Campus Units

Chemistry, Physics and Astronomy, Mathematics, Ames Laboratory

Document Type

Article

Publication Version

Published Version

Publication Date

7-9-2018

Journal or Book Title

The Journal of Chemical Physics

Volume

149

Issue

2

First Page

024101

DOI

10.1063/1.5037618

Abstract

The reaction yield for conversion of p-nitrobenzaldehyde (PNB) to an aldol product in amine-functionalized mesoporous silica nanoparticles (MSN) exhibits a 20-fold enhancement for a modest increase in pore diameter, d. This enhanced catalytic activity is shown to reflect a strong increase in the β€œpassing propensity,” 𝒫, of reactant and product species inside the pores. We find that 𝒫 β‰ˆ 0, corresponding to single-file diffusion, applies for the smallest d which still significantly exceeds the linear dimensions of PNB and the aldol product. However, in this regime of narrow pores, these elongated species must align with each other and with the pore axis in order to pass. Thus, 𝒫 reflects both translational and rotational diffusion. Langevin simulation accounting for these features is used to determine 𝒫 versus d. The results are also augmented by analytic theory for small and large d where simulation is inefficient. The connection with the catalytic activity and yield is achieved by the incorporation of results for 𝒫 into a multi-scale modeling framework. Specifically, we apply a spatially coarse-grained (CG) stochastic model for the overall catalytic reaction-diffusion process in MSN. Pores are treated as linear arrays of cells from the ends of which species adsorb and desorb, and between which species hop and exchange, with the exchange rate reflecting 𝒫. CG model predictions including yield are assessed by Kinetic Monte Carlo simulation.

Comments

The following article appeared in GarcΓ­a, Andres, Igor I. Slowing, and James W. Evans. "Pore diameter dependence of catalytic activity: p-nitrobenzaldehyde conversion to an aldol product in amine-functionalized mesoporous silica." The Journal of Chemical Physics 149, no. 2 (2018): 024101, and may be found at doi: 10.1063/1.5037618. Posted with permission.

Rights

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.

Copyright Owner

The Authors

Language

en

File Format

application/pdf

Available for download on Tuesday, July 09, 2019

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