Designed Synthesis of Mesoporous Solid-Supported Lewis Acid-Base Pairs and Their CO₂ Adsorption Behaviors

Conventional amines and phosphines, such as diethylenetriamine, diphenylpropylphosphine, triethylamine, and tetramethylpiperidine, were grafted or impregnated on the surface of metalated SBA-15 materials, such as Ti-, Al-, and Zr-SBA-15, to generate air-stable solid-supported Lewis acid-base pairs. The Lewis acidity of the metalated materials before and after the introduction of Lewis bases was verified by means of pyridine adsorption-Fourier transform infrared spectroscopy. Detailed characterization of the materials was achieved by solid-state ¹³C and ³¹P MAS NMR spectroscopy, low-temperature N₂ physisorption, X-ray photoelectron spectroscopy, and energy-dispersive X-ray mapping analyses. Study of their potential interactions with CO₂ was performed using CO₂ adsorption isotherm experiments, which provided new insights into their applicability as solid CO₂ adsorbents. A correlation between solid-supported Lewis acid-base pair strength and the resulting affinity to CO₂ is discussed based on the calculation of isosteric enthalpy of adsorption.