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This work presents a ceramic monolith with a honeycomb structure obtained from a natural zeolite (clinoptilolite), bentonite, and alumina. The monolith obtained by extrusion had a cell density of 57 CPSI (cells per square inch), an open frontal area of 52% w/w, and a wall thickness of 0.9 mm. The raw materials and the natural zeolite ceramic monolith (NZCM) were characterized by X-ray diffraction, N 2 adsorption-desorption at 77 K, CO 2 adsorption at 273 K, mercury intrusion-extrusion, axial compression tests, resistance to leaching at acidic and basic pH, and point of zero charge. The NZCM presented an S BET = 31 m 2 ∙g -1 , a modal micropore size of 0.44 nm, a porosity of 39%, the compressive stress = 14 MPa, and a pH PZC = 7.5. The NZCM was used as an inexpensive and easy-to-handle adsorbent to remove methylene blue (MB) dye in batch studies of kinetics and adsorption isotherms. From modeling of adsorption kinetic data, the predominant phenomenon in this system was physisorption. The modeling of adsorption isotherm data shows that the material has homogeneous active sites. The adsorption occurs by monolayer formation, finding a maximum capacity removal rate of 27 mg MB per gram of NZCM. Compared to other structured materials, a high capacity for removing MB with the ceramic monolith was obtained along with good mechanical properties and resistance in acidic and alkaline environments., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The need for greener procedures is a fact to reduce residues, to decrease industrial costs, and to accomplish the environmental agreements. In an attempt to address this question, we propose the addition of a natural resource, Brazilian diatomite, to an MFI zeolite traditional synthesis. We have characterized the resulting product with different techniques, such as X-ray diffraction, microscopy, and gas sorption, and, afterwards, we evaluate the greenness of the process by the Green Star method. The results were promising: We obtained the desired topology in the form of small crystallites aggregated and a pore diameter of 0.8 nm. In conclusion, the product has the necessary characteristics for an adsorption or catalytic future tests and escalation to industrial production.

The adsorption of CO 2 on Co, Fe and Ni mixed oxides derived from a commercial hydrotalcite and calcined at 500 °C was measured at several temperatures and pressures. Two types of experiments were considered in this work. In the first one, the adsorption temperatures were 25, 35 and 50 °C, with pressures of up to 1000 kPa. In the second, the adsorption temperature was 300 °C and the pressure up to 4400 kPa. The results obtained were compared with those found for four commercial microporous materials, namely the zeolite 13X, the MOF Basolite A100, an activated carbon and a synthetic alumina pillared clay. The microporous materials showed a higher CO 2 adsorption capacity, from 4.54 to 6.94 mmol·g −1 , than the mixed oxides, up to 1.44 mmol·g −1 , at 25 °C and up to 1000 kPa. The calcined hydrotalcite and the Ni mixed oxide presented the highest CO 2 adsorption capacity at 300 °C, 3.28 and 3.44 mmol·g −1 at 4400 kPa, whereas the rest of materials gave values of up to 1.75 mmol·g −1 . Ni mixed oxide showed sorption capacity considerably higher than those reported in the literature for hydrotalcite based materials under similar conditions. [ABSTRACT FROM AUTHOR]

The equilibrium adsorption and kinetics of CO 2 on several microporous materials has been studied at 273, 283 and 293 K and gas pressures of up to 100 kPa. The porous materials used in this work were two zeolites (5A and 13X), two metal–organic frameworks (Basolite A100 and Basolite Z1200), an activated carbon and two pillared clays (Al-PILC and Zr-PILC). The isothermal and non-isothermal diffusion models were applied to calculate the diffusion time constants ( D 0 / r c 2 ) from the uptake curves. The non-isothermal model was found to fit the experimental data well over the whole range of adsorption rates. The values found for the zeolites, which ranged from 0.020 to 0.043 s −1 , were lower than those for the metal–organic frameworks and pillared clays, which ranged from 0.036 to 0.081 s −1 , in the same interval of temperatures. Furthermore, the values of the diffusion time constants were found to depend on gas pressure. The pressure-dependence of the diffusion time constants was studied using the Darken equation. Finally, activation energy values were estimated from the temperature-dependence for all materials and it was found to increase in the order: Z1200 < Al-PILC < 13X < AC < Zr-PILC < 5A; A100. [ABSTRACT FROM AUTHOR]

The adsorption ofCO2on several microporous materialshas been measured at various temperatures (263, 273, 283, and 293K) over a wide range of pressures. The porous materials studied werethree zeolites (5A, 13A, and 13X), two metal–organic frameworks(Basolite A100 and Basolite Z1200), an activated carbon, and two pillaredclays (Al-PILC and Zr-PILC). The data obtained were fitted to theFreundlich, Langmuir, and Toth isotherms. Various methods were usedto calculate the Henry’s law constants. The values found forthe zeolites, which ranged from 8.95 to 36.02 mmol/kPa·g at 273K, were much higher than those for the metal–organic frameworks,activated carbon, and pillared clays, which ranged from 0.012 to 0.200mmol/kPa·g at the same temperature. The isosteric heats of adsorptionof CO2on the materials were calculated using the Clausius–Clapeyronequation, and the adsorbent–CO2affinity was foundto increase in the order Z1200 ≈ 13X ≈ 13A < 5A

• Zeolite type A was synthesized from natural resources under mild conditions. • Textural properties and crystallinity can be controlled through synthesis conditions. • Microporosity plays a key role on CO 2 /N 2 and CO 2 /H 2 O selectivies. • Under dry conditions, CO 2 is readily desorbed at moderate temperatures. • The presence of water hinders the desorption of the physisorbed species. In light of the urgent need of reducing the atmospheric CO 2 emissions, the use of low-cost adsorbents, that exhibit a high affinity and CO 2 adsorption capacity, is a promising method from the economic and environmental point of view to separate CO 2 from the flue gas emitted from large sources of emissions like power-fueled plants. Clay minerals are low-cost raw materials with high availability all over planet and great versatility in the fields of adsorption and catalysis processes. The present study pretends to elucidate the link between the reaction conditions during the synthesis of the zeolite from kaolinite and its CO 2 adsorption capacity. For that purpose, the type A zeolite was synthesized via hydrothermal process in alkaline solution using metakaolinite as a starting material. The metakaolinite was obtained by calcination of kaolinite at 600 °C and some parameters such as temperature and synthesis time were modified to optimize the synthesis aiming for a high CO 2 adsorption capacity adsorbent. Synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N 2 adsorption–desorption at −196 °C and CO 2 adsorption at 0 °C (up to 10 bars) isotherms and Nuclear Magnetic Resonance of solids (NMR). In addition, the adsorption capacity of CO 2 was evaluated by means of CO 2 adsorption–desorption isotherms at 25 °C up to atmospheric pressure. The obtained results indicated that synthesized zeolite 4A can be successfully prepared from natural kaolinite (via metakaolinization) at 100 °C for 48 h under alkaline conditions, showing chemical and physical properties similar to that of the commercial 4A zeolite. [ABSTRACT FROM AUTHOR]