Physical Adsorption of H2S Related to the Conservation of Works of Art: The Role of the Pore Structure at Low Relative Pressure

The adsorption isotherms of H₂S in selected adsorbents were determined at 298 K, at relative pressures up to about 0.005, aiming the use of these materials in the removal of that pollutant from the museums atmosphere. The Dubinin-Astakhov equation adjusts very well the experimental results, although one cannot interpret the pre-exponential factor w₀ as the limiting adsorbed amount. The parameter E, related with the adsorption energy, and the parameter n, that can be associated with the surface heterogeneity of the adsorbents, are correlated and the first is also correlated with the adsorbed amounts. It was not found any expectable relationship between the adsorbed amounts and textural parameters of the adsorbents such as the specific surface area or the microporous volume. This points out that the adsorption of H₂S is highly specific. In general, 13X and Y sodium zeolites seem to be the most effective adsorbents, but at lowest tested pressures, near the concentrations found at museums, a pillared clay prepared from a Wyoming montmorillonite seems to be more efficient.     

Influence of Cycle Temperatures on the Thermochemical Heat Storage Densities in the Systems Water/Microporous and Water/Mesoporous Adsorbents

The adsorption equilibrium of water on microporous adsorbents (zeolites of NaA-, NaY- and NaX-type as well as their ion exchanged forms) and on mesoporous adsorbents (different silica gels and composite material i.e. silica gel + salt hydrate) has been studied experimentally and theoretically. Using the Dubinin theory of pore filling the characteristic curves of the adsorption systems and other relevant dependences such as isotherms, isobars, isosteres and the curve of the differential heat of adsorption were calculated. For all systems investigated the adsorption were calculated. A_ads and the desorption potential A_des of the closed heat storage system were estimated. These values define the working range of the adsorption/desorption cycle and allow to calculate the specific heat storage density Δ h_sp. On the basis of Δ h_sp the different adsorbents were compared in order to select the optimal porous storage material for a given application. The presented experimental and theoretical investigations show that the adsorption systems water-zeolite and water-composites are promising working pairs for thermochemical heat storage processes for hot tap water supply and space heating of single family dwellings. The advantage of the water-composite system is the low desorption temperature (solar energy) the main shortcoming the low temperature lift. The advantage of the water zeolite system is the high temperature lift, the shortcoming are the relative high desorption temperatures.     

Specific features of the absorption of divalent manganese ions from aqueous solutions by zeolites

Sorption properties of natural zeolites from various Russia’s deposits for the Mn²⁺ ion were studied in comparison with various industrial adsorbents and some minerals. It was demonstrated that the equilibrium sorption capacity of these materials can be raised by their Na⁺-modification. The natural zeolites are advantageous at low Mn²⁺ ion concentrations over synthetic cation exchangers and activated carbons. The sorption capacity of the natural zeolites grows with increasing temperature.     

Adsorption of Gases, Vapors and Liquids by Microporous Adsorbents

Adsorption of Xe, Kr, Ar, N₂, O₂, H₂ CH₄, CO₂, He, and freons by PAU-10 and ACC microporous carbon adsorbents as well as by A and X zeolites was investigated over a wide range of pressures (0.1 Pa – 20 MPa) and temperatures (77, 120–600 K). The amount of gases, vapors and liquids adsorbed by microporous adsorbents increases steadily with increasing pressure and does not change dramatically if phase transitions occur in the adsorptive. Isosteres of adsorption constructed as a curve of ln P against f(1/T)_a retain a linear form over a wide range of pressures and temperatures. The slope of isosteres does not vary on going through the critical temperature of the gaseous phase. At high pressures, due to non-ideality of the gaseous phase and non-inert behavior of the adsorbent the differential molar heat of adsorption is dependent on temperature. At high fillings of micropores the differential molar isosteric heat capacities of adsorption systems show maxima that indicate the occurrence of structural rearrangements in the adsorbate.     

Preparation of ZSM‐5 Coated on Monolithic Interconnected Macroporous Al2O3 Using Cheap n‐Butylamine as Template

Using cheap n‐butylamine as template, ZSM‐5 zeolites have been successfully synthesized and coated on monolithic interconnected macroporous Al₂O₃ by the secondary growth method. The use of cheap n‐butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM‐5 zeolites were prepared from synthetic mixtures with different H₂O/Na₂O or SiO₂/Al₂O₃ ratio. The synthesized samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR) and N₂ adsorption‐desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n‐butylamine template as template. During the hydrothermal reaction process, the morphology of the micrometer‐sized support was well maintained. The irregular crystals were formed in a wide range of the H₂O/Na₂O or SiO₂/Al₂O₃ ratio of synthetic mixtures and coated on monolithic Al₂O₃. The relative crystallinity of the zeolites was highest at H₂O/Na₂O=250 or SiO₂/Al₂O₃=160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.     

Adsorption and Desorption of Cr(III) on Natural and Chemically Modified Slovak Zeolites

Natural and chemically modified zeolites from the Slovak Republic and Ukraine have been investigated as the adsorbents for the uptake of Cr(III). Model water solution of low radioactivity was used. The adsorption and desorption kinetics of chromium were established with the gradual radioexchange technique (tracer ⁵¹Cr) and flame AAS. The effect of the factors studied are examined and explained. The sorption coefficient , distribution coefficient K _D , sorption capacity , sorption rate S, and leachability of Cr were calculated in neutral, alkaline and acidic aqueous solutions. The sorption capacity of the modified zeolites was found to be greater by a factor of 2 to 16 than that of the unmodified ones depending on the modifying solution applied. The leachability of chromium from loaded zeolites into the neutral solution was negligible. The leachability into alkaline and acidic solutions increased over 40%.     

Synthesis Strategies for Ultrastable Zeolite GIS Polymorphs as Sorbents for Selective Separations

Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure‐directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic‐free syntheses of two polymorphs of the small‐pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H₂O relative to other light gases (e.g., H₂, N₂, CO₂). Our findings refute prior theoretical studies postulating that GIS‐type zeolites are excellent materials for CO₂ separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS‐type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis.     

Decorated Traditional Zeolites with Subunits of Metal–Organic Frameworks for CH4/N2 Separation

Metal–organic frameworks (MOF) materials are promising materials for gas separation, but their application still faces various challenges. A strategy is now reported for introducing subunits of MOFs into traditional zeolite frameworks to obtain applicable adsorbents with advantages of both zeolites and MOFs. The subunits of ZIFs were introduced into zeolite Y and zeolite ZSM‐5 for CH₄/N₂ separation. Both the molecular simulation and experimental results validated that the IAST CH₄/N₂ selectivity of the resulting samples greatly improved (above 8, at 100 kPa and 25 °C) with the incorporation of ZIF subunits into zeolites structure, and the selectivities were obviously higher than that of zeolites and even better than that of ZIFs. This strategy not only gave rise to an efficient adsorbent for CH₄/N₂ separation but also provided ideas for design of other adsorption and separation materials.     

The Compatibility of Compositional and Structural Features of Aluminous Large Pore Zeolites with Sorption Characteristics

The parent NaX and KL samples were prepared by hydrothermal crystallization and their corresponding K- and Na-exchanged forms were obtained by post-synthesis modification by conventional ion-exchange technique. NaX, NaKX, KL and NaKL samples were characterized by powder XRD, IR, low temperature nitrogen adsorption and chemical analyses. Their sorption uptake behaviour has been investigated by gravimetric method. The kinetics of sorption using different sorbate probe molecules such as water, benzene and n-hexane was measured at 298 K, at P/P ₀ = 0.5 for 90 minutes. All the results obtained were discussed in terms of the compositional and structural variations of the adsorbents. Lack of high dimensionality of the pore system, less openness in structure, low average framework oxygen charge and less number of accessible nonframework cations are some of the prominent factors which has resulted in reduced hydro- and organo-philicity in LTL type zeolites as compared to X-type. The size and concentration of the accessible nonframework cations were also found to influence the sorptive properties of these aluminous large pore zeolites. Among all the probe molecules, n-hexane was found to be as a promising probe for differentiating the structural peculiarities especially dimensionality of the pore system.     

Uranium (VI) adsorption on synthesized 4A and P1 zeolites: Equilibrium,kinetic, and thermodynamic studies

The present work deals with the investigation of the use of synthesized 4A and P1 zeolites in the adsorption of uranium (VI) ions from liquid effluents (with initial concentrations of 100, 85 and 80 mg·L⁻¹). Batch experiments were performed and the effects of temperature, solid–liquid ratio, pH and initial UO₂²⁺ ion concentration were studied, and the optimal parameters were determined. The kinetic and thermodynamic aspects of the process as well as the diffusion mechanism have been studied. The obtained results showed that 4A and P1 zeolites are very effective adsorbents.     

Faujasite-type zeolites modified with iron perfluorophthalocyanines: Synthesis and characterization

The synthesis and characterization of hexadeca- or perfluorophthalocyanine complexes of iron(II) (FeF₁₆Pc) in synthetic faujasite-type zeolites is reported. The encapsulation of FeF₁₆Pc in NaY zeolite by the template synthesis method as well as the synthesis of NaX around FeF₁₆Pc are discussed. A spectroscopic (UV—VIS, IR) and electrochemical analysis of the modified zeolites, providing evidence for encapsulation, is presented and compared with the unsubstituted FePc complex.     

Evaluation of the zinox and zeolite materials as adsorbents to remove H2S from natural gas

Mesoporous materials can be generally used as adsorbents to remove impurities from gases. During the past few years, H₂S has been removed from natural gas using materials such as dolomite, zeolites, and industrial compounds, which can be widely used by oil and natural gas companies. The present study focused on the use of Zeolite 13X and Zinox 380 as H₂S adsorbent at 25 °C. They were characterized by chemical analyses (X-ray fluorescence and atomic absorption), X-ray diffraction, particle size distribution analyses and FT Infrared spectroscopy. Adsorption reactions were carried out using proposed models. The results revealed that both materials studied could be used as H₂S adsorbents in natural gas exceeding the capabilities of industrial compounds.     

Electric fields in zeolites: fundamental features and environmental implications

A critical review of zeolites and their use in practical applications is presented. Specifically-considered are their role as media for selective light-induced oxidations using molecular O₂, and the relationship between this phenomenon and the surface electric fields that exist in zeolites. Methods for the determination of the strength of zeolite surface fields are discussed using sorbed molecules such as CO (with IR detection), spin-probes, di-tert-butyl nitroxide, and NO (measured using EPR spectroscopy). Relationship between the surface fields and molecular reorientation energetics for free radicals sorbed in zeolites, obtained using muonium as a spin-label, is explored. Finally, results obtained from exposing the naturally occurring zeolite, clinoptilolite, to high energy electrons as a means for activating materials toward selective removal of radioactive caesium and strontium cations from wastewaters of nuclear power plants are presented.     

Comparative study of adsorbents performance in ethylene/ethane separation

Some potential adsorbents for ethylene/ethane separation are ethylene selective while the others are ethane selective. Among different adsorbents, i.e., zeolites and metal organic frameworks (MOFs), a comparative study is critical to find the more suitable adsorbent for the separation. In this paper, binary ethylene/ethane adsorption performances of zeolites and MOFs, i.e., equilibrium selectivities and adsorption capacities are investigated utilizing ideal adsorbed solution theory (IAST). IAST model is applied at different gas compositions (0.1–0.9 ethylene mole fractions) and pressures up to 100 kPa. The results revealed that the most selective adsorbent toward ethylene is 5A zeolite while MOFs have higher equilibrium adsorption capacities. Among zeolites and MOFs, 5A and Fe₂(dobdc) have the highest selectivity (27.4 and 13.6) and capacity (≈2.8 and 5.8 mmol ethylene/g) at 100 kPa and 298 K for a 50/50 mixture. Among ethane selective adsorbents, Silicalite-1 zeolite and UTSA-33a (MOF) have the highest selectivity and capacity (≈2.9 and ≈1.5 mmol ethane/g) at 100 kPa and 298 K for a 50/50 mixture, respectively. Investigation showed that adsorption capacity of ethylene selective adsorbents is higher than that of ethane selective ones.     

Zeolites modified by CuCl for separating CO from gas mixtures containing CO2

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.     

Isotope exchange of strontium and molybdate ions in strontium polymolybdates

The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr²⁺ and MoO₄ ^2- ions in the strontium nitrate and sodium molybdate solutions have been studied using ⁹⁰Sr and ⁹⁹Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (K _ex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr²⁺ cations have a much higher affinity for exchangers than MoO₄ ^2- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (X _m ) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.     

Concerted Bimetallic Nanocluster Synthesis and Encapsulation via Induced Zeolite Framework Demetallation for Shape and Substrate Selective Heterogeneous Catalysis

Bimetallic nanoparticle encapsulation in microporous zeolite crystals is a promising route for producing catalysts with unprecedented reaction selectivities. Herein, a novel synthetic approach was developed to produce PtZn_x nanoclusters encapsulated inside zeolite micropores by introducing Pt²⁺ cations into a zincosilicate framework via ion exchange, and subsequent controlled demetallation and alloying with framework Zn. The resulting zeolites featured nanoclusters with sizes of approximately 1 nm, having an interatomic structure corresponding to a PtZn_x alloy as confirmed by pair distribution function (PDF) analysis. These materials featured simultaneous shape and substrate specificity demonstrated by the selective production of p‐chloroaniline from the competitive hydrogenation of p‐chloronitrobenzene and 1,3‐dimethyl‐5‐nitrobenzene.     

Ion exchangers in radioactive waste management

Adsorption of strontium ions from aqueous solution of Sr(NO₃)₂ on synthetic sodium titanate [(NaO)_x(TiO)_y(OH)_z] powder has beet investigated as a function of contact time, Sr(II) concentration and temperature. X-ray diffraction studies indicated poor crystallinity of the synthetic sodium titanate, which became more crystalline after annealing at ca. 1173 K for 6 h in air. The adsorption of strontium ions on sodium titanate was favored at higher concentrations of the adsorbate and at lower temperatures. The kinetics of the process follows a first-order rate law with respect to adsorptive concentration and obeys the Freundlich isotherm in the entire range of adsorptive concentration. The process of adsorption in the present system has been found to be of the ion-exchange type.     

低硅铝比ZSM-5分子筛的合成及其正庚烷裂化反应性能

以氨水为矿化剂,通过添加NH₄⁺离子水热合成了具有较低骨架硅铝比的ZSM-5分子筛。通过X射线衍射(XRD)、扫描电镜(SEM)、固体核磁共振(MAS-NMR)等表征手段,研究了硅源、铝源、矿化剂、阳离子等对ZSM-5分子筛的结晶度、形貌尺寸和骨架硅铝比等的影响,研究了ZSM-5分子筛的骨架硅铝比对正庚烷催化裂化反应的影响。研究表明,投料硅铝比越低,铝原子越难进入到分子筛骨架中;当氨水为矿化剂、正硅酸四乙酯为硅源时可以合成骨架硅铝比较低的氢型ZSM-5分子筛,添加NH₄⁺离子可以增强骨架铝的嵌入,进一步降低分子筛的骨架硅铝比(24.2)。正庚烷裂化反应结果表明,降低分子筛的骨架硅铝比可以提高正庚烷裂化反应的活性,但会降低低碳烯烃的选择性。     

Synthesis and characterisation of strontium carboxylates formed at room temperature and under hydrothermal conditions

A novel method was developed for the synthesis of highly pure strontium complexes in high yield. Syntheses proceeded along three pathways with optimum conditions being at T?=?120–140°C, a base?:?acid ratio of 1.2 and 15?min reaction-time in an autoclave vessel. Large crystals were readily obtained within hours. The crystal structures of strontium R-glutamate hexahydrate (I) and strontium di(hydrogen S-glutamate) pentahydrate (II) were determined by X-ray powder diffraction methods at 295?K with Rietveld refinement (I: Space group P2₁2₁2₁, Z?=?4, a?=?7.3519(2), b?=?8.7616(2), c?=?20.2627(5)?Å; II: Space group P2₁, Z?=?2, a?=?8.7243(1), b?=?7.2635(1), c?=?14.6840(2)?Å, β?=?100.5414(7)°). Synthesis at room temperature provided four additional new strontium compounds that may be applicable as constituents of pharmaceutical products for the treatment of bone conditions.