Titanium Silicate Porous Materials for Carbon Dioxide Adsorption: Synthesis Using a Structure Directing Agent, Detemplation and Inclusion of Alkaline Earth Metal Cations

A titanium silicate variant named UPRM-5 was prepared using tetraethylammonium hydroxide as a structure-directing agent (SDA). Characterization of the material by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques showed a homogeneous and crystalline solid powder phase, with unit cell dimensions of a = 6.8 angstrom, b = 11.7 angstrom, c = 13.4 angstrom, alpha = 102.9 degrees, beta= 92.8 degrees and gamma = 91.1 degrees Successful detemplation was achieved via ion exchange with NH4Cl as evidenced by thermal gravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy data. Effective functionalization was obtained after ion exchanging the detemplated material using SrCl2 and BaCl2. These ion exchanged variants were also characterized using XRD and porosimetry techniques. Thermal-vacuum activation of Sr-UPRM-5 at 90 degrees C resulted in a material with a surface area of ca. 240 m(2)/g, while activation at higher temperatures resulted in low surface areas and plausible structural distortion. On the other hand, the barium variant exhibited the best thermal stability, with an average surface area on the order of 250 m(2)/g after employing activation temperatures up to 180 degrees C. The differences in thermal stability may be a result of structurally coordinated water. Adsorption of CO, at 25 degrees C in Sr- and Ba-UPR.M-5 materials activated at different temperatures also co-corroborated the aforementioned thermal stability observations in addition to what appears to be cation relocation. Fitting of the CO2 adsorption data with the Dubinin-Astakhov model revealed a heterogeneous surface, which was corroborated by isosteric heats of adsorption estimated from the uptake data. For low partial pressures, the observed CO, adsorption capacities increased as follows: NH4-UPRM-5 < Sr-UPRM-5 < Ba-UPRM-5. Both the Sr- and Ba-UPRM-5 materials exhibited outstanding selectivity for CO2 over CH4, N-2, and O-2.