(289a) Confinement and Diffusion Effects in Hierarchical Zeolites for Diverse Reaction Networks

The microporous (d_pore < 2 nm) voids and channels surrounding active sites in prototypical zeolites provide stabilizing environments for reaction moieties, including those involving acid-catalyzed conversions of fossil-based or renewably-sourced hydrocarbons and oxygenates to fuels and chemicals. These voids of molecular dimension restrict diffusion of relatively bulky molecules to and from the active sites, impacting rates and selectivities in favor of undesired byproducts, while leading to premature deactivation due to buildup of bulky coke precursors. Unconventional liquid-phase reactions employed for a growing number of biomass-derived feeds amplifies these diffusion effects. Mesopores (d_pore = 2-50 nm) introduced to form micro/mesopore hierarchical zeolites via post-synthetic acid/base leaching or organic templating have demonstrated improved catalyst efficiency and increased selectivity of bulkier products for both gaseous and liquid-phase systems, but understanding of reaction-diffusion-deactivation relationships in the liquid phase is especially constrained by batch kinetics. Here we demonstrate how tuning mesopore volumes and distributions within hierarchical analogs of 3D (BEA, MFI) and 1D (MOR) zeolites in a highly diffusion-limited, liquid batch Friedel-Crafts alkylation of 1,3,5-trimethylbenzene (TMB) with benzyl alcohol (BA) to form 1,3,5-trimethyl-2-benzylbenzene (TM2B) can be leveraged to control the relative rates of alkylation to competitive self-etherification of benzyl alcohol to form dibenzyl ether (DBE). Deduction of the largely overlooked, secondary formation of TM2B from DBE and TMB at high BA conversions demonstrates an additional pathway for selectivity control for hierarchical zeolites capable of achieving high BA conversions due to reduced deactivation rates. Insight into selectivity control in diffusion-limited extremes according to mesopore accessibility validates the flexibility of zeolites in novel reaction systems.