Thermal Detemplation of Na-SAPO-34: Effect on Sr²⁺ Ion Exchange and CO₂ Adsorption

Abstract

Silicoaluminophosphate Na-SAPO-34 was studied with regard to the decomposition of tetraethylammonium (TEA + ) and its effect on the ion exchange of Sr 2+ and subsequent CO 2 adsorption. TEA + is the template used during the synthesis of the material. X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and pure component gas adsorption were used to characterize the materials' structural and textural properties. Coupled thermal gravimetric analyses (TGA)/Fourier transform infrared (FT-IR) spectroscopy results indicate that the decomposition of the TEA + in Na-SAPO-34 follows a three-step mechanism and is faster in air when compared to tests performed in helium. The transient spectroscopy and DRIFT methods also indicate that a detemplation temperature of about 430 °C gives formation to ammonium cations and possibly to other organic small fractions. Ion exchange of the resulting SAPO-34 materials with Sr 2+ followed by calcination at 500 °C resulted in materials with good textural properties for CO 2 adsorption, including surface area. Compared to materials detemplated straightforwardly at 500 °C, the two-step method treatment resulted in an increase of ca. 70% in CO 2 uptake at low partial pressure because of an increase in the amount of Sr 2+ cations in the SAPO-34 framework. Traditional one-step detemplation methods produce protons that occupy cation sites that are forbidden or inaccessible to divalent species during the ion exchange, which is the principal limitation to increase the concentration of particular adsorption sites in zeolitic adsorbents.

1H and 23Na MAS NMR spectroscopy of cationic species in CO2 selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

“…It should be mentioned that the 1 H NMR spectrum of the Na þ -SAPO-34 sample treated for partial detemplation of TEA þ (data not shown here) is similar to the one of NH 4 þ -SAPO-34. This is in agreement with the Fourier transformed infrared spectroscopy (FT-IR) studies performed by Zhang et al, where the formation of ammonium ions was followed during partial detemplation of SAPO-34 also prepared with TEA þ [36]. Fig.…”

“…A detailed description of the synthesis is available elsewhere [5,7,34]. Detemplation was performed in partial or complete fashion via calcination in a computer controlled muffle furnace [35,36]. Incorporation of ammonium cations was accomplished using the fully detemplated Na þ -SAPO-34 and liquid state ion exchange (LSIE).…”

Hydrothermal preparation of hierarchical SAPO-34 constructed by nano-sheets using rapeseed pollen extract as water and its CO 2 adsorption property

“…Large amounts of research work are thus carried out for the synthesis of SAPO-34 to improve its stability in this reaction [4][5][6][7][8][9][10][11][12][13] . On the other hand, SAPO-34 also exhibits high adsorption capacities in CO 2 [14][15][16][17][18][19][20][21] , alcohol [22] , etc., thus enabling its practical application in separation of CO 2 over CH 4 or N 2 [14][15][16][17][18][19][20] , and separation of short chain alcohols from long chain ones [22] . However, much less researches are conducted to examine the effect of SAPO-34 morphology and fine structure on its separation property.…”

Facile synthesis of SAPO-34 with small crystal size for conversion of methanol to olefins

“…Meanwhile, another relatively gradual weight loss of 0.78 wt.% at 529°C in the temperature range of 490-600°C is observed and corresponds to the oxidative decomposition of TEAOH. The addition of TEAOH is more useful to form protonated molecule with the negative charge of molecular sieve skeleton, resulting in a higher decomposition temperature [23]. From Fig.…”

“…Four weight loss peaks are observed for S34-L-M-T precursor. It has two small weight loss peaks in the range of 100-243°C and 243-322°C [23], centered at 117°C and 281°C, respectively, which are attributed to the desorption of water from the molecular sieve with a weight loss of 0.34 wt.% and 0.46 wt.%, respectively, corresponding to desorption of physically and chemically adsorbed water. One significant weight loss (5.12 wt.%) in the temperature range of 322-490°C centered at 432°C is detected and could be related to the oxidative decomposition of morpholine.…”