Structure and hydrothermal stability of Re(VII)-Oxo species grafted onto H-ZSM-5: A DFT study

Density functional theory (DFT) was used to assess the potential ReOx structures grafted onto H-ZSM5 by estimating the bond lengths, angles and vibrational spectra of possible Re-Oxo species. The interaction between water molecule and Re-ZSM-5 was investigated for the hydrothermal stabilities of Re-ZSM-5 zeolites at different temperatures. Local structures of one and two H2O molecules adsorbed on the Re-ZSM-5 zeolites reveal that the adsorption mode is changed, when the second H2O molecule is adsorbed. The tetrahedral Re-Oxo center is slightly distorted by the adsorbed water, and the Raman spectra calculated from the optimized structure shift accordingly. The absorption energy Ead is −23.47 and −33.88 kcal/mol for one and two H2O molecules adsorbed on the Re-ZSM-5, respectively. In addition, the calculated thermodynamic results show that Re-ZSM-5 zeolites are very stable at high temperatures.