SORPTION SITES, ENERGETICS, AND REACTIONS OF MOLYBDENUM HEXACARBONYL AND BENZENE COSORBED IN FAUJASITIC ZEOLITES

Molecular simulations of the siting locations and energetics of Mo(CO) (6) and C6H6 cosorbed in faujasitic zeolites Na(n)FAU (n = 0-96, Si/Al = 100-1) have been presented in combination with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The in situ DRIFTS t echnique was found to be an efficient tool to monitor the cosorption a t low coverage as well as the reaction of Mo(CO)(6) and C6H6 under the rmal activation within the void space of the Na(n)FAU zeolites. The mo lecular simulations are based on Monte Carlo calculations using the gr and Canonical ensemble and are derived from a suitable zeolite-metal c arbonyl-hydrocarbon potential set. From the present experimental and t heoretical results as well as earlier experiments related to the reage nts sorbed alone, a coherent picture of the cosorption and chemical be havior of Mo(CO)(6) and C6H6 within the void space of the faujasitic z eolites has been drawn as a function of the aluminum content. In silic eous faujasite (Si/Al = 100) the Mo(CO)(6) and C6H6 molecules are rand omly distributed within the void space and the molecular motions appro ach the rapid isotropic limits of liquids. The chemical behavior upon thermal activation is found to be analogous to that observed in soluti on. In Na(56)FAU (Si/Al = 2.5) the reagents are trapped in well-define d sorption sites in close proximity. Upon gentle thermal activation a fast reaction occurs to form Mo(CO)(3)(eta(6)-C6H6) inside the superca ge through a concerted mechanism including the electrostatic field and the basicity of the framework oxygens. In Na-(85-96)FAU (Si/Al = 1.25 , 1) the Mo(CO)(6) and C6H6 molecules are not encapsulated in close pr oximity. Mo(CO)(6) reacts thermally in the void space like in the abse nce of added C6H6 to lose sequentialy three CO ligands and form predom inently a Mo(CO)(3)(O-z)(3) species in which the three vacant coordina tion sites are occupied by three O-z framework oxygens.