Adsorption of CO 2 on amine-functionalised MCM-41: experimental and theoretical studies

Adsorption of CO 2 on MCM-41 functionalised with [3-(2-aminoethylamino)propyl]trimethoxysilane ( MCM-41-N2 ), N 1 -(3-trimethoxysilylpropyl)diethylenetriamine ( MCM-41-N3 ), 4-aminopyridine ( MCM-41-aminopyridine ), 4-(methylamino)pyridine ( MCM-41-methylaminopyridine ) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene ( MCM-41-guanidine ) was investigated. The amine-functionalised materials were characterised by 29 Si and 13 C solid-state nuclear magnetic resonance, N 2 adsorption/desorption isotherms, X-ray diffraction and transmission electron microscopy. CO 2 adsorption at 1.0 bar and 30 °C showed that the amount of CO 2 ( n ads /mmol g −1 ) adsorbed on MCM-41-N2 and MCM-41-N3 is approximately twice the amount adsorbed on MCM-41. For MCM-41-aminopyridine , MCM-41-methylaminopyridine and MCM-41-guanidine , the CO 2 adsorption capacity was smaller than that of MCM-41 at the same conditions. The proton affinity (computed with wB97x-D/6-311++G(d,p)) of the secondary amino groups is higher than that of the primary amino groups; however, the relative stabilities of the primary and secondary carbamates are similar. The differential heat of adsorption decreases as the number of secondary amino groups increases.