Multi-functionalization of nanoporous catalytic materials to enhance reaction yield: Statistical mechanical modeling for conversion reactions with restricted diffusive transport

Abstract

Multi-functionalization of catalytically-active nanomaterials provides a valuable tool for enhancing reaction yield by shifting reaction equilibrium, and potentially also by adjusting reaction-diffusion kinetics. For example, multi-functionalization of mesoporous silica to make the interior pore surface hydrophobic can enhance yield in dehydration reactions. Detailed molecular-level modeling to describe the pore environment, as well as the reaction and diffusion kinetics is challenging, although we briefly discuss current strategies. Our focus, however, is on coarse-grained stochastic modeling of the overall catalytic process for highly restricted transport within narrow pores (with single-file diffusion), while accounting for a tunable interaction of the pore interior with reaction products. We show that making the pore interior unfavorable to products can significantly enhance yield due to both thermodynamic and kinetics factors. Disciplines Chemistry | Mathematics | Physics CommentsThis article is from MRS Proceedings 1641 (2014) ABSTRACTMulti-functionalization of catalytically-active nanomaterials provides a valuable tool for enhancing reaction yield by shifting reaction equilibrium, and potentially also by adjusting reaction-diffusion kinetics. For example, multi-functionalization of mesoporous silica to make the interior pore surface hydrophobic can enhance yield in dehydration reactions. Detailed molecular-level modeling to describe the pore environment, as well as the reaction and diffusion kinetics is challenging, although we briefly discuss current strategies. Our focus, however, is on coarse-grained stochastic modeling of the overall catalytic process for highly restricted transport within narrow pores (with single-file diffusion), while accounting for a tunable interaction of the pore interior with reaction products. We show that making the pore interior unfavorable to products can significantly enhance yield due to both thermodynamic and kinetics factors.

Kinetic Monte Carlo Simulation of Statistical Mechanical Models and Coarse-Grained Mesoscale Descriptions of Catalytic Reaction–Diffusion Processes: 1D Nanoporous and 2D Surface Systems

“…For enhanced product reentry (α > 1), R rxn decreases faster than 1 – F , so overall reactivity is low. These strong changes in reactivity do not reflect a shift in reaction equilibrium but rather the effect of the changing the particle concentration, ⟨ X in ⟩, inside the pore with increasing F . , …”

“…The standard hydrodynamic theory sets D tr = 0 for SFD in a very long pore, so that J A = − D 0 ( A / X )∇ X . This choice can describe transient behavior such as pore filling. , But our focus is on steady-state behavior where X = constant, and thus which standard hydrodynamic theory sets to zero. We shall find that successful description of steady-state concentration profiles, which is dominated by fluctuations in adsorption–desorption at the pore openings, is not achieved with a MF or a hydrodynamic choice of D tr but rather a generalized hydrodynamic choice, as described in sections and .…”

“…Next, we present the key results for reactivity versus F for these models with modified product reentry. , We focus on the case of SFD. Figure a shows behavior for an irreversible reaction where one always has F eq = 1, so the reaction equilibrium is not affected by the value of α, and one might not anticipate that reactivity should strongly depend on α.…”

“…Results are shown where reentry of product, B, is blocked (α = 0), neutral (α = 1), or enhanced (α = 5). Reprinted with permission from ref . Copyright 2014 Materials Research Society.…”

“…This choice can describe transient behavior such as pore filling. 53,241 But our focus is on steady-state behavior where X = constant, and thus…”