The effect of framework organic moieties on the acidity of zeolites: A DFT study

Acidic properties of H-CHA, H-ZOL-C, and H-ZOL-N have been investigated using periodic density functional calculations to understand the effect of organic moiety incorporation on their acidities. Results from NH3 adsorption energy, deprotonation energy, and relative nucleophilicity calculations are consistent and show that the relative Brønsted acid site strength decreases in the order H-CHA > H-ZOL-C > H-ZOL-N. The geometrical parameters of the optimized structures indicate the easier incorporation of NH rather than CH2 in the chabazite framework. Moreover, the basicity of the lattice O, N, and C atoms increases in the order C < O < N.

Density functional calculations on periodic models of CHA topology were carried out to measure the effect of organic moieties incorporation, viz., CH2 and NH on the Brønsted acid site strength of zeolites. Results from adsorption energies of ammonia, deprotonation energies, and (sx+/sx−) are consistent and show the following order of decreasing the Brønsted acid site strength: H-CHA > H-ZOL-C > H-ZOL-N. Figure optionsDownload as PowerPoint slide