Title

Pore diameter dependence of catalytic activity: p-nitrobenzaldehyde conversion to an aldol product in amine-functionalized mesoporous silica

Publication Date

7-9-2018

Department

Ames Laboratory; Physics and Astronomy; Mathematics; Chemistry

Campus Units

Chemistry, Mathematics, Physics and Astronomy, Ames Laboratory

OSTI ID+

1464469

Report Number

IS-J 9645

DOI

10.1063/1.5037618

Journal Title

The Journal of Chemical Physics

Volume Number

149

Issue Number

2

First Page

024101

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.

DOE Contract Number(s)

AC02-07CH11358

Language

en

Department of Energy Subject Categories

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Publisher

Iowa State University Digital Repository, Ames IA (United States)

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