Toward an understanding of zeolite Y as a cracking catalyst with the use of periodic charge equilibration

Periodic charge equilibration (PQEq) is used to study a few of the roles that the zeolite Y lattice might play in cracking catalysis. Comparison of the partial charge distributions of HY and Na1HY suggests that atoms within 10 Angstrom of the sodium atom accept electrons from the sodium atom. The charge distributions of n-octane, benzene, and water adsorbed inside the supercage of zeolite Y and siliceous zeolite Y show that the lattice provides little perturbation to these molecules. In contrast, a local dipole in the zeolite Y lattice is found to induce a change in the partial charge distribution of a cracking hydride transfer transition state model (C4H9+ plus n-octane). The polarization in this transition state model is attributed to the increased size of the transition-state model in comparision to the size of n-octane. This polarization likely preferentially stabilizes species such as the transition state and is perhaps an explanation for the second-order dependence of hydrocarbon cracking rate on Al ion concentration in zeolite Y.