Carbon dioxide (CO 2 ) is considered one of the most important greenhouse gases in the study of climate change. CO 2 adsorption was studied using the gas chromatography technique, while the Freundlich and Langmuir adsorption models were employed for processing isotherm data in the temperature range of 473-573 K. The isosteric heat of adsorption was calculated from the Clausius-Clapeyron equation. Moreover, the thermodynamic properties ∆G, ∆U, and ∆S were evaluated from the adsorption isotherms of Langmuir using the Van't Hoff Equation. The four soil samples were recollected from San Juan Amecac, Puebla, Mexico, and their morphologies were investigated through X-ray diffraction (XRD) and N 2 adsorption at 77 K. The SJA4 soil has a crystalline Kaolinite phase, which is one of its non-metallic raw materials, and N 2 isotherms allowed for the determination of pore size distributions and specific surface areas of soil samples. The Barrett-Joyner-Halenda (BJH) distribution of pore diameters was bimodal with peaks at 1.04 and 3.7 nm, respectively. CO 2 adsorption showed that the SJA1 soil afforded a higher amount of adsorbed CO 2 in the temperature range from 453 to 573 K followed by SJA4 and finally SJA2, classifying this process as exothermic physisorption.

Due to the nanoporous nature of zeolitic materials, they can be used as gas adsorbents. This paper describes the effect of critical admission temperature through narrow pores of natural ERI zeolites at low levels of coverage. This phenomenon occurs by adsorption of CH4 and H2 on pores in natural erionite. The zeolite was exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, times, and temperatures of treatment. Experimental data of CH4 and H2 adsorption were treated by the Langmuir equation. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric heats of adsorption. The Ca2+ and Mg2+ cations favor the adsorption phenomena of H2 and CH4. These cations occupy sites in strategic positions Ca1, Ca2, and Ca3, which are located in the nanocavities of erionite zeolites and K2 in the center of 8MR. Following the conditions of temperature and the exchange treatment, ERICa2 and ERINa3 samples showed the best behavior for CH4 and H2 adsorption.

In this work, the chemical structural characterization of the erionite-type zeolite from Agua Prieta, Sonora, México, was performed on both pristine and Na, Ca, and Mg exchanged samples in order to identify the various modifications due to cation exchange. The samples investigated were those that showed the best behaviour of CO2 and CH4 adsorption at zero coverage levels and the higher values of surface area reported in our previous studies. According to the crystal-chemical formula (Na3.44K1.96Mg0.63Ca0.62)[Al8.21Si27.79O71.85]·29.63H2O, the pristine sample has been classified as erionite-Na. Morphological FE-SEM investigation performed on both pristine (ERIN) and Na-exchanged samples (ERINa3) showed a similar range of fiber diameters (27–37 nm). The chemical analyses of the ion-exchanged samples evidenced the upload of Ca and Mg following ion exchange with Na. Rietveld analysis results allowed the identification of the chemical structural modification caused by the ion exchange process, occurring mainly at the Ca1 site.

Palabras clave: clinoptilolita, nanoporosidad, fisisorción, contaminación atmosférica RESUMEN Se presentan los resultados de caracterización y adsorción de gases de bajo peso molecular en una zeolita natural proveniente de Escalerillas, San Luis Potosí, México. Este material fue sometido a diferentes tratamientos que mejoraron sus parámetros de textura y capacidad de adsorción, además de incrementar su relación Si/Al. Como resultado de dichos tratamientos se logró mejorar su capacidad de adsorción de gases como CH4 y H2, obteniéndose calores de adsorción superiores a los reportados en algunos materiales híbridos. Sin embargo, mientras que la muestra natural (N) de partida adsorbió una mayor cantidad de CO2 a temperaturas superiores a 548 K, las muestras modificadas químicamente presentaron un mejor comportamiento a temperaturas inferiores a 523 K.

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