Heating of Zeolites under Microwave Irradiation: A Density Functional Theory Approach to the Ion Movements Responsible of the Dielectric Loss in Na, K, and Ca A-Zeolites

We analyze the temperature increase in Linde Type A Na, K, and Ca mix zeolites under microwave radiation. Through the use of the density functional theory (DFT), we examine the movements of the most labile cations for dehydrated Na12, K12, and Na4Ca4 ideal A-zeolites. The kinetics of the ionic migration, responsible for dielectric heating, is described according to transition-state theory. For each composition, we find different relaxation processes caused by the jump of the most unbalanced cations to diverse metastable sites inside the Al–O–Si framework. The magnitudes of the calculated enthalpy barriers for the most probable jumps agree with the experiments and are inversely related to the heating rates. DFT calculations are an optimum approach to elucidate the cation migration in Zeolites, described by a thermally activated or Arrhenius-type process. We observe that the deposition of microwave energy drops significantly in the presence of Ca atoms independently of other cations.