Brønsted acid sites promote the diffusion of alkenes in small-pore zeolites by forming stable π-complexes that facilitate molecular hopping between adjacent cages . To evaluate this 5 effect in H-SAPO-RHO and Li-SAPO-RHO, a proton was positioned in the second window of the d8r being traversed (1Si-1H-8MR model), corresponding to positive values of the collective variable (ξ) in the free energy profiles.