Preface to the special issue “Commemorative contributions for the 30 years of the Catalysis and Porous Materials Division of the Portuguese Chemical Society (SPQ)”

More than thirty years have passed since the beginning of the Division of Catalysis of the Portuguese Chemical Society (SPQ), in 2001 expanded to Division of Catalysis and Porous Materials, in order to reflect the application of porous materials in non-catalytic processes, such as adsorption. We are commemorating this milestone in the Chemistry field in Portugal and, to honor the History behind its creation, consolidation and continuous challenges, we projected this Special Issue, entitled “Commemorative contributions for the 30 years of the Catalysis and Porous Materials Division of the Portuguese Chemical Society (SPQ)”.info:eu-repo/semantics/publishedVersio

Revisiting Tracer Liu-Silva-Macedo model for binary diffusion coefficient using the largest database of liquid and supercritical systems

This work compiles the largest database of tracer diffusion coefficients (D12) containing 6180 experimental points from 331 non-polar and weakly polar liquid and supercritical systems. Then, the Tracer Liu − Silva − Macedo (TLSM) model and its 1-parameter correlations (TLSMd and TLSMen) are evaluated using this database, taking into account the importance of phenomenological and reliable equations for D12 estimation. The TLSM model achieves good results with absolute average relative deviations (AARD) of 16.84 % while TLSMd and TLSMen show better performance with AARD of 4.53 % and 4.55 %, respectively. All properties and parameters needed for D12 estimation are compiled in Appendix. For comparison, the models of Wilke-Chang and Reddy-Doraiswamy, and the correlations of Magalhães et al. (LJ-1) and Dymond-Hildebrand-Batschinsky (DHB) are also assessed.publishe

Diffusivities of ketones and aldehydes in liquid ethanol by molecular dynamics simulations

The tracer diffusion coefficients of six ketones (propanone, butanone, pentan-2-one, pentan-3-one, hexan-2-one, hexan-3-one) and six aldehydes (methanal, ethanal, propanal, butanal, pentanal and hexanal) in liquid ethanol were computed by classical molecular dynamics (MD) simulations over 303.15-333.15 K and 1-150 bar. The calculated tracer diffusion coefficients, D12, compared very satisfactorily with experimental data from the literature, with average absolute relative deviations (AARD) between 9.48 % and 12.18 % for ketones, and between 6.30 % and 9.11 % for aldehydes. The trends of D12 with solute size and temperature were accurately simulated in all cases, while the weaker influence of pressure was not rigorously reached in all cases when jumping from 1 to 75 bar and then to 150 bar. Furthermore, a temperature-based correction to D12 was introduced, which decreased the AARD values of ketones down to the range 1.52 – 5.16 % and aldehydes to 2.94 – 3.45 %. The structural analyses of the spatial distribution functions and coordination numbers show that ethanol has more affinity with ketones than with aldehydes, though such affinity difference is not always translated to the computed D12 of ketone-aldehyde isomers. Nevertheless, the experimental diffusivities of both families of compounds are only ca. 7 % different, hence within the uncertainties associated with the calculated results.publishe

Diffusion of quercetin in compressed liquid ethyl acetate and ethanol

Supercritical fluids are alternatives to conventional harmful organic compounds. In the case of supercritical fluid extraction, CO2 is the most common solvent and can be advantageously modified with small contents of co-solvents like ethanol and ethyl acetate. The rigorous estimation of the tracer diffusion coefficients (D12) of solutes in supercritical mixtures (CO2 + co-solvent) requires their individual D12 values in pure CO2 and pure co-solvent under the same operating conditions. This essay focuses the diffusivity of quercetin (solute) in two compressed liquid co-solvents (ethanol and ethyl acetate). Quercetin is a natural compound possessing a wide variety of bioactive properties, used as one of the most noticeable dietary antioxidants. The tracer diffusivity measurements are accomplished by the chromatographic peak broadening technique over 303.15–333.15 K and 1–150 bar. The diffusion coefficients lie between 0.414 × 10−5and 0.813 × 10−5 cm2s−1 in ethanol, and between 1.06 × 10−5 and 1.69 × 10−5 cm2s−1 in ethyl acetate. Influence of temperature, pressure and hydrodynamic coordinates is analyzed and discussed based on the most relevant transport theories. Modeling is also carried out with eleven models from the literature and demonstrated the unreliability of predicting equations in opposition to the very good correlations available to fit D12 data. The influence of the accurate estimation of auxiliary properties (like solvent volume and viscosity) upon the calculated tracer diffusivities is also assessed, being possible to detect D12 differences as high as ca. 70 %.publishe

A DFT study on the interaction of small molecules with alkali metal ion-exchanged ETS-10

In this paper, we present a systematic quantum-mechanical density functional theory (DFT) study of adsorption of small gas molecules in cation-exchanged Engelhard titanosilicate ETS-10 crystalline materials. Adsorbates with a range of polarities were considered, ranging from polar (H2O), quadrupolar (CO2 and N2), to apolar (CH4) atmospheric gases. Starting from the base-case of Na-ETS-10, other extra framework cations such as Li+, K+, Rb+ and Cs+ were considered. The DFT calculations were performed with the M06-L functional and were corrected for basis set superposition error with the counterpoise method in order to provide accurate and robust geometries and adsorption energies. For all adsorbates, the adsorption enthalpies decrease in the order Li+>Na+>K+>Rb+>Cs+, while adsorbate – cation interaction distances increase along the same order. For the two extreme cases, the enthalpies calculated at the M06-L/6-31++G** level of theory for CH4, N2, CO2, and H2O interaction with Li+(Cs+) exchanged materials are −21.8 (−1.7) kJ·mol−1, −19.0 (−10.7) kJ·mol−1, −34.4 (−21.3) kJ·mol−1, and −70.5 (−36.1) kJ·mol−1, respectively. Additionally, the calculated vibrational frequencies are found to be in quite good agreement with the characteristic vibrational modes of alkali metal cation-exchanged ETS-10 and also with the available experimental frequencies for CH4, N2, CO2, and H2O interactions with alkali metal cations in the 12-membered channel of ETS-10

The dipole moment of alcohols in the liquid phase and in solution

Understanding polarization effects in condensed phases, like liquids and solutions, requires computational methods that can accurately predict dipole moments and energy of polarized molecules. In this paper, we report an improvement and extension of our recently developed Self-Consistent Electrostatic Embedding (SCEE) method, and apply it to determine the dipole moment of pure liquid alcohols, as well as of methanol dissolved in a variety of solvents (namely, other alcohols, water and hexadecane). We observe that the dipole moments of pure liquid alcohols are enhanced by ∼0.9 D over their gas phase values, which is similar to the dipole enhancement previously observed for water, and much higher than what is predicted by dielectric continuum models. Our results demonstrate the importance of accounting for local solvation effects, namely the formation of hydrogen bonds, when calculating the extent of liquid phase polarization. In fact, we argue that the dipole enhancement upon solvation can be explained as a superposition of two effects: bulk screening described by the solvent dielectric constant and local solvation that requires a discrete molecular-level description of the system. SCEE is able to account for both effects simultaneously, and is thus a powerful tool to estimate polarization effects in liquids and solutions

Pyrolyzed chitosan-based materials for CO2/CH4 separation

Chitosan is a biopolymer obtained by deacetylation of chitin extracted from sub-products of the food industry and it is rich in nitrogen content. Pyrolyzed chitosan– and chitosan-periodic mesoporous organosilica (PMO)– based porous materials with different pore structures and chemical features are prepared using different dry methods and ensuing pyrolysis at 800 °C, for application in the CO2/CH4 adsorption/separation. The highest CO2 adsorption capacity (1.37 mol·kg−1 at 100 kPa; 1.9 mol·kg−1 at 500 kPa) and the best selectivity for CO2/CH4 separation (95 at 500 kPa) is obtained using 1.5% (m/v) of chitosan solution dried under supercritical CO2. This material combines a good CO2 adsorption capacity with one of the highest selectivities for CO2/CH4 separation of the literature, arising as a promising alternative adsorbent for natural gas or biogas upgrading at reduced cost. The presence of high nitrogen content together with pores of diameter around 2 nm leads to an increase of the CO2 adsorption capacity. In the case of chitosan-PMO-based materials, the activation step using both acid and crushing methods is crucial to increase the CO2 adsorbed amount. Here, the highest CO2 adsorption capacity and the highest selectivity are obtained by the chitosan-PMO crushed adsorbent and the chitosan-PMO material activated with sulfuric acid, respectively. These observations indicate the importance of the controlled attack of the material surface to enhance the diffusion of the target gases within the adsorbent, avoiding the adsorption of other species.publishe

A new model for predicting adsorption of polar molecules in MOFs with unsaturated metal sites

Large-scale computational screening has the potential to translate the tailorability of metal-organic frameworks (MOFs) into actual applications, but requires the availability of accurate forcefields. Unfortunately, conventional molecular models fail to correctly describe interactions of adsorbates with coordinatively unsaturated sites (CUS) present in a large number of MOFs. Here, we confirm the failure of these models for a prototypical polar adsorbate, carbon monoxide, and show that simply adjusting their parameters leads to poor agreement with experiment isotherms when outside the fitting conditions. Building upon our previous work on non-polar hydrocarbons, we propose a new approach that combines quantum mechanical Density Functional Theory (DFT) with Monte Carlo simulations to rigorously account for specific interactions at the CUS. By explicitly including electrostatic interactions and employing accurate DFT functionals that describe dispersion interactions, our modeling approach becomes generally applicable to both polar and non-polar molecules. We demonstrate that this CUS model leads to substantial improvement in carbon monoxide adsorption isotherm predictions, and correctly captures the coordination binding mechanism. Furthermore, the model retains the transferability demonstrated in our previous work. This paper represents a major stepping stone in the development of a robust, transferable and generally applicable approach to describe the complex interactions between gas molecules and CUS, with great potential for use in large scale screening studies

A computational study of the interaction of C2 hydrocarbons with CuBTC

The adsorptions of ethane, ethene, and ethyne over the coordinatively unsaturated sites (CUS) of copper (II) benzene-1,3,5-tricarboxylate (CuBTC) were studied by means of density functional theory (DFT), using both cluster or periodic models. Exchange-correlation functionals from different rungs of the Jacobs ladder of the DFT were used and energies were corrected for the basis superposition error either through extrapolation to the complete basis set limit or upon the consideration of the Counterpoise method. From the calculated data, it was found that the adsorbate to CUS distances decrease in the order ethane > ethene ≈ ethyne and that the strength of adsorption increase in the order ethane to ethyne to ethene. The energies of interactions of ethene and ethyne with the CUS of CuBTC are approximately the double of that calculated for ethane. The calculated adsorption energies and geometries are in very satisfactory agreement with the available experimental results. The results of topological analyses confirm that the unsaturated bonds of ethene and ethyne form open shell like bonds with the CUS while interaction with ethane have predominant closed shell character

Electrolyte effects on the Amino acid solubility in water: solubilities of Glycine, l-Leucine, l-Phenylalanine, and l-Aspartic acid in salt solutions of (Na+, K+, NH4+)/(Cl–, NO3–)

The solubilities of glycine, L-leucine, L-phenylalanine, and L-aspartic acid in aqueous solutions of the salts composed by combining Na+, K+, and NH4 + cations and Cl− and NO3 − anions were measured up to 2.0 salt molality at 298.2 K by the analytical gravimetric method. Using these data along with a review of literature information, encompassing all amino acids for which solubility is available in the studied aqueous electrolyte solutions, allowed us to interpret the effect of the functional groups of amino acids on their solubility. The four amino acids studied here showed higher solubility in aqueous solutions of salts with the nitrate anion. Except for L-aspartic acid with a polar side chain, amino acids with apolar side chains presented the highest salting-in effect in aqueous salt solutions with NH4 +. The cations Na+ and K+ did not seem to establish relevant interactions with the amino acids and had little impact on their aqueous solubility.This work was developed within the scope of the project CIMO-Mountain Research Center, UIDB/00690/2020 and CICECO-Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology (FCT)/MCTES. Mehriban Aliyeva thanks FCT and European Social Fund (ESF) for her Ph.D. grant (SFRH/BD/139355/2018).info:eu-repo/semantics/publishedVersio