Heats of solution/substitution in TlNO3 and CsNO3 crystals and in RbNO3 and CsNO3 crystals from heats of transition: the complete phase diagrams of TlNO3-CsNO3 and RbNO3-CsNO3 systems

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope ΔH_t/x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, ΔH_s^°, of Tl⁺ in CsNO₃ crystal and Cs⁺ in TlNO₃ crystal and Rb⁺ in CsNO₃ crystal and Cs⁺ in RbNO₃ crystal along with their recovered lattice energies, ΔH_L^°, are reported. ΔH_s^° of Tl⁺ and Rb⁺ in CsNO₃ crystal are each found to be negligible or zero representing an ideal solid solution, i.e. ΔH_mix=0. The complete phase diagrams of the TlNO₃-CsNO₃ and RbNO₃-CsNO₃ systems with details of the sub-solidus regions are included. The properties of Tl_(1−x)Cs_xNO₃ and Rb_(1−x)Cs_xNO₃ compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl_(1−x)Rb_xNO₃.     

Ethylene adsorption on the Pt-Cu bimetallic catalysts. Density functional theory cluster study

The adsorption of ethylene on Cu₁₂Pt₂ clusters has been studied within the density functional theory (DFT) approach to understand the high ethylene selectivity of Cu-rich Pt-Cu catalyst particles in the reaction of hydrogen-assisted 1,2-dichloroethane dechlorination. The structural parameters for Cu₁₂Pt₂ clusters with D_4h, D_2d, and C_3v symmetry have been calculated. The relative stability of the isomeric Cu₁₂Pt₂ clusters follows the order: C_3v > D_2d > D_4h. Each isomer has an active site for ethylene adsorption that consists of a single Pt atom surrounded by Cu atoms. The interaction of ethylene with the active site yields a π-C₂H₄ adsorption complex. The strongest π-C₂H₄ complex forms with the cluster of C_3v symmetry; the bonding energy, ΔE_π(C₂H₄), is −15.6 kcal mol⁻¹. The bonding energies for the π-C₂H₄ complex with Cu₁₄ and Pt₁₄ clusters are −6.5 and −18.8 kcal mol⁻¹, respectively.The addition of Pt to Cu modifies the valence spd-band of the cluster as compared to a Cu₁₄ cluster. The DOS near the Fermi level increases when C₂H₄ adsorbs on the Cu₁₂Pt₂ cluster. As well, the center of the d-band shifts toward lower binding energies. Ethylene adsorption also induces a number of states below the d-band. These states correspond to those of gas-phase C₂H₄.The vibrational frequencies of C₂H₄ adsorbed on the clusters of D_4h and C_3v symmetry have been calculated. The phonon vibrations occur below 250 cm⁻¹. The intense bands around 200 cm⁻¹ are attributed to stretching vibrations of the Pt-Cu bonds normal to the cluster surface. The stretching vibrations of the Pt-C bonds depend on the local structure of the active site: ν_s(Pt-C) = 268 cm⁻¹ and ν_as(Pt-C) = 357 cm⁻¹ for the cluster of the D_4h symmetry; ν_s(Pt-C) = 335 cm⁻¹ and ν_as(Pt-C) = 397 cm⁻¹ for the cluster of the C_3v symmetry. Bands in the range of 800-3100 cm⁻¹ are attributed to vibrations of the adsorbed C₂H₄ molecule. The signature frequencies of the π-C₂H₄ adsorption complex are the δ_s(CH₂) deformation vibration at ∼1200 cm⁻¹ and the ν(C-C) stretching vibration at ∼1500 cm⁻¹. These vibration are absent for di-σ-C₂H₄ adsorption complexes.     

Characterization and ethylene adsorption of natural and modified clinoptilolites

The ethylene adsorption of Turkey clinoptilolite-rich tuff from Gordes and Bigadic region of western of Anatolia and their exchanged forms (K⁺, Na⁺ and Ca²⁺) were investigated. The clinoptilolite samples were characterized using XRD, TG-DTA and nitrogen adsorption methods. Adsorption isotherms for ethylene on natural and modified forms of both adsorbents at 277 K and 293 K were obtained at pressures up to 38 kPa. Uptake of ethylene increased as Na-CLN < Ca-CLN < K-CLN < Natural CLN for Gordes zeolite at 277 K, 293 K and for Bigadic zeolite at 277 K. For Bigadic zeolites at 293 K, uptake of ethylene increased in the order Ca-CLN < Na-CLN < K-CLN < Natural CLN. It was found that ethylene adsorption capacity of Bigadic clinoptilolite samples was much greater than Gordes clinoptilolite samples except K⁺ modified forms at both temperatures. These results show that both natural clinoptilolites have a considerable potential for the removal of ethylene.     

Variable-temperature FT-IR studies on the thermodynamics of carbon dioxide adsorption on a faujasite-type H-Y zeolite

Adsorption of carbon dioxide on a faujasite-type H-Y zeolite (Si:Al = 2.6:1) was studied by variable-temperature (200-290 K range) infrared spectroscopy. Adsorbed CO₂ molecules interact with the Brønsted acid Si(OH)Al groups located inside the zeolite supercage, bringing about a characteristic bathochromic shift of the O-H stretching mode from 3645 cm⁻¹ (free OH group) to 3540 cm⁻¹ (hydrogen-bonded CO₂ adsorption complex). Simultaneously, the asymmetric (ν₃) mode of adsorbed CO₂ is observed at 2353 cm⁻¹. From the observed variation of the integrated intensity of the 3645 and 2353 cm⁻¹ IR absorption bands upon changing temperature, corresponding values of standard adsorption enthalpy and entropy were found to be ΔH° = −28.5(±1) kJ mol⁻¹ and ΔS° = −129(±10) J mol⁻¹ K⁻¹. Comparison with the reported values of ΔH° for CO₂ adsorption on other zeolites is briefly discussed.     

Diffusion of ions in supercritical water: Dependence on ion size and solvent density and roles of voids and necks

We have performed molecular dynamics simulations of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and halide (F⁻, Cl⁻, Br⁻, I⁻) ions in supercritical water at 673 K. The calculations were done for water at three different densities of 1.0, 0.7 and 0.35 g cm⁻³ to investigate the effects of solute size on the diffusion of ions in supercritical water. On increase of ion size, we observe a maximum for diffusion of ions in supercritical water of higher densities (1.0 and 0.7 g cm⁻³). However, no such maximum is found for ion diffusion in the supercritical water of low density (0.35 g cm⁻³) or for diffusion of neutral solutes at all densities. These results are analyzed in terms of passage through voids and necks present in supercritical water. Correlations of the observed diffusion behavior with the sizes of ions and voids present in the systems are discussed.     

Infrared spectra and stability of CO and H2O sorption over Ag-exchanged ZSM-5 zeolite: DFT study

The infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag⁺ cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag⁺ cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag-ZSM-5. The free energy changes ΔG, −5.55 kcal/mol and 6.52 kcal/mol for one and two CO molecules, illustrate that the Ag⁺(CO)₂ complex is unstable at the room temperature. The vibration frequency of C-O stretching of one CO molecule bonded to Ag⁺ ion at 2211 cm⁻¹ is in good agreement with the experimental results. The calculated C-O symmetric and antisymmetric stretching frequencies in the Ag⁺(CO)₂ complex shift to 2231 cm⁻¹ and 2205 cm⁻¹ when the second CO molecule is adsorbed. The calculated C-O stretching frequency in CO-Ag-ZSM-5-H₂O complex shifts to 2199 cm⁻¹, the symmetric and antisymmetric O-H stretching frequencies are 3390 cm⁻¹ and 3869 cm⁻¹, respectively. The Gibbs free energy change (ΔGH₂O) is −6.58 kcal/mol as a H₂O molecule is adsorbed on CO-Ag-ZSM-5 complex at 298 K. The results show that CO-Ag-ZSM-5-H₂O complex is more stable at room temperature.     

Equilibrium and kinetic modeling of adsorptive sulfur removal from gasoline by synthesized Ce-Y zeolite

In this research, the adsorption of a model sulfur compound, thiophene, from a simulated gasoline onto Ce-Y zeolite in pellet and powder forms was investigated. For this purpose, zeolite Na-Y was synthesized, and Ce-Y zeolite was prepared via solid-state ion-exchanged (SSIE) method. Adsorptive desulfurization of model gasoline was conducted in a batch reactor at ambient conditions to evaluate the equilibrium and kinetics of thiophene adsorption onto Ce-Y zeolite. The equilibrium data were fitted to Langmuire and Toth models. Pseudo-n-order and modified n-order models, LDF-base model, and intra-particle diffusion model were evaluated to fit the kinetic of the adsorption process and to determine the mechanism of it. The corresponding parameters and/or correlation coefficients of each model were reported. The LDF-base model was used also to fit the mass transfer coefficient for both powder and pellet forms of the adsorbent. The best fit estimates for the mass transfer coefficient were obtained 4 × 10⁻¹¹ m/s and k = 3.1 × 10⁻¹²[exp( − t/τ) + 1/(t + 10⁻⁴)], for powder and pellet form adsorbents, respectively.     

A density functional theory study of ethylene adsorption on Ni10(1 1 1), Ni13(1 0 0) and Ni10(1 1 0) surface cluster models and Ni13 nanocluster

Ethylene adsorption was studied by use of DFT/B3LYP with basis set 6-31G(d,p) in Gaussian’03 software. It was found that ethylene has adsorbed molecularly on all clusters with π adsorption mode. Relative energy values were calculated to be −50.86 kcal/mol, −20.48 kcal/mol, −32.44 kcal/mol and −39.27 kcal/mol for Ni₁₃ nanocluster, Ni₁₀(1 1 1), Ni₁₃(1 0 0) and Ni₁₀(1 1 0) surface cluster models, respectively. Ethylene adsorption energy is inversely proportional to Ni coordination number when Ni₁₀(1 1 1), Ni₁₃(1 0 0) and Ni₁₀(1 1 0) cluster models and Ni₁₃ nanocluster are compared with each other.     

Stationary inverted Lyman populations and free-free and bound-free emission of lower-energy state hydride ion formed by an exothermic catalytic reaction of atomic hydrogen and certain group I catalysts

Rb⁺ to Rb²⁺ and 2K⁺ to K + K²⁺ each provide a reaction with a net enthalpy equal to the potential energy of atomic hydrogen. The presence of these gaseous ions with thermally dissociated hydrogen formed a plasma having strong VUV emission with a stationary inverted Lyman population. Significant Balmer α line broadening of 18 and 9 eV was observed from a rt-plasma of hydrogen with KNO₃, and RbNO₃, respectively, compared to 3 eV from a hydrogen microwave plasma. The reaction was exothermic since excess power of about 20 mW/cc was measured by Calvet calorimetry. We propose an energetic catalytic reaction involving a resonance energy transfer between hydrogen atoms and Rb⁺ or 2K⁺ to form a very stable novel hydride ion. Its predicted binding energy of 3.0471 eV with the fine structure was observed at 4071 Å, and its predicted bound-free hyperfine structure lines matched those observed for about 40 lines to within.01 percent. Characteristic emission from each catalyst was observed. This catalytic reaction may pump a CW HI laser.     

Hydrogen adsorption on the faujasite-type zeolite Mg-X: An IR spectroscopic and thermodynamic study

Hydrogen adsorption (physisorption) on the faujasite-type zeolite Mg-X was studied by means of variable-temperature (80-140 K) FT-IR spectroscopy. Perturbation of the adsorbed H₂ molecules by the cationic adsorbing centres of the zeolite renders the H-H stretching mode IR active, at 4065 cm⁻¹. Simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, for a series of spectra recorded at the increasing temperature, allowed standard adsorption enthalpy and entropy to be determined. They resulted to be ΔH⁰ = −13 kJ mol⁻¹ and ΔS⁰ = −114 J mol⁻¹ K⁻¹, respectively. Both, spectroscopic and thermodynamic results are discussed in the broader context of corresponding data for hydrogen adsorption on other alkali and alkaline-earth cation exchanged zeolites, showing that, while an approximate correlation exists between ΔH⁰ and H-H stretching frequency, deviations can be expected for the case of zeolites containing small metal cations.     

Drift study of the products formed by radiolysis and photolysis of alkaline nitrates

The products of the radiolysis and photolysis of crystalline sodium, potassium, rubidium, cesium nitrates have been investigated by the diffuse reflectance infrared Fourier transform spectroscopy. The bands in the 1260-1220 and 804-809 cm^?1 regions observed after the n -irradiation and photolysis by a light with the wave length 253.7 nm of crystalline alkali nitrates were identified as the vibrational modes of NO^? ₂ x ₃ and x ₂, respectively. The frequency of the x ₃ oscillation of nitrite ions decreases from 1260 cm^?1 up to 1220 cm^?1 with the increase of the atomic weight or polarizability of a cation. The detection limit of the nitrite ions (1 ‐ 10^?7 mol g^?1) for the diffuse reflection method has been determined. The bands observed in KNO₃, RbNO₃ and CsNO₃ spectra in the 947-940 and 722-737 cm^?1 regions appearing only after photolysis are due to stretch oscillations of the peroxide bond O-O and wagging oscillations of the -ON=O group of peroxynitrite accordingly.     

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.     

Characterization of methylidyne on Pt(1 1 1) with infrared spectroscopy

Methylidyne (CH) was prepared on Pt(1 1 1) by three methods: thermal decomposition of diiodomethane (CH₂I₂), ethylene decomposition at temperatures above 450 K, and surface carbon hydrogenation. Methylidyne and its precursors are characterized by reflection absorption infrared spectroscopy (RAIRS). The C-I bond of diiodomethane breaks upon adsorption to produce methylene (CH₂), which decomposes to methylidyne at temperatures above 130 K. Above 200 K, methylidyne is the only hydrocarbon species observed with RAIRS, although reaction channels for the formation of methane (CH₄) and ethylene (C₂H₄) are indicated by temperature programmed desorption (TPD). As is well known from numerous previous studies, ethylene decomposes to ethylidyne (CCH₃) upon exposure to Pt(1 1 1) at 410 K. Upon annealing to 450 K, ethylidyne dissociates through two reaction pathways, dehydrogenation to ethynyl (CCH) and C-C bond scission to methylidyne. Ethylene dehydrogenation on the surface at 750 K and under low ethylene exposures produces surface carbon that can be hydrogenated to methylidyne with C-H and C-D stretch frequencies of 2956 and 2206 cm⁻¹, respectively. Hydrogen co-adsorption on the surface causes these frequencies to shift to higher values. Methylidyne is stable on Pt(1 1 1) to temperatures up to 500 K.     

Heats of solution/substitution and of fusion of Cs(1−x)KxCl compositions 0<x<0.57 by differential scanning calorimetry

Measurements of the change in heat (enthalpy) of solid-solid transition ΔH_t and of fusion ΔH_fus in crystalline CsCl effected by the presence of guest ion K⁺ up to 56.5 mol% using differential scanning calorimetry are reported. The range of K⁺ solubility is found to be higher and at variance with the subsolidus region described in earlier reports. Novel features of ΔH_t and ΔH_fus dependence on solute composition are in contrast to parallel binary systems, viz. CsNO₃-RbNO₃, CsNO₃-TlNO₃ and RbNO₃-TlNO₃. Some fundamental solution quantities are calculated from heat of transition, viz. slope ΔH_t/x or and χ-apparent partial molar heat of solution and partial molar heat of solution at infinite dilution, respectively.     

Investigation of ethene adsorption on Hmordenite and modified Hmordenite by frequency response method

The frequency response (FR) technique has been applied to study adsorption mechanism of ethene in parent Hmordenite (HMor) and the HMor (CuO/HMor, Cs⁺/HMor) which were modified by CuO and Cs⁺. The FR spectra of ethene in HMor, CuO/HMor and Cs⁺/HMor were recorded at temperatures between 252 and 273 K under the pressure of 0.2-30.0 Torr, and then those FR spectra were investigated. The results showed that two parallel adsorption processes exist in ethene/HMor system. Those two processes were attributed to adsorption process of ethene on proton acid sites (low frequency adsorption) and on hydrogen cation sites (high frequency adsorption); meanwhile the number of sites available for adsorption of ethene is 0.692 and 0.828 mmol g⁻¹, respectively. The number of adsorption sites in low frequency is increased by the introduction of CuO which is located among the proton acid sites but covered the hydrogen ion sites in high frequency. Chemical adsorption of ethene is the main sorption process in CuO/HMor. The number of adsorption sites in low frequency is decreased by the introduction of Cs⁺ which counteracted proton acid sites in low frequency. Physical adsorption is the main sorption process in Cs⁺/HMor channels. The optimum content of CuO for modification is 5% (weight/weight). Combining the FR spectra and other methods such as isotherms and Langmuir model, a thorough understanding of the ethene adsorption processes on zeolites can be achieved.     

Evidence for Eley-Rideal abstraction mechanism in reactive ion scattering of Cs from Pt(1 1 1) adsorbed with CO and CO2

We studied the reactive ion scattering (RIS) of Cs⁺ from a Pt(1 1 1) surface adsorbed with CO and CO₂ leading to the emission of CsCO⁺ and . The RIS products were measured as functions of adsorbate coverage and ion incidence energy for the range of 10-60 eV. The yield and cross-section for the RIS processes were extracted from these measurements. The RIS cross-section is higher for weakly adsorbed CO₂ than for more strongly bound CO. The RIS energy-dependence shows a maximum at 15-20 eV and a decrease at higher energy. These observations provide evidence for the theoretically proposed mechanism of RIS, in which a slow Cs⁺ picks up an adsorbate in an Eley-Rideal abstraction reaction.     

Bulk viscosity and relaxation frequencies in molten alkali nitrates

Measurements of ultrasonic absorption and speed were carried out in molten LiNO₃, NaNO₃, RbNO₃, KNO₃ and CsNO₃ by the pulse method. The results indicate that the bulk viscosity is due to a structural mechanism. The hole theory provides a model for this mechanism. Comparing the results of measurements at ultrasonic and Brillouin frequencies, the values of relaxation frequencies were deduced. These results were compared to those provided by the hole theory.     

Improved electron injection of OLEDs with a thin PBD layer at Alq3/Cs2CO3 interface

In this study, the effect of one oxadiazole derivative (PBD) using as an electron injection layer (EIL) at Alq₃/Cs₂CO₃ interface has been investigated. The present of PBD EIL was showed an interesting enhanced electron injection for OLEDs although the nominal electron injection barrier for PBD based OLEDs is much larger, because PBD owns an obvious higher intrinsic the Lowest Unoccupied Molecular Orbital level (2.3 eV) than that of Alq₃ (3.0 eV). For example, the current density of OLEDs at 8 V was increased from 54 mA/cm² to 168 mA/cm² when inserting a thin PBD layer (5 nm) at Alq₃/Cs₂CO₃ interface. Here the increased current is suggested associating with the changed electronic structure of PBD when it contacts with Cs₂CO₃.     

Effect of irradiation on CsNO3, RbNO3., and NaNO2 crystal structure

Studies of the structure changes in heated (20–200°C) and γ –irradiated (10⁹- 5×10⁹ R, E = 1.3 Mev, Tirrad. = 40°C) crystals CsNO₃, RbNO₃ and NaNO₂ have been carried out by means of X-ray diffraction methods. The investigation of temperature effect on the crystal structure has shown that the phase transformation in CsNO₃ and NaNO₂ are of continuous type while that in RbNO₃ is discontinuous. It has been found that crystal structures of CsNO₃ and NaNO₂ change under irradiation in the same way, as they change under heating, No changes of RbNO₃ crystal structure caused by irradiation have been found. Experimental results agree with an assumption that radiation-induced structure changes of high-temperature type can be observed only in the compounds, the phase transition of which is of continuous type.     

The surface structure of Fe3O4(1 1 1) films as studied by CO adsorption

We have studied adsorption of CO on Fe₃O₄(1 1 1) films grown on a Pt(1 1 1) substrate by temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS) and high resolution electron energy loss spectroscopy (HREELS). Three adsorption states are observed, from which CO desorbs at ∼110, 180, and 230 K. CO adsorbed in these states exhibits stretching frequencies at ∼2115-2140, 2080 and 2207 cm⁻¹, respectively. The adsorption results are discussed in terms of different structural models previously reported. We suggest that the Fe₃O₄(1 1 1) surface is terminated by 1/2 ML of iron, with an outermost 1/4 ML consisting of octahedral Fe²⁺ cations situated above an 1/4 ML of tetrahedral Fe³⁺ ions, in agreement with previous theoretical calculations. The most strongly bound CO is assigned to adsorption to Fe³⁺ cations present on the step edges.