Assessment of the intrinsic interactions of mesoporous silica with carbon dioxide

Three mesoporous silica, SBA-16, SBA-15 and MCM-41, with different structures and porosities were synthesized via a hydrothermal method and their interactions with carbon dioxide (CO2) were investigated through thermal programmed desorption (TPD) and differential scanning calorimetry. TPD measurements provided precise assessments of the intrinsic affinity towards CO2, without the influence of moisture. All silica materials were found to exhibit intrinsic affinity towards carbon dioxide, but the surface basicity, expressed in terms of retained CO2 amount, is markedly influenced by increases in pore size and framework structures. SBA-15 displayed the highest CRC values, explained in terms of larger pore size, lower numbers of acidic out-of plane Si-OH and higher numbers of much less acidic in-plane silanols. These findings provide valuable information for a better understanding of the role of the silica structure in the intrinsic basicity, prior to further modifications for improving the affinity towards CO2 or merely for catalysis purposes involving CO2 as reagents, intermediates or products.