, the associated interaction parameter between nearest neighbors was estimated to be 5kJ/mol. The presence of small amount of gold on Ru(0001), apart of blocking the active sites, seems to remove the repulsion between nitrogen atoms.

Keywords: Adsorption; Kinetics; Nitrogen; Ruthenium; Gold; Statistical Rate Theory; Thermodesorption; Catalyst

Theoretical study of the influence of confinement and channel blocking on adsorption and diffusion of n-butane in silicalite-1 by Barbara Jagoda-Cwiklik; Lukasz Cwiklik; Marek Frankowicz (pp. 699-706).

Dynamic Monte Carlo simulations for the open coarse-grained model of MFI type zeolite were used to study the dynamics of adsorption and diffusion of n-butane in silicalite-1. We demonstrated the influence of the confinement of the structure of zeolite channels on both the dynamics of the adsorption process and the maximum loading of adsorbate. We showed that the confinement and channel blocking limit the adsorption and desorption processes. Moreover, they cause the maximum loading in the zeolite structure for moderate pressures to be higher than the one predicted by the Langmuir model for a flat and homogeneous system.

Keywords: Monte Carlo simulations; Adsorption; Diffusion; Zeolites; n; -Butane

Equilibrated thermodesorption studies of adsorption of n-hexane and n-heptane on zeolites Y, ZSM-5 and ZSM-11 by Wacław Makowski; Dorota Majda (pp. 707-715).

Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur.

Keywords: PACS; 83.80.P; 68.45.DZeolites; Adsorption; Temperature-programmed desorption; n; -Hexane; n; -Heptane

Elucidating alkane adsorption in sodium-exchanged zeolites from molecular simulations to empirical equations by E. Garc�a-P�rez; I.M. Torr�ns; S. Lago; D. Dubbeldam; T.J.H. Vlugt; T.L.M. Maesen; B. Smit; R. Krishna; S. Calero (pp. 716-722).

Configurational-bias Monte Carlo (CBMC) simulations provide adsorption isotherms, Henry coefficients and heats of adsorption of linear alkanes in sodium-exchanged MFI- and FAU-type zeolites. These simulations were carried out using our newly developed force field that reproduces experimental sodium positions in the dehydrated zeolites, and successfully predicts alkane adsorption properties over a wide range of sodium cation densities, temperatures, and pressures. We derived empirical expressions from the simulation data to describe the adsorption of linear alkanes in MFI- and FAU-type zeolites. These expressions afford a suitable substitute for complex CBMC simulations. In the low coverage regime we provide simple expressions that adequately describe the Henry coefficient and adsorption enthalpy of n-alkanes as a function of sodium density and temperature. The predicted Henry coefficients and heats of adsorption compare extremely well to available experimental data. In the high coverage regime we provide an expression for saturation capacities of linear alkanes in the zeolite. This expression, combined with the expression for the Henry coefficients, provides of the complete adsorption isotherms of pure adsorbents and mixtures, in good agreement with the adsorption isotherms obtained from CBMC.

Keywords: Molecular simulations; Empirical equations; CBMC

Irreversible adsorption of colloid particles on heterogeneous surfaces by Z. Adamczyk; K. Jaszczółt; B. Siwek (pp. 723-729).

Irreversible adsorption of polystyrene latex particles of micrometer size range at heterogeneous surfaces was studied experimentally. Model substrate surfaces of controlled site coverage (heterogeneity degree) used in these studies were produced by preadsorption of positively charged latex particles on mica sheets. Deposition kinetics of latex was studied as a function of the site coverage, particle to site size ratio λ and ionic strength of the colloid suspension. Particle distributions over surfaces and coverage were quantitatively evaluated by the direct microscope observation techniques using the diffusion cell. In this way, pair correlation function for various coverage degree and particle size ratio was evaluated. It also was determined the dependence of the jamming coverage of colloid particles on site coverage and ionic strength of the suspension. It was demonstrated that the decrease in the ionic strength of the suspension resulted in a significant decrease in the jamming coverage. This was attributed to the effect of the electrostatic field generated by the interface whose range was increased for low ionic strength. These experimental data revealed, in accordance with theoretical predictions derived from numerical simulations, that the multiple site coordination exerted a pronounced effect on the jamming coverage and the structure of adsorbed layers. It also was shown that this effect can be regulated by changes in the ionic strength of particle suspensions. This could allow one to produce particle clusters at the surface of targeted composition.

Keywords: Adsorption; Colloid particles; Ionic strength; Heterogeneous surface adsorption; Irreversible adsorption

Theoretical modelling of self assembly of zwitterionic surfactants at the silica/water interface by Mateusz Drach; Anna Andrzejewska; Jolanta Narkiewicz-Michałek (pp. 730-744).

A theoretical description of surfactant adsorption based on the model of the adsorbed phase being a mixture of single monomers and spherical and globular aggregates of different sizes has been developed. The assumed aggregate shapes were such that the cross-section of each aggregate parallel to the adsorbent surface was a circle with a radius depending on the aggregation number. The aggregates were allowed to move along the surface and all the lateral interactions between them were neglected except the “excluded area�? ones. With such assumptions the adsorbed phase could be considered as a 2D fluid of hard disks of various dimensions being under the influence of the potential field due to the adsorbent. Using the scaled particle theory (SPT), the expressions for adsorption isotherm and heat of adsorption were derived and next fitted to the experimental data for three zwitterionic surfactants adsorbed on hydrophilic silica. The detailed expression for the chemical potential of transfer of a surfactant molecule from the bulk phase to the surface aggregate proposed by Nagarajan and co-workers [E. Nagarajan, E. Ruckenstein, Langmuir 7 (1991) 2934; R.A. Johnson, R. Nagarajan, Colloids Surf. A 167 (2000) 21; R.A. Johnson, R. Nagarajan, Colloids Surf. A 167 (2000) 31] was incorporated into the model. On the basis of the obtained results the effect of the surfactant–surfactant and solid–surfactant interactions on the organisation of surfactant molecules at the solid–liquid interface is discussed.

Keywords: PACS; 68.45D; 83.70; 82.65DSurface aggregation; Zwitterionic surfactants; Silica; Surface heterogeneity

Evaluation of enthalpy of interfacial reactions from temperature dependency of interfacial equilibrium by Nikola Kallay; Ana Čop (pp. 745-751).

Temperature dependency of equilibrium at metal oxide–aqueous electrolyte solution interface was analyzed by numerical simulation. Derivations of inner surface potential with respect to temperature were performed at constant values of several different parameters. When surface charge density in inner plane was kept constant the reasonable results were obtained, i.e. the electrostatic contribution to enthalpy of protonation of amphotheric surface sites was found to be positive in the pH region below the point of zero potential and negative above this point. All other examined possibilities produced opposite results. Derivation of empirical interfacial equilibrium constant at constant surface potential indicated that electrostatic effect on protonation entropy is negligible and that electrostatic contributions to reaction Gibbs energy and enthalpy are equal and directly related to the surface potential in the inner plane.

Keywords: Surface potential; Enthalpy of surface protonation; Electrostatic effects at interface; Interfacial equilibrium; Interfacial thermodynamics

A Monte Carlo simulation of the heterogeneous adsorption of hydrogen ions on metal oxides: Effect of inert electrolyte by P. Zarzycki; P. Szabelski; R. Charmas (pp. 752-758).

Charging of the surface of an oxide caused by the adsorption of hydrogen ions and ions of inert 1:1 electrolyte was investigated by using grand canonical Monte Carlo simulation technique. In particular, adsorption isotherms of protons as well as of ions of the electrolyte together with the resulting charge density of the surface were obtained for different system parameters. Also, the effect of the surface energetic heterogeneity and the concentration of the background electrolyte on the isotherms and the charge density curves was examined. Furthermore, lateral interactions in the mixed adsorbed phase were taken into account in the modeling of the system behavior. The obtained results, in general, suggest that the three factors mentioned above may have substantial influence on the charging mechanism at the liquid/oxide interface.

Keywords: Electrolyte/oxide interface; Heterogeneity; Simple ion adsorption; Computer simulations

The effect of nature of polyions and treatment after deposition on wetting characteristics of polyelectrolyte multilayers by Marta Kolasińska; Piotr Warszyński (pp. 759-765).

The sequential adsorption of oppositely charged polyelectrolytes (PE) occurs to be a powerful tool for obtaining various materials of precisely defined properties. The interfacial features of PE multilayer films are governed by the choice of polycation/polyanion pairs and the conditions of film formation. Additionally, the long time exposure to the conditions different than that encountered during formation usually affects polyelectrolyte multilayer structure.The wettability of heterogeneous surfaces produced by ‘layer-by-layer’ (LbL) adsorption of polyelectrolytes was investigated in this work. We focused on the influence of film treatment after deposition on wetting properties of obtained multilayers. The effect of the nature of the first layer was also studied. Apart from simple arrangements: (polyallylamine hydrochloride)/(polysodium 4-styrenesulfonate) (PAH/PSS) and (poly-l-lysine hydrobromide)/(poly-l-glutamic acid sodium salt) (PLL/PGA) more complicated structures were considered having as a first layer two types of polyethylene imines (PEI) of different molecular weight.Wetting properties of such polyelectrolyte films were determined experimentally by contact angle measurements using technique of direct image analysis of the shape of sessile drop.

Keywords: ‘Layer-by-layer’ deposition; Polyelectrolytes; Multilayers; Contact angle; Wetting

Adsorption and catalysis: The effect of confinement on chemical reactions by Erik E. Santiso; Aaron M. George; C. Heath Turner; Milen K. Kostov; Keith E. Gubbins; Marco Buongiorno-Nardelli; Małgorzata Sliwinska-Bartkowiak (pp. 766-777).

Confinement within porous materials can affect chemical reactions through a host of different effects, including changes in the thermodynamic state of the system due to interactions with the pore walls, selective adsorption, geometrical constraints that affect the reaction mechanism, electronic perturbation due to the substrate, etc. In this work, we present an overview of some of our recent research on some of these effects, on chemical equilibrium, kinetic rates and reaction mechanisms. We also discuss our current and future directions for research in this area.

Keywords: PACS; 68.90.+g; 82.30.Lp; 82.30.Qt; 82.33.−zChemical reactions; Confinement; Porous carbons; Molecular modeling

Influence of the spacing between metal particles on the kinetics of reaction with spillover on the supported metal catalyst by Lukasz Cwiklik; Barbara Jagoda-Cwiklik; Marek Frankowicz (pp. 778-783).

The influence of the spacing between active metal particles placed on the supported metal catalyst on the kinetics of the catalytic reaction with spillover was investigated. The2A+B2→2AB reaction, modelling the CO oxidation on Pd/Al₂O₃ catalyst, was studied using Dynamic Monte Carlo simulations. It was shown that there exists an optimal spacing, that provides the maximum reaction rate. It was postulated that this optimum is a consequence of both competition and cooperative effects occurring between metal particles.

Keywords: Monte Carlo simulations; Catalysis; Surface chemical reaction; Surface diffusion; Palladium; Aluminum oxide; Carbon oxide

Lattice model studies of CO oxidation kinetic oscillation over nano-scaled Pt particle: Effect of temperature variation and diffusion by Ching-Cher Sanders Yan; Wan-Ting Chuang; Ajay Chaudhari; Shyi-Long Lee (pp. 784-792).

Monte-Carlo technique was applied to simulate the nonisothermal oxide formation/removal model for kinetic oscillation of carbon monoxide oxidation over nano-scaled catalysts. The nonisothermal oxide model interprets kinetic oscillation more properly with shorter oscillatory period and lower maximum CO coverage. Two channels transferring the system back and forth between low and high rate states are necessary to achieve kinetic oscillation. Oxide formation switches the state from high to low rate and found no changes in nonisothermal condition. Oxide removal reverses the process and it is accelerated in nonisothermal simulations cutting low rate period. The role of CO diffusion was found important for the kinetic oscillation. Without CO diffusion, oxide formation rate is increased keeping oxide coverage constant. Thus, the nondiffusive system is always in low reactive state.

Keywords: Heterogeneous catalysis; Monte-Carlo simulation; Model of surface reaction

Sensitivity of styrene oxidation reaction to the catalyst structure of silver nanoparticles by R.J. Chiment�o; I. Kirm; F. Medina; X. Rodr�guez; Y. Cesteros; P. Salagre; J.E. Sueiras; J.L.G. Fierro (pp. 793-800).

This study shows how different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant. Silver nanoparticles (nanowires and nanopolyhedra), prepared using the polyol process, were supported on α-Al₂O₃. For comparison, a conventional catalyst obtained by wet impregnation was also prepared. Phenylacetaldehyde (Phe) and styrene oxide (SO) were the main products for nanoparticles catalysts. The promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied. At 573K, the styrene conversion and selectivity to styrene oxide with the silver nanowires catalyst were 57.6 and 42.5%, respectively. Silver nanopolyhedra catalyst showed 57.5% conversion and 30.8% selectivity to styrene oxide. The promotion by cesium played an important role in improving the epoxidation of styrene. The samples were structurally characterized using X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were applied to characterize the oxygen species detected (O_β, O_γ) on the silver surface.

Keywords: Silver nanoparticles; Nanowires; Nanopolyhedra; Styrene; Selective oxidation

EPR and XPS measurements of polymeric catalysts doped with hereopolyacids in oxygen adsorption studies by Wincenty Turek; Mieczyslaw Lapkowski; Agnieszka Stolarczyk; Joanna Debiec (pp. 801-806).

The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H₅PMo₁₀V₂O₄₀, or H₄SiW₁₂O₄₀, and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O₂ and N₂ flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H₄SiW₁₂O₄₀), PPy(H₅PMo₁₀V₂O₄₀) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium–vanadium anion is more reduced than a silicon–tungsten one. The redox reactions of heteropolyacids involve the oxidation–reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H₄SiW₁₂O₄₀ shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H₅PMo₁₀V₂O₄₀, which is in line with the XPS results.

Keywords: PACS; 82.65.+r; 33.60.F; 33.35EPR spectroscopy; XPS spectroscopy; Heterogeneous catalysis; Oxygen adsorption

Effect of the crystallite size in the structural and textural properties of sulfated and phosphated titania by E. Ortiz-Islas; R. Gomez; T. Lopez; J. Navarrete; D.H. Aguilar; P. Quintana (pp. 807-812).

Sulfated and phosphated titania (TiO₂) were obtained by the sol–gel method. The sulfation was prepared in situ using sulfuric acid as hydrolysis catalyst, or by impregnation with ammonium sulphate. Phosphated sol–gel titania was synthesized with phosphoric acid. Long thermal treatments were carried out from 100 to 1000°C to study the crystallization process of titania. All present phases were nanocrystalline, and the anatase–rutile polymorphic transformation was dependent on the crystallite size of the materials and on the preparation method. The smallest crystallite values were obtained for the phosphated samples. Titania sulfated by impregnation was found to be an efficient and selective catalyst towards propene, whereas di-isopropylether was obtained only in the catalyst prepared in situ with H₂SO₄.

Keywords: PACS; 81.07.Bc; 61.10.Nz; 82.33.LnTitania; Sulfation and phosphation; Sol–gel method; X-ray diffraction; BET

IR studies of EDTA alkaline salts interaction with the surface of inorganic oxides by J. Ryczkowski (pp. 813-822).

The adsorption of alkaline salts of ethylenediaminetetraacetic acid (EDTA) on inorganic supports characterized by the different value of the isoelectric point of the surface (IEPS) has been investigated by transmission and photoacoustic (PA) FT-IR. The IR spectra in the 1800–1200cm⁻¹ region of the supported complexones are different from those of the unsupported compounds. The results obtained imply that the observed changes in the properties of adsorbed complexones are mainly due to interaction of the carboxyl groups of chelate molecule with inorganic oxide hydroxyl groups. The models of those interactions have been proposed. The IEPS value has a noticeable influence on the nature of the interactions observed. Based on the experimental data the ability of inorganic oxide interaction with the chelate molecule can be presented as follows: V₂O₅222O₃2-La2.

Keywords: Inorganic oxides; EDTA; IEPS; Adsorption; FT-IR; FT-IR/PAS

Dehydration of isopropyl alcohol used as an indicator of the type and strength of catalyst acid centres by W. Turek; J. Haber; A. Krowiak (pp. 823-827).

The subject of our studies was determination of the kind and strength of the catalyst acid centres on isopropyl alcohol conversion. The investigations were carried out for two groups of catalysts: typical Lewis acids γ-Al₂O₃ and ZrO₂ and Brønsted acids: H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀. Considerable differences between Lewis and Brønsted acids in the conversion of isopropyl alcohol were observed. The influence of Brønsted acid centres was studied for a group of catalysts with different strength: mixtures of two different heteropolyacids. It was observed that the increasing strength of Brønsted acids centres leads to higher catalytic activity but it does not significantly affect the activation energy of dehydration to propene.

Keywords: PACS; 82.65.+rIsopropyl alcohol conversion; Lewis acids; Brønsted acids; Heteropolyacids; ZrO; ₂; γ-Al; ₂; O; ₃

Acetone gas phase condensation on alkaline metals doped TiO₂ sol–gel catalysts by Marcial Zamora; Tessy L�pez; Ricardo G�mez; Maximiliano Asomoza; Ruth Mel�ndrez (pp. 828-832).

The vapor-phase condensation of acetone was studied over sol–gel prepared TiO₂ and TiO₂-doped with 1wt.% of Li⁺ or Rb⁺. The acetone condensation was catalyzed by basic sites and the obtained products were mesityl oxide (MO), isomesityl oxide (ISMO), mesitylene (M) as well as isophorone (IP) and phorone (P). The TiO₂ crystalline structure was characterized by XRD and the basicity of catalysts by means of CO₂ chemisorption. The number of basic sites was 0.057mmol CO₂/g for TiO₂ and Rb/TiO₂ and 0.676mmol CO₂/g for Li/TiO₂ catalyst. CO₂-TPD showed that the strongest of the basic sites follows the order Rb/TiO₂>TiO₂>Li/TiO₂. Activity was found of the same order in the three catalysts. Selectivity patterns shown that MO (70%) was the main product in Li/TiO₂ while for TiO₂ and Rb/TiO₂ comparable amounts of MO (41 and 44%) and M (39 and 39%) were obtained.

Keywords: Titania; Sol–gel titania; Lithium–titania; Rubidium–titania; Acetone oligomerisation; Sol–gel basic catalysts

Thermal diffusion of potassium on the modified iron surface by U. Narkiewicz; D. Moszyński; M. Brosławski (pp. 833-838).

The diffusion of potassium on the polycrystalline iron surface modified by adsorbed oxygen and nitrogen has been studied by means of AES. The migration of potassium atoms has been observed independently on the constitution of the iron surface in the temperature range between 300 and 450�C. The final concentration of potassium on the iron surface increases with temperature from 300 to 400�C, irrespective of what atoms accompany potassium on the surface. At 450�C, the final level of potassium concentration is decreased. The profiles of the concentration on the surface along the line crossing the source of potassium were also acquired. Applying the diffusion model of finite source, the diffusion coefficient of potassium for oxygen-covered and nitrogen-covered surfaces were evaluated.

Keywords: PACS; 82.80.P; 68.35. FSurface diffusion; Auger spectroscopy; Iron; Potassium

Molybdophosphoric acid in sol–gel titania: Physico-chemical properties by E. Ortiz-Islas; T. L�pez; R. G�mez; J. Navarrete; D.H. Aguilar; P. Quintana; M. Picquart (pp. 839-846).

Titania mixed with molybdophosphoric acid, HMoP, in various proportions (1, 15, 25 and 50wt.%) was obtained by the sol–gel method. The gels were dried and calcined in air at 400, 600 and 800°C. The crystalline phases were identified by X-ray diffraction (XRD), whereas the physico-chemical properties were characterized by Raman spectroscopy and³¹P MAS-NMR spectroscopy. FTIR was a technique used to determine acidic properties by pyridine adsorption. XRD showed that HMoP does not decompose until 700°C. The stabilization of the anatase phase and the Keggin HMoP crystalline structure were evidenced by Raman spectroscopy; whereas FTIR-pyridine adsorption spectra showed that titania-HMoP present Brönsted and Lewis acid sites. A correlation between the acid sites and the amount of HMoP was observed by³¹P MAS-NMR.

Keywords: PACS; 81.07.Bc; 61.10.Nz; 78.30.Hv; 82.56.DjMolybdophosphoric acid; Sol–gel catalysts; Titania catalysts; Raman spectroscopy; ³¹; P MAS-NMR

Studies of the activity of catalysts based on heteropolyacids by Wincenty Turek; Mieczyslaw Lapkowski; Joanna Debiec; Agnieszka Krowiak (pp. 847-852).

The catalytic activity of samples such as PPy(H₄SiW₁₂O₄₀), PPy(H₅PMo₁₀V₂O₄₀), PPy(H₂Fe(III)PMo₁₀V₂O₄₀), PPy(H₃Cu(II)PMo₁₀V₂O₄₀) has been examined in two different test reactions. The acid–base and oxidation–reduction properties were studied using the conversion of isopropyl alcohol to propene and acetone. Redox ability of catalysts was examined in the reaction of oxidation of allyl alcohol to glycidol. It was found that the activity of catalysts in the oxidation of allyl alcohol increases as the oxidation properties determined from the conversion of isopropyl alcohol increase. It was also observed that stronger oxidation–reduction properties of the catalyst result in a high rate of the consecutive reaction of glycidol to 3-hydroxypropanone.The phase composition of catalysts was determined by means of X-ray diffraction (XRD).

Keywords: PACS; 82.35.x; 82.65.+rConducting polymers; Polypyrrole; Heteropolyacids; Heterogeneous catalysis

Crystallinity effect in the textural properties of titania-TPA catalysts by E. Ortiz-Islas; T. Lopez; R. Gomez; M. Picquart; D.H. Aguilar; P. Quintana (pp. 853-857).

Catalysts based in titania mixed with tungstophosphoric acid (TPA), H₃PW₁₂O₄₀, in various proportions (1, 15, 25 and 50wt%) were obtained by the sol–gel method. The gels were prepared by hydrolysis and gellation of titanium n-butoxide with a TPA solution, using HNO₃ as a catalyst to obtain a pH 3. Fresh samples were thermally treated from 100 to 800°C, in a stepwise increment of 100°C during 20h per step. Specific surface areas were calculated by the BET method from the nitrogen adsorption isotherms; it was found that the surface area increased with TPA content. The crystallization behavior was followed by powder X-ray diffraction. Crystallite size measurements showed that anatase remains nanocrystalline in the studied temperature range. From the X-ray data, it was clear that below 700°C TPA is highly dispersed in an amorphous state.

Keywords: PACS; 81.07.Bc; 61.10.Nz; 82.33.LnTitania catalysts; Tungstophosphoric acid; Sol–gel method; X-ray diffraction

Infrared spectroscopic study of alkyl aldehydes adsorbed on cations supported by layer silicate by Jong Rack Sohn; Jong Soo Han; Jun Seob Lim (pp. 858-865).

The self-supported film specimen of Wyoming montmorillonite as a layer silicate exchanged by cations, Li⁺, Na⁺, K⁺, Ca²⁺, Ni²⁺, and Al³⁺ were allowed to contact acetaldehyde, acrolein and crotonaldehyde within the heatable gas cell. Adsorption mechanism of alkyl aldehydes on cations supported by layer silicate was studied by means of infrared spectroscopy and X-ray. The infrared spectra between 4000 and 1200cm⁻¹ at different pressures of adsorbates indicated bond formation through carbonyl oxygen. The intensity of the stretching OH was analyzed and resonance form of cationic hydroxyl was proposed as an adsorption site. The carbonyl stretching band, which shifted about 130cm⁻¹ to lower frequencies was observed only for Ni²⁺, Ca²⁺, and Al³⁺ supported by layer silicate and was attributed to >CO··· M n⁺ complex formation. A sharp band, which appeared as a shoulder at 1722 for acetaldehyde and 1690 for acrolein and crotonaldehyde, was responsible for the interaction of carbonyl with surface hydroxyl. The second broad band, which appeared at about 1710–1660, was responsible for hydrogen bonding between carbonyl oxygen and cationic hydroxyl group.

Keywords: Infrared spectra; Acrolein and crotonaldehyde; Carbonyl stretching band

The study of dehumidifying of carbon monoxide and ammonia adsorption by Iranian natural clinoptilolite zeolite by R.M.A. Tehrani; A.A. Salari (pp. 866-870).

The natural zeolite (clinoptilolite type) was obtained from the Neibagh region of Mianeh, the city in the west of Iran. The raw zeolite was tested for quality and quantity measurements including surface area and volumetric characteristics as well as thermogravimetry analysis. The acid activation process was used to increase the adsorption rate of zeolite and in order to obtain the optimum conditions: the effect of acid concentration, reaction time and the temperature were studied. A surface area measurement test was performed in each stage to get the best results. Thus, efficient condition was selected according to the produced highest surface area. The reaction was first obtained with hydrochloric acid, and then a comparison was made using the sulfuric acid. The hydrochloric reaction proved to be better. The result of activation was 2.5 times the increase in the surface area in relation to the raw sample. The result of elemental analysis conducted once again on the activated sample showed an increase in the ratio of Si/Al (approximately 0.6). Then, using CO, NH₃ and steam, the gas adsorption capacity of both the raw and activated samples was measured and compared. Since CO was not adsorbed at ambient temperature, but steam was adsorbed relatively well, the natural clinoptilolite zeolite of Iran was suggested as a suitable material for adsorbing humidity form carbon monoxide as well as synthesis gas (H₂ and CO mixture).

Keywords: Clinoptilolite zeolite; Adsorption; Surface area; Themogravimetry analysis (TG); Activated zeolite

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Applied Surface Science (v.252, #3)