Catalytic conversion in narrow pores is inhibited as product formed in the pore interior cannot readily pass reactants near the pore openings, and thus blocks reactant from reaching interior catalytic sites. Standard mean-field treatments of reaction-diffusion kinetics fail dramatically due to the development strong spatial correlations associated with the subtle interplay of restricted transport and reaction. Behavior can however be described by KMC simulation of stochastic molecular-level models, or by generalized hydrodynamic theories [PRL 108 (2012) 228301]. A key observation is the strong dependence of catalytic activity on the propensity for reactant and product species to pass each other inside the pore. These concepts are applied to interpret the strong increase in yield with modest increase in pore diameter observed for PNB conversion to an aldol product in amine-functionalized mesoporous silica [J Chem Phys 149 (2018) 024101]. The passing propensity for PNB and aldol versus pore diameter is first determined applying Langevin simulations [PRL 113 (2014) 038301]. These must reliably treat rotational as well as translational diffusion, since species must align with the pore and with each other in order to pass in narrow pores. This information provides input to stochastic models for the overall reaction-diffusion process for which KMC simulation shows behavior consistent with experimental observations.

Catalytic activity in nanoporous materials with inhibited transport: Pore diameter dependence of PNB conversion to aldol in MSN

2019 Fall National Meeting

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