A Theoretical Investigation on Stability and Chemical Shifts in ¹³C NMR of Formaldehyde Encapsulated in Faujasite Zeolites

The chemical properties of labile molecules dramatically change in zeolite nanocages. In our previous study, we discovered that a monomeric formaldehyde can be preserved in faujasite zeolites for a long time under ambient conditions, while at the same time being activated enough to react with nucleophiles. The present quantam chemical study revealed that the thermodynamic equilibrium between a monomeric formaldehyde and its oligomer, such as 1,3,5-trioxane, is reversed in favor of the monomer by the adsorption energy to extra-framework cations in the faujasite. In addition, the difference in the NMR chemical shifts of the carbonyl carbons of the formaldehyde in zeolites with different Si/Al ratios was found to be due to the difference in the type of adsorption sites.